[RE-wrenches] Design Question re Battery Bank Sizing

[Marv Dargatz]

Allan,

You might consider low ESR/ESL capacitors in parallel with the batteries to provide motor start surge.  Much cheaper and require no maintenance.


See ya!

Marv
Director of Technology and Support, North America
SolarEdge Technologies, Inc.
Tech Support North America:  +877.360.5292
Mobile: +530.392.0356

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
Sent: Wednesday, February 15, 2012 9:53 AM
To: RE-wrenches
Subject: [RE-wrenches] Design Question re Battery Bank Sizing

Esteemed fellow Wrenches,
We need to size a battery bank for a GTWB just for starting a well pump. The well is on its own meter, so as long as the battery voltage does not crash when the pump starts there will be plenty of capacity left over for minimal loads.  We'll be using sealed batteries, most likely Concorde SunXtenders. According to theSunXtender Technical Manual, Concordes can handle up to a C/0.2 charge rate (500A for a 100Ah battery), but there is no discussion of maximum discharge rates or voltage drop due to large surge loads.

The pump is 3HP and is conventional 3-wire, not soft-start. The well is 940ft. and the depth to water is unknown. It pumps into a pressure tank, not open discharge. Customers are not interested in replacing the pump, but might be talked into adding a soft start Franklin controller, although at this preliminary design stage we're not certain one is available for this particular model. The inverter would be a Radian, so system voltage is 48V.

I would think that configuration would make a difference, as well as size. Using 12V batteries in series/parallel would minimize interconnect and terminal resistance. I think that it would also allow multiple paths for discharge current, reducing the voltage dip.

What's your best guess at the smallest size battery bank that would reliably start this pump, and how would it best be configured?

Thank you,
Allan

Allan Sindelar
Allan at positiveenergysolar.com<mailto:Allan at positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com<http://www.positiveenergysolar.com/>







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