Originally Posted by Al_The_Man  What style of CT are you using, is it a module type with internal electronics like the MicroSwitch or a passive CT with just a secondary and the plasma cable as primary?
A passive type has to be used on AC to get any meaningfull readings and also it is a Current transformer, and should not be used open circuit or lightly loaded, due to excessive high voltages appearing on the secondary, if you have a 15ohm res. as a shunt the secondary current can be calculated by knowing the ratio of the CT.
Al. |
It is a secondary transformer of the 200:1 value. At one point I did the calculations to figure what kind of voltage I should expect with the given variables. Machine is rated at 40amps so I used that number along with the 200:1 reduction and a 15ohm shunt resistor. The only problem is, I can do all the math I want, all day long but I still need to see the equipment put out the numbers. No matter how many winds I did through the CT I would get relatively the same voltage all of the time.
I used a clamp on harbor freight am-meter to determine actual amp draw during cut and firing into thin air. Cutting at 40amps (as indicated on the dial of the machine) did not indicate 40+ amps at the clamp on am-meter.
Torchead has several times in this forum and other forums that machines like mine that us power correction can have an affect on actual amp draw.
I did have the reed switch connected as suggested earlier. It is a small ac-dc wall socket converter for somekind of household electronics (i dont remember what it was for). It had on leg going to the switch that then connected to the THC board. The other leg went direct to the THC board. The switch (N/O) would leave an open circuit until flowed through the work clamp. I had it setup just as Miller designed it.
The only things that i can think of that are frying the switches are spike from the crappy wall converter or high frequency from the plasma machine could be inducing an extra current into the switch. You can correct me if Im wrong, the high frequency may not be a problem.
I bought a few extra switches so I may try and experiment with a different power supply. Does anybody think that the powersupply is messing up the switch? Any suggestions on what kind of power supply to use? Some exact examples would be nice. At this point, if the power supply costs $100 i am still better off than getting a new plasma cutter. Thanks again, Steve