Could Regeneration overcharge the battery?

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FloridaSun

FloridaSun

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I wondered about the situation where someone lives on top of a mountain and charges their car to 100% and then proceeds to drive downhill and uses Regen Level of 3. Could the regen actually overcharge the battery? What would happen to the produced energy if the battery is already full?
 
There is charge headroom in the capacity, but I'm sure the BMS would ensure it couldn't overcharge. Another issue is that a battery at high SOC probably can't take the 60-70kW regen that the car can produce.
If it was producing too much, it would just reduce the regen. Some cars actually give a warning on the dash about regen not being available when the battery is at a high SOC.
 
I have got a message in the dash when i try to regen downhill after charging to 100%. It says something like regen not available. My drive to work is downhill so I have got the message a few times
 
The regen level set isn't going to matter, brake pedal regen would make up for it. When possible the car will use regen instead of the brakes one way or the other. There appears to be 1.0 - 1.5% SoC available past the displayed 100% but in the end this is one reason the Kona is equipped with normal brakes.
 
The reason why I bring this up is because I was leaving a free DC fast charger at 90% SoC. At 90%, the car was only pulling 25 kwh at the DC fast charger. However, when I monitored the regen when braking via regen, the display showed over 50kw in regen. It appears that the regen kwh exceeded the kwh limit by twice the amount that the car would accept at that SoC on any EVSE or DC fast charger.
 
Gjpzee said:
I have got a message in the dash when i try to regen downhill after charging to 100%. It says something like regen not available. My drive to work is downhill so I have got the message a few times
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Interesting.. I never got this message..
 
BlueKonaEV said:
...I was leaving a free DC fast charger at 90% SoC. At 90%, the car was only pulling 25 kwh at the DC fast charger. However, when I monitored the regen when braking via regen, the display showed over 50kw in regen...
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The difference is that fast charging is expected to be continuous and regen is not. The BMS would allow short term high charging rates that are not normally allowed on a continuous basis. A standard "1C" charging rate on the 180 Ah battery is 4.2 x 98 x 180 = 74,088 watts. That's about the peak you would see on a 100kW charger, actually 77kW is commonly seen. The highest recorded regen at top speed is 133 kW.
 
KiwiME said:
The difference is that fast charging is expected to be continuous and regen is not. The BMS would allow short term high charging rates that are not normally allowed on a continuous basis. A standard "1C" charging rate on the 180 Ah battery is 4.2 x 98 x 180 = 74,088 watts. That's about the peak you would see on a 100kW charger, actually 77kW is commonly seen. The highest recorded regen at top speed is 133 kW.
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Very interesting! Thanks for posting!
 
Gjpzee said:
I have got a message in the dash when i try to regen downhill after charging to 100%. It says something like regen not available. My drive to work is downhill so I have got the message a few times
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why don't you just limit the charge to 90% then?
 
I'm usually charging to 80% unless I'm planning a road trip. In that case, I charge to 100%..
Last night, I used free charging in downtown to get to 80% and then I used the factory EVSE to get to 90% over night as I'm without a L2 EVSE right now as I had to send it to Mustart and they will send me a replacement. I drive more miles in a day than the factory EVSE can replenish, so I would eventually run out of charge if I wouldn't use public chargers. Hopefully, by tuesday or wednesday, I will have my replacement EVSE.
 
So just out of curiosity, when regen is not available, does that mean all we have left are friction brakes? I assume that the BMS can't burn off the extra juice as heat like locomotives using dynamic braking. So does that suggest on long or steep downward gradients, at full charge, we're going to hope like heck we don't boil our brake fluid? With no down shift option and an electronic parking brake, that is a scary if unrealistic scenario.
 
DelRider said:
So just out of curiosity, when regen is not available, does that mean all we have left are friction brakes? I assume that the BMS can't burn off the extra juice as heat like locomotives using dynamic braking. So does that suggest on long or steep downward gradients, at full charge, we're going to hope like heck we don't boil our brake fluid? With no down shift option and an electronic parking brake, that is a scary if unrealistic scenario.
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Nope, I don't think so. The motor still brakes the car but there's no current sent to the battery. It feels identical.
 
DelRider said:
So just out of curiosity, when regen is not available, does that mean all we have left are friction brakes? I assume that the BMS can't burn off the extra juice as heat like locomotives using dynamic braking. So does that suggest on long or steep downward gradients, at full charge, we're going to hope like heck we don't boil our brake fluid? With no down shift option and an electronic parking brake, that is a scary if unrealistic scenario.
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Out of curiosity...why is this scenario scarier for you than if you were doing it in an ICE car? Brakes perform the same way. :S
 
When the battery is full then you can't use the motor to slow down the car anymore. The energy needs to go somewhere and in the car it can only go in the battery.

In that case you can only slow down with the mechanical brakes like any other car.
 
victor_2019 said:
When the battery is full then you can't use the motor to slow down the car anymore. The energy needs to go somewhere and in the car it can only go in the battery.

In that case you can only slow down with the mechanical brakes like any other car.
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It's been a while but I'm not sure that's true. When I charge to 100% and it's really cold I have no regeneration available, but (if memory serves) I can still stop with the paddles. I will be able to experiment again in about 5 or 6 months!
 
There's two types of electrical braking: regenerative and dynamic.
In dynamic braking a resistor is connected to the motor and the current heats up the resistor.
In regenerative braking the power goes back to the source, either the electrical grid or in the case of a car, the battery.

If you stop with the paddle then the energy must go in the battery.

There's no resistor to dissipate the energy as heat.
 
victor_2019 said:
There's two types of electrical braking: regenerative and dynamic.
In dynamic braking a resistor is connected to the motor and the current heats up the resistor.
In regenerative braking the power goes back to the source, either the electrical grid or in the case of a car, the battery.

If you stop with the paddle then the energy must go in the battery.

There's no resistor to dissipate the energy as heat.
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Assuming you're responding to me: If I can stop with the paddle but the dash prompt is telling me that regeneration is unavailable (and my foot's not on the brake) what's slowing me down? Again, this happened months ago in winter so my memory may be faulty, but I don't recall having to suddenly stomp the brakes when a paddle unexpectedly failed
 
Wildeyed said:
Nope, I don't think so. The motor still brakes the car but there's no current sent to the battery. It feels identical.
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OK, so it's not using electrical resistance, but a friction brake on the motor's axle? I don't know actually, but it seems like if it is generating electricity, it has to go somewhere and if not to a battery, then sent off as heat.
 
robxb said:
Out of curiosity...why is this scenario scarier for you than if you were doing it in an ICE car? Brakes perform the same way. :S
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Because in an ICE, I can downshift and use engine resistance rather than relying on friction brakes. On long grades, you do not want to overheat your friction brakes which could, in the extreme, boil brake fluid and lead to a loss of all braking. With a cable driven emergency brake I have a fall back. I never tried to deploy an electronic emergency brake at speed. Hope I never will, actually ;-)
 
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