My Dual Battery Setup- Diagram Check

[Dusty T.]

Well, here it is.

I've spent several weeks researching and thinking about how I want my next dual battery setup to be for my "new" 2002 Tacoma. I have yet to put together a parts list, but have a pretty good idea of what I will need and where to find it. Still I have questions....

Have a look at the attached diagram below showing my proposed setup. Hopefully it makes some sense. My goal here is to not only run a dual battery system, but also allow some accessories (mainly the in-dash power plugs) C.B. and stereo to be switchable between the two batteries should I choose to remove the second battery, or decide not to draw any power from it alltogether. Here, I'm using a constant-duty solenoid to isolate and connect the batteries for charging. I went with a constant duty solenoid on my last setup without a problem- but that was on a completely different vehicle. I know some floks prefer to use isolator units.

Here's where it gets interesting......
My last dual battery setup did not incorporate running the stereo and sub off of the aux battery. This time around, I am tapping into the aux battery for stereo power for both mobile and stationary use. On this setup, I am running an override switch (via an SPDT Relay). With the override switch in the ON position, the stereo "switched" signal wire can receive power without the need to have the key in the ACC or ON position. This should elliminate the risk of running the main battery down while running the radio with the engine off. Turning the override switch to the off position will allow the stereo to resume being switched by the key in ACC or ON.

Now, for the questions..... I'm certain a couple more will come around as the project progresses!

1. Charging Power:
At the most, my Tacoma has an 80A alternator. I was looking at BajaTaco's battery setup www.bajataco.com, and it doesn't appear that he upgraded the alternator with his setup. What you see on the diagram is what I will be running the most. Putting it very simply, it's basically 200W sub, and aux battery to be charged with the occasional use of a high volume air pump (30A max). There are no plans to add lights or a winch anytime in the forseable future. I would like to hook up a 1000W inverter to the aux battery someday, but that's about all I see happening. Will the alternator need upgrading, or the "Big 3" i.e. grounds, and battery cable to be upsized? I've seen some Tacomas around the boards with fridges, lights, air pumps, radios, etc and no mention of having to run a larger alternator. Where do I draw the line here?

2. The Auxiliary Battery:
I'm looking at the Optima D31T Yellow Top (75 Ah). This will be mounted in the bed (with shell) in a Taylor aluminum battery box (provided it fits!). Not mounted under the hood. I'm not planning on being able to start my engine should the main battery fail. Would a Blue Top be a better choice? Since it is in an enclosed sleeping space I do not want a battery that offgasses. Only myself! :rolleyes:

3. Switching The Isolating Constant Duty Solenoid:
My last setup used ignition ON to connect the two batteries. Never had a problem starting- even with a low aux battery. Has this worked fine for other Tacoma owners here? I know some people hook into the "alterntor good" circuit to close the solenoid, but I have no idea where that could be located.

4. Wire Size:
This time, I'm running #2 power and ground wire between the main and auxiliary battery posts. While this will eliminate voltage drop, won't it cause the battery to charge more quickly, thus drawing more amps from the alternator and putting unneeded stress on the battery? Or is that what the alternator's internal regulator is for? Note, I'm running relatively small 80-amp Mega fuses on each end of the wire if that should make any difference. I know this probably sounds kind of dumb, but it really goes back to the alternator output.....


Thanks for reading and input/suggestions are greatly appreciated. I'm looking forward to ordering up the parts and to begin putting this together!

[Switch]

Well, here it is.

I've spent several weeks researching and thinking about how I want my next dual battery setup to be for my "new" 2002 Tacoma. I have yet to put together a parts list, but have a pretty good idea of what I will need and where to find it. Still I have questions....

Have a look at the attached diagram below showing my proposed setup. Hopefully it makes some sense. My goal here is to not only run a dual battery system, but also allow some accessories (mainly the in-dash power plugs) C.B. and stereo to be switchable between the two batteries should I choose to remove the second battery, or decide not to draw any power from it alltogether. Here, I'm using a constant-duty solenoid to isolate and connect the batteries for charging. I went with a constant duty solenoid on my last setup without a problem- but that was on a completely different vehicle. I know some floks prefer to use isolator units.

Here's where it gets interesting......
My last dual battery setup did not incorporate running the stereo and sub off of the aux battery. This time around, I am tapping into the aux battery for stereo power for both mobile and stationary use. On this setup, I am running an override switch (via an SPDT Relay). With the override switch in the ON position, the stereo "switched" signal wire can receive power without the need to have the key in the ACC or ON position. This should elliminate the risk of running the main battery down while running the radio with the engine off. Turning the override switch to the off position will allow the stereo to resume being switched by the key in ACC or ON.

Now, for the questions..... I'm certain a couple more will come around as the project progresses!

1. Charging Power:
At the most, my Tacoma has an 80A alternator. I was looking at BajaTaco's battery setup www.bajataco.com, and it doesn't appear that he upgraded the alternator with his setup. What you see on the diagram is what I will be running the most. Putting it very simply, it's basically 200W sub, and aux battery to be charged with the occasional use of a high volume air pump (30A max). There are no plans to add lights or a winch anytime in the forseable future. I would like to hook up a 1000W inverter to the aux battery someday, but that's about all I see happening. Will the alternator need upgrading, or the "Big 3" i.e. grounds, and battery cable to be upsized? I've seen some Tacomas around the boards with fridges, lights, air pumps, radios, etc and no mention of having to run a larger alternator. Where do I draw the line here?

2. The Auxiliary Battery:
I'm looking at the Optima D31T Yellow Top (75 Ah). This will be mounted in the bed (with shell) in a Taylor aluminum battery box (provided it fits!). Not mounted under the hood. I'm not planning on being able to start my engine should the main battery fail. Would a Blue Top be a better choice? Since it is in an enclosed sleeping space I do not want a battery that offgasses. Only myself! :rolleyes:

3. Switching The Isolating Constant Duty Solenoid:
My last setup used ignition ON to connect the two batteries. Never had a problem starting- even with a low aux battery. Has this worked fine for other Tacoma owners here? I know some people hook into the "alterntor good" circuit to close the solenoid, but I have no idea where that could be located.

