Dummy needs help !!

[Steve Curren]

I have a trailer with the deep cycle battery in the nose box, I want to put another battery in the rear. My question / concern is how I can wire the rear battery to the charging system from the tow vehicle without the other battery pulling power from it. I am not sure if it would suck the juice from either one but I want to hook it up corectly.
Thanks,
Steve

[DaveInDenver]

Do you need to be able to selectively switch the batteries? If not, you can isolate the two batteries with a pair of diodes. Feed the +12V to the both diode anodes and connect one cathode from each diode to the + side of the battery. Each will get current only from the common feed, not from the other battery. You will get a slight voltage drop across the diode, up to 0.7V but could be as low as 0.3V. Depends on the type of diode you pick. What's your budget for the project?

[Steve Curren]

I don't imagine I need to switch the batteries, I just want to be able to charge them both without taking power from the other. Now for the important quesiton what's a diode? I have no idea how much this would cost but I would like to keep it as low as possible yet do a good job. I would like to get the diode that restricts the voltage flow the best.

[articulate]

To make it simple, I'd call Wrangler Northwest Power Products and talk to Steve. He'll be able to talk you through it and suggest a product or two.

Hope it helps.

[DaveInDenver]

To make it simple, I'd call Wrangler Northwest Power Products and talk to Steve. He'll be able to talk you through it and suggest a product or two.

That's probably the right answer here. Think of a diode as a semiconductor check valve, current flows one way, but is blocked from flowing back.

[Steve Curren]

Guys,
Thanks for the info, I now have a good idea what a diode is and I am looking up Northwest Power Products.

Steve

[eugene]

yep, its a one way valve. Surepower makes a lot of battery isolators which are a pair of diodes stuck in an aluminum case. You have three terminals, one for input and one for out to each battery. The diodes prevent current from flowing from one battery to another.
Napa sells surepower gear with their name on it. You need to size the isolator large enough to handle the load, for example for my 105A alternator I used the 120A isolator.

[Steve Curren]

Thanks, I looked up the Surepower and have fond one I believe that will work.
If I was to get a 120 A isolator how can I determine the output of my alternator?

Thanks,
Steve

[eugene]

The alternator output should be marked on the alternator or on the specs for your truck somehwere.

[articulate]

Steve, the output on the OEM Jeep Rubicon (through 2006) alternator is 117 amps.

:)

[Steve Curren]

Gents,
Thank you ever so much for your kind assistance. I have the battery installed and will order a 120Amp Isolator, one question more if you please. Can I use a common ground for both the batteries without messing up the works once again??

I owe a drink to all, I will be at Pyramid Lake and you can collect there.

Steve

[DaveInDenver]

Gents,
Thank you ever so much for your kind assistance. I have the battery installed and will order a 120Amp Isolator, one question more if you please. Can I use a common ground for both the batteries without messing up the works once again??

I owe a drink to all, I will be at Pyramid Lake and you can collect there.

Steve
Yup, all the negatives are connected together. You don't have to physically tie each ground wire together, taking a ground cable to a common thing like the frame is fine.

[Steve Curren]

Thanks, I will just tie the negative posts of both the batteries to the ground coming from the Jeep..
Once again I am in debt to those on Expedition Portal, great group of folks.

Steve

[eugene]

Check the surepower instructions and see if you need the isolator with the 4th pin. Some alternators require it, like my GM.

[Steve Curren]

Thanks for the heads up, I have a Jeep and it looked like the Chrysler products didn't. I did see a certain type of GM product that was different.

Steve

[Steve Curren]

Hey electric folks... I called Sure Power and a tech said what I needed was a separator and not an isolator,any ideas or input?

Thanks for your help and patience,
Steve

[ntsqd]

Diodes suffer from a small voltage drop (can think if it as taking a little power to keep that check valve open).

A seperator must be what is used on boats to seperate battery banks. I'm not very familiar with that term.

Another option, if you have some way to switch it is to use a constant duty solenoid. When the switch is on the batteries are hooked together. When the switch is off the batteries are seperated. That switch can be the ignition switch of the tow rig.

Another option, & one that I'm particularly interested in, is called an "ACR" meaning "Automatic Charging Relay." Here's one at West Marine. (http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/223149/0/0/ACR/All_2/mode%20matchallpartial/30/0) These look like the simplest to install.

[Grim Reaper]

Thanks, I looked up the Surepower and have fond one I believe that will work.
If I was to get a 120 A isolator how can I determine the output of my alternator?

Thanks,
Steve

Most Feeds from the tow vehicle are rated 30amp max and will not be able to carry 120 amps on the existing wire nor would you EVER want to try to carry that amount. If there isn't already a breaker or Fuse on the feed line I would recommend adding one.

On a RV/camper you also need to consider its shore power charging circuit. It will already be wired to charge the existing battery.

This is where things are going to get tricky on what you plan to do with the second battery. Fill in the blanks of what you are trying to do so we can mull over how to make it happen.

