Friendly Reminder to Check Battery Temps

Dan,
That was a very interresting read. I have been denied EV mode a few times and was thinking what is causing that???? My battery must have been getting too warm. And a few days ago, I had the battery fan come on in back for the first time and like you, I was freaked out. I wanted to take my baby to the Emergency Room, but the fan when off fast enough.

Your directing the AC back to the rear seat gave me an idea. I wonder if one could build some kind of small duct from AC direct to battery compartment.

 

Dan,

Great post on a matter that we tend to forget about... until it happens
to us... "up close and personal" as it were.

Recently, I experienced an EV denial on exiting an open parking lot
after parking in the baking mid-day sun for 3 hours -- and there was
nothing in the hatch area. At first I was taken aback; What the heck is
this?

But thanks to posts I've read here over the last ~18 months, I was
able to consider the evidence and conclude that it was a hot HV
battery. Like you, I took some quick remedial steps and shortly all
returned to normal. In my case, I opened all windows to exhaust the
hot air, and turned up the air cond for a short while.

Thanks again.

 

I'm not sure high battery temperature is an absolute "EV deny" criterion. Last summer I made a trip to the mountains of VA with a passenger aboard, doing a CAN-View play-by-play as we went along. Battery temperature peaked at 116F during the descent. (Sorry, Dan, you know I speak Fahrenheit. ) I pointed this out and explained that EV mode (previously described to him) would not activate. I tried to demonstrate it -- and EV mode activated! SOC was at 82% at the time, so it seems at those levels the car has a greater desire to reduce SOC than to limit EV. I realize in Houston you likely won't see these conditions (unless you're force-charging prior to an MPG competition ), so for ordinary driving with typical SOC I can't dispute that 113F/45C is an upper limit of battery temperature at which EV is allowed.

Here's another interesting observation I made, presumably caused by a hot battery (though well below 113F): a spontaneously aborted S4 glide at 26 MPH.

Ever since that event, I've watched battery temperature rather closely throughout our hot spells. Being the large thermal mass that it is, radiant and convective cooling is slow regardless of whether the AC is running. I am convinced that (pardon the cliché) prevention is the best medicine. I have window tinting, I keep my windows cracked (with the interior protected from a sudden rain shower with window deflectors), and (perhaps most important) I always try to park in the shade during prolonged daytime periods. And of course your advice to keep the battery well-ventilated is on target as well.

Taking it a step further, heat is an enemy of battery life. It seems we're seeing a small but growing number of battery failure reports from owners in hot climates. So besides the immediate operational impact, these steps should help the battery live a long, happy life.

 

JimboK,

Thanks for the info.

Next time I descend any of the towering mountains in the Greater
Ballamer area, I'll keep an eye out for high HV battery temps.
<< Check my avatar picture<<

I think that an over-temp HV battery has implications beyond just for
EV use. I would suspect that in an over-temp condition, the HSD would
also restrcit power going to MG2 to prevent further heating. This would
mean that on start-up during the initial ICE and catalytic converter
warm ups, MG2 would not provide the significant power that it usually
does. The car would feel very sluggish, especially if directly entering a
freeway or climbing a steepish hill. I don't see either situation in my
commutes or typical driving, so I don't really know.

But it would be good to be aware that high HV battery temps could
have such a result.

Any thoughts/comments?

 

I have read that NiMH batteries are much happier over the long term if they can be kept below 45 oC while working. Unfortunately, though the prius knows its battery temperature, that information is not readily available to the operator. Who might make sensible responses to the situation...

 

I think you're right on target, especially if the AC is on. In the thread I linked above, in addition to the spontaneously aborted glides, I describe sluggish acceleration. See Wayne' post #5 for the explanation.

It wasn't the major factor in my deciding not to pull the trigger on the III, but it was a consideration that I wouldn't be able to use CAN-View and the possibility (now proven) that GIII CAN data would need to be decoded anew.