Degraded Regenerative Braking - Cause for caution?

I live on a fairly steep hill and I really appreciate the regenerative braking and love how little I have to use my friction brakes. Normally, when I roll down the hill and gain some speed, I 'touch' the brake pedal and the Energy Level Gauge easily pegs to the bottom of the "charge" segment slowing me down significantly.

Every now and then, I discovered on the same hill, same route and same brake pedal 'touching' technique, the Energy Level Gauge would not go past the 'r' in the word 'charge' (about half way down) and would not give me that satisfying extra tug to slow me down. I would have to then press harder on the brake pedal, engaging the wasteful friction mechanism! Further into my drive, after a couple minutes, the regenerative braking begins to perform as intended. I was thinking there was some sort of malfunction!

I think I might have discovered a possible cause. I started to see a pattern of this happening only after a full charge. Maybe this is a 'feature' to prevent the batteries from being overcharged? Sounds reasonable. Anyone else experience this? Going down hill and expecting your regenerative braking to kick in, and then it doesn't, could turn into a possible safety issue (albeit rare). That extra split second to engage the friction brake could increase your expected stopping distance. But now that I know what to expect, I can anticipate the behavior better. Maybe a warning in the user's manual would be in order. Or did I just miss it...

Still love the car!!! -John

I am sure your initial regeneration is limited to prevent any overcharging of the batteries when they are already full. I have not experienced this on the I-MiEV so far, but on the LEAF and my old RAV4-EV it was a fact. On a full charge, on either of those cars, your regeneration might vary from zero to minimum for a mile or two at most and then normal brake feel and regeneration would return. Some people on the LEAF forum seem to live on the top of mountains and never fully charge so they can time the use of regeneration to top off the battery by the bottom of the hill.

Yea, I can confirm.

What I have seen is, fully charged, 1/3 uphill and down the other side regen is a bit soft and down at the bottom of the other side almost goes away. 14/16 charged, regen works normal. I am driving in "B" most of the time.

Cheers
Peter and Karin

shifttrans said:

I think I might have discovered a possible cause. I started to see a pattern of this happening only after a full charge. Maybe this is a 'feature' to prevent the batteries from being overcharged? Sounds reasonable. Anyone else experience this?

Click to expand...

Yes. I drive in the 'B' mode all the time and regenerative braking is nearly nil when the pack if fully charged. I rarely recharge to 100% so it's not something I experience very often

Don

Thanks for the replies. Good to know this is normal. It's interesting how your EV driving habits differ so much from the ICE car! -John