Thanks, but I already acknowledged the difference. What I was saying was that the vendor described what I ordered as "heavy duty."
How to make a cheap isolated dual-battery setup for $50
- Thread starter evldave
- Start date
Thanks, but I already acknowledged the difference. What I was saying was that the vendor described what I ordered as "heavy duty."
The first photo shows the FTZ starter lugs - which slipped out using the #25 dies - after using the smaller-than-recommended 16 dies. Please don't get on me about the condition of the wire. I was messing with these samples. In my good crimp (2nd photo) using the other lugs and the "recommended" 25 die size, the copper strands are neatly inserted straight into the lug.
No need to get punitive, John. Without having the item in hand, how is one to differentiate between item description and marketing language? Manufacturers are known to differentiate levels with such descriptors. I certainly wouldn't have thought that FTZ, if known for their quality [true] heavy-duty lugs would be cheap on their regular-duty starter lugs.
another_mike
Adventurer
Compared to regular copper lugs, that starter lug is thicker.... but its still a starter lug. Anything with a flare on the outside is the giveaway its not as heavy duty as the power lugs.
Agreed. And I''m sharing it on this forum so others can learn from my mistakes.
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I've used the better part of an evening reading this thread; operative word is "used" - I've learned a lot of new info and brushed up on some concepts that were a bit fuzzy. Thanks for the education!
Still, as for how many amps one can expect the house battery to pull during charging, I'd like to know more. The electrical wizards here have gone deep on just about every other subject, but in this case, it's "it depends". Can we make some assumptions and get close? As another poster said (years ago?), Math me bro!
I'm mostly interested because I've already run my Starter batt -> house batt wire, it's on the small side (#8, whoops), but for what I'm doing now, it's fine. I'm not wholly confident in my estimates for power usage in this rig, and if I need to upsize my system later, I'd rather run the bigger wire now so it's plug and play. Definitely don't want to do it if it's not worth it however. The explanation here (http://www.smartgauge.co.uk/nosurge2.html) was the best I found but leaves out some of the math at the end I would need to get close. Help? I'd like to build my own "worst case scenario" so I can size the wire appropriately.
Connecting two banks up "live" has too many variables to be more precise.
If you take a very large fully charged bank, and jumper it to a depleted bank of high CAR chemistry (charge acceptance rate) or one with an internal short you didn't know about, you can **melt** undersized and unfused wire, start a fire.
If the depleted bank is healthy standard (low CAR) FLA, the connections are good and/or you have proper wire gauge or a properly sized fuse, then no problems.
The only way to tell what the actual current flow rate will be is to put in some oversized wire, an accurate ammeter, set it for the right ballparked​ range, or a properly sized shunt-based monitor.
The real key to safety is the fuse, sized 20% lower than the safe rating for the wire. If that blows, put in bigger wire.
Or oversize the wire, and fuse for whatever the biggest ampacity you ** want** to see flow there.
If you take a very large fully charged bank, and jumper it to a depleted bank of high CAR chemistry (charge acceptance rate) or one with an internal short you didn't know about, you can **melt** undersized and unfused wire, start a fire.
If the depleted bank is healthy standard (low CAR) FLA, the connections are good and/or you have proper wire gauge or a properly sized fuse, then no problems.
The only way to tell what the actual current flow rate will be is to put in some oversized wire, an accurate ammeter, set it for the right ballparked​ range, or a properly sized shunt-based monitor.
The real key to safety is the fuse, sized 20% lower than the safe rating for the wire. If that blows, put in bigger wire.
Or oversize the wire, and fuse for whatever the biggest ampacity you ** want** to see flow there.
As far as the alternator current goes, if your bank is large and high CAR, you should have a VR capable of derating alt output, both via explicit settings and/or dynamically based on temp sensing both at the alt and bank.
Or put in a DCDC charger with ampacity lower than what you want to try to pull from the alt.
