So it's my understanding that, ideally, regen braking intensity should reduce or be entirely eliminated under several conditions, such as: batteries too cold temperature, batteries already full.
In these scenarios, it would make sense to actively brake by applying negative throttle and using battery power to reverse the motor against the natural flow.
In the screenshots for the program, I see you can set max current limits for regen breaking, but I'm wondering if the regen breaking logic is smart enough to restrict the regen power based on the battery fullness? I don't see a place to set an explicit threshold voltage, but I assume it's possible to simply use the upper bound for battery voltage from elsewhere.
I've heard rumors of people accidentally overcharging their batteries with VESC regen and tripping the BMS in such a scenario, so I want to clarify. Even if it can be avoided with better planning, it would be good to know the capabilities and limitations.
And while on the topic.. does anyone know if regen braking uses CCCV charging? Or does it just do CC with whatever maximum energy it can obtain?
Thanks for your time!
roro
Based on my observations, regen is not scaled back from the set up value under any conditions you mentioned. If I remember correctly, in one of these discussions, the rationale was that occasional jolts of current into the battery are not that damaging, and the battery would discharge pretty quickly to a point where it would safe to regen high current into it. This might be true for a skateboard but not for a heavy 200lbs bike, for example.
The power does scale down based on the temperature thresholds, I've tested that part and it works well. But this is not affecting regen. I think the premise is that weakening regen power would be a safety issue, so regen amp limit stays constant according to what you set them to.
However, my take on this is that limiting regen would be beneficial under certain conditions you mention. Most importantly, cold temperatures. You don't really want to push high current into the batteries when they are cold. Limiting regen until batteries warm up a bit is a standard practice on most EVs. limiting regen in the 90-100% state of charge is also a good practice to reduce the stress on the battery. In a nutshell, it would a good feature to have but it's not there yet. It shouldn't be too hard to implement it as a new app.
There are no CC or CV stages when regenerating. The amount of current pushed back into the battery is whatever the motor is generating at that moment and it's likely to fluctuate all the time. It may be somewhat constant if you roll at a constant speed downhill for a prolonged period of time.
My solution right now is to never charge the battery more than 90%. It's good for the battery and lack of dynamic regen limit is a non-issue. I also never set negative battery current less than 1C of the entire pack.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
Can the VESC brake the motor in any way other than charging the batteries?
The kinetic energy has to be converted to some other form or energy. The only alternative to electrical energy I can think of is heat. Where would the VESC dump this heat? I don't see a large resistor with a heat sink. I have a hard time believing the heat sink on a VESC could handle all the heat which would be produced if the energy weren't being routed back into the batteries.
Duane Degn
Thank you vadicus, that was a very helpful comment!
Teslas (and other EV's I'm sure) do limit regen braking when the battery is full / not warmed, so sometimes drivers are surprised by the lack of regen breaking. It's certainly startling to drivers but not a safety issue for an attentive driver IMO. I personally think the greater safety issue would be accidentally overcharging the battery in these scenarios, causing a battery fire or tripping the BMS and losing all motor power (and braking!).
Yeah the scenario in my head is starting off at the top of a hill with full battery. I suppose keeping the battery at 90% SoC is probably the safest solution for now. -1C is a good conservative charge rate.
Duane, I don't think the VESC has a resistor for dissipating the energy. However, it can adjust the strength of the regen braking (configurable in the software) I believe. Ideally in these situations, your regen braking would not activate, and the user would be required to apply some other brakes or negative throttle to offset their acceleration due to gravity.
Under most conditions, you would want to use the battery as your load for braking because you recover some of the energy that otherwise would be lost. Whenever it is not desirable, you want to use your regular mechanical brakes that must be installed on a vehicle anyway for safety. Regen must not be relied upon as the the only brake option. Braking with a load resistor is possible and not hard to implement but would be unnecessary for most situations.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
"or negative throttle to offset their acceleration due to gravity"
I'm trying to figure out how "negative throttle" would work.
If the kinetic energy of the rider/vehicle isn't being converted back to electrical energy, the excess energy most likely needs to be converted to heat. Without some sort of mechanical brake, I don't understand where the heat would end up. Do the motors get extra hot if regen braking is limited?
"mechanical brakes that must be installed on a vehicle anyway for safety"
I imagine most e-bikes have mechanical brakes but I don't think many e-skateboards do.
It's not something I really need to know but I am curious about what gets hot if regen isn't used. Is regen really turned off at times?
Before starting to build my own e-skateboard (with several VESC), I purchased an Ownboard. The Ownboard manual includes a warning against riding down hill with a fully charged battery. Based on what I understand of the VESC, I'd think the same warning applies.
Duane Degn
If you can't get some sort of mechanical brakes, your best bet would be to never charge the battery more than 90%. Then you would be able to use regen under most conditions. Of course, if you roll 10 miles downhill fresh of the charger, you would likely need to charge even less, maybe 80%.
Regen energy needs to be put somewhere to produce the drag/braking force. It can be a battery or some sort of a load. It's best not to waste it. Hence the recommendation is to undercharge the battery if you know you would be generating more than you are using. The battery will thank you later. 100% of charge is too much stress for a battery anyway, it will live longer if you keep state of charge between 30-80%.
NextGen FOC High voltage 144v/34s, 30kw (https://vesc-project.com/node/1477)
hi guys I have this problem that when I brake the regeneration stops everything but I don't know where how to eliminate the regeneration completely can someone help me?
dump load could be used, it sinks the current on a high power resistor, when overvoltage on battery occurs.
https://spintend.com/collections/frontpage/products/over-voltage-protect...
This is a curious topic to me as well.. For those of you discussing only charging the battery to 80-90%, if you are using a BMS, would the cells ever balance? It is my understanding that balancing occurs at peak pack voltage. I am wondering if using this solution could cause additional issues and overtime if the pack would become unbalanced.
Andrew Dorman
This is a curious topic to me as well.. For those of you discussing only charging the battery to 80-90%, if you are using a BMS, would the cells ever balance? It is my understanding that balancing occurs at peak pack voltage. I am wondering if using this solution could cause additional issues and overtime if the pack would become unbalanced.
Andrew Dorman
For some context, I have recently observed some e-scooter motor controllers actually consuming power from the battery when at a high SOC and still providing negative torque.
From my own testing, they seem to be burning this energy off as heat in both the motor & MCU (both battery power draw + mechanical power). I've read of Maximum Torque Per Watt control (rather than MTPA), so I wonder if they've derrived Minimum Torque Per Watt instead.
I wonder if any of you have a take/any thoughts on this as currently I cannot think what control algorithm they'd be using to achieve this.
I did think they could be shorting the phases together with PWM to provide some control, but this wouldn't explain the power draw from the battery pack in this scenario