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160VDC power supply

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monkeyalien

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Here is my situation:

I am trying to get an automatic height controller to work with a CNC plasma cutter. The controller is supposed to be set to a certain voltage based on the type & thickness of the metal to be cut and the set amperage it will cut at according the manufacturer. The plasma cutter manual has voltages from 134 to 153, but there must be errors because plotting voltages versus thicknesses for the same metal at the same amperage producing some wild looking graphs. Most points look like they follow an equation but there are outliers in between. When I cut something at a good speed & with a constant distance between the torch & metal with the controller just reading the voltage and not controlling the torch the voltage readout changes too fast to see what it is. I want to what good set voltages would be for different thickness and amperages, and test the controller without using the plasma cutter.

So, I made a computer program to read and plot DC voltages with an IO module. The maximum voltage the IO module can receive in 3.3VDC so I need a voltage divider. I've tested it at smaller voltages and want to test it the voltages the plasma cutter will produce. I think running AC from a wall receptacle into a variable autotransformer, rectifying, and filtering it would be a good way to make a variable DC power supply up to 160 or s0 volts but I've never rectified & filtered that high of an AC voltage. I have diodes rated for 1200V and 30A but I might use stud diodes. I guess I'll use a big capacitor like you'd find to start or run a big induction motor. The voltage divider will provide a lot resistance but there will be some amount current draw so I'm not sure how much of a capacitance I'd need. I thought I'd ask around for some input before testing this.

Thanks.
 
A variable autotransformer does not provide mains isolation, so the arrangement you propose is dangerous.
If I've understood you correctly you want to make a variable ~160V DC supply which (1) will be applied to the controller and (2) will be monitored by the computer via a voltage divider?
How much current does the controller need to draw from the 160V supply?
 
I thought about an isolating transformer and I do have one so I'll it. You've understood me correctly. I hadn't considered the draw from the controller. It must be quite low because the wire the plasma cutter manufacturer, Miller, provides to connect it to the controller is quite thin and they must make it for every height controller on the market.
 
I've worked with plasma systems, but not cutters. One RF system had a port to measure DC. We used that to determine if the plasma existed. In that case, I used a commercial isolation amplifier. This was interfaced to a computer.

I did, however, have a TIG torch in my hand a few times.

For high voltages you can use resistors. For a 15 kV divider, it was a string of 625K power resistors.
 
So why are you trying to make a complicated height control system when a set of rollers will do the job?

Just curious being I have worked on plasma cutter systems for years and I know the simple roller system works.
 
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