How to fix a plasma cutter

How to fix a plasma cutter. How to fix a 40 amp plasma cutter, 50 amp plasma cutter, 60 amp plasma cutter.

How to repair a plasma cutter.

This page could potentially help out someone who owns any of the following plasma cutters:

Lotos CUT40 plasma cutter
Lotos CUT40A plasma cutter
Lotos CUT40D plasma cutter
Lotos CUT50 plasma cutter
Lotos CUT50A plasma cutter
Lotos CUT50D plasma cutter

Volt Silverline CUT40 plasma cutter
Volt Silverline CUT40A plasma cutter
Volt Silverline CUT40D plasma cutter
Volt Silverline CUT50 plasma cutter
Volt Silverline CUT50A plasma cutter
Volt Silverline CUT50D plasma cutter

Simadre CUT40 plasma cutter
Simadre CUT40A plasma cutter
Simadre CUT40D plasma cutter
Simadre CUT50 plasma cutter
Simadre CUT50A plasma cutter
Simadre CUT50D plasma cutter

Riland CUT40 plasma cutter
Riland CUT40A plasma cutter
Riland CUT40D plasma cutter
Riland CUT50 plasma cutter
Riland CUT50A plasma cutter
Riland CUT50D plasma cutter


Chicago Electric CUT40 plasma cutter
Chicago Electric CUT40A plasma cutter
Chicago Electric CUT40D plasma cutter
Chicago Electric CUT50 plasma cutter
Chicago Electric CUT50A plasma cutter
Chicago Electric CUT50D plasma cutter

Why? Because when trying to fix my Lotos CUT40 plasma cutter, people sent me resistor values for their plasma cutter's high voltage rectifier circuit and the values were all the same even though the plasma cutters were made by different manufacturers and the models were different.

Continue reading this blog to find out if your defective plasma cutter has the same problem as mine: burned out diode, leading to a burned our resistor.

There are extremely high voltages and currents inside a plasma cutter. I take no responsibility for anyone doing any repair work on their plasma cutter. Before working on any internal components, unplug the power, hold the trigger switch so the capacitors discharge (you will hear them), then hold a screwdriver or other insulated device across one of the four large capacitors on the bottom power board so you see a spark. Good luck!

Fixed

Today I spent a little more time trying to figure out why the plasma cutter still isn't working, and more specifically why the new resistor gets so hot.

Well, I found the problem!!!!!! With the multimeter on the diode setting, one of the diodes in the rectifier bridge was reading 0.284V in both directions which isn't correct. The other diodes have a reading of 0.84V in one direction and 0V in the other direction.

The bad diode is a 2000V RU1H fast recovery diode. I couldn't find one in stock anywhere, so I just put three 1000V 1N4007 general purpose diodes in series. I also added a 470,000 ohm shunt resistor across each diode to help protect against transients. There are already disc capacitors across each diode in the bridge, so I didn't worry about adding any more.

As an aside, I noticed that there are two diodes in series in one position of the rectifier bridge, so the designers must have figured their diode choice wasn't big enough. They should have doubled up all four diodes right off the bat.

Original RU1H diode that burned out:




New replacement "diode". Three in series = 3000V:



New diodes installed where burned out diode was.





Thanks again to everyone who helped me find the resistor value!