Regen braking: confirmed!

[lutach]

Originally Posted by Pdelcast

Yes, that amperage is going back into the pack during braking. Many data loggers do not have the ability to measure negative currents, so some just show zero current (like the Phoenix ICE data logger -- it does not have reverse current measurement, so it shows zero current during regen.) And some will show positive current, even though the current is negative. It depends on how the current sensing is achieved.

Sounds good. Thank you for coming in here to explain it to all of us.

[Pdelcast]

Originally Posted by BrianG

For example the Eagletree 150A uses a Hall-Effect sensor that is unidirectional. It would be nice to upgrade the HE sensor to a bidirectional version of the IC, but my email to ET asking about that is as of yet unanswered.

We made the decision on the ICE controllers to use a unidirectional current sense to increase the accuracy (dynamic range) of the current sense. Eagletree may have made the same choice for the same reason.

Originally Posted by Pdelcast

..................

And yes, the actual braking action is achieved by just shorting the windings together through the FETs.

What happens is this -- the ESC shorts the windings of the motor, and forces the motor to start acting like a generator. Remember that a turning motor generates a specific voltage -- back EMF. This voltage is actually the voltage induced in the windings by the moving magnets.

....................

My English isn't very good, and the translator is even worse. But doesn't shorting means connecting + and - together? But, that can't be possible, there should be a fire then, right? So what does shorting actually means?

Thank you,

Patrick

[lutach]

Originally Posted by Byte

My English isn't very good, and the translator is even worse. But doesn't shorting means connecting + and - together? But, that can't be possible, there should be a fire then, right? So what does shorting actually means?

Thank you,

Patrick

I might be wrong, but I don't think the shorting Patrick meant is the same as a + and - shorting of a battery for example. It's basicaly 2 motor phases shorting to achieve braking. I'll be waiting for the experts to answer it in more details though .

[BrianG]

That's right; I am 100% sure Patrick did NOT mean to short the battery leads. That would be "bad". He did mean shorting the motor leads together via the FETs. Try this sometime: spin a motor by hand and note the resistance. Then, somehow ties all three motor wires together and spin it again. You'll see how much more resistance there is. And the faster the motor is spinning, the more resistance it will have when the wires are shorted.

Originally Posted by BrianG

That's right; I am 100% sure Patrick did NOT mean to short the battery leads. That would be "bad". He did mean shorting the motor leads together via the FETs. Try this sometime: spin a motor by hand and note the resistance. Then, somehow ties all three motor wires together and spin it again. You'll see how much more resistance there is. And the faster the motor is spinning, the more resistance it will have when the wires are shorted.

Ok... But if I brake with my ESC, it also goes like "connecting all three wires together", but then it goes via the FETs and no energy goes through them?

[BrianG]

I'm guessing the FETs don't stay shorted (otherwise the brakes would lock up), but pulse on/off. It's when the FETs switch off when the voltage charges the batteries.

Originally Posted by BrianG

I'm guessing the FETs don't stay shorted (otherwise the brakes would lock up), but pulse on/off. It's when the FETs switch off when the voltage charges the batteries.

Hmm, that would be pretty logical. And how more often they switch on/off how harder you break, right?

[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