Is Regenerative Braking Real? Does it work as we thought?

[rmay635703]

Originally Posted by ShadeTreeMech

Another thing to consider is the amount of braking power given by regen brakes. Seems like I read about Ben Nelson's friend with the AC powered electric car who hardly used his service brakes due to the regen braking strength of his motor.

That is one benefit is less brake service.

Something I've noticed, my "antique" 05 48v miles zx40 mini van with a series wound motor is that it uses about 65-75 amps at top cruising speed which is typically (NOW) in the 26-29mph area, using field reduction I can go 32-38mph and draw 100amps. (usually ends up at about 35/36 depending on SOC)

The funny part is the same car AC powered 72v Miles ZX40 uses the SAME number of amps to go the same speeds I go and its 72v NOT 48v.

Seems to me the motor must not be as efficient (or controller) or its just that my tire inflation and lubrication practices make that big of a difference.

So perhaps in these situations motor and controller efficiency are more important than some other factors like regen?

[ExplodingDinosaurs]

Here's a post I made to the EVTV.me blog:

Jack, thanks for the testing and publishing your results.

How long had the car sat before the test? If the car sat for a few days, I could see the oil being stiffer and the batteries less responsive for the regen test. Then the batteries would be a bit stronger for the non-regen test the next day since they have been recently exercised.

Ideally you'd do "ABABAB..." type testing -- regen one day, nonregen the next, multiple times. This would accomplish 2 things: One is to look for system drifts, like batteries working better due to recent use. The other is to give you some statistics -- if the numbers are jumping around you might not have a statistically significant difference (or sameness).

I have a car with regen, I'll have to try your test myself. One thing I have noticed: If I do strong regens (like occasional 200+ Amps), my lead acid batteries stay very well balanced with no BMS (all within about 0.03 Volts). With weak regens (50 Amps), the batteries quickly drift to be 0.5+ Volts apart. Jack have you seen anything like that with your cars and lithiums?

[myzter]

I noticed a voltage driftt aswell, are you measuring the volts identically ?
could be that the batts have different internal resistances.

[Rokeby]

I've watched the videos and my first comment is they desperately need
to find an editor. The videos could easily be cut in half and increase
their content ratio by 100%. Maybe Count DaMonay can help.

I'm not competent to comment on the purely electrical elements and
calculations, especially when carried out to 4 decimal places.

That said, I think there was some experimental design errors or
misunderstandings in the original 356e tests that has lead to this
brouhaha.

As I understand it, three conditions were tested with the 356e:

C1 - Brake pedal regen only
Brake pedal - deceleration by regen and friction brakes
No pedals - freewheeling ( I'm not saying "glide" as it has Prius-specific
meaning and includes a small power draw on the HV battery.)
Accelerator - acceleration only.

C2 - Max regen
Brake pedal - deceleration by "aggressive" regen and friction brakes
No Pedals - constant "aggressive" deceleration by regen
Accelererator - acceleration only

C3 - No regen
Brake pedal - deceleration by friction braking only
No pedals - freewheeling
Accelerator - acceleration only

The perceived problem came up when the figures suggested that the
car used less power over the 47.6 mi. course for the second condition
over the first, and the third case - no regen whatsoever - over the
second.
Overall conclusion: regen in an EV offers no energy savings/efficiencies.

In C1 there is freewheeling and some regen via the brakes.
In C2 there is no freewheeling and a lot of regen.
In C3 there is a lot of freewheeling and no regen.

My observation is that C2 is not about regen at all. It is about
essentially constant deceleration at all times except when the
accelerator is depressed. It would be like driving with a dragging brake
shoe. You would have to accelerate -- that is use power -- to maintain
speed when you would otherwise be freewheeling.

To me, this is not a surprising experimental result.
It would also be less efficient to drive around dragging a 200 lb. anvil behind.

I do not yet understand why C3 -- no regen -- looks more efficient than
C1 -- some regen. I suspect that, as is noted later in the series, it has to do
the nature of the road course driven, having to do with stops/starts,
topography, and ratio of city vs. country, regen "friendly" vs. "unfriendly"
driving.

There may be two additional things that would confound accurate energy use
and efficiency analysis between C1 and C2. I am at/beyond the limits of my
EV/battery understanding here.

Both the test runs for C1 and C2 were made on the same day.

1. Someone said long ago that to properly warm up a Prius for a FE/MPG,
trial, the car needs to be driven for 20 miles or so before the event. In this
way you get, for lack of a better term, a "whole car" warmup, including all
rotating equipment; transmission, rear axle, wheel bearings, pump bearings,
etc.

There is no mention of the 356e being warmed up prior to C1, this could
mean that the the 356e would have been less efficient on the C1 run
compared to the C2 run.

2. The internal temps of the drive batteries during the runs could have
fuzzed-up the data. I believe that the C1 and C2 test runs were done on
a warmish, 90 degF day. It is well known for the Prius anyway that when the
HV battery gets up over 100 degF, it suffers from both reduced capacity and
reduced ability to receive a charge and deliver power.

I don't know how effective the 356e's drive battery cooling system was/is.
Without taking temps before/during/after each run there is the possibility that
temps were not equal for both runs.

Which run this would favor would depend which run was at the hottest part of
the day.

[ShadeTreeMech]

Originally Posted by Rokeby

I've watched the videos and my first comment is they desperately need
to find an editor. The videos could easily be cut in half and increase
their content ratio by 100%. Maybe Count DaMonay can help.

I'm not competent to comment on the purely electrical elements and
calculations, especially when carried out to 4 decimal places.

That said, I think there was some experimental design errors or
misunderstandings in the original 356e tests that has lead to this
brouhaha.

etc.

I think this wordy reply would be summed up by saying how many tests were there? An individual test can be discounted if the data provided is sullied in any way. So how many tests of each condition were there?

Common sense says wise use of regen braking is better than friction braking. Or am I alone in this foresight?

[Rokeby]

Good points.

As to the second; only one run of each condition with unaddressed variables...
inconclusive results.

[Patrick]

From Jack Rickard's blog post of 7/16:

". . . We're kind of going over it now, but we've changed things a bit and gotten quite a different result.

In my mind, the URBAN part of the drive was about half. That's because it takes about half the time. As it turns out, it comprised 11 of the 48 miles. The rest were more freeway like (about another 10 or 11) and rolling country blacktop county road (26 miles}. PLenty of hills and curves on the county road, but really one of the reasons I like to drive that is the Porsche handles it so well. That' s probably not good for regen, and probably IS good for free coasting.

We did a very different drive out US 61 through Cape to Jackson, the urban part, and then the urban part back. Though 21 miles, it takes almost the same amount of time as the 48 mile drive we were doing. And we're getting very different results on both the kWh meter and the AH meter - and showing really quite impressive gains in fact.

So I'm probably going to have to fall on my sword on this one. I was measuring the percentage of road style based on time instead of distance, and probably mischaracterized the drive pretty badly.

The latest results are based on precisely TWO drives, so it's still pretty preliminary. I'm learnign that this stuff is quite a bit more variable than I had thought. So before going into further detail, we're going to do a series of drives in the MIni Cooper. . ."

[MPaulHolmes]

hello!

[user removed]

My 94 VX has just passed 59k miles and the original front brake pads have 50% left.

I guess that confirms that coasting is better, but coasting and regeneration would be even better in the inevitable circumstance of forced stops.

I read somewhere that a single 60-0 stop wastes the energy that could maintain the original speed for .7 mile.

The key is to have the ability to regenerate without a massive weight penalty, as well as to store and reapply the energy at much higher efficiencies than are possible with electric configurations.

regards
Mech