4. Wire Size:
This time, I'm running #2 power and ground wire between the main and auxiliary battery posts. While this will eliminate voltage drop, won't it cause the battery to charge more quickly, thus drawing more amps from the alternator and putting unneeded stress on the battery? Or is that what the alternator's internal regulator is for? Note, I'm running relatively small 80-amp Mega fuses on each end of the wire if that should make any difference. I know this probably sounds kind of dumb, but it really goes back to the alternator output.....

Thanks for reading and input/suggestions are greatly appreciated. I'm looking forward to ordering up the parts and to begin putting this together!


Caveat: I would not call myself an expert on dual batteries but I did a lot of reading before doing mine and it has been working fine for the past year. The write ups I did on the ttora web site include alot of links to other projects that may help you in your research (links at bottom). In general your set up seems more complicated than it needs to be given your goals. Two Odessey 1200's will fit in the stock location (I'm pretty sure two Optimas can fit the stock location too, not sure what size). Also you if run two deep cycle batteries, you can just run everything off of one battery and have the second battery just as a backup. This will greatly simplify wiring and switches - the money saved could go into two matching batteries, a better isolator, higher quality wire, and higher quality switches. If you locate the 2nd battery in the engine bay, you can use the factory ground point and it won't take up space in the bed. If you are particulary concerned about draining the battery down completely (not good for any battery) there are products that can shut off the load when the battery drains to a certain point (like this: http://www.colehersee.com/pdf/hot_feed/D-614_LowVoltageDisconnect.pdf
). I supose you already know all of this, so I'll stick to addressing your questions.

1: Charging power: The issue with a smaller alternator is that it will run at it's max output more frequently (if you drain battery down alot or have lots of auxilary stuff). So it will not last as long. Whether you need "Big 3" or not depends on the amount of current you are using at any one time. If you use more than 80A your battery will drain down while your alternator works as hard as it can.

2: Blue top: A yellowtop will do just fine. Gases are not an issue with either.

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money. I looked into serveral isolators before going with Hellroaring (not inexpensive). There are isolators designed to switch based on voltage levels of the respective circuits, have overide switches, and are designed for voltage sensing alternators. If you prefer solenoid based isolators, the Surepower Battery Separator 1315-200 comes to mind. Less wire, less work, better functionality.

4: If you put 2nd battery in bed, you will still get some voltage drop due to the lengh of wire needed, about .1 to .25V depending on wire length (see http://www.bcae1.com/wire.htm). Also you should be able to find out the max charging current draw from Optima's website. A good isolator will make this consideration a non-issue.

General comments:
I noticed that you plan to use a fuse block with a negative buss. That seems like extra work and wire given that there are plenty of factory ground points on the truck. Consult the the factory service manual for ground point locations.

Connecting the batteries at the negative terminals with a #2 wire would not be necesary if you had a good ground point closer to the second battery. This will also reduce voltage drop.

You don't need #2 wire to the battery selector switch if #8 is sufficent for your aux fuse block.

These links have my write ups and references: dual battery and aux fuse block (http://www.ttora.com/forum/showthread.php?t=67738), and aux switch panel (http://www.ttora.com/forum/showthread.php?t=71296):

Hope this helps, be sure to post up pics when you are done.

[keezer36]

If you don't have one already, here's a wire sizing chart: http://www.rbeelectronics.com/wtable.htm. Though I no longer have the reference, I know that these numbers are intentionally conservative.

My two cents is to save money using the wiring required and buy a good isolator. I too have a Hellroaring and bought their remote switch. They have a variety of diagrams for various setups. Just mind the diode configurations on the different isolators for what you want to do.
Mike at Hellroaring is good about emailing back and providing all the info you need for a successful job.

http://i188.photobucket.com/albums/z235/keezer36/DSC00096.jpg
Backup configuration with parallel #4 from the backup to #1 to the starter solenoid.

http://i188.photobucket.com/albums/z235/keezer36/DSC00097.jpg
Excuse the woodworking skills, one eye is lower than the other. The hole was for a switch for a harebrained idea I had before I took a good look at the diodes of the 300 isolator.

http://i188.photobucket.com/albums/z235/keezer36/DSC00103.jpg
In auto position, the LED will stay on after you shut the motor off as long as you have a surface charge. A good way to gauge the condition of your battery. I set the switch in one of my blanks.

Next up is a Tripp Lite 1000W inverter.

[Dusty T.]

1: Charging power: The issue with a smaller alternator is that it will run at it's max output more frequently (if you drain battery down alot or have lots of auxilary stuff). So it will not last as long. Whether you need "Big 3" or not depends on the amount of current you are using at any one time. If you use more than 80A your battery will drain down while your alternator works as hard as it can.

2: Blue top: A yellowtop will do just fine. Gases are not an issue with either.

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money. I looked into serveral isolators before going with Hellroaring (not inexpensive). There are isolators designed to switch based on voltage levels of the respective circuits, have overide switches, and are designed for voltage sensing alternators. If you prefer solenoid based isolators, the Surepower Battery Separator 1315-200 comes to mind. Less wire, less work, better functionality.

4: If you put 2nd battery in bed, you will still get some voltage drop due to the lengh of wire needed, about .1 to .25V depending on wire length (see http://www.bcae1.com/wire.htm). Also you should be able to find out the max charging current draw from Optima's website. A good isolator will make this consideration a non-issue.

General comments:
I noticed that you plan to use a fuse block with a negative buss. That seems like extra work and wire given that there are plenty of factory ground points on the truck. Consult the the factory service manual for ground point locations.

Connecting the batteries at the negative terminals with a #2 wire would not be necesary if you had a good ground point closer to the second battery. This will also reduce voltage drop.

