Regen braking: confirmed!

[BrianG]

Actually, it's not so much "how often", but what percentage of "on" vs "off" they are.

[zeropointbug]

Thanks for posting that Pdelcast (Patrick?), a good explanation for the not so tech savy.

Byte, yes the FET's do not continuously short the motor windings out, it uses the same principle as working normally as a motor, it's called PWM (pulse width modulation) and basically the more braking you input on your Tx, the wider the 'pulses', and hence more braking action. PWM is usually at a set frequency, but not always, and if it is variable, will change according to motor speed. Some controllers vary PWM in normal forward/throttle operation, usually to increase efficiency at lower rpm's, as the higher frequency PWM you go, the more heat is created because of eddy currents.

[jhautz]

I'm just wondering how much this "regen" actually can effect run time. it cant be much.

I understand that when you spin the magnet inside the coils the motor acts like a generator. But wouldnt it act like a generator while its just coasting too? Why does it take shorting the motor phases to generate energy? Just not making sense to me.

If you lock up the tires when stopping, then the motor is then no longer spinning so it cant be generating any power to send back to the battery, but it must consume some energy in order to keep the motor from spinning. How can it not take engergy to prevent the motor from moving?

I guess I am still not clear on this.

[zeropointbug]

I'm just wondering how much this "regen" actually can effect run time. it cant be much.

Not much no, very small amount, it's not really optimized in these R/C applications vs. real electric cars regen brakes.

I understand that when you spin the magnet inside the coils the motor acts like a generator. But wouldnt it act like a generator while its just coasting too? Why does it take shorting the motor phases to generate energy? Just not making sense to me.

Yes, when you are coasting there is potential between all three phases, however there is no current, hence no power being produced. The way the braking works is basically a 'controlled' short, you spin a motor in your hand, and it spins quite freely, then short out the leads and you have a dead short, that is basically the most braking action you can get from the thing. The FET's just control this by 'pulsing' the shorting action, thus the amount of braking effect.

If you lock up the tires when stopping, then the motor is then no longer spinning so it cant be generating any power to send back to the battery, but it must consume some energy in order to keep the motor from spinning. How can it not take engergy to prevent the motor from moving?

Despite what you may THINK you are seeing, the wheels really aren't locked up, they are spinning a little bit, and that little bit is basically the motor doing 100% braking action under those circumstances. And you are correct in your assumption that the motor cannot be generating potential when it is not moving... it's just that the motor IS moving, just very slowly, it doesn't take much to induce a potential into the windings, and thus currents.

I guess I am still not clear on this.

[whitrzac]

I haven't read the thread, but...
I luv my eagletree

this is a maxcraps pack....





next is jason hills losi truggy with mechanical brakes/clutch, losi 1700 system, 5s batt
high amps: 141.90
low voltage: 15.97
Mah: 2300
watts: 2395

note the regenerative braking on jason's truggy

[BrianG]

ET graphs do show voltage peaks during regen, but you can't see the current spikes because they are negative currents and the current sensor in the ET only measures positive currents.

[whitrzac]

Originally Posted by BrianG

ET graphs do show voltage peaks during regen, but you can't see the current spikes because they are negative currents and the current sensor in the ET only measures positive currents.

but you can see it a little with the voltage spikes...

my question is, how come it has those voltage spikes with a mech. brake setup and a clutch

[pinkpanda3310]

Originally Posted by whitrzac

but you can see it a little with the voltage spikes...

my question is, how come it has those voltage spikes with a mech. brake setup and a clutch

Could it be that breifly the motor is still doing high rpm hence the clutch is still engaged

[BrianG]

Originally Posted by Whitrzac

my question is, how come it has those voltage spikes with a mech. brake setup and a clutch

When you go quickly from any throttle to neutral, the magnetic field in the motor will collapse and generate a small voltage. Won't be near the amount that a brake setup has though, unless the motor IS in fact doing a little braking without you realizing it.

Originally Posted by Bolt_Crank

I've seen my truck go from the 12 - 13 volts when sitting without the truck running, to 16 - 17 volts when I turned off my rack-o-lights... Though, that might be a strange backflow due to the relays themselves...

Relays are coils and generate inductive kickback when shut off. Most circuits simply place a reverse-biased diode in parallel with the coil to shunt that spike.

[teknorc]

Originally Posted by whitrzac

my question is, how come it has those voltage spikes with a mech. brake setup and a clutch

Are you sure the brakes on the ESC are completely disabled? No drag brake, brakes at 0%?

[whitrzac]

Originally Posted by teknorc

Are you sure the brakes on the ESC are completely disabled? No drag brake, brakes at 0%?

I highly doubt it....

[maneba]

This scientific article by a MGM Ing. explain everything...
http://mgm-compro.com/pdf/en-motor-braking-050409-g.pdf

Voltage jumping back up after going from under load to no load?

Battery voltage can jump like crazy going from full load to no load...

[whitrzac]

Originally Posted by Bolt_Crank

Voltage jumping back up after going from under load to no load?

Battery voltage can jump like crazy going from full load to no load...

no... some of the peaks are above the voltage of the pack starting out....

I've seen my truck go from the 12 - 13 volts when sitting without the truck running, to 16 - 17 volts when I turned off my rack-o-lights... Though, that might be a strange backflow due to the relays themselves...