[RE-wrenches] low batteries with a sunny island

[R Ray Walters]

C40 charge controllers used to have that problem too; if battery voltage dropped so low that it didn't think it had a battery to charge, the whole system just sits there crashed, batteries sulfating, sun shining....(customer stewing....)
I'd just charge them on a 12 v automotive charger, 2 at a time. You can attach the leads to any 12 volts of series connected batteries, without having to disconnect all the cables. I would remove the main pos cable though. 
I've even jumped my truck to the battery bank before with jumper cables, just be careful and check your charge rate with an amp meter. Heat and gas from a dead cell in a sealed battery can blow the top right off the battery! You might just need 30 minutes per 12 v set. (2 Hrs total?)
When you get each battery up close to 6 v, you can probably get the system back up on the Sunny boy, unless any of the batteries have dead cells (won't charge over 4 or 5 volts per 6 v battery)
If that's the case, you should consider replacing the whole set. My understanding is that AGMs don't like to sit for long periods of time completely discharged. If they're not toast already, they definitely have just had their life severely shortened.

R. Walters
ray at solarray.com
Solar Engineer




On Nov 17, 2010, at 7:54 PM, August Goers wrote:

> Hi All Battery Friendly Wrenches -
> 
> We have a situation I haven't crossed yet - we have a Sunny Island grid tied battery back system system with a 48 V battery bank consisting of eight 6 Volt AGM batteries. The charging breaker feeding the Sunny Island in the main electrical panel was shut off by another contractor for about 3 months which caused the Sunny Island to slowly drain the batteries until it fully shutoff in order to protect the batteries. The bank now reads 24  Volts. That's low! The Sunny Island is, according to SMA, powered directly from the battery bank and won't even turn on. SMA tech support is recommending that we charge the batteries and then turn the system back on. 
> 
> Any ideas about the best way to charge a 48 V battery bank?
> 
> Thanks for your advice,
> 
> -August
> 
> -- 
> August Goers
> VP, Engineering
> 
> Luminalt Energy Corporation
> 1320 Potrero Avenue
> San Francisco, CA 94110
> O: 415.641.4000
> M: 415.559.1525
> august at luminalt.com
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