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Adventures in Battery Conditioning (relim. findings IRT battery cooling criteria)

19131 Views 78 Replies 24 Participants Last post by  bro1999
So I've been gathering data and observing when and how my car has been running it's battery cooling processes under different scenarios. I've gathered quite a bit of preliminary data, I haven't poured over the Torque logs yet (I'm not a data analysis guy) so there are some gaps but I feel like I have enough of an insight into when and how the car does battery conditioning to be of use to fellow owners (especially since we're still knee deep in summer.

The first thing I've observed is that the car REALLY cares about whether it's "plugged in" and will definitely cool sooner and to a lower temperature if it's plugged in vs not. FTR I've only observed being "plugged in" to a L2 charger, I don't know whether connecting to L1 or DCFC will produce the same results.

The second major criteria is whether or not the car is "on", this changes the conditioning behavior both "plugged in" and "unplugged".

I have yet to observe any evidence of battery conditioning when the car is both "off" and "unplugged". I've seen battery temps as high as 37C/99F with ambient temps as high as 42C/108F and the car has not decided to cool the battery even with high states of charge (above 80%). I have heard that other owners have witnessed off/unplugged battery conditioning but I've never seen it so I have no idea what temp might be required to trigger it other than above 37C.

One of the things I don't know is what specific temperature sensor(s) the car is looking at when it decides to cool the battery. There are several OBDII PIDs for battery temperature and several for electronics temperature. Most of the time these sensors all have different temperature measurements within 1C-3C of each other. I'm sure this is something that could be nailed down looking at the data.

Also note that all the numbers I'm using are Celsius meaurements as observed via Torque because that's what the car uses. I've converted many of these numbers to Farenheight for the benefit of my fellow countrymen but I've used standard rounding so 31C becomes 88F not 87.8F.

There are two main modes of battery cooling that I've observed, I'll call these "aggressive" and "weak" modes. I have only observed aggressive mode cooling when the car was plugged in.

Under aggressive mode cooling the car will start cooling at about 33C/91F and stop cooling at about 27C/81F (battery temperature)

Under weak mode cooling the car will start cooling at about 35C/95F and stop cooling at about 31C/88F.

OK with all that out of the way here is the list of different scenarios I have seen.
off/unplugged - n/a
on/unplugged - weak mode
off/plugged/charging - none
off/plugged/not charging (charge complete or charge not needed) - aggressive mode
on/plugged/charging - aggressive mode

Some other notes:

If the vent fan for the passenger compartment is on when the car is performing battery cooling you will get cool air into the cabin whether or not you have "heat and AC" on in the climate settings. Interestingly this will also cause the displayed percentage of your power used for climate settings to increase and the car will attribute more power to climate settings than it will to battery conditioning by about a 2:1 margin.

The converse is not true, if you are running cabin air conditioning and the battery is as warm as 32C/90F the car will make no effort to cool the battery.

If anybody wants to pour over the data themselves I've got all my Torque logs uploaded to a shared Dropbox folder. Feel free to peruse.

Conclusions:
I'm actually quite disappointed in the decisions that GM made when designing the battery conditioning profiles for the Bolt. Really the only time the car decides to prioritize cooling the battery is when the car is plugged in. I'd expect that most people who live in hot climates are like me and do not usually have ready access to an L2 charger during the hottest part of the day. Now I understand that many people would not want to see their range being decreased due to battery conditioning but IMO they have gone too far and are allowing the battery to get and stay much too hot which will negatively effect the long term capacity retention of the battery.

Between this frankly pathetic approach to battery conditioning and the lack of options for limiting the maximum SoC it's abundantly clear to me that GM does not remotely prioritize the long-term health of the battery. I expect that a Bolt battery will still significantly outlast a Leaf battery that completely lacks active battery cooling but I don't expect it to perform nearly as well over the long term than a Tesla Model S battery. Being that the average amount of time that new car buyers keep their cars is only about 6 years combined with the reality that many Bolt drivers are lessees instead of purchasers I suspect that GM (correctly) figures that most of the people who will have to deal with the repercussions of this approach will be 2nd or 3rd owners.
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{...}

I was able to speak briefly with a guy at Battery University who suggested that the higher ambient temperatures have little affect on the longevity of a modern, actively cooled EV battery. He emphasized that by far the best way to prematurely kill any EV battery was:
A.) Frequent Fast charging (DCFC - Where a Fast charging session could raise a pack temperature to 140掳F)
{...}
I think that the temp of the battery pack during charging (especially during DCFC) depends quite a lot on both the rate of charge, and how much you cram into it at once (and the SoC when you stop).

I rarely charged my Spark EV up to over 90% at any charge rate (generally 80-85% when I charged, which wasn't every night), When I DCFC'd (which I did every couple of weeks, to add a quick 40 miles), I rarely charged past 65% or so - thus keeping the battery temp lower. Also (mainly because I had found a free 24 kW charger that I used for about a year) I generally charged at lower kW rates.

I saw very, very low degradation of the main battery over a 2 year period with my Spark EV - less than 5%.
I would be interested in hearing if battery conditioning is triggered when plugged in to the default 120V EVSE (at 8A and at 12A) - even if the conditioning pulls more current than supplied by the EVSE (i.e., it drains the battery a tad while running). If so, plugging your Bolt into the 120V EVSE could be just the thing to do when your garage is at 95+ degrees F : conditioning happens, but battery isn't filled up. You'd leave it plugged in until garage became < 90F.

(Although based on raitchison's OP it seems that car would have to be " on/plugged/charging " {{ start cooling at about 33C/91F and stop cooling at about 27C/81F (battery temperature) }} . )

Of course, if the battery was that hot to begin with, plugging in to L2 and then 'remote starting' the Bolt (and letting it cool the battery for 10-15 minutes) would seem to be a good idea ...

Question for raitchison : have you tried setting "off-peak charging only" (so that the car is plugged in to EVSE, but not actively charging) when battery is very warm, to see if battery conditioning occurs ?
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If I may answer out of turn: I have. And it does. During this hot weather I've been plugging in my 120V EVSE, using "off-peak only" charging and my Bolt does condition the battery when not charging. However it seems to condition at a more subdued level. Much less noise than when plugged in to my L2 EVSE.
Thank you!
" I turned on the cabin air conditioning before I plugged in. "

Did you set the A/C temp to anything special (really low, or 68-70F, or was it just 'ON') ?
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