Hi: I didn't know that there were systems out there where a PWM charge controller such as the C-40 was producing an unhealthy, high battery voltage. Since there are, I may have a possible explanation.
The C-series and other PWM type charge controllers operate by PWM whereby they very very quickly connect/disconnect the solar module to the battery bank. The amount of time which the module is connected to the array is the PWM on-period. These controllers do not have the ability to "smooth out" the output voltage. All they can do is apply the full module voltage OR not apply any module voltage to the battery. Here are some graphs that show this, It 's supposed to work out when the battery absorbs, smooths out and averages the output voltage pulses coming out of the PWM controller. Except, I'm hearing that, that is not necessarily true. It sounds like on some systems the batteries will not average voltage very well over time and indeed experience increasing and undesirably high terminal voltages over time. If this is the mechanism, I think one way alleviate or perhaps even eliminate the rising voltage problem is by matching the module Voc voltage to the desired battery float voltage. For example, if a 28 VDC float voltage was desired, then the solar module Voc should be chosen as something slightly above 28 VDC. i.e. I think the trick is to match the module Voc voltage to the desired battery float voltage. Perhaps a 32 Voc module for a 28 VDC float voltage. I'm not sure what the right number is, but if I'm correct about this mechanism, then a 50 Voc module on a 12 VDC battery, should the kind of system which experiences this overcharging/over voltage problem. You guys have seen many systems. Maybe you can comment on whether the systems which have had this trouble are also ones where the module Voc is much higher than the desired battery float voltage. Perhaps the "trouble systems" also tend to have a specific battery chemistry or even particular battery type. JARMO _____________________________________________________________________________________ Jarmo Venalainen | Schneider Electric | Xantrex Brand | CANADA | Sales Application Engineer Phone: +604-422-2528 | Tech Support: 800-670-0707 | Mobile: +604-505-0291 Email: jarmo.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail ----- Forwarded by Jarmo Venalainen/Canada/Schneider on 05/18/2015 07:02 PM ----- From: Drake <drake.chamber...@redwoodalliance.org> To: jarmo.venalai...@schneider-electric.com, Date: 05/18/2015 03:35 PM Subject: Re: Fw: [RE-wrenches] Xantrex C-40 Drifting Hi JARMO, The battery bank consists of four, 415 AH in a Full River AGM deep cycle batteries wired in a 24 volt series. The 80 W array is strictly a maintainer to keep the batteries charged when the AC coupled system is detached from the direct grid tie inverters. The only constant loads on the system are about 3 W of power that keeps the metering awake. The batteries are low self discharge. Thanks, Drake At 07:47 PM 5/14/2015, you wrote: Hi: 80W is a really small PV source, so I'm wondering how it can raise the battery voltage so much. What size is the battery? JARMO _____________________________________________________________________________________ Jarmo Venalainen | Schneider Electric | Xantrex Brand | CANADA | Sales Application Engineer Phone: +604-422-2528 | Tech Support: 800-670-0707 | Mobile: +604-505-0291 Email: jarmo.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail ----- Forwarded by Jarmo Venalainen/Canada/Schneider on 05/14/2015 04:45 PM ----- From: Drake <drake.chamber...@redwoodalliance.org> To: re-wrenches@lists.re-wrenches.org, Date: 05/14/2015 04:30 PM Subject: [RE-wrenches] Xantrex C-40 Drifting Sent by: "RE-wrenches" <re-wrenches-boun...@lists.re-wrenches.org> 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 Drake Chamberlin Athens Electric LLC OH License 44810 CO License 3773 NABCEP Certified Solar PV 740-448-7328 http://athens-electric.com/ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________
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