You don't need #2 wire to the battery selector switch if #8 is sufficent for your aux fuse block.

These links have my write ups and references: dual battery and aux fuse block (http://www.ttora.com/forum/showthread.php?t=67738), and aux switch panel (http://www.ttora.com/forum/showthread.php?t=71296):

Hope this helps, be sure to post up pics when you are done.

Hey, thanks for the links and input.

I'm am still on the fence as far as going again with a solenoid (though there were no problems with my last setup), or the isolator. I'll spend some more time looking into it, though. The Surepower sounds like a good alternative from what I researched on bajataco's site. The solenoid setup doesn't appear to be too popular with the tacoma crowd, but I really do like it's simplicity, but dislike the risk of killing BOTH batteries should the alternator fail.

Should have cited some of my sources, but I've spent the last few weeks reading through a number of the links you sent, and will most likely re-read them again! The bcae site was a great source for helping me size up wire.

I am pretty set on mounting the battery in the bed. Underhood would probably be optimal, but I just don't have the means to fab up a battery bracket. I feel silly enough as it is paying for an aluminum battery box, when I could make my own in a machine shop.

Could you clarify grounding the aux battery? From what I'm reading, it sounds like I should just ground it to the frame. I did this last time, but felt that the frame connection would corrode too easily, or come loose. That, and I would probably need to upsize the ground wire off the main battery as well. Sorry if I'm missing your point.

Back to making adjustments.

Thanks

Dusty

[TACODOC]

Great thread! :lurk:

[Terracoma]

Subscribed.

... Hey, pass the popcorn!

:lurk:

[Dusty T.]

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money.


I got to thinking about the above and wanted to pick your brain a bit about why the solenoid is not the optimal choice? By the way, I must give you props on your system- the workmanship looks very well done. Seeing photos of a quality finished product is always inspirational!

I've read a couple arguments both for and against using an isolator vs. a solenoid. To generalize, it seems that the isolators initiate a voltage drop to the battery being charged due to the isolator's internal diodes. Now, this doesn't seem to be the case so much with the Hellroaring unit if I read their material correctly. The advantage I see with the isolator is the ability to monitor the second battery (via LED indicator lights), start the engine off the aux battery (not a critical feature for me), and reduce the risk of running both batteries down should the alternator fail (a good feature).

Of course, the arguments I've read regarding using the solenoid is it's simplicity. Should it fail, it will simply open the circuit and isolate the battery. Now looking over my schematic, you can see I would be able to override that with the manual Blue Sea switch should the solenoid fail.... Either way, my budget isn't terribly tight since I want this system to be as trouble-free for years as possible.

In the meantime I'll read a little further on these isolator units, and make a final determination as to whether the alternator will do the trick. I guess those are my main two concerns.

Oh, and glad to see we have an audience here! :clapsmile

I'll be sure to post pics when this system is finished in the next few months!

Thanks

Dusty

[Switch]

I got to thinking about the above and wanted to pick your brain a bit about why the solenoid is not the optimal choice? By the way, I must give you props on your system- the workmanship looks very well done. Seeing photos of a quality finished product is always inspirational!

I've read a couple arguments both for and against using an isolator vs. a solenoid. To generalize, it seems that the isolators initiate a voltage drop to the battery being charged due to the isolator's internal diodes. Now, this doesn't seem to be the case so much with the Hellroaring unit if I read their material correctly. The advantage I see with the isolator is the ability to monitor the second battery (via LED indicator lights), start the engine off the aux battery (not a critical feature for me), and reduce the risk of running both batteries down should the alternator fail (a good feature).

Of course, the arguments I've read regarding using the solenoid is it's simplicity. Should it fail, it will simply open the circuit and isolate the battery. Now looking over my schematic, you can see I would be able to override that with the manual Blue Sea switch should the solenoid fail.... Either way, my budget isn't terribly tight since I want this system to be as trouble-free for years as possible.

In the meantime I'll read a little further on these isolator units, and make a final determination as to whether the alternator will do the trick. I guess those are my main two concerns.

Oh, and glad to see we have an audience here! :clapsmile

I'll be sure to post pics when this system is finished in the next few months!

Thanks

Dusty

Thanks, the credit goes to the guys that wrote up their projects online and Al at Arc Battery in Sausalito who helped me with selecting many of the components.

I can’t say I have my own opinions as much as I’ve relied on that of others. The reasons I went with the Hellroaring are the reasons you cited. I would have used the Surepower solenoid but it was too large to fit in the available space.

Making a dual battery mount for the stock location would not be that hard. (for an example see CNADNtacoma’s write up
http://www.ttora.com/forum/showthread.php?t=52489).
That said, one advantage of locating your battery in the bed is that you can mount larger batteries in both locations.

For grounding the #2 battery, just ground to frame. No need to run a wire back to engine bay.

BTW, I can say from experience that the painless performance fuse blocks are junk compared to the Blue Sea.

[ntsqd]

Some personal experience has led me to try to always share the exact same grounding point with multiple batteries. This is considerably more important when they are wired directly in parallel, but would also apply when there is some sort of key off separation. By not sharing the same grounding point there can be a small voltage drop across the two negative battery posts. In my paralleled experience this led to spontaneous charge/discharge cycles (high battery trying to raise the low battery) that ruined one battery and hurt the other. This would still be true in a key-off separated system, though of less importance.

My next dual battery system will use a Blue Sea Automatic Charge Relay (ACR) (http://bluesea.com/category/2). I think the CL series will work the best for me.

If they weren't $20 each I'd only use the Anchor breakers. As it is I'll likely still use them on critical circuits.

[keezer36]

If you have a multimeter, check continunity between the block ground point and frame where you intend to ground. If there's no resistance, there'll be no voltage drop.