Or put in a DCDC charger with ampacity lower than what you want to try to pull from the alt.
dwh
Tail-End Charlie
Umph. Well, the math isn't difficult - it's just your bog-standard Ohm's law applied to get a current value:
http://www.physicsclassroom.com/class/circuits/Lesson-3/Ohm-s-Law
The first problem comes from trying to fill in the blanks with correct values. To get a current value (amps flow) you need the resistance of the battery, which is a moving target (a variable which keeps changing values). Also the resistance of the wire, another moving target.
You also need the electrical (energy) potential difference expressed as voltage.
(That is not only a moving target, but for battery charging it's also totally different than the examples in the Physics Classroom link, which I'll get to in a moment.)
Nevertheless, at any given moment (set of prevailing conditions), each of the variables will have a certain value, so you can run the formula with X values filling in the blanks, run it again with Y values, and yet again with Z values - and then plot the three (or better yet three-hundred) sample results on a curve to make your predictions.
BUT...(there's always a but)
In those examples on the Physics Classroom page, the voltage potential is a finite value. You start at say 3.0v and it's all downhill from there. That's fine for figuring loads supplied from a battery (or other source with a fixed finite (regulated) max voltage, such as an electric grid) and the various online "voltage drop calculators" are all based on that sort of scenario so they work fine for that.
However...the second problem is that when charging, the battery is at a certain voltage, say 12.2v (just to pull a number out of my... hat) but the alternator (or other source, such as solar) is running wide open (voltage not regulated) - a theoretically infinite voltage potential difference - until the voltage of the system reaches a point where the voltage regulator (VR) (or solar charge controller) starts limiting the voltage.
Now how in hell do you apply Ohm's law when one of the numbers, voltage potential, is "infinity"? Obviously, you can't.
<and now a brief interlude>
With muti-stage battery chargers, for example an Iota, the bulk stage is done in "constant current" mode, but the absorb (and float) stage is done in "constant voltage" mode. What is the difference?
In constant current mode, the voltage is unregulated, allowing it to theoretically rise to infinity, in order to get the maximum current flow allowed by the resistance of the circuit. Of course, a current limiter is installed to protect the charger, so a 30a Iota charger is "current limited" to a max of 30a.
In constant voltage mode the voltage is regulated (limited), so it cannot theoretically rise to infinity.
So you start out with a voltage potential difference of battery vs. infinity.
In that situation the battery regulates (limits) the voltage of the charging circuit. The total resistance of the circuit regulates (limits) the current (unless the resistance is low enough that the charger's current limiter comes into play).
This continues until the voltage of the battery (and thus the voltage of the charging circuit) reaches the bulk->absorb transition set point programmed into the charger. At that point, the charger starts regulating the voltage (switches from constant current mode to constant voltage mode) to prevent the battery voltage from rising beyond the programmed voltage limit.
And the total resistance of the circuit is still regulating (limiting) the current. But since the battery voltage is roughly the same as the regulated source voltage, AND the resistance of a lead acid battery rises as its SoC rises, the current flow isn't enough to bring the charger's current limiter into play, and the current flow becomes less and less as the battery absorbs.
Ultimately, the voltage potential of the battery and the voltage potential of the source become equal, and no current flows.
(Actually, an Iota with IQ/4 brain will change the regulated voltage from absorb voltage to float voltage after 8 hours, others will switch to float voltage when the current flow drops below a set value - some below 3a, some below 2a, etc.)
The purpose of this digression is because the terms "constant current", "constant voltage" and "current limited" are important to the topic at hand - taking a guess at how much current can be expected to flow from an alternator to a house battery in an overland vehicle.
[Don't want to hit the post character limit, so I'll continue in the next post.
"More to come..."]
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dwh
Tail-End Charlie
Okay, so back to the original question: How to estimate the current flow in order to choose the right size wire?
You mentioned, "making assumptions". Well, that's how it's done. Also known as "taking a WAG" (wild-assed guess).
