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Old 05-23-2017, 11:29 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, 07:00 AM   #2
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Old 05-26-2017, 11:34 AM   #3
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Show wiring diagram
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, 11:45 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, 12:09 PM   #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, 12:43 PM   #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, 12:48 PM   #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, 12:53 PM   #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, 02:49 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, 03:04 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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Old 05-26-2017, 03:51 PM   #11
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Quote:
Originally Posted by PNW_Steve View Post
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...
i thought you could take deeop cycle batteries down to 8 or 9 volts without issue..
-Christopher
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Old 05-26-2017, 04:21 PM   #12
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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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Just noticed this thread after being away all week.
I believe you may have a 260 amp alternator, not 260 watts. A major difference there in power available. Seems your alternator and voltage regulator are normal.

As has been said in other posts below, #8 wire is good for only 40 amps in total. The surge to dead batteries is likely many times higher than that. You have a fire hazard using such small cable. Find something larger say 2/0 (2ott) as they say minimum and you'll be able to have a lot less resistance as well as the cable not melting down and shorting out causing a fire. You don't want that at all.
You can only be sure of the amperage with a clamp on ammeter. Well worth the investment as a tool.

Instead of going directly to the batteries do you have a solar charge controller? If so can you list its specs? Maybe then we can figure what went wrong. The controller should have been fed likely rather than the battery bank itself.
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Old 05-26-2017, 04:31 PM   #13
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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
Not sure here Christopher...you have 2 #6 guages for pos and neg? That allows for a max of 120 amps per leg. If your breaker is only 80 amp it might be undersized when batteries need a heavy charge.
#6 is good for 60 amps in one conductor and you used 4 of them rather than say #2 which would be less maintenance and quite capable of a 100 amp load. I think I'd be changing those cables myself.
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Old 05-26-2017, 04:36 PM   #14
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Hi all. May I chime in...

First Pirate... 260 watt alternator? That's only about 25 amps thereabouts. I think you need to check that. Most alternators will give you 60 plus amps. Some upwards of 200. Your bus alternator is probably capable of 100 or more amps.

Second... Checking battery state-of-charge by a volt meter can be VERY mis-leading. The battery must sit for several hours without charging or draining before a voltage reading will mean ANYTHING. If you have a solar charging system for house batteries and plan to USE them for more than charging your cell phone, you will want to invest in a good monitor for your house batteries. You will spend a couple hundred bucks on one but it's almost a requirement. Having a reliable solar system without a good monitor is like driving without a fuel gage. I use the Victron BMV-702. There are others that work equally well. Read up on it.

The best way to determine state-of-charge on your battery bank is by pulling a filler cap and testing with a hydrometer. Though this method is the most reliable, it is also the most inconvenient.

A 100% fully charged battery, after sitting for some hours or overnight (with no additional charging or drain) should read 12.7 volts. Thats the magic number. 12.5 volts is about 90% charge. 12.4 volts is about 80% and so on. Anything below 10.5 volts is pretty much dead!

When 12 volt batteries are charged we charge them with greater voltage than the battery's stated voltage. Higher voltage is required to "push" more energy back into the battery. Alternators charge at about (help me here... anybody?) 14.4 volts? I think that's right. As a battery approaches a full charge, the battery voltage will itself rise above 12.7 volts. This is the nature of lead acid batteries as they are charged. But once allowed to sit, they will drop back to 12.7 (or whatever true state-of-charge they were at.

If you want a battery bank to last, then never approach 50% state of charge or lower. This will kill your batteries within a year or two. It's safe to use about 20-25% of your battery bank's capacity but you must always re-charge them fully after use. Leaving batteries stored at a low state-of-charge for any period of time is very hard on the batteries. Keep them topped off to get the most years from your battery bank.

I hope this clears a few things up.

Regards!

Ross
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Old 05-26-2017, 05:43 PM   #15
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Quote:
Originally Posted by cadillackid View Post
i thought you could take deeop cycle batteries down to 8 or 9 volts without issue..
-Christopher

FLA Deep cycle - 50% SOC If I recall that is around 12.4V . "Dead" = 12.0V.