[ntsqd]

The problem is that even a tiny difference in potential results in the see-saw self-discharge mode. Even a 10,000 Ohms resistance results in a 1.2 mA current. That's enough to do damage if the vehicle sits for periods of time.
BT,DT.

Even crossing a weld in the frame can increase the resistance significantly. Some racer types who've moved the battery to the trunk end up with slow cranking form a battery that worked fine when in the engine bay. Once they run a ground cable up to the engine the problem disappears.
I prefer to just avoid that potential problem from the start, I can find new ones without revisiting the previous ones. :)

[Dusty T.]

I
Mike at Hellroaring is good about emailing back and providing all the info you need for a successful job.


I was looking over your setup, and was wondering which model isolator are you using? I actually spoke with Mike at Hellroaring today (nice guy), and had a couple questions about which isolator would be the best for me to go with. My thoughts were running wild last night, and I thought "how about using the aux battery as BOTH a second starting battery as well?". Mike advised against this, which makes sense, since the aux battery has the potential of being drained by accessories when it may bee needed to perform, so it is NOT completely idiotproof. Mike also mentioned that I could combine both batteries should the main battery fail, and after several minutes, this should give me enough charge to start up the engine. I'd say that's good enough for me. If worse came to worse, I like bringing a 50W solar panel in the backcountry with me anyway to charge the aux battery while out for a day hike.

Now I've gone around and around between going with the solenoid and solid state isolator. The biggest plus I see with the Hellroaring (and perhaps others) is their feature which isolates both batteries automatically should the alternator fail. That's what really attracts me toward using their product.

With regards to the negative wire- I'm pretty set on running the negative cable back to the main battery. I have a slight suspicion that my old aux battery setup may have caused the radiator to prematurely corrode on my Ranger, due to the lack of proper grounding paths for my battery and some accessories (electrolysis). It's just a very slight suspicion.

What really has me paralyzed in the design/decision phase of this project, is determining what size wire and fuse combo to run to the aux battery. Since the battery will certainly be bed-mounted, #2 AWG looks like a good choice to cover the ten to twelve foot distance with minimal voltage drop. The 80 amp or smaller fuse would prevent too much current from flowing, but wouldn't it blow when trying to charge a discharged battery since #2 wire is good up to 200 amps?

Talking with Mike from Hellroaring (hopefully I'm not twisting his information around here), he recommended a smaller gauge wire, i.e. #8 as a charging wire for the aux battery. This would prevent the battery from drawing more current during its charge cycle, which could overwork my 80-amp alternator- supposing it is 80 amps. I would like to use the Optima D31T rated at 75 amp hours. I also called Optima and asked about the required amps to charge this battery should it be completely discharged. I didn't get a very direct answer, but their tech guy thought my alternator would do just fine.
Sorry if this sounds ridiculous, but I'm stumped on what size wire to go with, especially if I want to use the charging wire to also power some accessories up front in the cab without incurring too much voltage drop.

[keezer36]

I bought the 95300B. If your main concern is running the aux stuff and don't mind waiting for a charge if your main battery goes dead, I do believe the 95150 is the proper buy. The "A" or "B" afterwards is if the unit has the sense resistor built in (cleaner look).

No, it is not idiotproof. Hence the hole drilling in the side of my box for a BlueSea switch thinking I could get the best of both worlds until I took a good look at the diode configuration of the two different models. With the 95300, you have to run your aux stuff off the engine bay battery.

Mike told me that for a backup battery, run the negative to the engine block where the cranking battery's negative is mounted. For an aux battery, the frame is okay. This, he went on to say way due to the the higher current draw of cranking. He did add, if I had a good current path, engine to frame, I could ground to the frame for a backup configuration. So I connected a wire to the ground point on the block, crawled back to where I wanted to ground on the frame and checked continunity with my Fluke multimeter. I got zip, no resistance at all so I went with the frame. Perhaps I'm still missing something here but...Google Ohm's Law Wheel or verify with Mike. I don't think you need to go back to the engine for an aux setup but it can't hurt, that's for sure.

Fuse: Bounce this off Mike, but if I remember right, as an aux battery setup, use 8 AWG for 15-20 ft. and an 80 amp fuse. This will, of course have waiting to charge a dead cranking battery which you've said you're okay with.

When you get indirect answers from techs, it's been my experience that they just don't want to say "I don't know".

I'm not real hip on alternators, but it's my understanding that anymore they have circuit protection from being overworked.

I really recommend using Hellroaring's electrical drawings.

[ntsqd]

V = Volts
I = Current
R = Resistance

V = I * R

R = V/I

I = V/R

Note with this last version of the formula that a tiny resistance results in a large current.
E.G. 12 volts, 1 Ohm; 12/1 = 12 amps
but that a large resistance results in a tiny current. Seems logical.
12 volts, 10,000 Ohms; 12/10,000 = .0012 amps

However, in the case of a small resistance between two grounding points the full battery voltage would not be applied, so the current will be less than it would be if the full battery voltage were applied.

With any method that separates the batteries when the vehicle is sitting this isn't so much of an issue. It would only matter during charging and might result in one battery being slightly less charged.
In my case the OE dual battery wiring had no such separation provision.


If the 8 ga. wire will support the max charge over the distance involved, why would you need a larger cable? Do you plan to discharge that battery at rates higher than 80 amps?

[Switch]

If you have a multimeter, check continunity between the block ground point and frame where you intend to ground. If there's no resistance, there'll be no voltage drop.

X2 on that. If you run a #2 copper wire to a common ground point, you have the resistence of the wire to worry about. Not an issue for short lenghts but with the 2nd battery in the bed, you are talking about ~.10V drop on a +10ft wire. I'm inclined to think that the frame would offer less resistance than an #2 copper wire. MTC

[ntsqd]

snip.....
I'm inclined to think that the frame would offer less resistance than an #2 copper wire. MTC
Not in my experience. I've been through this several times with various race cars with relocated batteries. They ground near the battery to save the weight of the ground cable. Then the car has slow cranking speed problems. Grounding to the engine block has yet to fail to fix this.

