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Old 07-07-2016, 10:29 PM #1
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Default How to control MYJG-40 power supply? (CO2 40W)

Thanks for reading..

I intend to build my own CO2 laser cutter/engraver, and use the MYJG40 power supply.

I saw that it has input for a 5K variable resistor to control power output.

I also saw that you have to "ground" 2 inputs:
Interlock loop / J3 (connect P+ to G) and
Test / J4 (connect K to K+)


Question 1: What is better?
1) leave the variable resistor at maximum and control power by PWM the digital inputs, or
2) leave the variable resistor at desired power and turn laser ON when needed


Question 2: Is there a way to replace the variable resistor with an analogue signal?
It looks like a voltage divider, maybe if I inject 0..5V to terminal that originally connects to center tap of variable resistor...
Anybody tried that?

Question 3: What are good values for PWM?
You all know that a 50% duty cycle can be achieved with a 1 day on / 1 day off and 1pico-second on / 1pico-second off...


Iīm not sure about the names of the pins, itīs very hard to find any info about this power supply.

Thanks!



Last edited by ambr; 07-07-2016 at 10:37 PM.
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Old 07-07-2016, 11:47 PM #2
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Default Re: How to control MYJG-40 power supply? (CO2 40W)

Are all three terminals of the pot separately wired into the PSU? Then an analog signal is possible. The power supply may not have adequate bandwidth to modulate at any impressive speed, but it will work. You need to measure the voltage going to the pot, however, and ensure the signal voltage is scaled to this as needed. It may not be 5V.
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Old 07-12-2016, 01:58 AM #3
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Default Re: How to control MYJG-40 power supply? (CO2 40W)

Yes, all 3 terminals of pot are connected to PSU, one of them is labelled "5V", so... Iīll keep it safe and just use a pot!
I donīt like things that have 5V on one end and 30KV on the other end..

About PWM, I thought later that itīs not good, it is better to buy a PSU with analog control.

BTW, how do you measure current output? You put a milli-amp meter in series with laser tube??? Obviously not...

Thanks.
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Old 07-12-2016, 03:46 AM #4
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Default Re: How to control MYJG-40 power supply? (CO2 40W)

Quote:
Originally Posted by ambr View Post
it is better to buy a PSU with analog control.
Your PSU obviously has an analog input though, from your description.

Quote:
Originally Posted by ambr View Post
how do you measure current output? You put a milli-amp meter in series with laser tube??? Obviously not...
Sure you can. An ammeter is electrically about the same as a piece of wire. It helps safety if you put the meter on the "low" side of the tube, assuming the tube is grounded. Mains powered meters should not be put on the high side, because 30kV-to-gound is more than enough to jump through to the meter's ground. Mains powered meters would be okay to use on the low side, however.

Best practice would be to use a handheld (isolated) meter, and physically wire it in between tube- and PSU-. Loose connections will cause arcing. Although it would theoretically be safe, it would also be best not to touch the meter while the tube is active, since a loose connection could potentially occur.
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