Here’s my two cents, If you do end up putting in two new batteries, and you leave everything wired the way it is, you’d better really watch the rest of the batteries that are in that string. The new batteries will have a lower internal resistance, so the two strings that are all old batteries will have a lower current. This means they charge much more slowly, and the one string that has the two new batteries in it will charge much more quickly. This increased current in the one string often results in overheating of the weakest cells that are in the same string with the new cells. While charging, the old batteries that are in the same string as the new batteries will have a higher voltage because of this internal resistance.
The worst cells will get the hottest, then the heat will cause the internal resistance to increase, which will cause more heat. The batteries can seem good at first, but after a little while, this cycle can get dangerous. The last time that one of my clients tried this maneuver of replacing two “bad” L16s in the bank of otherwise “good” L16s, the plastic started melting and I believe it was close to a catastrophe. Unless you’re running a laboratory experiment, I strongly recommend never mixing all the new batteries. Make sure you are fully aware of the hazards, do you know what to expect in terms of internal resistance is changing the charging characteristics. Best of luck, Kienan Green-Go Solar Distribution LLC Maxfield Solar LLC (installation and consulting company) maxfieldso...@hotmail.com<https://maxfieldso...@hotmail.com/> (801) 631-5584(Cell) www.distribution.solar On Apr 5, 2023, at 7:34 PM, frenergy via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote: Wrenches, I feel compelled to chime in here. Ten years ago, we installed 24, Rolls 2-KS-33P, 2 volt batteries for the shop. Though they were in a climate-controlled environment and maybe went to 50% SOC a dozen times over 10 years, usually ranged 75-100% SOC, we had the first failure just before 7 year warranty ended. Unfortunately soon after there were two more failures we had to pay for, then most recently 2-3 more were very difficult to maintain good SGs and were sagging more in voltage when loaded. We tried several EQs and then deep discharges and hard and long re-charges to try and de-sulphate without luck. So we recently replaced the pack. We know how to care for FLA batteries, been doing so since the 80's. I'm not faulting Rolls/Surrette, Steve Higgins tried to help, maybe I should take some responsibility but the reason I am sharing this bad experience (I was expecting 15++ years from this kind of battery) is at some point after installation I checked the date codes and found there were 5, count them FIVE different dates, one or two of which were more than a year old when purchased. Ouch. Another expensive lesson learned. Hopefully Rolls has a better handle now-a-days on their post manufacture supply chain. Do you think the different distributors that sent their "back-in-the-corner" unclaimed 2-KS-33p's to my distributor to make up my pack had their 2V chargers floating the batteries all that time? me neither. Moral of the story: Check date codes on that big beautiful pack of lead you're ready to load onto the truck. I'm now making it clear to our distributor that I won't be loading batteries on my truck unless dates codes match, which they did on the replacement SimpliPHI's. Bill Feather River Solar Electric Bill Battagin, Owner 4291 Nelson St.(shipping) 5575 Genesee Rd. (USPS, UPS) Taylorsville, CA 95983 530.284.1925 Office/ 530.258.1641 Cell CA Lic 874049 Solar powered since 1982 On 4/4/2023 4:42 PM, Dave Angelini Offgrid Solar via RE-wrenches wrote: Hurts my head ! Agree that you will have more trips to this house after the next one. This is most likely not going to get you 2 more years. All of the wiring is good, clean, and tight? Who really knows how long it could last? Probably fine thru summer and fall. Much better with the next L16 size up and 24 (2V) cells. Lot's of capacity choices there from Rolls and others. Almost Cheers time ! Dave Angelini Offgrid Solar "we go where powerlines don't" http://members.sti.net/offgridsolar/ e-mail offgridso...@sti.net<mailto:offgridso...@sti.net> text 209 813 0060 On 2023-04-04 4:21 pm, Ray Walters via RE-wrenches wrote: So the 24 batteries are actually 72 individual cells that are trying to charge equally, with essentially no BMS. Its not just max strings, but max # of cells, and that's double my maximum. You mentioned they use it pretty hard, so that's the other big part of how long L16s will last. If the customer is barely using the available capacity, I've seen batteries last closer to 10 years, but in this case, I think the remaining cells are close to finished. I'm into using batteries for as long as possible as well, but customer and installer suffering come into play, as well as the fact they'll use much more water at the end of life, and cause a lot more corrosion damage. Not to be a turd at the