Copper (0.00000170 ohm-cm) (http://www.matweb.com/search/DataSheet.aspx?MatID=30) is a much better conductor than steel (0.0000159 ohm-cm) (http://www.matweb.com/search/DataSheet.aspx?MatID=6809&ckck=1). The only possible way that the frame could be a better conductor would be thru a larger cross section. Looking at those resistivity numbers the cross section would need to be ~10 times larger. That's not very likely. If the actual current path crosses any welds, those have a surprisingly high resistance.

[Switch]

Not in my experience. I've been through this several times with various race cars with relocated batteries. They ground near the battery to save the weight of the ground cable. Then the car has slow cranking speed problems. Grounding to the engine block has yet to fail to fix this.

Copper (0.00000170 ohm-cm) (http://www.matweb.com/search/DataSheet.aspx?MatID=30) is a much better conductor than steel (0.0000159 ohm-cm) (http://www.matweb.com/search/DataSheet.aspx?MatID=6809&ckck=1). The only possible way that the frame could be a better conductor would be thru a larger cross section. Looking at those resistivity numbers the cross section would need to be ~10 times larger. That's not very likely. If the actual current path crosses any welds, those have a surprisingly high resistance.

That is an excellent point. And so we learn. Thanks.

[keezer36]

ntsqd,

Though I could not find much about this see-saw effect between the batteries, if I understand it, I would think that a sense resistor as on the Hellroaring units would prevent this, they have a tolerance of .2 VDC.
Another point, wouldn't this also occur simply by having two different batteries especially if one is older than the other and does not hold a charge as well?
What do you think?

One other thing I thought of was with two different ground points (frame/engine), if there was resistance or resistance built up over time, would there be a voltage measured negative post to negative post?

[ntsqd]

This is sort of getting away from the original topic, my apologies for that.

If you connect two batteries in parallel they will equalize their charge state. The battery with the higher potential (voltage) will charge the battery with the lower potential. With perfect conductors they will reach a state of equilibrium. Note that this equilibrium will happen thru both conductors, not just the one on the positive side.
Even superconductors aren't perfect. Any resistance, no matter how small, will dissipate some of the stored energy as heat. It may be such a small amount of heat that it is difficult to detect at home (because the resistance is tiny), but it does happen.

I'm not entirely clear on the actual mechanism of the see-saw effect. My best guess is that the high potential battery pushes enough current into the low potential battery that there is an effect similar to inertia. Think of this as an ocean wave. There is always a low point in the water behind each wave that is lower than the level of the ocean itself. The water in the wave's peak had to come from somewhere. The high battery will actually flow enough current towards the low battery that it's own charge level is reduced to a point below that of the other battery. Which then, in turn, tries to charge the formerly high battery. And back and forth that goes until neither battery has enough charge to do anything. If either the conduction path on the positive side or the negative side has some measurable resistance then this process is accelerated because a resistor drops voltage so the low battery "looks" even lower to the high battery than it really is. Compound that with the heat dissipation caused by the resistance.
Note that batteries have an internal resistance. (Don't try to measure this with a normal Ohm meter - neither of you will be happy with the results.) If the two batteries connected together don't have the same internal resistance then the external conductors could be perfect and the see-saw effect would still occur at an accelerated rate. This is the root of wanting two batteries as identical as possible. Any resistance in the circuit makes one battery "look" to be at a lower charge state to the other battery. If they are both at the same level of charge then they each "look" to be the same voltage to the other battery and no current flow takes place.

If you add some sort of disconnector to either conductor you stop the process. Which is one of the purposes of the ACR or the Hell-Roaring product, a simple diode bridge ("battery isolator"), or even the old constant duty charging solenoid.

None of this addresses how the batteries interact with an external charging source. That is a huge topic by itself. Suffice to say that the standard automotive alternator & regulator are at the low end of what is available and possible. egn posted a link to amplepower (http://amplepower.com/) a while back. Some of their stuff is very interesting.

[Switch]

What really has me paralyzed in the design/decision phase of this project, is determining what size wire and fuse combo to run to the aux battery. Since the battery will certainly be bed-mounted, #2 AWG looks like a good choice to cover the ten to twelve foot distance with minimal voltage drop. The 80 amp or smaller fuse would prevent too much current from flowing, but wouldn't it blow when trying to charge a discharged battery since #2 wire is good up to 200 amps?

Talking with Mike from Hellroaring (hopefully I'm not twisting his information around here), he recommended a smaller gauge wire, i.e. #8 as a charging wire for the aux battery. This would prevent the battery from drawing more current during its charge cycle, which could overwork my 80-amp alternator- supposing it is 80 amps. I would like to use the Optima D31T rated at 75 amp hours. I also called Optima and asked about the required amps to charge this battery should it be completely discharged. I didn't get a very direct answer, but their tech guy thought my alternator would do just fine.
Sorry if this sounds ridiculous, but I'm stumped on what size wire to go with, especially if I want to use the charging wire to also power some accessories up front in the cab without incurring too much voltage drop.

I bit my tounge yesterday hoping someone with more experience than I would chime in on this point. Maybe my stab at this will at least draw some attention to your dilemma.

Short answer:
You have a choice between #2 wire w/ 150A fuse OR #4 wire w/ 100A fuse OR #6 wire w/ 80A fuse. DO NOT use a smaller wire/fuse than #6. If it were my project, I would go with the #2 wire w/ 150A fuse.

Long answer:
I think you should size wire based on safety, cost, and appliction. I used this tool for sizing wire: http://www.bcae1.com/wire.htm
In the following example the wire size is too small:
http://i174.photobucket.com/albums/w113/parallelkiller/Dual%20Battery/wiresize.jpg
With a lenght of 12 feet you can safely use any gauge less than #8. A larger wire cost more and will be more hassel to install. If it were my project, I would not worry about cost and use #2 to minimize voltage drop. I would use the best wire I could find, tin coated, made with lots of fine wire threads so it can bend easily. I'd also protect it with split conduit tubing.