AGM Deep cycle - 20% SOC

You can discharge them deeper but at the expense of longevity.
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Old 05-26-2017, 06:23 PM   #16
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Not sure here Christopher...you have 2 #6 guages for pos and neg? That allows for a max of 120 amps per leg. If your breaker is only 80 amp it might be undersized when batteries need a heavy charge.
#6 is good for 60 amps in one conductor and you used 4 of them rather than say #2 which would be less maintenance and quite capable of a 100 amp load. I think I'd be changing those cables myself.
I agree on the maintenance aspect but the wire was free so I used it...

and yes I have a total of 4.. 2 POS to NEG.. thus far i havent tripped a breaker.. but then that bus has air brakes and my usual routine is to start the bus at idle.. run it up to 800 RPM where the alternator excites.. and then it sits and idles as i do my walk around... waiting for air pressure to build, thump the tires, check the lights, etc...

by that time the batteries have started to back off of their full on charge.. then when I do take off most times theres a bit of stop N go before I hit the freeway.. so maybe ive just been lucky that my 80s havent kicked... or other stuff in the bus is drawing power including topping off my starting batteries, A/C, heat, etc.. so that I never have enough to run up 80 per leg..

-Christopher
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Old 05-26-2017, 07:15 PM   #17
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With the time you spend on the road and all those miles, those batteries will not likely ever get discharged. And I do like your thoroughness in all that you do.
Thx Chris for clarifying.

John
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Old 05-26-2017, 10:52 PM   #18
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Damn. It was late. That watt amp was a typo. I do use a charge controller. Its a 30 amp mppt. I wasn't going through the charge controller. I was using an isolator. I think now it was because my batteries were at 8v. Very low. I used a battery charger to get back to 13.4 volts. Or seems to be ok, i want to get my 260 amp alternator back inn the game. I'll go with the larger gauge. I don't usually let my battery bank get that low.

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Old 05-26-2017, 10:53 PM   #19
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Originally Posted by rossfree View Post
Hi all. May I chime in...

First Pirate... 260 watt alternator? That's only about 25 amps thereabouts. I think you need to check that. Most alternators will give you 60 plus amps. Some upwards of 200. Your bus alternator is probably capable of 100 or more amps.

Second... Checking battery state-of-charge by a volt meter can be VERY mis-leading. The battery must sit for several hours without charging or draining before a voltage reading will mean ANYTHING. If you have a solar charging system for house batteries and plan to USE them for more than charging your cell phone, you will want to invest in a good monitor for your house batteries. You will spend a couple hundred bucks on one but it's almost a requirement. Having a reliable solar system without a good monitor is like driving without a fuel gage. I use the Victron BMV-702. There are others that work equally well. Read up on it.

The best way to determine state-of-charge on your battery bank is by pulling a filler cap and testing with a hydrometer. Though this method is the most reliable, it is also the most inconvenient.

A 100% fully charged battery, after sitting for some hours or overnight (with no additional charging or drain) should read 12.7 volts. Thats the magic number. 12.5 volts is about 90% charge. 12.4 volts is about 80% and so on. Anything below 10.5 volts is pretty much dead!

When 12 volt batteries are charged we charge them with greater voltage than the battery's stated voltage. Higher voltage is required to "push" more energy back into the battery. Alternators charge at about (help me here... anybody?) 14.4 volts? I think that's right. As a battery approaches a full charge, the battery voltage will itself rise above 12.7 volts. This is the nature of lead acid batteries as they are charged. But once allowed to sit, they will drop back to 12.7 (or whatever true state-of-charge they were at.

If you want a battery bank to last, then never approach 50% state of charge or lower. This will kill your batteries within a year or two. It's safe to use about 20-25% of your battery bank's capacity but you must always re-charge them fully after use. Leaving batteries stored at a low state-of-charge for any period of time is very hard on the batteries. Keep them topped off to get the most years from your battery bank.

I hope this clears a few things up.

Regards!

Ross
Thanks. plenty to digest in there

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Old 05-27-2017, 12:19 PM   #20
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Originally Posted by PNW_Steve View Post
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...
Yes they are. I have a better handle on it now. Thanks

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