Date: Thu, 25 Jan 2018 09:40:23 -0800 From: "Cor van de Water" To: "Electric Vehicle Discussion List" Subject: Re: [EVDL] LiIon thermal management question (Chevy Volt) Message-ID: Content-Type: text/plain; charset="us-ascii"
Peter, Storing LiIion batteries is usually not the problem, although it is recommended for long life to not store them fully charged, especially not in hot environment. Damage is done when (fast) charging in cold - the colder, the slower they need to charge to avoid damage. Nissan Leaf only has battery warmers, those will only come on when the car is on or plugged in and below a certain temp (I believe -30) I don't know about the Volt, it might simply stop maintaining the temp when the EVSE is disabled, you can find out by simply trying and see if the state of charge of the Volt changes when the EVSE is not enabled. Cor. Thanks, Cor. FWIW the Volt never allows the battery to fully charge or fully discharge. This means that even though it has an 18.4kWh battery, only 14kWh is available. The thermal management does both heating and cooling. From what I've read all (electrical) heating is done with resistance heaters, cooling is done with a heat pump (cooling mode only, i.e. AC) 'Fast' charging is also not an option. While it does support Level-2 charging, it tops out at 3.6kW which is about 6% of the batteries maximum charge rate. I suspect you may find that the Volt still uses energy to keep the battery within its desired temperature range, but simply uses battery energy instead of EVSE energy. You should be able to detect that by watching the range after the car sits unplugged or the EVSE is disabled, compared to range after the car sits with the EVSE providing power overnight. Mike Thanks, Mike. That's a good point. I hadn't thought about it using the battery energy to maintain temp. I'll have to try leaving it unplugged and see what happens. However, I'm not sure if this would actually tell me anything. It's possible that, even if it does use the batteries, I won't see a reduction in range right away. It might just dig a bit more into the reserve so that it can provide the same 14kWh. I gather that's what it does as the pack ages so that even after 6 years the 'available' capacity remains the same as it was when new. I'm far from a lithium expert, but I've read that while lead batteries lose performance at low temperatures, cold can wreck lithiums if you're not careful. As I understand it, they should never be charged when their temperature is below freezing. I think that even discharging them gets risky if they sink too far below 0 deg C. They also degrade faster (have shorter lives) when they get hot while fully charged. They don't seem to like being fully charged at all. The rule of thumb I read years ago for laptop batteries was that you should store them at 50-70% SOC. So I'd guess that thermal management is probably pretty important for your Volt's battery. BTW, welcome back to the EVDL, Peter. It's been years since we've heard from you. Good to know you're OK. Hi David, Yeah, it's been a while hasn't it? I've been busy, but I have a new job that leaves me with a lot of free time, occasionally. Fortunately we rarely get below freezing and even then it's typically for only a few hours. Plus the Volt never allows the battery to get fully charged or fully discharged. The geek in me wishes that Chevy would provided a way to get more detailed info about the battery, etc. There is no SOC display, just a 10 segment display that shows how much of the allowed 14kWh you've used. The predicted range display for a fully charged pack is not a constant, it varies significantly depending recent performance and possibly takes current environmental conditions into account. There used to be a lot of information available through the OnStar link, but recently they have removed quite a lot of the data, including the data about battery level and charge state. I've seen some folks are working on hacking the canbus to get at the data, so I might try that. Thanks everyone. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20180126/67c49454/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