The fuse has two functions: safety and to protect the equipment. It does not regulate curent as implied by your question. I am unaware of an electrical code for cars but the electrical code for boats specifies that the fuse should be within something like 18" or 24" from a power source. If a short circuit occurs the fuse will blow but your truck will not burn. The hellroaring site mentioned that typical batteries draw about 60A when recharging. So an 80A would be fine but then you need to consider the opposite case, power needed when cranking and for running your car. Practically speaking the fuse is really only protecting wire in this application so a larger fuse will just be less likely to blow under normal use. For example if your primary battery is drained down and you want to start your truck, the second battery will be pumping out current to charge the primary battery AND crank the engine AND run lights etc. I used the 150A fuse and fuse holder sold by hellroaring. For your application, even though you could go with a smaller wire and smaller fuse, the only reason I can see to do so is cost of labor and materials.
If you value your time, you know that most of the cost of these projects is time spent on design, followed by time spent doing the work, followed by materials. Time spent trying to save a few bucks on materials is time wasted, since you are not going to do 10,000 dual battery projects. Hope this helps.

[Dusty T.]

Short answer:
You have a choice between #2 wire w/ 150A fuse OR #4 wire w/ 100A fuse OR #6 wire w/ 80A fuse. DO NOT use a smaller wire/fuse than #6. If it were my project, I would go with the #2 wire w/ 150A fuse.


I certainly agree with your points. I'm looking to go with #2 or #4 wire due to the additional length. This definitely helps reduce voltage drop, and will allow me to piggyback on that same charging wire to run power back to the cab from the aux battery to run the stereo, sub, CB, mini fridge, etc.... I guess I see the smaller 80 amp fuse preventing the alternator from being overloaded, but it's probably overkill.

I actually used the bcae1 wire site to aid me in my battery system design. That is an excellent quick reference guide to building electrical systems.



The hellroaring site mentioned that typical batteries draw about 60A when recharging. So an 80A would be fine but then you need to consider the opposite case, power needed when cranking and for running your car.

Where did you pick up this tidbit of information? Mike from HR seems like a great source of info for this system, but their website is a bit muddled. 60A still seems like alot to charge a battery but if there is some chart or reference for this, I'd like to see it!

Switch- I checked out your dual battery system on ttora. http://www.ttora.com/forum/showthread.php?t=67738
Now, you mention that the HR isolator is the incorrect isolator and should be the 95150, and not the 95300. The isolator in the photo looks like a 95300. Do you mean this is the incorrect isolator for your application? From what I read, your setup uses the second battery as a backup ONLY- not aux. Seems to me that the 95300 would be perfect for this setup. Pardon my misunderstanding regarding this, and thanks in advance for the clarification!


I really appreciate everyone's feedback here. This is probably the millionth post regarding dual battery setups so your patience has been much appreciated. I'll definitely take pictures when the setup is complete. It's always fun to compare notes.

[keezer36]

I believe the diodes of the isolators are rated at 90A. If you're sure your alternator is 80A, then your fine with running the larger wire. The reason the Hellroaring website recommends the 8AWG wire on the 95150 is the smaller diameter wire will limit the current through the isolator should your alternator be pushing more than 90A.

The 90150 is for hooking up your aux load on the second battery. The 95300 is for using your second battery primarily as a backup for cranking. If you used the 95300, you would have to hook up your engine off aux loads on the cranking battery. This is due to the diode configuration of the two isolators being different. If you ran a 95300 and had aux loads running on the second battery, there is nothing stopping the drain of the primary. Notice the 95300 has three posts and the 95150 has two. With the 95300, you can double your current carrying capacity because you have two posts available for hooking up the second battery.

If you plan on running aux loads with the engine off, the 95150 is the one to use and those aux loads should be hooked up to the second battery only.

[Switch]

I certainly agree with your points. I'm looking to go with #2 or #4 wire due to the additional length. This definitely helps reduce voltage drop, and will allow me to piggyback on that same charging wire to run power back to the cab from the aux battery to run the stereo, sub, CB, mini fridge, etc.... I guess I see the smaller 80 amp fuse preventing the alternator from being overloaded, but it's probably overkill.

I actually used the bcae1 wire site to aid me in my battery system design. That is an excellent quick reference guide to building electrical systems.



Where did you pick up this tidbit of information? Mike from HR seems like a great source of info for this system, but their website is a bit muddled. 60A still seems like alot to charge a battery but if there is some chart or reference for this, I'd like to see it!

Switch- I checked out your dual battery system on ttora. http://www.ttora.com/forum/showthread.php?t=67738
Now, you mention that the HR isolator is the incorrect isolator and should be the 95150, and not the 95300. The isolator in the photo looks like a 95300. Do you mean this is the incorrect isolator for your application? From what I read, your setup uses the second battery as a backup ONLY- not aux. Seems to me that the 95300 would be perfect for this setup. Pardon my misunderstanding regarding this, and thanks in advance for the clarification!


I really appreciate everyone's feedback here. This is probably the millionth post regarding dual battery setups so your patience has been much appreciated. I'll definitely take pictures when the setup is complete. It's always fun to compare notes.

I have a 95300. Before I installed the PC1700 I used the PC925 for aux power which is NOT the way the 95300 was supposed to be used. Sorry about the confusion on this point.

On this page it says "A starting battery rarely accepts more than 60 amps from an alternator"
http://www.hellroaring.com/bic75150.php

[ntsqd]

I have a hard time with sizing a wire to be a current limiter. Unless it is designed to be so (Fuseable Link) the potential for a fire is great. Just not a good idea.

Size the wire to deal with the max current that can flow in the circuit. Nothing less. Fuse or breaker the circuit to prevent over-current events.

