No Regen During Braking for First Mile

Hi,

We've had our FFE since early Nov 2012 and have about 3,500 miles on it. I am the primary driver and I've noticed about 1/3 of the time when starting out from home that there is no regenerative braking for a mile or so.

It only happens when I head out going north which is slightly uphill. First stop sign is level, next stop sign is downhill, second stop sign is downhill. Next is a traffic light at the top of a small hill. Through all of that, no regenerative braking as indicated by the braking coach and (lack of) braking score. Finally, after the stop light, when I get to a stop sign on level ground, I get regenerative braking, as indicated by improvement on the braking coach and the braking score.

When I leave my house in the opposite direction (downhill), I have never had this happen. However, I drive up the hill first 90% of the time.

Anyone else experience this or heard of this?

TIA

Is your battery always charged to 100% just before the routine you describe?

I don't know for sure, but it make sense for regenerative braking to be disabled until some energy has been consumed from a fully charged battery, in order to avoid overcharging it.

As I said, this is just a theory, but it would fit the behavior you described... during your first few stops, your battery is basically full and the energy captured from regen cannot be stored. The car doesn't want to "lie" to you, so it doesn't show any regen feedback and it doesn't give you a braking score until it can actually store the captured energy.

Have you tried your routine with a partially charged battery (say, 90% full) to see if regen occurs immediately then?

I can confirm WattsUp's theory... at work after charging to 100% and then reparking a half mile away where my office is, I occasionally get some regen after braking the first time (not sure why), but then I never get any regen on subsequent braking (three stop signs and four speed bumps, max speed under 20mph). There have been a couple of times that I recharged for only an hour or so (just enough to get home - want at least 15kWh in "the tank"); on those occasions I got regen at every stop sign and speed bump.

That being said, I'd expect cleavel's situation to be reversed of what he described, i.e. would expect no regen when leaving downhill, and regen when leaving uphill.

WattsUp said:

Is your battery always charged to 100% just before the routine you describe?

I don't know for sure, but it make sense for regenerative braking to be disabled until some energy has been consumed from a fully charged battery, in order to avoid overcharging it.

Click to expand...

This isn't just a theory, this is fact.

I live on top of a large hill, about 1000 ft above the valley and each morning I have a long steep descent. When I start out fully charged I don't get any regen going downhill unless I cause the car to consume enough energy that the regen has "room" to put it back in the battery. (e.g. running the heater at high temp).

It's immediately noticeable because going downhill with the car in L is just like being in Neutral. There's no braking effect from the motor, and I have to use the brakes to avoid from "running away", with no indication of regen on the dash.

As soon as I consume some energy, the braking effect from the L position immediately kicks in causing the car to slow, and if I touch the brakes I see the regen indication on the dash. What's weird/annoying is that as I leave the car in L on the long downhill, the motor braking effect comes and goes as the heater turns on/off and I have to modulate the brakes accordingly to keep from racing away.

But of course this makes total sense. Where would the energy go if the battery was full? For those familiar with off-grid renewable energy systems (solar, wind, hydroelectric) you'd need a dump load for this situation, only no such things exists in a car. So instead they just open the circuit and stop charging.


WP

Thanks All! What you've written makes total sense. My "uphill" run out of my driveway is no more than 20 feet of elevation gain over maybe 200 feet of road. The first stop sign is at like 1/8 of a mile and after that there's about an 80 foot descent over about 1/2 mile. As I think harder about leaving my house in the opposite (downhill) direction, maybe the car is never fully charged since I almost never go that direction first thing in the morning.

Question to those who have experienced something similar, does the Driving Coach show bad brake regeneration performance when the car does not use regenerative charging?

I have noticed the same effect and it too is when I leave from home fully charged. I hadn't considered the full charge component of this and see how it completely explains the behaviour. Thanks.

Hi,

I am experiencing the same thing. I live on a small hill and every morning after a full charge do not get any regen until I am at the bottom of the hill, approx 1/2 mile. This did not happen during winter, just now that it is getting warmer. Maybe in colder weather, the battery never "fully" charges and thus has a little more capacity for initial regen.

Thanks,

cleavel said:

Question to those who have experienced something similar, does the Driving Coach show bad brake regeneration performance when the car does not use regenerative charging?

Click to expand...

Yes, for me it does... today the bar got down to about 60% before regen kicked in, which was at about 0.5mi on a 1.5mi trip from the charging station to another building at work (max speed about 35 mph). Bar ended up at about 80% at the end of the trip. Seems to me that our Coach has unreasonably high expectations.
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When I shut down, the trip stats reported 99% brake regen, so it must not have counted all the braking I did during the first 0.5mi toward that statistic.

cleavel said:

Question to those who have experienced something similar, does the Driving Coach show bad brake regeneration performance when the car does not use regenerative charging?

Click to expand...

Yes, it gets in the yellow for me right away and is how I noticed the issue.

Is your vehicle "preconditioned" when this happens or not?

I ask because of the following:
On a recent vacation we had rented a C-Max hybrid for the trip and I noticed a similar behavior to this thread by the C-Max. Looking in the owners manual for the C-Max it stated something to the effect of: regen doesn't happen when the vehicle is cold--it will wait until the battery is warmed up enough to properly accept a charge. If you're not preconditioning the car I wonder if something similar is happening here?

Note: I also experienced regen stopping when the battery was 100%: We were driving around a pretty mountainous area; on one long downhill section of road I rode the brakes and watched the regen circle going. About 1/2 way down it stopped and the conventional brakes kicked in when the battery meter showed 100%.