Swordfish 240 ESC, program box VS pc link.

[IRON-PAWW]

Hi All,

Looking into programming the Swordfish 240 esc I just bought off Steve. Got the program box with it, but is there any benefit with linking the ESC to a Pc to program it? Are there extra parameters you can set through a Pc link? I keep reading there is sometimes an issue with Swordfish ESC's not allowing full throttle at times? What is the story behind that?

What is the PWM rate?

Cheers!

[HTVboats]

I have several SF controllers and both the programing box and the PC link. Other than reading data I rarely set parameters on the PC. The box has the same functions and is much faster to use. At the pond setting with a PC is a pain where the box is just handy.
Mic

[kodiak ak]

+1 Whats the PWM rate adjust?

[IRON-PAWW]

Found the following about PWM settings over on the helifreak forum.

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The PWM rate has mostly to do with the motor inductance. The higher the inductance (actually it is the ratio of inductance "L" divided by the resistance. "R"), the lower you can run the PWM rate. This "L/R" time constant actually acts to smooth out the current flowing in the motor. A low PWM rate, giving long on/off pulses to the motor is pretty inefficient.

The motors really have no issue with high PWM rates. I run my Scorpions at 12 to 24 kHz and have excellent results. I have no idea why 8kHz is magic for Scorpions. Maybe the big ones have such a large value of L/R that 8kHz is fine. But so would 12kHz too.

On the other hand, the ESC prefers as low a rate as possible. The faster the switching, the the hotter the FETs run. That's because when the FET is transitioning between off (~infinite resistance) and on (very low ~milli ohms), there is a region of finite resistance. This short time span produces most if all of the ESC heat (why CC claims ~80% throttle is the hardest on the ESC). The faster the PWM rate, the more of these transitions occur in a period of time, so more heating.

Since most info about PWM rates we get comes from the ESC manufacturer, it is no surprise that they recommend going for as low a PWM as possible.

In one test I did, I found I was modestly more efficient at 24kHz than at 12kHz (Scorpion 3020 motor, ESC, and battery).

Another detail is the commutation speed. You do want the PWM rate to be higher than that speed by some factor, and I think that is what the formula given by Sparky is effectively calculating.

AFAIK, the outrunner mode is trying to use that calculation to change the PWM rate dynamically as your motor rpm changes, but I don't think it has been too successful. I really don't see a downside to the higher PWM rates, as long as the ESC isn't complaining!

JUST IMHO!


With the following formula used to work out what to set it to?????



Here's a formula I ran across thats supposed to figure the proper PWM that so far has been working for me.
Kv x Volts (nominal you are using) x Pole count / 20
For my 500 my motor is 8 pole 1760kv running on 5s so
1760 x 18.5 = 32560 x 8 = 260480 / 20 = 13,024 so i have rounded down & set my PWM at 12k & it has performed flawlessly.
On the Scorpions I dont use it & just go directly to 8k as the Castle Guys recommended & it works. Should try the formula on them & see if it ='s out to the same or if 8k is just a good all around setting??

*****


Thanks to users Sparky and Ahahn on the helifreak forum for those explanations. Boats may be an entirely different story.

Just what I read elsewhere. Just relaying it here for discussion.

[IRON-PAWW]

Thanks for your reply HTVboats. Appreciate it. I've got some older swordfish 200 amps attached to an MR200 radio.

(1) can I program the older Swordfish 200's with the program box currently for sale here at OSE?

(2) Did I read that there's an issue with some swordfish ESC's and spektrum radios?