That's a pretty good size battery bank compared to the charge coming in, normally you only see this with very small battery banks.
A battery when under charge is going thru a chemical reaction, this reaction doesn't immediately stop when you remove the charge, if you have a strong source on a small battery bank. The chemical reaction can keep going on for several minutes after the charge has been removed. The battery isn't charging it's self the chemical reaction is just still continuing. To test this, you can put a small DC load (couple of 12volt light bulbs in series) across the battery, when you shut off the controller, turn on the dc load for a second or two and see where the voltage is... Compare it to cooking a roast... when you pull it out of the oven, it's still cooking for about 30-45 minutes past the time you remove it out of the oven. Some controller manufactures will actually back feed the panels for a short period of time to regulate, and prevent the overvoltage. On flooded batteries this isn't much of a problem, but VRLA's if the time is excessive it can be an issue in the long term for the batteries. Just a note... those full rivers can accept a bit more voltage than a standard AGM... http://www.fullriverbattery.com/product/batteries/DC400-6 From: RE-wrenches [mailto:[email protected]] On Behalf Of Drake Sent: Monday, May 18, 2015 4:58 PM To: RE-wrenches Subject: Re: [RE-wrenches] Xantrex C-40 Drifting Hi Steve, The battery bank consists of four, 415 AH in a Full River AGM deep cycle batteries wired in a 24 volt series. That is a new concept to me. Does the battery bank charge itself through its own chemical reaction? Would there be any issues with gassing in the VRLA batteries? Would you recommend doing anything about this situation, like change charge controllers? Thanks, Drake Drake Chamberlin Athens Electric LLC OH License 44810 CO License 3773 NABCEP Certified Solar PV 740-448-7328 http://athens-electric.com/ At 07:10 PM 5/18/2015, you wrote: Content-Language: en-US Content-Type: multipart/related; boundary="_004_414D424906AE60489EF1829E1EFA55712C9C56F2sbcexchsbcdomai_"; type="multipart/alternative" Hey Drake, How large is the battery bank? I've seen this before on VRLA's with a couple of companies controllers. Usually this will happen with small battery banks. Best way to explain it is when the battery bank is charging and you remove the charge, the battery is a chemical reaction... it's still charging for a short period of time even though you have removed the source. Steve Higgins Technical Services Manager P: +1.902.597.4020 M: +1.206.790.5840 F: +1.902.597.8447 Surrette Battery Company Exclusive manufacturer of [[]]<http://www.rollsbattery.com> From: RE-wrenches [ mailto:[email protected]] On Behalf Of Drake Sent: Friday, May 15, 2015 7:10 AM To: RE-wrenches Subject: Re: [RE-wrenches] Xantrex C-40 Drifting I was thinking of a Blue Sky or a Morning Star replacement. The Full River AGM L-16 batteries recommend a 29.4 absorption, very high for a maintenance free battery. I've triple checked this one. At 09:30 AM 5/15/2015, you wrote: HI Drake, Iv'e never seen this happen. Â But have you considered a small morningstar or similar? A question, you list 29.4v, that seems high? jay On Thu, May 14, 2015 at 5:12 PM, Drake < [email protected]<mailto:[email protected]>> wrote: I have a Xantrex C-40 that won't keep its settings. It is important that it does because it is for a maintainer array (80 W) on an AGM battery bank, on an AC coupled backup system. Not only could high voltage damage the batteries, but when the voltage goes over 30 Volts, the AUX relay opens and the grid tie inverter is isolated from the grid. After numerous sessions of reprogramming, Xantrex tech support sent me a new unit. The problem persisted as before. A new temperature sensor helped, but the settings still drift. It seems that rebooting the charge controller helps for a day or so, but then it drifts again. The potentiometer settings are way below the calculated setting for 29.4 V, but it still peaks in the high 30s. I check the temperature compensated voltages on the Outback Mate, and the temp compensated voltage runs high. In a related side issue, the AUX relay of the FX inverters is not based on temperature compensated voltage, which makes setting AC coupling charge set points more problematic. Has anyone experienced a C-40 CC that drifts in its settings. What would be a good (inexpensive) charge controller to accurately control 80 W of PV? Thanks, Drake -- Jay Peltz Peltz Power [email protected]<mailto:[email protected]> _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected]<mailto:[email protected]> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org/> This email and its attachments have been scanned by mailWatch E-Mail Firewall for viruses, spam, and malicious content. The information transmitted in this email is intended only for the entity or person to which it is addressed and may contain confidential/privileged material. If you received this in error, please contact the sender and delete the material from any computer. 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