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perfo
Posts: 102
Joined: Mon Jan 30, 2012 2:42 am

RPI controlled EDM drilling

Fri Jan 10, 2020 5:10 pm

https://www.youtube.com/watch?v=rpHYBz7ToII

I fancy trying to make and EDM drilling machine like the one in the youtube link above..
I've scoured the internet and can't find out the exact details but I've gleaned the current has to be pulsed with an unequal mark space ration
so something like 30Khz to 200Khz and up to 50 amps. I'm thinking of using my arc welder to supply the high current DC and some module controlled by the RPI to switch it on and off. Using the code below I appear to be able to alter the frequency and the mark /s pace ration of the PWM output on the PI. Something strange is happening to the frequency at higher levels (ie a setting of 20000 doesn't produce 200Khz but 10 does appear to creat 10 hz. Anyway I'm sure I'll figure this bit and actual frequency isn't important as long as I have enough range and can easily adjust it up and down. My question is, would anyone have recommendations on how to get the PWM output to control a DC supply at these currents ? I'm thinking MOSFETS but looking at the various data sheets it doesn't jump out on me which ones are drive able by an RPI output and can manage say 60 A 200 Khz.... Any suggestions ???
Thanks

Code: Select all

import RPi.GPIO as GPIO # Remember to run as superuser (sudo) and use python 3 
print("EDM PWM tests")

pwmSetMode(PWM_MODE_MS)
GPIO.setmode(GPIO.BCM)   
GPIO.setup(18, GPIO.OUT) # GPIO 18 is thePWM output.

pwm = GPIO.PWM(18, 10)   # 18 is pin number , 10 is frequency in hz ???? maybe ...
                       
print("mark space 50% at 10 hz")      
pwm.start(50)         
input("Press Enter to continue...") 

pwm.ChangeFrequency(50)  

print("m/s at 5% and 50 hz")
pwm.ChangeDutyCycle(5)   
input("Press Enter to continue...")          # 0.5 seconds till the next change

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