4x4junkie
Explorer
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.
Never said there was. But there are easier/simpler/cheaper and harder/more complex/more expensive ways to do just about anything.Yea, you DO keep harping on that. The problem is this - TANSTAAFL.
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.
I don't believe it does. But OK if you say so...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'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.
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...And *that* is what a typical automotive "charging system" is designed to cope with.
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.
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