Hi Lee, Dan and All,First I agree BMS is best but one needs to look at all the facts. One I've found is high C rate cells are very stable and last far longer the low C cells and only works for Li-ion, not LFP which has completely different charge profile.Vs Li-ion is much closer to lead in that voltage is an indication of charge allowing much easier monitoring.My Volt pack after 2.8 yrs of charging abuse including accidentally charging 20% above rated Kwh the cells are STILL within 1/100 of a Volt of each other. Using a timer or set voltage power supply stops charging abuse.So I'll likely still use the good parts that were not shorted out in the crash as I'm frugal. And let's remember this was in a Volt for 3 yrs before I got them.So near 7 yrs old and NO deviation from 1/100vdc balance. At some point one has to admit that is how it is vs previous thoughts.I don't use the Volt BMS as would need several different size ones and there are no good choices and those that are, are more prone to fail than the cells are data clearly shows on LG cell modules..Since NO change in balance 6 yrs old one should except that will be the trend though continue to check and verify. I expect another 5 yrs from them but we'll see.You are correct about temp variations and why I told Dan to use the cooling system if nothing else but to keep each cell the same temp in such heavy use.Vs I didn't in my 700 lb EV trike pickup but such light use unlikely any temp difference as high rate cells don't make much heat and never run or charged at high rates. Though certainly others with high power and charging. I'm cooling air my Bolt pack because of the way it is set up.So if you cool and limit max charge voltage to 4.12/cell, there is about nil chance of fire. From Tesla data, a medium C rate of 4-6c depending on yr EV battery life is way beyond our dreams at 300k miles.I think the Volt modules might be million mile cells their trend says as no detectable degradation in the ones I've went through 5-7 yrs old.7 yr old ones lab tested every yr showed the same 1k amp output each yr.As for costs let's compare them to lead the cost is about the same as as well bargained/shopped lead golfcart batteries but 35% of premium like Yt/kwh so even if they only last 5 yrs they are cheaper, superior in every way even without a BMS my, other's data shows.If you pay full list for GC batteries Volt modules cost 30% less/kwh.So overall I find the Volt modules a bargain and very safe inside voltage, temp specs even without a BMS we shouldn't ignore as a great low cost way to upgrade from lead or for a new EV. Yes you have to monitor them but saving $2-5k, that is worth it.I hope the Bolt, 2020 US made NIB, other LG cell modules do as well.Luckily Tesla, some other BMS have been hacked so you can and should use them. And anyone using Leaf module MUST use a BMS as a low c-rate cell and easily degrades, gets out of balance.Thus I don't use Leaf modules.That's what I have to say, found.Jerry Dycus Dan Baker via EV wrote: > I guess where the Volt pack is so reliable you can go without an electronic > BMS although it sounds like a terrible idea.
The Volt *does* have a BMS. It's in the battery pack. GM is no fool; they would face all sorts of expensive problems under warranty if it didn't have one! When people re-use a Volt pack in their own projects, they might leave the BMS in place and still operating; they might leave it in place but not fully operating; or they might take it out altogether. I don't know which option Jerry chose; perhaps he can tell us. It sounds like he left the BMS connected to the batteries so it could shunt small amounts of excess charging current; but it was *not* connected to the controller or charger, so it could not prevent running the cells dead or overcharging them with an overly exhuberant charger. Now... if you're going to go without a BMS, it's better to do so with *quality* cells. The automakers do a lot of testing, so their cells are much better balanced than random vendors on ebay. They will survive better even without a BMS. But all batteries age. They will gradually drift farther and farther apart. With no BMS to "herd" them together, they will eventually wander far enough apart to cause problems. And with no BMS to *warn* you that there's a problem (no "idiot" light), you're headed for a disaster! > I suppose one could write a pre-flight checklist like a plane/boat to > ensure all systems are checked including some kind of manual BMS check. Jerry did say he had one of my batt-bridges on his pack. This is a quick-n-easy LED indicator that lights if the voltage of one half of the pack doesn't match the other half (indicating that something is wrong). It tells you something is wrong; but it doesn't stop you from driving anyway. And like David Roden said, Jerry was acting as his own BMS -- a manual BMS, if you like. I used to do that, too. But it gets old, and you forget. You can read up on my battery balancing experiments here: <http://sunrise-ev.com/balancer.htm> > Everyone that owns an ICE vehicle should check their oil regularly and the > there really is no safety to that-by the time the oil light flickers lots > of damage is likely already done. Older cars had an oil pressure gauge or "idiot" light. It would tell you the pressure was low, but it didn't stop you from driving anyway. Most newer cars have interlocks to prevent you from driving with no oil pressure, or no water, or some other catastrophic problem. I suspect the manufacturers had too many warranty claims from people "driving their cars to death". People like my uncle: He bought a new car every few years, and just drove it with no maintenance. No oil changes, no checking the tires; no dealer visits at all. Most of his cars managed to run for 3 years OK. He bragged about how much he was saving on maintenance and repairs. Then one of them had some problem that caused it to run out of oil. He ignored the warning light and kept driving until the engine seized. The dealer wouldn't cover it under warranty. So he sold the car (at a big loss) and just bought another one... and kept doing the same thing. > Sometimes safety systems actually do more harm than good. Yes, that's true. People tend to buy the cheapest BMS they can find. Then *it* fails, and destroys the pack. > I can't find one article where a Volt caught fire sitting on a > charger or for any cause other those that were in accidents. That's because the Volts all have an effective BMS. Lee Hart -- There is a computer disease that anybody who works with computers knows about. It's very serious, and interferes completely with your work. The trouble with computers is that you 'play' with them! (Richard Feynman) -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20210308/2d809a84/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
