Cold weather regen braking anomoly

Dsinned · Dec 29, 2012

For the past week or so while there has been a cold snap in the weather (OAT ~ 40 to 50F) with occasional rain, every time I drive my RAV4 EV for the first several miles, and shifted to "B" to intensify regenerative braking, the RH side I/P displays a message saying, "Regenerative Braking May Be Limited. Vehicle Deceleration While Coasting May Be Reduced". Eventually, the message goes away, and normal regen braking is restored, but not until after the brakes apparently have warmed up, or so it would seem. This did not happen before when the weather was warmer (55F or greater). Thus, I think this braking anomoly may have something to do with how cold it is outside. I do not get this message while coasting to a stop in "D".

Anybody else seeing this or have any comments to offer?

TonyWilliams · Dec 29, 2012

Yes, I get the same. The battery will limit regen as the battery is both cold, and/or near the top of its charge, just like it would with a regular charge.

One nice feature from Tesla is that it has not yet gone to zero regen. The LEAF absolutely does, and since I live on a hill, I've had my breath taken away more than once when it felt like the brake pedal wasn't working. It's a dumb way to do it, but obviously, the same will happen with a Tesla battery coming down a long hill.

At some point it has to restrict regen to zero when the battery is "full".

One thing I'm surprised at is the battery isn't warmed up. I prefer that it be warmed while plugged in before I go driving. For whatever reason, that doesn't appear to be the case.

Lots to learn on the TMS, but hopefully our CAN bus scrounging will help us learn what's going on.

Dsinned · Dec 30, 2012

This is happening even when my battery is partially depleted and always while OAT is in the 40 degree F range, but eventually goes away after several miles of driving in stop and go traffic.

Tony, what you say makes sense when the battery is already fully charged, but that is not the case in my situation. So, this must be some kind of low temperature protection scheme either of the battery or the regen braking system or both. Or, maybe it has something to do with the traction motor not being sufficiently warmed up.

BestDay · Dec 30, 2012

Funny, I just noticed today (in the forties outside) that my revenue braking was limited to half. This was while in drive with a half full battery. The braking felt different so I looked down and saw that no matter how hard I pressed on the brake my regen meter would only show half regen.

Bill

SparkyAZ · Dec 30, 2012

There is a CAN bus signal on the Prius called Charge Current Limit, which is visible on the Scangauge. It sounds similar to what you are looking for, it varies depending on battery temp and state of charge. Nominal value is 125 Amps.

Ampster · Jan 2, 2013

SparkyAZ said:
There is a CAN bus signal on the Prius called Charge Current Limit, which is visible on the Scangauge. It sounds similar to what you are looking for, it varies depending on battery temp and state of charge. Nominal value is 125 Amps.

I have been noticing the same message when the outside temp is around 45 degrees. At first I noticed it when my RAV was fully charged. The Curtiss controller on my VW conversion will limit voltage and amps when the battery is full to prevent overcharging the battery. I know that regen braking can deliver a fair amount of Amps.

Then I noticed that this also happened this morning when my battery was not fully charged so I concluded, before I read this thread that this must be some way to protect the battery when it is cold. That seems to be the general conclusion here. I have read on some other forums that battery capacity is reduced by temperature extremes so that is consistent.

Have you tried your scanguage on your RAV? I finally found mine and got it operating but not set up. I am not even sure what I am looking at but I think that is the topic of another thread.