You start by throwing out the idea of "voltage drop". It doesn't apply to battery charging. The source voltage is running wide open (infinite), and the charging circuit voltage is being regulated by the battery, so there is no voltage drop - the entire charging circuit is at battery voltage regardless of wire size.
(Until the battery / charging circuit voltage reaches the point where the automotive voltage regulator, or the solar charge controller, or the multi-stage shore power charger starts regulating the voltage of the charging circuit. And guess what? The charging circuit is still at battery voltage, so there still isn't any voltage drop.)
So now it's "all about the Benjamins". Well, actually, it's all about the current, or amperage (same thing). (And hey, Poor Richard invented electricity, so...get it?)
So you start by guessing at the max amps of the source. That's easy with a current limited source such as a shore powered charger or solar array. Well hell, alternators are current limited too. Their limit is based on temperature though (same with solar). The alternator might be capable say 100a when cold, but they put out less when hot.
"Temperature ratings are often determined using a military standard of 122°F, measuring the ambient air temperature in the vicinity of the alternator. Sustained operation in hot engine room conditions will reduce alternator output. A “hot” alternator, operating at approximately 180°F -200°F will only supply about 80% of its rated capacity. Large-frame models generally run cooler than their smaller siblings because of their ability to dissipate heat. Small case alternators are not designed for continuous high-output operation."
https://www.westmarine.com/WestAdvisor/Selecting-an-Alternator
But for guesstimating purposes, I just figure the max possible amps. So I figure 100a even though I know when it's hot it will be more like 80a.
Then you use the resistance (impedence) values of the battery and wire to reduce the amp flow number down from say 100a to...whatever.
Yea...good luck with that. As you know from reading Smartguage's "no surge" document, the resistance is a curve and based on SoC. According to that doc, the bottom of the curve (lowest resistance) is around 40%, and the curve goes up at both ends (higher resistance at low SoC and at high SoC).
Lifeline used to publish tons of graphs for their batteries. Resistance curve was one of them. Can't find it now. Probably still out there somewhere if you want to spend the time looking. Or try finding that data for whatever battery you actually have.
Or do what I do - fuhgedaboudit.
Anyway, here's my method...
1. Assume max possible amps. We'll say 100a.
2. Check the Lincoln Welding wire size chart:
http://m.lincolnelectric.com/en-us/...ges/selecting-proper-size-welding-cables.aspx
Well hell...it starts at 125a and #6 welding cable - for a 30% duty cycle. Which is for welding cable with an isulation temperature rating of 75C.
So whatever kind of #8 you are using should be good for 100a. For a while anyway.
But that's fine, a while is all you need. DiploStrat had a modern Chevy truck with dual 125a alternators, a huge battery bank and BigAss™ wire (1/0 welding cable..or maybe 2/0, don't recall offhand). And he would regularly run the batteries down with the microwave, electric induction stove, air conditioning and various sex toys (just seeing if he's paying attention
). He would see up to 150a going into his battery bank...for a half hour. After that the rising battery voltage/resistance would cause the amp flow to start dropping.
If you size the wire to handle the max expected amp load, then it's going to end up oversized. Even if it wasn't, at most it would shave a couple amps off the charge current during the initial part of the bulk charge. For a while. Half hour maybe. After that, as the amp flow drops, it certainly will be oversized for the remainder of the many hours it will take the battery to finish absorbing.
So that's my method of choosing a wire size for battery charging: Size the wire to handle the max expected amp load. Size the fuse to protect the wire.
Ignore voltage drop, it's irrelevant - it doesn't exist in this situation anyway. (And even if it did, it would go away in a short while.)
That method will result in wire that is oversize during at least 90% of the charge cycle - and more likely 100%.
(I use a different method to size wire to supply loads FROM a battery. Voltage drop certainly DOES exist in that situation.)
You mentioned, "making assumptions". Well, that's how it's done. Also known as "taking a WAG" (wild-assed guess).
