Regen Come Back!

[tstafford]

Wow I miss regen braking!

Nashville has been cold - we get a spell of very cold once or twice a winter and we are in one now. Having taken delivery in August this is my first winter with the car. Really miss regen. My trips are short each day - yesterday (according to Visible Tesla) I had two 8 mile trips (work and back) and two 3 mile trips (going to the greenway to walk). Never saw full regen.

Just lamenting the fact that I don't live in a regen friendly climate like La Jolla or Miami.

 

[RedSoxFan18]

Wow I miss regen braking!

Nashville has been cold - we get a spell of very cold once or twice a winter and we are in one now. Having taken delivery in August this is my first winter with the car. Really miss regen. My trips are short each day - yesterday (according to Visible Tesla) I had two 8 mile trips (work and back) and two 3 mile trips (going to the greenway to walk). Never saw full regen.

Just lamenting the fact that I don't live in a regen friendly climate like La Jolla or Miami.

It was so cold yesterday morning that I received a message warning me that regen was completely disabled. The cold also impacted my range, my 85D could handle 150 miles and before the battery was down from 90% to 10%.

 

[Barry]

For the last month or two, when I get into my car in the afternoon, regen is limited to low. That seems just fine for me, even with the 3000 ft downhill elevation change (over 25 miles) I often drive, I rarely touch the brake.

 

[gavine]

OP: Are you using range mode? If so, the battery heater is disabled. For very short trips (picking kids up at the bus stop), range mode OFF is okay. No sense heating the battery for that, but an 8 mile trip would seem worth it to have range mode OFF to warm the battery. The regen energy captured is greater than the energy used to warm the battery (in most cases).

Also, have you tried scheduling your charging so that the charging ends right-around your departure time? Charging the battery warms it up, so why not use that to your advantage?

 

[Max*]

It was so cold yesterday morning that I received a message warning me that regen was completely disabled. The cold also impacted my range, my 85D could handle 150 miles and before the battery was down from 90% to 10%.

Yeah, I got that too...

 

[scaesare]

I had regen completely disabled the other day as well. Which seems different than behavior under previous similar conditions (temp/windchill) when parked at work for the same duration. I'd typically be limited, but not completely disabled.

Perhaps a tweak in the 7.x firmware...

 

[McHoffa]

For the last month or two, when I get into my car in the afternoon, regen is limited to low. That seems just fine for me, even with the 3000 ft downhill elevation change (over 25 miles) I often drive, I rarely touch the brake.

As a side note, how's your range on the climb back up?

 

[Cottonwood]

I live in cold Colorado and have seen limited regen many times. It's -16˚C., 4˚F., this morning in Pagosa Springs. Here are a few tricks if that will help reduce the regen limit:

• As @gavine said, make sure range mode is off.
• Park in an enclosed garage. Heated is best, but just an enclosure is usually warmer than outside. I keep my garage heated to 8-10˚C., 46-50˚F. I often have a little regen limit, but it goes away in a few miles of driving.
• Try to time your charging to finish just before a drive. 80 Amp charging with dual chargers seems to be the best, but 40 Amps helps a lot.
• Preheat the cabin. There is a question about whether this warms the battery, but a warm cabin is certainly a pleasant luxury. I just wish preheating would turn on the seat heaters as well.

 

[RAW84]

One thing that you can do to help this is be sure to precondition the car when plugged in and to keep range mode OFF. This will help the battery pack warm up allowing for more regen, faster

 

[RedSoxFan18]

I find it puzzling that range mode inhibits regenerative braking. Is the entire point of regenerative braking to increase range? I'm feeling pretty dense at the moment.

 

[Max*]

I find it puzzling that range mode inhibits regenerative braking. Is the entire point of regenerative braking to increase range? I'm feeling pretty dense at the moment.

huh? who said that range mode inhibits regenerative braking?

 

[gavine]

Range mode turns-off the battery warmer. The idea behind it is that you are going on a long highway trip where regen isn't needed so it conserves that otherwise wasted energy to warm the battery. If you're going on a stop-and-go trip, you want range mode off so that you get regen sooner. Basically, regen puts-out too many amps for a cold battery which is why it is limited when the battery is cold.

 

[RedSoxFan18]

Range mode turns-off the battery warmer. The idea behind it is that you are going on a long highway trip where regen isn't needed so it conserves that otherwise wasted energy to warm the battery. If you're going on a stop-and-go trip, you want range mode off so that you get regen sooner. Basically, regen puts-out too many amps for a cold battery which is why it is limited when the battery is cold.

Good explanation thanks. Understood the role of the battery warmer and limitations on regenerating a cold battery. Just thought that the power recovered by regenerative braking would offset what was lost by the battery warmer so that it would be a net positive and therefore that range mode should leave the battery warmer alone. But I can see that the limited braking and hill descents on the highway do not result in enough regenerative braking for it to make sense.

 

[Brass Guy]

I've found that in my ~25 minute commute the battery heater cannot heat the battery completely by the time I get home. (I avoid the parking lots we call highways.) It definitely uses more energy than it allows to be regenerated on most trips. 6kW is 1kWh every 10 minutes, or 3 rated miles. That's a lot of regen.
I can see where 15-20 minutes into your drive you come across a long steep descent, that's the only case I can see the battery heater would save energy overall.
That's not to guess what's best for long term battery health though.

 

[jgs]

Range mode turns-off the battery warmer. The idea behind it is that you are going on a long highway trip where regen isn't needed so it conserves that otherwise wasted energy to warm the battery.

I would have guessed a slightly different, though related, rationale: the idea is that you are going on a long highway trip where the battery will heat up soon enough just from supplying the energy to drive the car. Indeed my experience has been that happens -- regen stops being limited within maybe twenty minutes or less of getting on the highway -- although I haven't taken a road trip in really bitter cold, just teens and twenties (F).

 

[Barry]

As a side note, how's your range on the climb back up?

Uses about 40 miles of range on the way up for the 25 mile segment.

This morning I drove to ski country (best snow of the season today!), ~70 miles from 5500' ASL to destination at 9300' ASL, with a high point at 11000' ASL (Eisenhower tunnel). Used ~105 miles of range. The return trip uses about 30 miles of range, using zero miles of range for the majority of the trip.

 

[jgs]

I would have guessed a slightly different, though related, rationale: the idea is that you are going on a long highway trip where the battery will heat up soon enough just from supplying the energy to drive the car. Indeed my experience has been that happens -- regen stops being limited within maybe twenty minutes or less of getting on the highway -- although I haven't taken a road trip in really bitter cold, just teens and twenties (F).

I decided to test this theory the other day. Driving on the highway at about 300 Wh/mi with ambient temperature 27F, range mode on, starting cold, my regen went pretty quickly from about 15 kW to about 40 kW... and then stuck there for 25 minutes. But, the first serious regen I did (the off-ramp) regen limiting immediately cleared. Don't know if the heat from 40 kW of charging was all it took, or if it corrected its estimate.

 

[FloridaGary]

I find it puzzling that range mode inhibits regenerative braking. Is the entire point of regenerative braking to increase range? I'm feeling pretty dense at the moment.

Me too. I thought regen was only limited when your battery was fully charged. I agree with RedSoxFan that range mode inhibiting regen seems counter productive.

 

[jgs]

Me too. I thought regen was only limited when your battery was fully charged. I agree with RedSoxFan that range mode inhibiting regen seems counter productive.

I don't think range inhibits regen. It just doesn't spend additional energy to promote regen. If it really inhibited it, now that WOULD be nuts.