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Consistent regen performance with load dump resistor - idea

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#23
Having upgraded from a 10 year old Jetta TDI that never seemed to have a full set of working glow-plugs I find it a little amusing that my biggest cold weather complaint about my Tesla is getting it to stop!! I have to use BOTH pedals to drive now?! :wink:
 
#24
wycolo said:
> descending a big mountain, the brakes sometimes overheat [abasile]

This is interesting. You certainly are a candidate for a brake upgrade, if indeed one is available for MS. Do you sense overheating by smell or loss of braking force?
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Some loss of braking force. When I had into the shop for the next tire rotation (do them every 3000 miles) I'll ask them to check out the brakes.

Living on a mountain does present challenges for EV ownership. When I eventually get a Tesla, it would be nice if I can charge to below 50% and thereby still have sufficient regen in the cold.
 
#25
SOC has very little to do with most of the limited REGEN discussed on this thread. Lithium Ion batteries suffer irreversible damage if charged below a certain temperature. I've descended 6000' over 12 miles and only regained 12 miles of range or ~5%. For some context; if you were able to descend from 21000' to sea level and recover 100% of that potential energy that would yield ~45 kWh.
 
#27
nwdiver said:
SOC has very little to do with most of the limited REGEN discussed on this thread. Lithium Ion batteries suffer irreversible damage if charged below a certain temperature.
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As expected, my LEAF certainly allows more regen at lower SOCs, even when it's colder. Of course, the cold does limit it more. I'm not talking about really low battery temperatures, though, maybe 0 C / 32 F. Is this not similar to Tesla S behavior?
 
#28
abasile said:
As expected, my LEAF certainly allows more regen at lower SOCs, even when it's colder. Of course, the cold does limit it more. I'm not talking about really low battery temperatures, though, maybe 0 C / 32 F. Is this not similar to Tesla S behavior?
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My REGEN limiting observations are

~45F limited to ~75%
~32F limited to ~50%
~20F limited to ~25%
~15F NO REGEN

I've never seen a REGEN limit <90%SOC at temps >50F.

This is BATTERY temperature... once the car is warm is usually stays warm. I drove over Grants Pass in Oregon with temps in the teens with full REGEN the entire trip. I'm basing battery temp on outside temp when I get in after it sits outside all night.... yes, my Tesla sleeps outside... I hope to fix that soon.
 
#30
Just use the entire bottom of the battery. It's a nice large surface area and it would also help warm up the cells. The problem might be not applying too much heat too quickly or uneven heating of the cells. Perhaps just increasing the amount of heating to the cooling loop would help.
 
#35
This has been proposed before on this forum. One of the issues is that the dump resistor would get very hot, and therefore would have to be physically large and have lots of cooling, which is kinda redundant to the friction brakes. Friction brakes have an advantage of being able to get a lot hotter than would be safe for a resistor.
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Hmmm, what about liquid cooling of the brake fluid? When
you apply the brakes, they heat up and the brake fluid also heats up. Where does the heat go now? I suppose in the air, radiated from discs as there is no dedicated cooling system for brake fluid.
Tesla would only need to add a liquid/liquid heat exchanger for this to work.
Regen still wouldn't work with cold battery, but driving off the high mountain would at least heat up the battery a bit quicker and maybe friction brakes wouldn't overheat (so fast).
Add a solenoid to cut the heat transfer into battery/motor cooling lines when its temperatures are already high enough.

Win/win?

Tesla does have electric battery heaters designed in to the Model S.
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They are not strong enough to 'eat' the regen power.
 
#36
scaesare said:
Tesla does have electric battery heaters designed in to the Model S.
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Not big enough apparently. A 15-30Kw heating element inside the coolant loop would mean there would be simulated regen when the batteries are too cold - simply dumping the energy into the coolant, and the batteries would warm up _very_ quickly with that much heating.


None of the extravagent stuff with a load resistor is required. This is _common_ technology that is used across million of households, just needs some engineering work to make it work with Tesla power electronics and software.
 
#37
Way back in 2007:
The Magic of Tesla Roadster Regenerative Braking | Blog | Tesla Motors
...Some other companies note that they have some sort of shunt resistor to turn excess regen energy into heat when the batteries are full. It sounds like you decided not to go that route and simply cut back on regen when you dont need it... (?)
Wouldn't it be a better overall driving experience if the regen was consistent and you just threw away any extra energy recaptured when you didn't need it?
I would find it disconcerting if I usually got a little bit of slow down from lifting the throttle, but then halfway down a hill I started "rolling" more than usual...
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- - - Updated - - -

I think some trains use regen to power cooling fans.
You could use the regen power to spin some electric fans that blow air through the radiators or directed at brake rotors.
 
#38
AWDtsla said:
Not big enough apparently. A 15-30Kw heating element inside the coolant loop would mean there would be simulated regen when the batteries are too cold - simply dumping the energy into the coolant, and the batteries would warm up _very_ quickly with that much heating.
Click to expand...

The typical stove element is 2600 watts, so 30kW is equivalent to 11.5 stove elements all running full power. That _would_ toast the battery quite quickly!
 
#39
AWDtsla said:
Not big enough apparently. A 15-30Kw heating element inside the coolant loop would mean there would be simulated regen when the batteries are too cold - simply dumping the energy into the coolant, and the batteries would warm up _very_ quickly with that much heating.


None of the extravagent stuff with a load resistor is required. This is _common_ technology that is used across million of households, just needs some engineering work to make it work with Tesla power electronics and software.
Click to expand...

You are assuming that the system (coolant capacity, pack volume, pump capacity, individual cells, etc...) would be able to handle 30kW of direct heating.

A big, assumption, IMO.
 
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