Another question about Min-Power setting

[RyanT]

@parsec

Try $33=1000 then unplug power and unplug USB from the laser wait 15s plug and check.

@ednisley

It’d be interesting to set $33=1.5 and see if that produces a 1500 Hz output. If so, then the units are kHz.

No dice. The only values $33 would accepted are 0 and 1.

I checked the PWM coming out of the controller with a large circle cut at 20mm/s:
LB Power: 00%, Duty Cycle: 0% Hz: 0 (probably undetectable)
LB Power: 01%, Duty Cycle: 12% Hz: 10k
LB Power: 25%, Duty Cycle: 34% Hz: 10k
LB Power: 50%, Duty Cycle: 56% Hz: 10k
LB Power: 75%, Duty Cycle: 78% Hz: 10k
LB Power: 99%, Duty Cycle: 78% Hz: 10k
LB Power: 100%,Duty Cycle: 0% Hz: 0 (probably undetectable)

Interesting that 1% power gets a 12% duty cycle. It’s probably something monport did in the firmware to keep everything within minimum firing current?

First I thought the 10kHz was hitting my multimeter limit, but specs say the meter can read up to 60Mhz. 10k seems rather high. Can the PSU and the tube handle such high frequency?

[ednisley]

@RyanT

Hz: 10k

Well, that’s a better match to the power supply’s PWM demodulation filter, even if the control setting makes no sense.

@RyanT

10k seems rather high

Ruida controllers default to 20 kHz, old-school Arduino controllers use 1 kHz, and the power supply converts all those PWM signals into the equivalent analog voltage to control the tube current. Ruida controllers also have an analog voltage output that works fine, too.

[jkwilborn (Jack Wilborn)]

How do you know that the controller is using minimum power on your tests?

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@ednisley I’ve noticed that Monport is using the IN input for pwm unlike most of the K40 types…

[ednisley]

@jkwilborn

Monport is using the IN input for pwm unlike most of the K40 types

Which makes sense based on how those supplies seem to work, but AFAICT the jank is strong with Monport:

@RyanT

the monport controller’s pwm is connected to IN, K+ and L are open. P (Water Protection) is connected to a limit switch triggered by the lid cover.

I no longer profess to understand anything about K40 flavored lasers and their HV supplies, because there are so many variations on the old theme.

[jkwilborn (Jack Wilborn)]

They either set them up to run as the analog device or they hack them into a digital type operation. I think it’s pretty simple.

It’s a very low cost unit for entry level hobbyists.

[RyanT]

@jkwilborn

How do you know that the controller is using minimum power on your tests?

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@ednisley I’ve noticed that Monport is using the IN input for pwm unlike most of the K40 types…

Not sure what you mean. When LB is trying to fire at 1%, the duty cycle is 12%. Are you saying the physical power knob on the ammeter doesn’t affect duty cycle and lower the output power in a different way?

How are most K40 types wired up?

[ednisley]

@RyanT

the physical power knob on the ammeter doesn’t affect duty cycle and lower the output power in a different way

I believe that’s correct, based on what we’ve seen with similar HV supplies used with Ruida controllers.

The PWM input controls the current between zero and whatever the maximum the power supply can produce.

The knob reduces the maximum value the power supply can produce.

So the same PWM input to the power supply can produce any output from the “normal” value with the knob fully clockwise to “zero” with it fully counterclockwise.

Which means you have no idea what power the laser will produce for a given PWM percentage without also knowing the knob’s position on an uncalibrated scale.