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Old 05-23-2017, 10:29 PM   #1
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Alternator charging solar bank problems

When i run a wire from my main battery to my solar bank it blows even a 40 amp fuse. I have a 260 watt alternator.volt meter reads 14.2 volts when the engine is running. Confused

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Old 05-24-2017, 06:00 AM   #2
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Old 05-26-2017, 10:34 AM   #3
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Quote:
Originally Posted by somewhereinusa View Post
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Im so busy. Had to drive the bus to summercamp. Its just a wire from the bus battery tp the solar bank. 8 gauge. I could show pictures, but don't really have a diagram.

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Old 05-26-2017, 10:45 AM   #4
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First thing that comes to mind for me:

What is the state of charge of the solar bank?

If they are really down the coach charging system may be trying to stuff more than 40A into the solar bank.

That said.... I would not recommend direct connection between the coach charging system and the house batteries without a battery isolator installed in between. The FET based isolators are what I am looking at for my bus.
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Old 05-26-2017, 11:09 AM   #5
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I tried it both ways. Through the isolator and fused wire. The bank was really low. Like 8 volts. Its sunny today so I'm back to 12.4 on the bank. Maybe i should try again.

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Old 05-26-2017, 11:43 AM   #6
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8 Volts.....

I would be concerned about that. Deep discharge can kill batteries.

I would suggest that you charge the batteries, disconnect any charger or load, let the batteries rest 6+ hours and check the voltage. It should be in the 13V range. If it is significantly lower then you may have failed batteries and that would contribute to your problem.

Perhaps someone a bit more knowledgeable will step in and give more precise numbers?
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Old 05-26-2017, 11:48 AM   #7
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Seems we are on the same page.I've already tested the bank. I'm fine. I'm at 13.4 just from the panels. I did a charge right before i drove. Im just miffed by the 40 amp fuse being blown

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Old 05-26-2017, 11:53 AM   #8
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Have you tried connecting it again with the house bank charged?

When you connected deeply discharged house batteries to your coach charging system I would expect it to blow a 40A fuse.
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Old 05-26-2017, 01:49 PM   #9
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you need much more than 8 gauge and 40 amps to charge a deep cycle battery from 9 volts via alternator.. on my bus I ran dual 6 gauge lines up for charging.. each is circuit breakered at 80 amps. I havent yet blown one but a clamp meter shows at times i was pulling 60 on EACH line when charging from nearly dead...
my alternator is 200 amps maximum..
-Christopher
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Old 05-26-2017, 02:04 PM   #10
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Quote:
Originally Posted by cadillackid View Post
you need much more than 8 gauge and 40 amps to charge a deep cycle battery from 9 volts via alternator.. on my bus I ran dual 6 gauge lines up for charging.. each is circuit breakered at 80 amps. I havent yet blown one but a clamp meter shows at times i was pulling 60 on EACH line when charging from nearly dead...
my alternator is 200 amps maximum..
-Christopher
There you go! Some real world, first hand information.

I would certainly agree with all of the above. 8 gauge fused at 40A may work for "topping off" your house batteries while driving but never to bring them back from the state of discharge that you described. Hence my suggestion to charge them first from another source.

I would strongly recommend that you not let them reach that state of discharge again as it will certainly shorten the lifespan of your batteries.

Batteries are expensive...
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