Daniel:
I feel your pain: In October of 2021 one of our off-grid clients had failed flooded L-16 batteries. We needed 16 replacement batteries and chose Rolls VRLA batteries. We could not get 16 due to supply chain constraints so we went for 8 with a back order for another 8. It took until May of 2022 before we could get 8 more. The Rolls batteries subsequently failed. We were denied warranty relief in part because we mixed the exact same batteries but delivered 7 months apart. The cost of resolution came out of my pocket. If you can’t mix the same batteries of slightly different age, I would extrapolate that you can’t mix batteries of different manufacturer. My guess is if you mix batteries the entire array would experience a hastened decline. This conclusion is consistent with research done over many years. I looked up the S550 batteries and learned they are 6 volts units. Assuming the system is 48 volt nominal this would be 3 strings of 8. Three strings is pushing the envelope of acceptable design. Multiple parallel strings encourage circulating currents resulting in a process I call “battery cannibalism”: Lower voltage batteries discharge the higher voltage batteries over time. If it were me I would rearrange the batteries into two strings of the best batteries and wait for the rest of them to fail. I would then redesign the system for one string with an appropriate AH rating. Two volt cells are a practical way to achieve this. Also look carefully at your thermal compliance. Make sure you are using the proper temperature compensation value applied to all charging sources. Avoid re-radiated heat from sunlit surfaces and proved good ventilation. I hope this helps. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Daniel Young via RE-wrenches *Sent:* Monday, April 3, 2023 11:04 AM *To:* RE-wrenches *Cc:* Daniel Young *Subject:* [RE-wrenches] replace part of rolls battery bank 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
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