Daggers
10 mW
I'm thinking of building an electric longboard and want to use regenerative braking but how would that be achieved? My knowledge of electronics is pretty low but I learn fast and can follow instructions pretty well.
furp said:Well, it would be nice to know how efficient it would be, how much % of the power that would be needed to drive the motor is regenerated when it spins free. in another topic, we came to the conclusion that regen 'braking' can not really works, since braking is reversed current and therefor needs power. However, if the motor is turned by riding down a hill without throttle, it generates a little power, would just be nice to know how much.
Murfix said:As furp said, it's actually regen coasting instead of regen braking. When the motor is forced to spin (ie. coasting) it acts as a generator. We coast a lot so we can regen a lot.
The esc has to be able to send the current in the opposite direction and you can only store the amount of current into your battery that is defined by the C-rate for charging of your pack. There's also some losses to be taken into account, mainly in the ESC, because all the power that it uses (switching and stuff) has to come from the generator instead of the battery.
Short: you need a special ESC and the higher the charging C-rate, the more efficient (up to a certain point).
Murfix said:I have to revise my statement. It was wrong.
A generator supplies power when an electrical load is connected.
Normal braking is applying an electrical load by the ESC. The generated power can't be used so it has to be dissipated into heat. that's why braking is tough on ESC's.
When regen braking, the electrical load is the energy stored into the battery (+ losses). The more energy you are storing, the stronger the braking will be.
Coasting is having a generator with no electrical load attached, so no useful energy is supplied by it. There's only the energy required to overcome the mechanical load of spinning the generator.
So it IS regen braking and NOT regen coasting.[/
How would brakes work without regen? I imagine they'd have to use power to brake. You'd put electricity to the motor but timing it to counter it's movement. So if we supposedly have regen is it using energy or retrieving it... Or starting to retrieve at low levels but using energy when braking hard?
Murfix said:We brake by shorting motor phases at the correct timing. This allows current to flow. The generated power is dissipated through heating of the wires and mosfets. With regen, we don't have to dissipate the power because we now have a use for it --> battery.
You can try this by connecting 2 motor wires together and then try to spin the motor. It will be a lot harder!
Hummina Shadeeba said:on youtube there's a video of the boosted board guy stating their board gets about 40percent regen. that's pretty substantial. I wonder how true it is and I wonder why people dont integrate it into the controller more often if it's possible.
Hummina Shadeeba said:on youtube there's a video of the boosted board guy stating their board gets about 40percent regen. that's pretty substantial. I wonder how true it is and I wonder why people dont integrate it into the controller more often if it's possible.
torqueboards said:Hummina Shadeeba said:on youtube there's a video of the boosted board guy stating their board gets about 40percent regen. that's pretty substantial. I wonder how true it is and I wonder why people dont integrate it into the controller more often if it's possible.
If that was true -- wouldn't they get more then 6 mile range?
Murfix said:As furp said, it's actually regen coasting instead of regen braking. When the motor is forced to spin (ie. coasting) it acts as a generator. We coast a lot so we can regen a lot.
The esc has to be able to send the current in the opposite direction and you can only store the amount of current into your battery that is defined by the C-rate for charging of your pack. There's also some losses to be taken into account, mainly in the ESC, because all the power that it uses (switching and stuff) has to come from the generator instead of the battery.
Short: you need a special ESC and the higher the charging C-rate, the more efficient (up to a certain point).
The motor is still using power to stop. In other words, ESC braking is not free. The 'regenerative' part is that it can recapture small (if not tiny) amounts of power in between the pulses while the braking power is applied. After all, a force is essentially being applied in the opposite direction to bring the car to a stop, just as it would if it was starting from a standstill. This is also why motor brake setups run hotter since the motor is working in both directions. Also, braking force is usually applied more abruptly than while accelerating. AFAIK, a single mechanism (the motor) can't function as a generator and a source of power at the same time. You must use power to brake the car. I'm not an electrical engineer, but I know a few things about physics and the forces that are present and being applied in this scenario simply can't be ignored.
Please correct me if I'm wrong here because our results coincide with jhautz and others that have found mechanical brakes to be more efficient. I'm not arguing that some energy isn't being harnessed or regenerated while braking, I'm saying that it does in fact use power to brake and that the overall net of the system is negative, not positive. Mechanical brakes are obviously using power as well (servo), but compare a servo's energy requirements to a 1/8th brushless motor's requirements and I think the picture becomes clearer.
torqueboards said:I agree -- while it still does most likely have it.. It's not worth much in gold besides the marketing aspects.
I like this one here..
http://www.rc-monster.com/forum/showpost.php?p=264746&postcount=16
The motor is still using power to stop. In other words, ESC braking is not free. The 'regenerative' part is that it can recapture small (if not tiny) amounts of power in between the pulses while the braking power is applied. After all, a force is essentially being applied in the opposite direction to bring the car to a stop, just as it would if it was starting from a standstill. This is also why motor brake setups run hotter since the motor is working in both directions. Also, braking force is usually applied more abruptly than while accelerating. AFAIK, a single mechanism (the motor) can't function as a generator and a source of power at the same time. You must use power to brake the car. I'm not an electrical engineer, but I know a few things about physics and the forces that are present and being applied in this scenario simply can't be ignored.
Please correct me if I'm wrong here because our results coincide with jhautz and others that have found mechanical brakes to be more efficient. I'm not arguing that some energy isn't being harnessed or regenerated while braking, I'm saying that it does in fact use power to brake and that the overall net of the system is negative, not positive. Mechanical brakes are obviously using power as well (servo), but compare a servo's energy requirements to a 1/8th brushless motor's requirements and I think the picture becomes clearer.