PB1:
No, not in standard bldc mode. This is what I have been saying all along. You have to think two separate circuits, the only link is Watts (not voltage and not amps, only Watts)
One side is battery and esc input. It’s DC voltage of the battery and the amps are whatever is needed (if not constraint by anything).
The other side is esc output and motor. It’s AC voltage. And the voltage is based on rpm and Kv of the MOTOR (plus something for loss).
IT IS INDEPENDENT OF THE BATTERY VOLTAGE!
Yes!!
So voltage at the motor is only dependent on rpm and Kv! And current is drawn from the esc. How much? As much as needed to have enough Watts to propel the rider.
NOT THE SAME AS BATTERY CURRENT, NORMALLY MORE.
And of course the rider has to open the throttle enough to convert (commutate) enough V and A from the battery side to the motor side.
Wattage is the link! Both sides have the same Watts (neglecting losses). They have different A and V.
No. Why such confusion. I’m saying voltage gets converted to amperage by the vesc. That’s what we’re talking about. That’s what I keep saying. That’s all I’m saying.
There is a duty cycle program and a current control program. There are a couple different things going on and FOC being probably the most complicated. Ask Vedder if u have a question. But as far as voltage being converted to amps that’s as much as I can say
I don’t think it works in the typical way. As has been said the current can be infinately large and there is a transformer-like action occurring. This is what Ren and Vedder have written and I’ve linked and quoted.
@devin, our esc are not converters in the true sense (yes, they convert, but… ). Don’t look up converter or step up / down. It’s wrong.
The technique used in bldc controllers is the same as for brushed motors. A commutator is used. In our case an electronic commutator. They create something that looks like AC using pwm. Your pictures above are correct.
And there are no large capacitors to store and forward energy.
Calculation for NO LOAD RPM is the same. Kv * maximum voltage = Kv * battery voltage.
Remember, it’s a theoretical value that cannot be reached by powering the motor off battery and ESC.
I turn my head for two days. Man this thing lit up and I am loving the science.
PB1 hit the nail, KV is KV. A lovely, horribly misunderstood constant.
You can have a similar argument with a Tesla specialist. Their claims used to be that the vehicles were based on variable AC motors which, for the most part, is true. However the hardware resembled BLDC tech on longboards more than you might realize. An active Tesla hacker found that the BLDC drivers only resembled AC signaling but did not product true AC signals as expected from Tesla’s claims. The modulated signals we use for BLDC are neither true AC nor true DC. We may need to find the name or come up with one for the particular sinusoidal effect we generate.
@VladPomogaev " There is a lot of misinformation is this thread. Anybody wanting to learn anything useful should take the information here with a lot of salt "
Like everything you read somewhere in an Internet forum.
Would you like to point out which information might be flawed?
In short, tesla uses induction motors which are very similar to our bldc motors. Main difference is that these motors use coils and variable current instead of permanent magnets and control is somewhat different. They are the synchronous motors I mentioned in my original post but driven by converted AC.
BTW tesla uses liquid cooling for their power train and still has to deal with excessive heat. You can’t push a tesla for very long at full power. It backs off in order to protect the electronics and motors.
So indeed the whole Tesla set up looks very similar to what we are using. Gee, we are leading edge!!!
That’s a great article. I remember reading it awhile back.
The reason they use an induction motor is because it’s cheaper to manufacture, just iron and copper basically. Magnets for the same power PMSM motor would be more expensive and the motor would be heavier, but the PMSM has better peak efficiency. Tesla probably put quite a nice amount of RD into developing that liquid cooled induction motor.
how bout you add some to our knowledge with a credible source? I think wer’re all looking. the quick no citation answer for why a hub motor gets hot is it somehow has to do more work for the same output as a geared system so needs to be bigger. a bigger motor will be more efficient simply until it’s so big the iron losses take over the copper losses. we’re all in copper losses with our small motors.
I saw a video on the production of the Tesla and one thing we dont do that he does and seems really worth it especially with the rough conditions our motors are subject to is pot the windings. I’ve read about potting windings being a boon for dissipating heat but in my experience doing it it was a detriment. I had good fancy resin as well. Wish I knew what he used. Maybe it’s a compromise for the car and ends in more secure windings but a bit hotter and the cooling system can handle it.
