Help with my multi battery setup

[4x4junkie]

Since I've made that statement myself here a couple of times recently - I think it's probably safe to assume that I already knew that.

So, what's your point?

Apparently not if you think a discharged battery can't receive full current from an alternator if it's holding the bus voltage below it's set point...

No, they are typically *rated* to do that, but they don't unless there is 80a of load.



No, there is no full brunt. The alternator makes only as much power as is being drawn from the bus. If the battery can only accept 20a due to its resistance, then even a million amp alternator is only going to produce 20a.

Hoover Dam has a 2000 megawatt potential capacity, but if there is nothing hooked up but a 20w light bulb, than 20w is all the power that is produced. The rest is just "unused potential".

Ok very well... Lets take the article you linked and extract some of the figures from it.
The discharged battery in the example given is resting at 11.8V. The article also says charging can't take place until the battery is brought up approx 0.3 volts above it's resting volts before it will accept a charge current. So this makes 12.1V.
Now lets take the 0.02 ohm internal resistance figure they gave near the bottom for the discharged battery and see what happens when we apply an 80 amp charge current to it.

80 amps across 0.02 ohms (it's internal resistance) produces an additional potential of 1.6 volts on the battery's terminals. Adding 1.6V to the 12.1V needed before current flows, we have 13.7V. This would be the terminal voltage of the example battery while taking 80 amps of charge current.
13.7V is certainly below the 14.4V that is an alternator's set point, so explain how that would not cause the alternator to produce it's full output into the battery.

The article also mentions a battery's internal resistance is less when it has a greater state of charge, however the figures used above do not take this fact into account. So as the battery continues to charge, it's terminal voltage may even decrease some as it charges, sucking the alternator's bus voltage down even further from it's set point.

Still very much the opposite of what you say.

Of course, I recall his proposed bank size. If you'll read what I wrote, I specifically mentioned, "So for a typical 105ah deep cycle battery, that would be 25a." I was pointing out that *if* a 100a alternator actually dumped 100a, then that would be too much for a typical battery.

And I agree; with 4 deep cycle batteries and a 100a alternator, he's not going to exceed the charge rate *on that battery bank*. Even if the alternator put out 100a, which most of the time - it won't.

So why mention it then?

Because the battery bank is going to hit surface charge (relatively) quickly and then the amp flow is going to be minimal anyway because the voltage-regulated alternator is a constant voltage charging system, not a constant current charging system.

Which is why, with that size bank, he should be using a 3-stage charger that can do a constant current bulk stage.

I believe the Diehard Platinums are supposed to be re-badged Odysseys. And I did specifically mention the charge current rating of Odysseys.

Surface charge is not something you "hit" while charging a battery. A surface charge is nothing more than a voltage shift from an unevenness in the acid concentration caused by charging, and is why you would normally let a battery sit for several hours for it to dissipate before taking a voltage measurement to determine it's state of charge (it is also what brings the need to do absorption charging).
The only thing to be 'hit' during charging would be a battery's maximum applied voltage rating, which just so happens to be right at (or in some cases maybe a hair higher than) what an alternator's set-point voltage is (or that of a 3-stage charger's Absorb mode).

And again, modern alternators do operate as both a constant-current and constant-voltage charging system. They are regulated for both. Only thing they don't have is an ability to Float-charge a battery.

Yea, you DO keep harping on that. The problem is this - TANSTAAFL.

Never said there was. But there are easier/simpler/cheaper and harder/more complex/more expensive ways to do just about anything.

As I've said already: If he wants to minimize engine run-time, he's gonna need a proper charger because a crappy stock automotive charging system isn't gonna get the job done properly on a 400ah bank bank in a short time. If he depends on his voltage-regulated alternator and short engine run times, he's gonna kill an expensive battery bank.

And no, the DC-DC 3-stage isn't going to magically get it done in any sort of "short time" either. But it'll get it done in a "shorter" time, and that's what is meant by "minimizing run-time". Which, I also already mentioned.

See above 2nd from top.

In that example I was specifically showing that a *cranking battery* typically never does get drained very much (10th of a percent maybe). So recharging it is trivial. Takes a few minutes to recharge every time you start the engine.

I don't believe it does. But OK if you say so...
I'm still trying to find that car that puts out only 13.8 volts from it's charging system. Closest I've found was a '68 Volkswagen bug with it's generator and mechanical regulator (13.9V IIRC). Technology was a lot different back then.

And *that* is what a typical automotive "charging system" is designed to cope with.

Why do vehicle alternators (trucks especially) typically have specifications 3-5× above what a vehicle's electrical system could possibly ever use? Why do Ford and others offer higher-output (or dual) alternator options on some models? Certainly it can't be just to replenish 0.21Ah after starting the engine...

