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pwm for clutch
(2020-07-24, 01:24 AM)seandepagnier Wrote: The clutch output is on a pwm pin as I had considered this possibility, so the code needs to be modified to use timer0 in place of timer2 so that timer2 can be used for this, not hard to implement.

The problem is, the schematic has a rather soft start for the mosfet (arduino is driving gate directly)   The gate is charged through a 560 ohm resistor which gives a softer start to avoid as hard of voltage spikes since the clutches are typically inductive.   There is a diode of course, but even still...   So I don't really think it will work in the ultrasonic frequency so it may make an audible sound if you didn't filter the output.

If your clutch only needs momentary power to engage, then this will need a different setting and changes to the code, but completely possible.   Is it spring loaded?   How does it work?   Could you just use a capacitor in series to get it to turn on, or would the capacitor be too big?

The solution of using a resistor and capacitor comes to mind and is a good way to limit power, but you are trying to avoid resistor losses too, could you attach a cheap dc-dc converter to the clutch output and dial in whatever voltage you need?   This is basically required already to operate a 12v clutch if the motor runs at 24 volts.

Can you find out what voltage is needed to engage the clutch and what voltage is needed to hold it?

Maybe it's possible to use the dc-dc converter to the hold voltage with diode on output, then put this in parallel with a capacitor if a higher voltage is needed to engage.

The next controller version, I'll consider a mosfet gate driver so pwm can work at high frequencies.

I'd think the situation would be similar to pwm the motor?
Particularly when engaged suspect that the inductance will be significant and will draw less than expected from the resistance with short pulses.  Will probably have to experiment. Will be annoying if one can hear it.
Maybe a choke and capacitor to make it into dc? Choke may be pricey particularity for those that do not need it.

From my calculations to have .2a holding and about 100ms to pull in should have 2000uf and 50 ohms over 2 watts.
From the junk box found 3000uf and 12 ohm. Seemed to work fine and even that helps with about 500ma holding current.
For any that may want to try use wire wound and not carbon composition resistor. When a carbon resister gets hot the value goes down ultimately burning out. A hot wire wound resistors value goes up.

For Syles21 need some resistance in parallel to so the capacitor can discharge when deactivated. Make big enough that it does not hold.

Messages In This Thread
pwm for clutch - by johnm - 2020-07-23, 03:32 PM
RE: pwm for clutch - by Styles21 - 2020-07-23, 07:54 PM
RE: pwm for clutch - by johnm - 2020-07-24, 12:25 AM
RE: pwm for clutch - by seandepagnier - 2020-07-24, 01:24 AM
RE: pwm for clutch - by johnm - 2020-07-24, 08:30 PM
RE: pwm for clutch - by Styles21 - 2020-07-24, 03:08 AM
RE: pwm for clutch - by seandepagnier - 2020-07-24, 01:22 PM

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