Kienan, First, my advice is be sure to have a release of liability signed by the owner before you start working on this system. Improperly treated or poorly designed Li batteries can be dangerous. A major problem with the upswing of Li batteries being imported is poorly designed and undocumented BMS's. There are MANY startup Li companies (over 2000 on www.madeinchina.com) that have no problem exaggerating themselves and their products. I am flooded with emails from these companies.
This type of battery chemistry, LiFePO4 or LFP, is the safest cell chemistry of Li batteries on the market but that won’t matter as much if the BMS does not have all appropriate protections. It is highly unlikely that there is no BMS, but possible. Note that not all drop-in type Li batteries can be used series. The BMS must be designed for series connection. It is safe to conduct the test that Jay recommended. First understand that in order to use these 12 volt packs in series, all battery packs must be individually fully charged before series connection is made so the SoC of each pack is identical. If you test just one battery pack, it must be returned to the same SoC as all other batteries. Therefore for testing, I recommend charging the entire battery pack to 58.4V. Disconnect the battery bank pull one battery and apply about 16 volts (this is safe for testing any LFP chemistry). If the battery reaches 16V and has not turned off, these batteries should not be used. I recently was at a show and saw a 12 volt LFP battery with the warning on the label: DO NOT CHARGE BELOW FREEZING. The sales rep was clueless why and tried to tell me it really did not really matter. It matters! Lithium plating is a hazardous degradation mechanism that happens primarily when charging a cell below 32°. This will typically accelerate dendrite formation. Dendrite growth can tear the separator and cause internal short circuit at any time in the future of the battery. This can cause spontaneous combustion. If the DKD battery can be charged below freezing or does not have low and high voltage disconnect, it may be a dangerous battery without external control. Did you get that release form yet? Just FYI about us, since 2013 we have designed and sold Li battery power systems now numbering hundreds of customers. Larry Crutcher Starlight Solar Power Systems On Mar 4, 2019, at 6:23 AM, Kienan Maxfield <[email protected]> wrote: Hello all, I just got back from looking at an off-grid system that is only about 4 months old or so, and it has several problems. I have specialized in off-grid for 8 years, so most of the problems will be easy for me, but there's just one thing that is a bit perplexing and I'm hoping someone might have some advice. The system was "designed" by some retailer in Texas (I don't know who) and the home-owner found some local installer to put it together for him (they already charged a ridiculous price and they won't come back). The battery is a big bank of DKD LiFePO4 batteries, each one says 100 Ah @ 12.8V. They are in series sets of 4 for 48V. I think there were 5 strings (500 ah total). There are no com wires from battery to battery or anything like that (nor did I find anywhere for com ports). I have not yet been successful in finding any information about these batteries online. I'm not that familiar with this type of battery and I'm hoping that some of you might have some info/insight on a couple of questions about this situation. Here's a picture of one of the batteries, <IMG_4362.jpg> The biggest question is if this configuration is okay. I'm not familiar with this type of batteries, but I saw at least one brand that said not to put their batteries in series. They said that (at least with their brand) if you needed a 48V battery, you couldn't use (4) 12V batteries. Does anybody have any thoughts (positive or negative) or experiences with these batteries? Does anybody have any technical information (like a voltage/SOC curve or anything else) for these batteries? I will be fixing the other things in his system, but when he asks what I think about his battery bank, I don't know what to tell him at this point. He also has no idea how to tell how full his batteries are, and since it doesn't seem like his batteries have any kind of readout or anything, I'm not sure what to tell him on that either. If I could find a Voltage/SOC curve or a voltage/SOC conversion table, that would help on that front. Thank-you, Kienan Maxfield Solar [email protected] <mailto:[email protected]> (801) 477-0-SUN (477-0786) (801) 631-5584 (Cell) (preferable contact number) www.members.re-wrenches.org <http://www.members.re-wrenches.org/>
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