If you put the isolator between on the battery lead out of the RV powwer panel yes you will be able to charge both but that wire also feeds back to the panel when the RV is running on battery so a Isolator has to be able to bypass the Isolator. This may be an instance where you would be better off buying two new batteries with the exact same ratings and wire them in parallel if you are just trying to increase your battery reserve power.

[Steve Curren]

What I have is a Chaser with the original battery that was installed when I bought it. I have a Jeep Wrangler as a tow vehicle, I used the harness purchased at the Dealership. I want to put a second battery of the same type in the Chaser also. I guess I have two options, firstly I can have the two batteries separate and I would like to know how to hook up the batteries so they can charge but not drain one or the other when the Chaser is not hooked to the Jeep. I can hook both batteries together and increase amps and be sure that they both would charge from the Jeep. I read that hooking in parallel is the best as it keeps the voltage the same but increases the amps, is that the way to hook them up?

Thanks to all for the help..
Steve

[ntsqd]

I see three ways to do this simply at the trailer.

1) Use an isolator. The downside is that there is a voltage loss across the diodes. Diode isolators are falling out of favor because of this. Alternator regulators can be tweaked to offset this, but now should you need a replacement alternator you no longer have an off the shelf part.

2) Use a marine combiner switch like this one. (http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/91533/0/0/battery%20switch/All_2/mode+matchallpartial/0/0) Fully manual, absolute control all the time. Fully manual, if you forget to switch it.......
I have this on my Sub, and have suffered the forgetful part.

3) The ACR that I linked above. As best as I can tell this high current relay (think continous duty starter solenoid) connects like an isolator, 3 terminals. One for each battery and one for the charge wire. When the tow rig is running the relay closes and both batteries get charged. When the tow rig is not running the batteries are seperated. Simple & ntsqd-proof........
I have one on my short list of things the Sub needs.

[Steve Curren]

Thanks for the info, I guess I will have to get the one for the brainless and see if I can install it. I am kinda worried about heat as inside the nose box there is no air movement, I hope..

Thanks again to one and all for input.:bowdown:

Steve

[eugene]

I see three ways to do this simply at the trailer.

1) Use an isolator. The downside is that there is a voltage loss across the diodes. Diode isolators are falling out of favor because of this. Alternator regulators can be tweaked to offset this, but now should you need a replacement alternator you no longer have an off the shelf part..

Most modern electrical system have an external regulator, usually integrated into the engine control computer. This compensates for the diode loss so the isolator drops .7v and the regulator ups the alternator output by .7 volts so it evens out. So you don't have low voltage anywhere everything is still as before. The only downside it if you hit the absolute max output of the alternator where the regulator has to compensate for the voltage drop caused by the extreme load then it might not have as much range that it can compensate for so you may hit max a couple amps lower then without it but your not going to be having a lower voltage normally or have to rig anything up.
On GM vehicles for example you have to run an extra wire, other vehicles don't need the extra wire because its already in the alternator control circuit.

What tends to happen with relays is you have been using the second battery all day long so its pretty low. Then you have a 4-5 year old starting battery so its getting marginal so as soon as you turn the key the relay connects both batteries and the low one loads the marginal one down to where it can't crank the engine. A diode isolator prevents that. Its a rare condition though but I've seen the car audio guys run into it.

[ntsqd]

I've no knowledge of real late model stuff, but most of the 90's stuff still has an internal regulator, they just also have the ability for the computer to remote control them. Witness GM CS series alts being functional w/ or w/o a computer connected to them.

The ACR is not like older relays that require a seperate trigger wire. As best as I can tell they sense charge current and turn on. So no charge = no connection; charge = connection. I would suggest that a constant duty solenoid be used in the engine bay in the charge wire. This so that the trailer batteries don't try to help start the tow rig thru too tiny a wire.
Connect it's trigger to a run mode (not a start and/or run mode) source. That way all of the trailer stays disconnected during starting.
Alternately one could use two ACR's, one in the engine bay on the charge wire and one on the trailer btwn the two batteries. That would be the spendy solution, and I'd want to verify first that ACR's can run in series like that.


http://i168.photobucket.com/albums/u196/ntsqd/acr.jpg

Thinking further on this, the boat industry has already fought all of these battles. Perhaps it's time to look at what they do and how that might be adaptable to this application. An Amazon search (http://www.amazon.com/s/ref=nb_ss_gw/103-3144739-0178250?url=search-alias%3Daps&field-keywords=12+Volt+Bible&Go.x=12&Go.y=8&Go=Go) turned up several titles on the subject.

[eugene]

The problem with using the run power to trigger the soloniod is most ignition switches pass through run before start so your relay turns on then off then back on causing an extra switch each time. Then your still not isolating the batteries since they are completely connected so the discharged secondaries are still drawing off the primary where the diodes in the isolator prevent this.
The other advantage to the isolator I've found is it filters out the noise. I don't pick up power window motor noise in my comms on the second battery since the it gets blocked by the diodes. So all the spikes and surges on one side doesn't get passed to the other.

[ntsqd]

Which relay are you talking about? The continuous duty solenoid, or the ACR?

Not all IGN switched leads also function in crank mode. In one particular case I know that the 'tickler' for the alt is not live during cranking.