But to answer your question: What makes you think that an absorb stage is intended to save time? It surely isn't. It's the constant current bulk stage that saves time, not the absorb stage. If you're gonna have to simmer the battery anywhere from 4-12 hours anyway, you want to get it bulked up and switch to absorb as quickly as you can.

Please show me where I said the absorb stage saves time. Because I never did.

 

[dwh]

Why do vehicle alternators (trucks especially) typically have specifications 3-5× above what a vehicle's electrical system could possibly ever use? Why do Ford and others offer higher-output (or dual) alternator options on some models? Certainly it can't be just to replenish 0.21Ah after starting the engine...

Accessories.







Notice, they do a load test with a carbon pile tester.

Then, they do an amperage test on the alternator output wire.

With all accessories running, the total load is nearly 100a.

Then, when they turn off the accessories, the *charging* current is only about 25a.

If what you have been saying were correct, then the battery would be charging at 100a.

It isn't. It's charging at 25a.


Later, near the end of the video, they do another load test, with a resistance load tester. They first run one of them, then they run two in parallel.

By this time, they've drawn that battery down a pretty good amount.

Then they do a charging test again.

The amp flow hits 100a immediately, but within a few seconds, it's down to about 50a.

Again, if what you have been saying was correct, it would have stayed at 100a until the voltage regulator cut out.

But it didn't. Because that's not how it works.


If they'd continued that charging amp test, the charging amps would have continued to fall off over time. Eventually (not long - a few minutes), it would have hit the same 25a that we saw in the first charging test they did. Later, it would have been even less. Because the charging system is NOT a constant current charger.

Current limited yes, but current limited is not the same as constant current. Current limited just means it won't do more than the limit. Even constant voltage battery chargers are current limited.

Please show me where I said the absorb stage saves time. Because I never did.

"So then what is the whole purpose of chargers that are equipped with an "absorption" stage that lifts the battery's voltage to 14.2-14.4 volts if it's to accept a full recharge in any reasonable amount of time? " [emphasis added]

 

[4x4junkie]

Accessories.







Notice, they do a load test with a carbon pile tester.

Then, they do an amperage test on the alternator output wire.

With all accessories running, the total load is nearly 100a.

Then, when they turn off the accessories, the *charging* current is only about 25a.

If what you have been saying were correct, then the battery would be charging at 100a.

It isn't. It's charging at 25a.

Yeah, there's a couple problems there...
If you were paying attention, the engine was also at an idle when that 25A was measured, though that isn't as likely why it read 25A as is the following:
250 amps for 1 minute (3 20-sec cycles) is 4.1666~ Ah. A battery of the size shown is probably in the neighborhood of 60-65 Ah if it was to carry such a rating. 4.166 AH is probably less than 7% of it's total charge. A battery at better than 90% state of charge is not going to pull much current before the voltage rises to an alt's setpoint. Perfectly normal behavior for a lead-acid battery.

Later, near the end of the video, they do another load test, with a resistance load tester. They first run one of them, then they run two in parallel.

By this time, they've drawn that battery down a pretty good amount.

Then they do a charging test again.

The amp flow hits 100a immediately, but within a few seconds, it's down to about 50a.

Again, if what you have been saying was correct, it would have stayed at 100a until the voltage regulator cut out.

But it didn't. Because that's not how it works.


If they'd continued that charging amp test, the charging amps would have continued to fall off over time. Eventually (not long - a few minutes), it would have hit the same 25a that we saw in the first charging test they did. Later, it would have been even less. Because the charging system is NOT a constant current charger.

Current limited yes, but current limited is not the same as constant current. Current limited just means it won't do more than the limit. Even constant voltage battery chargers are current limited.

Again, the battery was not hugely discharged (those testers were only 120A each, and they didn't show loading it for the same 3 20-second cycles as the first time either, as they were only demonstrating them). By this time the battery might've been around 10-15% discharged (85-90% state of charge). And between those two particular tests he had also run the test with the Snap-On analyzer, which could've brought the battery back up slightly as well (or maybe not... we don't know). The result would've been quite very different had he continued loading it for 6 minutes or more to get the battery's SoC down around 50%.
It was effectively running just as it would in Absorb (you do recall an absorptive charge tapers off the current right? That's precisely what the gauge showed).


So... What exactly is your interpretation of a current-limited and a constant-current power source?, since in your mind they must be different. Last time I checked, a constant-current power source operates irrespective of voltage. It simply puts out voltage until a continuous current is achieved and then it limits the current to that point (the voltage is whatever it is, as long as it remains less than 14.4V). If 14.4V should be reached, then at that point it's operation changes to constant-voltage. This is absolutely no different than the first two stages of a 3-stage charger.

