PWM setting

[Zen]

On a swordfish program card there is a setting for pwm. What does it stand for. And how does it change the esc's performance.

[NativePaul]

Pulse Width Modulation, the PWM Hz is the frequency that the ESC switches the on and off to simulate a lower voltage than the battery actually has, the higher the HZ the closer it replicates an actual lower DC voltage, but it is doing a lot more work to do so, Castle said going from low to high would be about 20% extra heat in the ESC and to start of with 8kHz (or the lowest yours will go) and if there are no issues leave it there, only raising it if you have to.

[Kris Flynn]

What issues would we have that might want us to raise the PWM?

[Fluid]

Some high rpm motors may work better at higher PWM and throttle precision may be better for throttle-critical flying etc.


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[NativePaul]

For us not much, personally I have never had to raise mine. I have heard that it can help with some outrunners, and they are typically 12 pole but can be more, my guess is that the high commutation speeds could be the issue, but I regularly spin 6 pole Mega Motors at 40k rpm which is around 250k commutations a minute so you would have to spin one much faster than the 10-15k rpm that is typical for planes if that is the case. Jay, you have used Scorpion outrunners in boats haven't you \i guess you were spinning them faster, are they 12 pole? How fast were you spinning them? Were they OK on low PWM?

[Fluid]

Scorpion recommends using 8 kHz for their 8- and 12-pole outrunners. I use that setting on mine and they work great up to 25,000 rpm (the fastest I have spun mine). Here is what Schulze said about it:

"When selecting the switching frequency the general rule is this: the lower the motor’s inductivity, the higher the switching frequency should be. Increasing the switching frequency reduces the ripple in the current flow in part-load mode, but at the same time causes a rise in eddy current losses in the motor and switching losses in the controller. The simplest method is to try out different switching frequencies, and select the one at which the motor and the future heat up the least."

the higher the switching frequency should be. Increasing the switching frequency reducesthe ripple in the current flow in part-load mode, but at the same time causes a rise in eddycurrent losses in the motor and switching losses in the controller. The simplest method is to

try out different switching frequencies, and select the one at which the motor and the future heat up the least."

[Zen]

Thanks for the info guys. It ain't broke so I ain't fixxin it.

[NativePaul]

Interesting info, thanks Jay. I had no idea that increasing the PWM Hz heated up the motor as well as the ESC. I have a few 1D wind motors that should have very low inductance, but only really uses them at full throttle the vast majority of the time. I have recently started running at partial throttle in one of my boats and will probably spread this driving style to the rest of my race fleet, so it is a topic I should revisit and do some testing on.

[SweetAccord]

Interesting info, thanks Jay. I had no idea that increasing the PWM Hz heated up the motor as well as the ESC. I have a few 1D wind motors that should have very low inductance, but only really uses them at full throttle the vast majority of the time. I have recently started running at partial throttle in one of my boats and will probably spread this driving style to the rest of my race fleet, so it is a topic I should revisit and do some testing on.

There is a formula for this if the ESC say has an option of a PWM for 8 Khz or 16 Khz for example.

Kv x Volts (nominal you are using) x Pole count / 20

A 2223 motor is 6 pole 3500kv running on 3s so; 3500 x 11.1 = 38850 x 6 = 233100 / 20 = 11,655 so rounded down the PWM would be set to 8 KHz rather than 16 KHz if you had both options.

Hope that helps.

[Darin Jordan]

Just be careful... When Pro Boat had me test some new ESC programming a few years ago, PWM was one of the programming options. I played with it and when I raides it to 16, it fried the system.

I think there is a general rule of thumb on this that the quality of the motor matters. Motors with higher IR, etc.. need lower PWM.

I guess the stock PB 1800 wasn't one of them!

[SweetAccord]

Just be careful... When Pro Boat had me test some new ESC programming a few years ago, PWM was one of the programming options. I played with it and when I raides it to 16, it fried the system.

I think there is a general rule of thumb on this that the quality of the motor matters. Motors with higher IR, etc.. need lower PWM.

I guess the stock PB 1800 wasn't one of them!

I agree Darin, nothing is set in stone when it comes to matching motors with ESC's.