[RE-wrenches] Sealed battery test/maintenance

Peter Parrish peter.parrish at calsolareng.com
Wed Dec 17 09:22:36 PST 2008


I am very interested in this thread as we too have about a half-dozen
grid-tied battery backup system in the field. I used to be a ham radio
operator and I remember using large, wire-wound resistors encased in an
aluminum casing. The case could be bolted to a heat sink. 

I looked up one of these puppies and found them rated up to 50W continuous.

Here is a simple tester:

Assume a single 12 V battery. If you want to test battery banks, I think
that that would be a different ballgame altogether.

Use a number of 5 ohm / 50 watt resistors in parallel. The number you use
depends on the current you want to test to. Assuming that you want to run at
C/20, here is how you determine how many resistors you need.

A 5 ohm resistor will draw 2.4 amps. Assuming C/20, a single resistor would
be an appropriate load for a 48 Ah battery. The power drawn is 28.8 W which
is fine for a 50 W resistor as long as it is bolted to a good heat sink. Two
5 ohm resistors will draw 4.8 amps, appropriate for a 96 Ah battery. The
general formula is "battery capacity divided by 48 gives you the number of 5
ohm / 50 W resistors you need in parallel". The power dissipated in each
resistor will always be the same regardless of the number in parallel.

I will probably rig one of these loads up one day soon if a better solution
isn't out there already.

One could add a high current switch or DC rated circuit breaker, voltage
probe point and a high precision shunt to measure current.

I have no idea what sort of voltage as a function of time should be. Has
anyone spoken to battery manufacturers about the specs under C/20?

- Peter

Peter T. Parrish, President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Glenn Burt
Sent: Wednesday, December 17, 2008 7:41 AM
To: 'William Miller'; 'RE-wrenches'
Subject: Re: [RE-wrenches] Sealed battery test/maintenance

Thanks for the reply William,

When you load the battery bank, are you using the inverter as the source of
the load (obviously with its loads), or do you use an independent DC load
like a carbon pile (auto battery tester)?

Glenn 

-----Original Message-----
From: William Miller [mailto:wrmiller at charter.net] 
Sent: Tuesday, December 16, 2008 2:07 PM
To: glenn.burt at glbcc.com; RE-wrenches
Subject: Re: [RE-wrenches] Sealed battery test/maintenance

Glenn:

There are a combination of tests, none as decisive as we might like:  Load
the battery bank and test per cell voltage (more often we find warm
connections revealing related problems).  Measure the at rest voltage.
Measure voltage over time at load.  If you are serious about this, establish
base lines when batteries are new.

Good luck.

William Miller


At 09:55 AM 12/16/2008, you wrote:
>Good Holiday Season to all:
>
>Does anyone have a sealed (gel & AGM) battery test/maintenance 
>procedure they would feel comfortable sharing with the group?
>I have been tasked with creating one for our company now that we have 
>more than a couple of grid tied systems with battery backup.
>
>Hate to re-invent the wheel with so much talent available here.
>Thanks in advance!
>
>Regards,
>
>Glenn Burt
>Technical Specialist
>
>Renewable Power Systems, LLC
>PO Box 967
>Averill Park, NY 12018
>V: 518-674-5808
>C: 518-810-3174
>F: 518-514-1175
>E: gburt at RPSPower.com
>www.RPSpower.com
>
>
>
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