Also, note that modern vehicles are designed with the alternator as the primary current provider, not the battery. The battery is really only intended for starting the engine. We alter that intent when we starting adding all of our various overlanding gear and asking that the battery support them with the engine off.

[Dusty T.]

I have a hard time with sizing a wire to be a current limiter. Unless it is designed to be so (Fuseable Link) the potential for a fire is great. Just not a good idea.

Size the wire to deal with the max current that can flow in the circuit. Nothing less. Fuse or breaker the circuit to prevent over-current events.

Also, note that modern vehicles are designed with the alternator as the primary current provider, not the battery. The battery is really only intended for starting the engine. We alter that intent when we starting adding all of our various overlanding gear and asking that the battery support them with the engine off.

I know, it seems strange to size a charge wire this way, but the closest analogy I could think of is the size hose you are using to fill a bucket. Of course, the smaller, #8 gauge charge wire would have a 50 amp fuse at each end.


I received some info back from Hellroaring regarding the charge wire size. Very quick customer service! See the attached PDF for their recommendation.

I'm still tempted to go with between #6 to #2 wire to charge the aux battery. As mentioned earlier, I would like to use ONE wire between the main and aux battery for both charging and providing power to the accessory fuse box in the cab. The #8 wire sounds dangerously small for this task. Otherwise, it seems that I would need to run one #8 wire to charge the battery, and run another #6 wire back to the fuse box in the cab. Seems like even more overkill than my setup already is!

[ntsqd]

If the battery's maximum rate of charge is 60 amps, then regardless of the alternator's capacity the circuit will only flow 60 amps at most. I see their point, I'm not buying it for a single aux. battery. Maybe for a large battery bank comprised of several to many batteries in parallel. I still think the basic approach is wrong, but I've no experience with such systems.

[Dusty T.]

If the battery's maximum rate of charge is 60 amps, then regardless of the alternator's capacity the circuit will only flow 60 amps at most. I see their point, I'm not buying it for a single aux. battery. Maybe for a large battery bank comprised of several to many batteries in parallel. I still think the basic approach is wrong, but I've no experience with such systems.


That's where I'm at as well. This would leave 20A at the very least to run the engine and some other accessories during MAX charge for the aux battery.

You know, rather than me beating a dead horse with ampacity, voltage drops, and wire sizes, I need put a parts list together with some #4 wire, a 60-80 amp fuse, and start building this sucker!

[ntsqd]

If the battery's maximum rate of charge is 60 amps, then regardless of the alternator's capacity the circuit will only flow 60 amps at most. I see their point, I'm not buying it for a single aux. battery. Maybe for a large battery bank comprised of several to many batteries in parallel. I still think the basic approach is wrong, but I've no experience with suchLarge
systems.

Fixed it.




You know, rather than me beating a dead horse with ampacity, voltage drops, and wire sizes, I need put a parts list together with some #4 wire, a 60-80 amp fuse, and start building this sucker!
WHAT!? You mean this wasn't just a mental exercise?
LOL........

Looking at it this way, say the aux battery is a 200Amp-Hr unit. That's one amp for 200 hours, or (in theory, not sure the conductors would live there very long) 200 amps for one hour. So with a 100 amp alternator the worst possible case would require maximum output for 2 hours (ignoring what such a thing would actually do to the battery). An automotive alternator can probably do that, but it's pushing pretty hard.
With a multi-battery aux bank of, say, 1000 amp-hrs that alternator will expire before a full state of charge is achieved.
In that context what they are saying makes sense. I just disagree with their solution.

[Dusty T.]

WHAT!? You mean this wasn't just a mental exercise?
LOL........

Looking at it this way, say the aux battery is a 200Amp-Hr unit. That's one amp for 200 hours, or (in theory, not sure the conductors would live there very long) 200 amps for one hour. So with a 100 amp alternator the worst possible case would require maximum output for 2 hours

I've had a headache all week thinking about this!

Wow, 200 Ah. The Yellow Top I'm looking at is 75 Ah- about the same size as the aux battery used on my last setup. I failed to mention my last setup did use a #8 charging wire which seemed to work okay, but I wasn't using that same wire to also run additional accessories off of that battery. It was strictly for charging.....

So conceptually, it would likely take less than one hour to fully charge the 75 Ah aux battery without running the alternator at full capacity during that period of time. As the battery would charge, its current draw would gradually decrease until it was fully charged. Perhaps a voltage drop could occur when the alternator is maxed out, thus causing the isolator to stop charging the aux battery? Just a thought, anyway.....

I was also considering the 95300B isolator to simply run everything off of the "main" battery and have the second battery for startup purposes only. Either way, there will still be a drained battery needing a charge. HR's standpoint with this setup is that there is only ONE battery being drained since the backup starting battery is completely isolated from loads. The aux system, however, has the potential of having both batteries drained from their respective loads, hence Hellroaring recommends the smaller charging wire to prevent two (instead of one) drained batteries from overloading the charging system. Personally, I see two drained batteries as a very unusual occurrence for my setup since the stereo will almost always be connected to the aux battery anyway. Not to mention Toyota has gone through great lengths to make running down the main battery nearly impossible by automatically switching off accessories when the key is removed.

In the meantime I'm going to get back to designing and slowly building this setup over the next couple weeks or possibly months as time permits. I certainly can't wait to get a more improved aux battery system up and running again for those future back country trips!

[Dusty T.]

It's been a busy few weeks between work, and squeezing in a little trip to Nevada's Black Rock Desert for the Tacos first camping trip. Good Times!

Looking for a second opinion on cable routing..... I was debating the location of the aux battery and decided on mounting it on the passenger side, front end of the bed for better weight balancing.