"So then what is the whole purpose of chargers that are equipped with an "absorption" stage that lifts the battery's voltage to 14.2-14.4 volts if it's to accept a full recharge in any reasonable amount of time? " [emphasis added]

lol
Ok, well you do seem to misinterpret what I'm saying with some regularity, so I guess I can see how that got misinterpreted too.
I was referring to a battery getting recharged before one were to shut the engine back off (a reasonable amount of time). 13.8V is not going to do that at all. But 14.4V will at least do it somewhat.

 

[JCTex]

Bigger Alternator?

Hope this is not a hijack; question should be close to OP's.

I'm building a 2013 JKUR that comes w 160A alt. I'm putting on a National Luna Dual Battery System & monitors. Taking out the rear seat and behind the passenger seat will be battery box containing 2 Lifeline AGM 4CT 6-volts, each 220A rated, for total 220A rated 12V. In an adjoining Electrical Box will be the cat fuse, shunt, a Xantrex 1000W interter (w/o auto switch), and an Iota charger. The distribution 12V panel/circuit breakers/outlets will also live there, along w/ the usual suspect marine switches.

On top will be 2-100W solar panels feeding a non-MPPT controller. This misses the rule of thumb of 1W per Amp; but if I keep to the 50%-or-so limit, a sunny day should get me home.

I'll use the mega-amp computation one of the posters above figured and assume for this question the answer will be ~225A max load. I'll use that and the length of runs against the wire sizing tables and figure out what AWG cable is needed. Based also on the above, looks like that may be #0 to get me from the front corner of the engine, down through the firewall, under the console, and behind the pass seat area, and back.

My question is do I need a bigger alternator? I don't know who makes Mopar alts but most modern automobile cases are big enough to be re-wound above 200A. I plan to rewire the alt with something bigger than #10 AWG if that's all it has, probably #6 fine strand, tinned marine UNLESS you experts think that's too thick.

JC

 

[4x4junkie]

Hope this is not a hijack; question should be close to OP's.

I'm building a 2013 JKUR that comes w 160A alt. I'm putting on a National Luna Dual Battery System & monitors. Taking out the rear seat and behind the passenger seat will be battery box containing 2 Lifeline AGM 4CT 6-volts, each 220A rated, for total 220A rated 12V. In an adjoining Electrical Box will be the cat fuse, shunt, a Xantrex 1000W interter (w/o auto switch), and an Iota charger. The distribution 12V panel/circuit breakers/outlets will also live there, along w/ the usual suspect marine switches.

On top will be 2-100W solar panels feeding a non-MPPT controller. This misses the rule of thumb of 1W per Amp; but if I keep to the 50%-or-so limit, a sunny day should get me home.

I'll use the mega-amp computation one of the posters above figured and assume for this question the answer will be ~225A max load. I'll use that and the length of runs against the wire sizing tables and figure out what AWG cable is needed. Based also on the above, looks like that may be #0 to get me from the front corner of the engine, down through the firewall, under the console, and behind the pass seat area, and back.

My question is do I need a bigger alternator? I don't know who makes Mopar alts but most modern automobile cases are big enough to be re-wound above 200A. I plan to rewire the alt with something bigger than #10 AWG if that's all it has, probably #6 fine strand, tinned marine UNLESS you experts think that's too thick.

JC

I'm not sure if the OP is still here after all the above lol

But I think your stock alt would be plenty.

I have basically the same capacity on mine (210 Ah) with a 95-amp-rated alt and it's kept up with all my needs no problem (running a fridge, stereo, and 10-30 watts of LED camp lighting for hours each night).
Of course how much you run your engine plays into how much energy is returned to your batteries... If you drive at least a couple hours a day, then should be no problem getting them back up at least around 80-85% charged, but less engine run time than that and running a lot of loads it might not recover them enough (in which case a bigger alt can help, but be sure the batteries can handle such a large amount of charge current).

But here's the caveat: even a few hours of driving (regardless of alt size) isn't likely to get the batteries much above 90% charged unless you were to drive most of the day, as it takes more time (not more current) for them to absorb that last little bit. This is where your solar panels and/or your Iota would come in handy, either one should easily be able to put that last 10% charge in after you get yourself situated in camp (or if the vehicle will be stored for a few days or longer) since your alternator has already done a majority of the work.

Something to keep in mind, rewinding an alternator for higher output tends to sacrifice output at idle speeds (at least this has been my experience). For me this was unacceptable because it left me unable to significantly charge my batteries without having to rev the engine up pretty high (like 1800 RPM or so), which then just wastes gas. With the stock wind I'm able to get somewhere around 60-70% output at 1200 RPM (just a little above idle).


Edit:
Just looked up the specs on those batts... I think they'll be fine with any size alt that you could fit practically under your hood lol (550 amps max charge rate), so no worry there.