<div>It is a timed test to do it correctly, load the bank to 25 amps or what ever load the spec is and measure the battery voltage every 15 minutes (take a starting voltage unloaded first)</div>
<div>until the first battery drops below 1.75 VPC </div>
<div>That is the first battery to fail. Do it till they are all at 1.75 VPC. The battery that make it closest to 6 hours is the best, the ones that fail first are the worst ones. Bet you figured that out without me...</div>
<div>You have to adjust the load as it moves around as the battery gets discharged fully. </div>
<div>When done charge them back up. Hard to do in an off grid situation.</div>
<div>When new the entire pack should take the load and be dead at 6 hours of draw.</div>
<div> </div>
<div>Bob <br><br></div>
<div class="gmail_quote">On Wed, Dec 17, 2008 at 12:22 PM, Peter Parrish <span dir="ltr"><<a href="mailto:peter.parrish@calsolareng.com">peter.parrish@calsolareng.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">I am very interested in this thread as we too have about a half-dozen<br>grid-tied battery backup system in the field. I used to be a ham radio<br>
operator and I remember using large, wire-wound resistors encased in an<br>aluminum casing. The case could be bolted to a heat sink.<br><br>I looked up one of these puppies and found them rated up to 50W continuous.<br><br>
Here is a simple tester:<br><br>Assume a single 12 V battery. If you want to test battery banks, I think<br>that that would be a different ballgame altogether.<br><br>Use a number of 5 ohm / 50 watt resistors in parallel. The number you use<br>
depends on the current you want to test to. Assuming that you want to run at<br>C/20, here is how you determine how many resistors you need.<br><br>A 5 ohm resistor will draw 2.4 amps. Assuming C/20, a single resistor would<br>
be an appropriate load for a 48 Ah battery. The power drawn is 28.8 W which<br>is fine for a 50 W resistor as long as it is bolted to a good heat sink. Two<br>5 ohm resistors will draw 4.8 amps, appropriate for a 96 Ah battery. The<br>
general formula is "battery capacity divided by 48 gives you the number of 5<br>ohm / 50 W resistors you need in parallel". The power dissipated in each<br>resistor will always be the same regardless of the number in parallel.<br>
<br>I will probably rig one of these loads up one day soon if a better solution<br>isn't out there already.<br><br>One could add a high current switch or DC rated circuit breaker, voltage<br>probe point and a high precision shunt to measure current.<br>
<br>I have no idea what sort of voltage as a function of time should be. Has<br>anyone spoken to battery manufacturers about the specs under C/20?<br><br>- Peter<br><br>Peter T. Parrish, President<br>California Solar Engineering, Inc.<br>
820 Cynthia Ave., Los Angeles, CA 90065<br>Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885<br>CA Lic. 854779, NABCEP Cert. 031806-26<br><font color="#888888"><a href="mailto:peter.parrish@calsolareng.com">peter.parrish@calsolareng.com</a><br>
</font>
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<div class="Wj3C7c"><br>-----Original Message-----<br>From: <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a><br>[mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of Glenn Burt<br>
Sent: Wednesday, December 17, 2008 7:41 AM<br>To: 'William Miller'; 'RE-wrenches'<br>Subject: Re: [RE-wrenches] Sealed battery test/maintenance<br><br>Thanks for the reply William,<br><br>When you load the battery bank, are you using the inverter as the source of<br>
the load (obviously with its loads), or do you use an independent DC load<br>like a carbon pile (auto battery tester)?<br><br>Glenn<br><br>-----Original Message-----<br>From: William Miller [mailto:<a href="mailto:wrmiller@charter.net">wrmiller@charter.net</a>]<br>
Sent: Tuesday, December 16, 2008 2:07 PM<br>To: <a href="mailto:glenn.burt@glbcc.com">glenn.burt@glbcc.com</a>; RE-wrenches<br>Subject: Re: [RE-wrenches] Sealed battery test/maintenance<br><br>Glenn:<br><br>There are a combination of tests, none as decisive as we might like: Load<br>
the battery bank and test per cell voltage (more often we find warm<br>connections revealing related problems). Measure the at rest voltage.<br>Measure voltage over time at load. If you are serious about this, establish<br>
base lines when batteries are new.<br><br>Good luck.<br><br>William Miller<br><br><br>At 09:55 AM 12/16/2008, you wrote:<br>>Good Holiday Season to all:<br>><br>>Does anyone have a sealed (gel & AGM) battery test/maintenance<br>
>procedure they would feel comfortable sharing with the group?<br>>I have been tasked with creating one for our company now that we have<br>>more than a couple of grid tied systems with battery backup.<br>><br>
>Hate to re-invent the wheel with so much talent available here.<br>>Thanks in advance!<br>><br>>Regards,<br>><br>>Glenn Burt<br>>Technical Specialist<br>><br>>Renewable Power Systems, LLC<br>>PO Box 967<br>
>Averill Park, NY 12018<br>>V: 518-674-5808<br>>C: 518-810-3174<br>>F: 518-514-1175<br>>E: gburt@RPSPower.com<br>><a href="http://www.rpspower.com/" target="_blank">www.RPSpower.com</a><br>><br>><br>
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