Re: [RE-wrenches] C60 setpoint question

[Allan Sindelar]

Brian, Re: Do you know what the daily Ah consumption is, or alternatively what the daily DOD is on the batteries?: We don't have that data. The home has an E-Meter, but the programming settings were far enough off that I wouldn't trust the historic data. Also, Eden has memorized TriMetric (and more modern datalogging) operation, but I realize that there are so few E-Meters still in use that he doesn't know how to extract avg. DOD and other historic data from one of these relics. The C60 has no DVM, so there's no input data. This is not uncommon around here, where people have lived with funky off grid systems since the earliest days. The home has a Frigidaire conventional refrigerator of unknown vintage and efficiency, so it's safe to assume that the batteries seldom are full. As a rule of thumb, I generally tell clients that a kilowatt of array is pretty much the minimum to run an off grid home with a carefully-selected AC refrigerator (and we neither recommend Sun Frost or LP refrigerators). The array includes a couple of 102W Evergreens, a couple of 100W Photowatts, a 103W Sharp, and even a set of 5V Carrizo Tri-Lam SuperGolds (105W estimate when "new"), so it's reasonable to suspect that age and incompatibility will reduce the output from 48A. The measured input yesterday, which was hot, was 35A in in late morning, a C/25 rate with nothing on at the time. I just spoke with Dave, senior tech support at Concorde. 1) These four year old batteries are already likely already shot from chronic undercharge. 2) We could run at bulk all day with this array and never get them full. 3) The batteries begin to recombine at around 13.5V, which depending on current causes enough pressure to cause release of gasses, as the caps are rated at 2.5 psi, so 4) If we tripled the array it would still not fill them, but then we would want to set float voltage at float range of around 13.1-13.2 V. 5) The C60 with its one-hour absorption is a poor match, and 6) the whole system should be torn out and replaced. In short, we can't solve her problems, but yes, as it is now set up we could set the float voltage to be the same as the bulk voltage and still not get the batteries full. Thank you, Allan Allan Sindelar al...@positiveenergysolar.com NABCEP Certified PV Installation Professional NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc., a Certified B CorporationTM 3209 Richards Lane Santa Fe, New Mexico 87507 505 424-1112 office 780-2738 cell www.positiveenergysolar.com   On 8/1/2013 4:27 PM, Brian Teitelbaum wrote: Allan,   Do you know what the daily Ah consumption is, or alternatively what the daily DOD is on the batteries?   830W of PV on a PWM controller should have a peak amperage of about 48A (830W ÷ 17Vmp = 48.82A). This is only about a C/18 charge rate, which is fairly low but should be workable as long as solar production keeps up with load demand. Of course, with old modules you may not see that many amps, especially in hot weather.   If they don’t have an amp-hour meter installed, that should be an upgrade priority. Every off-grid system should have an amp-hour meter, especially a rental house.   Without some DOD battery info it’s hard to tell exactly what’s going on, but I think that as long as some energy is consumed each night I don’t see any reason why you couldn’t set the float voltage the same as the bulk/absorption voltage, at least in this case. The charging day is limited to hours of sunlight, and as long as you stay under the gassing voltage it should be fine. But as Eric Benson noted, the battery manufacturer should have the final word.   Brian Teitelbaum AEE Solar       From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Allan Sindelar Sent: Thursday, August 01, 2013 1:20 PM To: RE-wrenches Subject: [RE-wrenches] C60 setpoint question   Wrenches, Eden, our main off grid field tech, came across a situation about which I want to ask the group for advice, please. The system: existing old/funky off grid 12V residential system, done by others over many years; this was our first visit. Owner out of state, currently rented, owner's complaint is that the old Heart 2800 EMS inverter is shutting down at times. Six four year old Concorde SunXtender PVX-3050Ts, so 900 rated amp-hours in three strings at 12V. Approximately 830 watts of a hodgepodge of older modules, but well below rated output at present, though no obvious failures. Trace C60 charge controller. Our assessment after a site visit is that the batteries have been chronically undercharged and are showing signs of premature sulfation. With AGM batteries such as these, we have been encouraged (by Midnite tech support and others) to set really long absorption times - we have some systems with six-hour absorptions. The logic is that theese batteries can tolerate - indeed thrive on - staying at absorption voltage of 14.2 - 14.4 V (for 12 V nominal) indefinitely, and given the fickle nature of off grid PV charging, this maximizes the likelihood of their getting full most days. This logic makes total sense to me. Most modern MPPT charge controllers have a programmable absorption time, and some have a done amps (a.k.a. float transition current), to allow them to transition to float if the charge current necessary to maintain absorption voltage drops below a set threshold (typically 1-3% of battery capacity). The C60 has neither, but rather has a nonadjustable two-hour timed absorption. This brings the question: is there any good reason that the float voltage on the C60 should not be set to the same voltage as the bulk/absorption voltage, such that they never drop into float? When sufficient input is available to get the batteries full, they are just allowed to stay in absorption mode indefinitely, slowly getting the energy necessary to reach 100%. We have installed many Concorde AGM batteries, but never with an old C-series controller. This idea seems wacky, but the more I think about it, the more I can't see any problem with it. What do the rest of you advise? Thanks, Allan -- Allan Sindelar al...@positiveenergysolar.com NABCEP Certified PV Installation Professional NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc., a Certified B CorporationTM 3209 Richards Lane Santa Fe, New Mexico 87507 505 424-1112 office 780-2738 cell www.positiveenergysolar.com

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