You start by throwing out the idea of "voltage drop". It doesn't apply to battery charging. The source voltage is running wide open (infinite), and the charging circuit voltage is being regulated by the battery, so there is no voltage drop - the entire charging circuit is at battery voltage regardless of wire size.
(Until the battery / charging circuit voltage reaches the point where the automotive voltage regulator, or the solar charge controller, or the multi-stage shore power charger starts regulating the voltage of the charging circuit. And guess what? The charging circuit is still at battery voltage, so there still isn't any voltage drop.)
So now it's "all about the Benjamins". Well, actually, it's all about the current, or amperage (same thing). (And hey, Poor Richard invented electricity, so...get it?)
So you start by guessing at the max amps of the source. That's easy with a current limited source such as a shore powered charger or solar array. Well hell, alternators are current limited too. Their limit is based on temperature though (same with solar). The alternator might be capable say 100a when cold, but they put out less when hot.
"Temperature ratings are often determined using a military standard of 122°F, measuring the ambient air temperature in the vicinity of the alternator. Sustained operation in hot engine room conditions will reduce alternator output. A “hot” alternator, operating at approximately 180°F -200°F will only supply about 80% of its rated capacity. Large-frame models generally run cooler than their smaller siblings because of their ability to dissipate heat. Small case alternators are not designed for continuous high-output operation."
https://www.westmarine.com/WestAdvisor/Selecting-an-Alternator
But for guesstimating purposes, I just figure the max possible amps. So I figure 100a even though I know when it's hot it will be more like 80a.
Then you use the resistance (impedence) values of the battery and wire to reduce the amp flow number down from say 100a to...whatever.
Yea...good luck with that. As you know from reading Smartguage's "no surge" document, the resistance is a curve and based on SoC. According to that doc, the bottom of the curve (lowest resistance) is around 40%, and the curve goes up at both ends (higher resistance at low SoC and at high SoC).
Lifeline used to publish tons of graphs for their batteries. Resistance curve was one of them. Can't find it now. Probably still out there somewhere if you want to spend the time looking. Or try finding that data for whatever battery you actually have.
Or do what I do - fuhgedaboudit.
Anyway, here's my method...
1. Assume max possible amps. We'll say 100a.
2. Check the Lincoln Welding wire size chart:
http://m.lincolnelectric.com/en-us/...ges/selecting-proper-size-welding-cables.aspx
Well hell...it starts at 125a and #6 welding cable - for a 30% duty cycle. Which is for welding cable with an isulation temperature rating of 75C.
So whatever kind of #8 you are using should be good for 100a. For a while anyway.
But that's fine, a while is all you need. DiploStrat had a modern Chevy truck with dual 125a alternators, a huge battery bank and BigAss™ wire (1/0 welding cable..or maybe 2/0, don't recall offhand). And he would regularly run the batteries down with the microwave, electric induction stove, air conditioning and various sex toys (just seeing if he's paying attention
). He would see up to 150a going into his battery bank...for a half hour. After that the rising battery voltage/resistance would cause the amp flow to start dropping.If you size the wire to handle the max expected amp load, then it's going to end up oversized. Even if it wasn't, at most it would shave a couple amps off the charge current during the initial part of the bulk charge. For a while. Half hour maybe. After that, as the amp flow drops, it certainly will be oversized for the remainder of the many hours it will take the battery to finish absorbing.
So that's my method of choosing a wire size for battery charging: Size the wire to handle the max expected amp load. Size the fuse to protect the wire.
Ignore voltage drop, it's irrelevant - it doesn't exist in this situation anyway. (And even if it did, it would go away in a short while.)
That method will result in wire that is oversize during at least 90% of the charge cycle - and more likely 100%.
(I use a different method to size wire to supply loads FROM a battery. Voltage drop certainly DOES exist in that situation.)
