Battery Alternator Charging

GallenH · 08-14-2022, 03:17 AM

I should know this but....So on my 1997 PW I have an isolator. On the house side there's also a 40A breaker before the isolator line hits the battery. My alternator is c.140A.

I'm guessing that. since I've never tripped the breaker. what's coming from my alternator via the isolator never reaches 40A. Even when I'm driving during the day with no lights and no AC on.

Why is that? What's regulating the current flowing from the isolator to the battery?

Thanks.glenn

mkguitar · 08-14-2022, 03:33 AM

the demand of the battery.

if you put a pile of batteries back there and a blow dryer or 2, the alternator would try to meet demand

and a breaker would pop.

current draw ( amps) is a demand thing

@Michael · 08-14-2022, 03:27 PM

Quote:

Originally Posted by mkguitar

current draw ( amps) is a demand thing

^^This

The nature of the wiring between the alternator/starter battery and the isolator/house battery might matter also. When I went from 8ga. wire to 4ga., I was able to draw 60A from my alternator instead of just 40A, presumably because there was less resistance/voltage drop. (?)

booster · 08-14-2022, 04:23 PM

The alternator is going to try to put out as many amps as the coach will accept as the load is what controls the output of the alternator up to it's max level.

The coach will take amps for whatever is running like a frig on DC or a 12v charger charging a laptop, or an inverter doing something like running a crockpot.

The coach will also take what ever amps the battery will accept at it's current state of charge and voltage it sees. A 100 amp AGM will surge to maybe 80-100 amps if at under 40% SOC and seeing decent voltage. Wet cells will be less than that by quite a bit depending on the chemistry.

When AGMs were getting more popular for wet cell replacements a number of years ago we heard of people complaining about repeated clicking of what turned out to be the auto reset breakers when they put in AGMs.

The OP has an isolator so that drops the voltage quite a bit, but probably not low enough to hold to 40 amps in all cases.

The only real solution is bigger wiring to the coach and larger breakers (on both ends of the wiring). Switching to a relay type separator/charge controller would also not drop the voltage and likely give better charging, also.

GallenH · 08-14-2022, 06:24 PM

Yeah. I definitely was confused. I always thought that on my computer devices like cell phone and pad, that having a charger with a greater A output would charge them faster.

So in my case -- with a 100AH battery -- would a higher output alternator make any difference in the speed at which my battery charges? The specs for my LifeLine give an example somewhere that shows how to calculate the charging speed and the amp output of the charger is a factor in the calculation.

booster · 08-14-2022, 06:53 PM

Quote:

Originally Posted by GallenH

Yeah. I definitely was confused. I always thought that on my computer devices like cell phone and pad, that having a charger with a greater A output would charge them faster.

So in my case -- with a 100AH battery -- would a higher output alternator make any difference in the speed at which my battery charges? The specs for my LifeLine give an example somewhere that shows how to calculate the charging speed and the amp output of the charger is a factor in the calculation.

Higher output chargers will charge faster in many cases, but only if the device is designed to take that much phones have gone higher lately with out latest one at 31 watts, the older is 19 watts and before that much lower still. Same with RV batteries and chargers.

A lifeline battery can charge at about 40 amps per 100ah based on watt I see on ours. Beyond that for more than maybe 20 minutes will start to heat them up too much.

A bigger alternator might charge you a bit faster, but you would need bigger wiring and breakers to that, as mentioned earlier.

Increasing the voltage by ditching the isolator for a relay style separator/charge relay might help charging speed, but remember that the faster charging will only be until you get to about 75-80% full. After that the acceptance of the battery starts to taper off as you get higher SOC. To get truly full it can easily another 6 hours of full voltage charging.

mkguitar · 08-14-2022, 07:17 PM

Glenn,

are you actually having a problem ?

as touched on above the "diode type" battery separator you may have will drop the voltage. the typical 14.7 volts from the alternator may be reduced to 13.4 ( ish) as it passes through the diodes.

this is my experience with my old blue surepower 16023

I am considering a change to the victron FET style which should be closer to 14.3 ( ish) volts available to my batteries.

I'm not really experiencing any problems but I suspect that a chronic low voltage supply may shorten my battery life ( although the interstate coach battery from costco lasted 5.5 years)

it's just that it bugs me to look at the dash voltmeter and see a low reading.

GallenH · 08-14-2022, 08:02 PM

Mike, No problems. Just dawned on me that I might not be getting ample charge from alternator and wanted to see what others thought. I also have a blue sure power (1202). If you decide to change out for the Victron it will be interesting to hear about.

I've thought about a B2B in place of the isolator. Don't know which is more efficient with regard to voltage loss though

Glenn

booster · 08-14-2022, 08:55 PM

Quote:

Originally Posted by GallenH

Mike, No problems. Just dawned on me that I might not be getting ample charge from alternator and wanted to see what others thought. I also have a blue sure power (1202). If you decide to change out for the Victron it will be interesting to hear about.

I've thought about a B2B in place of the isolator. Don't know which is more efficient with regard to voltage loss though

Glenn

The most efficient would be a relay separator at nearly no loss. B to B will cost you about 20% of the power, an isolator probably around 5%.

GallenH · 08-15-2022, 04:25 AM

Thanks to all of you for the info. I have a better understanding now.

SteveJ · 08-15-2022, 12:36 PM

If I may, with our 2000 Chevy 200 when it had an isolator the alternator output was in the low 15 volt range with the output around 14.5 going to the batteries. When I switched the diode unit out in favor of the Blue Sea 7610 automatic two way charge relay the alternator output dropped to about 14.5.

So it would seem that whatever is controlling the voltage is adjusting for whatever separator device is used with the caveat that there is energy being wasted using a diode unit so the alternator has to work a bit harder.

booster · 08-15-2022, 01:28 PM

Quote:

Originally Posted by SteveJ

If I may, with our 2000 Chevy 200 when it had an isolator the alternator output was in the low 15 volt range with the output around 14.5 going to the batteries. When I switched the diode unit out in favor of the Blue Sea 7610 automatic two way charge relay the alternator output dropped to about 14.5.

So it would seem that whatever is controlling the voltage is adjusting for whatever separator device is used with the caveat that there is energy being wasted using a diode unit so the alternator has to work a bit harder.

There is a lot posted on various sites about what you have. I ran across it first on a truck camper site a long time ago.

The isolator must have a alternator must have a sense wire and it has been moved to the coach side of the isolater from the alternator side.

Depending on how the setup is wired this can be good or not so good. If all the the original van running stuff is also after the isolator it is not all that bad but if that stuff is still on the alternator side it can cause overvoltage on the van side and be hard on bulbs and some electronics, especially if you live in cold areas and the voltage gets kicked up due to low temps.

IMO, much better to just go to a relay style and have all the voltages be the same and consistent.

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