That said, I'll probably run the #4 charge cable up under the bed closer to the muffler than I'd like to. It will attach to the underside of the bed where the end of the tape measure is shown (see attached photo). What I'm wondering is whether this is dangerously close (within 6") to the hot exhaust? I do plan on wrapping the wire in plastic loom and covering it with that adhesive metallic fiberglass insulation to help deflect some of the radiant heat coming off the exhaust. The only other routing I can think of is running the wire up into the bed behind the bedliner..... I personally can't see this cable being exposed to higher temps than under the hood, but just wanted to be sure this isn't a recipe for disaster.

Thanks for the help once again! :o

[ntsqd]

This would be an ideal place for Firebraid sleeving. Woven fibreglas tube covered in high temp orange silicone.
http://www.longacreracing.com/images/products/construction/4950.jpg
Longacre p/n 49750 (http://www.longacreracing.com/catalog/item.asp?id=116&catid=4) 36" for $21.50 or p/n 49770 (http://www.longacreracing.com/catalog/item.asp?id=117&catid=4) 10' for $57.35
Use adhesive lined heat shrink on each end of the sleeve to keep grit from getting in and slowly grinding thru the cable's insulation.

[Dusty T.]

That looks to be pefect for that application, thanks!

What I'll probably do is cover the charge wires in split wire loom (swear by that stuff for finish and longevity), and then run the Firebraid sleeving over the loom..... I called Longacre to double-check and according to them that is acceptable.

Thanks.

[Dusty T.]

Well, I've kicked off the ordering process, and purchased the BIC 95150B yesterday. Mike has patiently answered numerous questions I've emailed to him, and I think this product will work nicely for my setup.

I did come up with one snafu now that I am getting ready to order up wire. The length between the two batteries (via the charge wire) is about 20 feet. A good long distance I know.... I used some voltage calculators to match up a good wire size and realized that the length between batteries may need to be be doubled to gain the correct voltage drop. Now, does this need to be done between two batteries, or only for branch circuits? Suddenly, the #2 charge wires (positive & negative) I was thinking about using look to be potentially too small to both charge the aux battery and run some accessories at the same time without a massive voltage drop..... I'm rethinking running the negative through the chassis since this may elliminate the return (negative) wire distance, since it is now a mass of iron....

As if this isn't overengineered enough as it is! :drool:

[Dusty T.]

So, any ideas on calculating voltage drop versus using the frame as a ground, or running a dedicated wire between the two batteries?

I ask this because I went round and round about this over the past week regarding whether to use the frame as a ground or to run a dedicated negative wire back to the main battery. I also came to the realization that I could go all out and also be able to jump start the engine in an emergency situation (provided the aux battery is properly charged). This would be easily done by using the high amp marine switch to bridge the two batteries and bypass the Hellroaring isolator for higher amp current draw when starting. I have considered using the frame to ground between the two batteries, but have no idea what the resistance of the steel frame would be....

I also looked at several voltage drop calculators that seemed to indicate that the chassis or frame distance along the circuit path of travel could be disregarded when calculating voltage drop. On the other hand, when running a dedicated negative wire back to the main battery, that distance would now need to be considered. Now it seems to me that the frame would provide more resistance due to weld joints, poorer conductivity compared to copper, and the likelyhood that the current would travel through crossmembers welded to the frame rails (assuming the batteries are grounded to opposite frame rails). Not to mention resistance at the ground wire to frame connections in a wet/muddy/salty environment (and we all know how much our Tacoma frames like to corrode).

I read the arguments both for and against the dedicated ground wire. One thread I caught addressed my question nearly to a tee: http://www.exploroz.com/Forum/Topic/54859/wire__cable_size_calculations.aspx

Needless to say, I bit the bullet and purchased both positive and negative #2/0 wire to run between the main battery and bed-mounted battery (nearly a 20' distance) to be used as both the charging and starting conductors. Got a decent deal on the copper, so it didn't totally break the bank to run a dedicated ground wire back to the battery anyway.

So what's everyone's take on using the frame as a grounding conductor? I know I'm a stubborn (and possibly certifiable) fool for ordering up the extra cable at #2/0 nonetheless, I'd still like to hear other input on this grounding conundrum. My main goal after building this system is for it to be as maintenance and thought-free as possible..... :ylsmoke:

[keezer36]

If you've already bought enough wire, why not run it back just to be sure?
I'll be doing the voltage drop tests as discribed here: http://www.aa1car.com/library/voltage_drop_testing.htm and depending on my findings, I may do the same. I've a couple other mods on my plate right now so I don't know if I'll get to this in the next couple weeks.

[Dusty T.]

Hey thanks, keezer for the link. I checked it out and may give that a go after the project is built. Worst case scenario, I double up on the negative return wire by bolting it to the frame near the bed-mounted battery- thus using both the frame and wire as a ground path......

The design phase is pretty much over and parts have been trickling in this week. Installation will begin this weekend. Still getting over the price of copper these days despite working in the electrical industry! :Wow1:

[Dusty T.]

Well, it's finally finished after a year of starting and stopping! The battery is installed and connected, the Hellroaring isolator seems to be working as it should, with all systems up and running. There will be a writeup to follow in a couple weeks as time permits.

Got one more obscure question about cabling before I call it quits with this project. How much movement can I expect to get between the body and frame? Of course the body is mounted on rubber bushings, but how much does it really move independently of the frame itself? I ask because I'm running a battery cable that passes between the frame and cab with about 1/4" of clearance (it's been trimmed up after the pic below was taken). The same cable is also connected to the frame and then onto the body where it goes into the engine compartment. Does the cable need much if any slack for this transition? Just wondering if this is an issue when on very uneven terrain with some frame and body flex in mind.

Thanks. I'm trying to make this as robust as possible. There's a pic included showing the clearance I have.

http://top5rq.blu.livefilestore.com/y1pMiRhqQCPxgQfG2wkyu0-LwZQEn5Dwzw_cXPZohYlLuGaaKRnQuL73pD8BmbI8aoMg5VlLB dS4voEMlT_i_2QrA/IMG_5407.jpg