[RE-wrenches] low batteries with a sunny island

[August Goers]

Thanks all, this is helpful stuff. We'll see if the batteries are dead or
not which would be a real shame since they're only 6 months old... -August

On Wed, Nov 17, 2010 at 7:32 PM, Mick Abraham <mick at abrahamsolar.com> wrote:

> 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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>
> ++++++
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-- 
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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