[RE-wrenches] low batteries with a sunny island

[Mick Abraham]

Hello, August~

Assuming that you don't want to buy a proper (but costly) 48 volt deep
cycle battery charger, here are a few suggestions:

Find this Craig's List seller in Redwood City:

http://sfbay.craigslist.org/pen/bfs/2059216588.html

and ask if they'll rent their 60 volt variable power supply to you for
a couple of days. OR maybe you can beg or borrow a similar DC power
supply closer to home & set it for 60 volts constant voltage. The amps
on this one are tiny...only 5 amps...but maybe that's just what you
need to gradually wake up that battery string. OR:

++++++++++++++++++++

Connect a string of 120 to 150 PV cells in right polarity to the
battery...with nothing but a fuse or breaker and a watchful eye. As
soon as things come up enough for the Sunny Island to go live, you'd
want to disconnect the PV's then allow the SI to complete the
recharge, since the unbridled PV string would have no voltage
regulation. OR:

+++++++++++++++++++++++++++

The eight units could be temporarily unwired from the Sunny Island
unit, then wired up series/parallel (2s4p) as a 12 volt pack. I advise
that route instead of Ray's suggestion (about charging 12v increments
within the 48v string) because you'll have fewer cell imbalance
problems if you connect series/parallel so every two batts can level
their combined voltage against the other pairs. If all eight units are
wired series/parallel for 12 volt nominal, that pack could handle the
output from a  60 amp 12v charger intended for deep cycle AGM's but if
an automotive type 12v charger is all you can come up with
readily...use that...since you're only trying to bootstrap the system.

Happy Thanksgiving,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675



On Wed, Nov 17, 2010 at 7:54 PM, August Goers <august at luminalt.com> 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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