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)
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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.
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.
That's a good point. I hadn't thought about it using the battery energy to
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
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
BTW, welcome back to the EVDL, Peter. It's been years since we've heard
from you. Good to know you're OK.
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
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.
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