DiploStrat
Expedition Leader
... And he would regularly run the batteries down with the microwave, electric induction stove, air conditioning and various sex toys (just seeing if he's paying attention
"Steely Dan" is not just the name of a band. :Wow1:
To the news-you-can-use: With big lead acid batteries, say, >200Ah, and a big alternator(s), say >100A, and a property charging voltage say >14.2v, then you probably hit the point of diminishing returns at 1/0 AWG. In my case, the 1/0 AWG wire was doubled as a 1/0 AWG overheated when used with a Sterling A2B and a 600Ah bank drawn down to 11v. Most folks will never hit that situation, which was > 190A.
While I am a charter member of the A@$$ Wire Club (the $$ are not accidental) and love to run the voltage drop calculator a certain amount of voltage drop, say <3%, (aka resistance in the wire loop) is not that big a problem at the start of the charging cycle as the voltage differential will still be enough to get a good charge. The only "good" news that voltage drop is not much of an issue at the end of the charging cycle when voltage and time are most important for completing the charge cycle. You can "prove" this by running the voltage drop calculator down at 15A or or so; even with long distance and small wires the drop is trivial.
While you DO want big wires, again, say > than 1/0 AWG, the real challenge is finding a way to complete the hours of absorb charge at the proper high voltage. As most vehicles drive less than six hours a day, the answer is almost always solar or shore power. (Why not your genset? Primarily because at the end of the charge cycle, the absorb stage, you are burning a lot of fuel for very few amps. Use your genset (or run your engine) at the start, when you are frying the ends, drying your hair, testing your Steely Dan, or when your batteries are seriously discharge. Then you will get lots of amps for your fuel.)
Thoughts on wiring and intelligent charging. USCG Wiring
I'll get back with some specific answers as I am reading this on phone while driving and making spaghetti.
Firstly the United states Coast Guard Marine wiring chart will be more use to you then the Lincoln welding cable chart. There is a picture in this aux battery writeup and you can google it.
http://www.engineeredobsolescence.com/2017/06/17/auxiliary-battery-setup/
One thing I have learned is that batteries have soecific charging needs, and companies like Ctek are exceptional at providing a proper chsrge based on the condition of the battery. With the Ctek dual I used I can also connect solar as needed to the same unkt and the battery will intelligently charge from either source based on the condition.
Lastly putting an aux. battery in the *** end of my Jeep with a 15' run allowed me to run 6 or 8 gauge which I had laying around from a set of booster cables.
The Ctek only draws a max of 30 or 40 amp which makes cables smaller (read cheaper) more easily protectable. i use a 30 amp blade fuse, and is infinitely better for the battery. Batteries need higher, but controlled volts to take a charge. Have a look at what Jay Leno has to say about Ctek and a few videos on youtube. I dont work with and am not affiliated, but for me the piece of mind, smaller wiring and ease of setup for both alternator and solar was a no brainer.
Will add some more later when noodles have cooked and I am off the higheay.
I'll get back with some specific answers as I am reading this on phone while driving and making spaghetti.
Firstly the United states Coast Guard Marine wiring chart will be more use to you then the Lincoln welding cable chart. There is a picture in this aux battery writeup and you can google it.
http://www.engineeredobsolescence.com/2017/06/17/auxiliary-battery-setup/
One thing I have learned is that batteries have soecific charging needs, and companies like Ctek are exceptional at providing a proper chsrge based on the condition of the battery. With the Ctek dual I used I can also connect solar as needed to the same unkt and the battery will intelligently charge from either source based on the condition.
Lastly putting an aux. battery in the *** end of my Jeep with a 15' run allowed me to run 6 or 8 gauge which I had laying around from a set of booster cables.
The Ctek only draws a max of 30 or 40 amp which makes cables smaller (read cheaper) more easily protectable. i use a 30 amp blade fuse, and is infinitely better for the battery. Batteries need higher, but controlled volts to take a charge. Have a look at what Jay Leno has to say about Ctek and a few videos on youtube. I dont work with and am not affiliated, but for me the piece of mind, smaller wiring and ease of setup for both alternator and solar was a no brainer. Will add some more later when noodles have cooked and I am off the higheay.