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
