Divider Resistor discussion.

[phil-barrett]

The readme has a bit on calculating the upper divider resistor (R1 in the diagram below). However, there are other issues that I would like people's input on. In particular I worry that the Varc cable will be a conduit for EMI. Here is my current thinking on how to deal with that. Should R1 be encased in an earth ground shield? I have the ADCI_1 set up to allow R1 to be external or on the PCB. I think external is the safest way to go.

Thoughts? Comments?

[sntlewis]

Well let me start... I'm no EE or Systems Engineer so my opinion is just that an opinion.

I'm leaning heavily to a plasma cutter that has a built in 50/1 divider in order to reduce high voltage into/near the control portion of the system so that limits the exposure for me. However, for those running raw voltage, keeping that away from the control is imperative.

I have always used the thought line of distance and proper shielding to be most effective in dealing with EMI. Putting the resistor inline and outside accomplishes both. Maybe inside cable connector at Plasma cutter end?

Further by shield drain at table/cutter end, that would drain the emi away from control system. My opinion is this is another safe guard against EMI.

[phil-barrett]

If the cable from the cutter to the controller is shielded then it probably won't matter where resister is. Though, it might be hard(er) to fully shield the resistor connections so unshielded portions being farther away from the EMI source is better.

FWIW, I'm thinking of making a little PCB that will hold the resistor, have a ground plane and 2 screw terminals on each end to make it easy to connect to the cable. Maybe it could be encased in a grounded metal pipe. May be overkill?