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Old 12-13-2016, 06:16 PM   #1
Bud
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Default Adding Amps

Maybe someone could assist me with my application.

I'm mostly happy with an 05/04 Roadtrek 190 that has the usual 145 amp alternator and 2 group 27 marine batteries, about 180 amps. Much like booster had originally, now more like an electrical work of art.

I would like to add more amps as needed boondocking. I would not do it a lot as I move a lot or the solution would be more battery amps to start with I suppose. So there is Solar but that is noticeable expense wise, and it rains, etc. ........ I'm Not going to run that LOUD onan to charge batteries, and it takes forever compared to starting the cold Express Van engine and using the alternator. questions:

What rpm might be most efficient, ideal to charge the batteries, higher than idle?

At that ideal rpm how long might it take to add 50 amps from being down say 50%, or at what amp rate might the batteries be charging?

Is there a noticeable downside to doing this?

With only adding 50 amps is there any reason to spend the $'s to go the route of an additional alternator, wiring, and more yet....?

Thank you.

Bud
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Old 12-13-2016, 06:47 PM   #2
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Your 190 probably has an isolator and 50 amp breakers and a #6 cable to the batteries, so you are maxed at 50 amps right now. Moving up to 80 amp breakers and a #4 cable would get you 30 amps more. Ditching the isolator for a separator would give higher voltage to the batteries and charge faster, as the isolator costs about 3/4 volt in drop.

80 amps is nearing what the 145 amp alternator can do for extended periods considering it is also putting at least 15 amps to run the engine. Extended charging is hard on factory alternators as they aren't designed for that kind of use.

Some also depends on what you have for batteries and what they will accept. Count on about 20-25% of capacity max for wet cells, and more than you can likely deliver for nearly all AGM setups max.

A higher output alternator (maybe 185 amps or so) that is also better for handling heat might be needed for reliability, or carry a spare because it is your only alternator. If you can connect the coach batteries to run the engine easily, you could probably get by without the spare as the coach batteries would be big enough to run the engine as long as long as the alternator hasn't seized up or other catastrophic failure. That would get you to the store or shop to get a replacement.

About 1000 rpm engine should get you to nearly full output and a good compromise. If you look at the output curve for an alternator, the engine would be running at about 1/3 the speed of the alternator with the stock pulley.

You could likely do the alternator with an better quality one, change to a separator, and upgrade wiring and breaker to be at 80 amps, for about $600 in parts and some work. Probably $200-$250 without an alternator.

Depending on the bank size, you start to taper amps pretty early anyway, so that reduces need as you finish charging, but you would really only be doing a quick recovery of some capacity while idling, I assume, so you would be at full capacity the whole time. You would gain a little overall charging time while driving.
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Old 12-13-2016, 07:30 PM   #3
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Thanks booster, but my head is starting to hurt trying to understand.

"About 1000 rpm engine should get you to nearly full output and a good compromise."

I forgot to mention that the 2 group 27 'marine' batteries are the inexpensive, add water kind.

So if I started the cold van engine with 50% left, 90 amps, about how long at 1000 rpm would it take to add 25 amps or 64% charged, and 50 amps or about a 78% charge?

Bud
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Old 12-13-2016, 07:51 PM   #4
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other ways of thinking about it- what uses power?

all my lights are now led and my total lighting load with everything on ( never happens) is less than 2 amps cost about $80 my TV is 12 volt native 21" samsung, costco $125

the only things I have which need AC are the A/C and the microwave.

2.) get a small solar panel charge controller combo ( suitcase style) you can set up outside and kick it towards the sun every couple of hours.

Mike
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Old 12-13-2016, 08:05 PM   #5
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If those are the marine starting batteries, which is likely, they will be able to take the 50 amps you currently have available, but not a lot more, at 50% down. It will likely stay at the 50 amps, or close to it, up to 65-70% full, so about 30 minutes or bit longer, I would guess, to get the 25ah. With those batteries, going bigger in the charging system probably isn't going to get you much.

After that it will likely start slowing down, but every battery type and mfg is somewhat different. To get the next 25ah to get to the 78% might take twice as long, or 90 minutes total. Going to 100% could take upwards of 8 hours, so it really slows down. Would be ahead, I think, to just do the 25ah, and then do it again when you get to 50% again. Since you are not getting full anyway, the wear factor on the batteries will not be significantly different either way.

I don't mind wet cells, as we had them for years without major problems, but they are a kind of bad fit if you want more rapid changing available, or want to run a bigger inverter.
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Old 12-13-2016, 09:00 PM   #6
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Yes, some would say cheap batteries too.

Thanks, very Helpful booster.

I have some thinking to do as the minutes involved over time are not too bad. Or then, maybe I need to attend that great big rv show in Florida in mid or late January. It has other solutions, new B's.

Bud
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Old 12-14-2016, 12:06 AM   #7
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Quote:
Originally Posted by booster View Post
Ditching the isolator for a separator would give higher voltage to the batteries and charge faster, as the isolator costs about 3/4 volt in drop.
I'm not sure but I think that by this year model, a separator is employed. But in any event, don't OBD II computers monitor battery voltage and adjust the alternator field windings to compensate for voltage drops experienced between the alternator and the battery?
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Old 12-14-2016, 12:51 AM   #8
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Not a separator, and I've looked.

Bud
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Old 12-14-2016, 01:07 AM   #9
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Quote:
Originally Posted by cruising7388 View Post
I'm not sure but I think that by this year model, a separator is employed. But in any event, don't OBD II computers monitor battery voltage and adjust the alternator field windings to compensate for voltage drops experienced between the alternator and the battery?
Bud answered the separator question, and a 2004 won't have the PCM controlled voltage regulation, so no problem. All it does is monitor the field % and adjust the van idle to compensate if it thinks it needs it. the voltage regulation is old school and built in to the alternator. Even our 2007 Chevy is the same way, as they didn't change until later than that.
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Old 12-14-2016, 08:13 PM   #10
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Bud answered the separator question, and a 2004 won't have the PCM controlled voltage regulation, so no problem. All it does is monitor the field % and adjust the van idle to compensate if it thinks it needs it. the voltage regulation is old school and built in to the alternator. Even our 2007 Chevy is the same way, as they didn't change until later than that.
Thanks for the correction. That surprises me because Chrysler as early as 1990 (OBD 1) implemented voltage regulation with PCM full control of the alternator field windings. Also the Surepower separator (1314) was in production back then. I notice that current RT Chevys with the Onan generator employ a 200 amp bidirectional version which IMO are inferior to the Blue Sea line of latching relay separators.
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