pool party, but its not reasonable to plan on another 2 years of service. My guess is that you will probably have more cells fail by the time you return with the prorated warranty replacements. Certainly rolling into the summer months, more cells are going to start failing like pop corn. (Pop, pop, pop) Fortress is a good battery, but some of the programming, (especially LVD) can be tricky with older inverters. I had to use the aux out on the CC to switch off the inverters. IF the inverters are Outback, they have a remote switch, if its something else, you might have to actually switch off a relay on the AC output. Ray On 4/4/2023 2:45 PM, Daniel Young via RE-wrenches wrote: Thanks all for the advice. I figured it was not worth trying on a different battery brand. I honestly needed to be able to tell them I researched it and asked my peers. The client really uses the 3 x strings they have and did not really want to go down to 3. They are currently choosing to get the two Rolls under the prorated warranty, and hopes to get another 2 useful years out of the bank before planning to replace. Already prepared him on the cost of the equivalent Li+ at todays prices. So he knows roughly where he is heading. Side note: I am in the camp of trying for 2 x strings when possible (agree that 3 x strings is the absolute limit, and not the best option), simply because if a single cell goes bad, I don't want a client with essentially nothing available until we can get a replacement and get on site. With 2 strings, they can make due at least. That'll go out the window with Lithium though. Looking at Fortress Power for the next battery bank for this client. But we will see what changes in the market by the time it's needed. With Regards, -- Danny Young NABCEP PV Installation Professional #031508-90 Engineering Team Lead Solar Energy Solutions Lexington | Louisville | Bloomington | Cincinnati | Evansville | Indianapolis 513-448-5176 (mobile) 877-312-7456 (Main Office) da...@sesre.com<mailto:da...@sesre.com> From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org><mailto:re-wrenches-boun...@lists.re-wrenches.org> On Behalf Of Dave Angelini Offgrid Solar via RE-wrenches Sent: Monday, April 3, 2023 4:34 PM To: RE-wrenches <re-wrenches@lists.re-wrenches.org><mailto:re-wrenches@lists.re-wrenches.org> Cc: Dave Angelini Offgrid Solar <offgridso...@sti.net><mailto:offgridso...@sti.net> Subject: Re: [RE-wrenches] replace part of rolls battery bank 5 years old on 3 strings, it might not matter to mix, better get ready for a new bank. I have never used more than 1 string for my clients and get closer to 10 years life, so maybe there is better advice out there. Good Luck! Dave Angelini Offgrid Solar "we go where powerlines don't" http://members.sti.net/offgridsolar/ e-mail offgridso...@sti.net<mailto:offgridso...@sti.net> text 209 813 0060 On 2023-04-03 11:03 am, Daniel Young via RE-wrenches wrote: Hello Wrenches, Have a client with 24 x Rolls S550's. 2 of the batteries have given up the ghost. Rolls will replace them under the pro rated warranty. The issue us, the client is wanting to replace them with non Rolls batteries to save $. They can get 400AH 6V L-16 form factor FLA batteries from a local battery house for the same price I am going to get the new Rolls for. And that also means they don't need to pay for freight. The net result is that they could save $4-500 by getting the batteries locally. No freight, and no markup on the batteries we provide (I can technically add the lost markup back in as labor, we do need to make something off of the 3hr one way drive to swap the batteries) Question is, has anyone got experience mixing battery brands like this? 3 x strings of 8 c S550's (L-16HC would be the replacements) both dead batteries are on the same string. Whole battery bank is near the 5yr old mark. The last rolls battery bank the client had lasted them 10 years. (they baby the battery bank to be sure, and take maintenance seriously) I understand where the client is coming from, but do not want to let them shoot themselves in the foot, and I simply do not know what the chances are of swapping in batteries from a different brand. In my head, I don't see a big issue, even if they are sub par, they will likely just get older faster, and fail around the same time as the rest of the 4-5yr old battery bank. But I'm unsure if there are any more subtle issue that these other batteries would cause. Client has been loyal for more than a decade, so I want to give them a fair shake at saving some $ now, as they plan to move to lithium when the whole battery bank finally gives out. With Regards, -- Danny Young NABCEP PV Installation Professional #031508-90 Engineering Team Lead Solar Energy Solutions Lexington | Louisville | Bloomington | Cincinnati | Evansville | Indianapolis 513-448-5176 (mobile) 877-312-7456 (Main Office) da...@sesre.com<mailto:da...@sesre.com> _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. 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