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View Full Version : Strangeness with my new Rotary Phase Converter.



HackerMechTech
10-12-2008, 11:19 PM
Hey All:

I got my 7.5HP rotary working today with three nice phases showing up on the outputs. With one huge issue. There's 80+V AC showing up on the case of the electronics box. The only thing touching the case metal are the run time caps. Each leg has .130F of oval metal can caps in parallel. Is this where that voltage is showing up? Is this a regular problem with these things? Is it standard to insulate them from the case electrically? Everything else is isolated.
Are these AC eddy currents induced by the high current running between the cap banks? Will a short to outside ground solve this problem. I'm afraid to touch it and use a broom handle to control things.

And ideas would be welcome.

Andrew

Al_The_Man
10-12-2008, 11:26 PM
80v with respect to what?
If you are measuring from the artificial phase to ground, there will be a voltage to the enclosure which should be grounded.
The Caps should be self isolating from ground if they are AC motor run style.
Al.

HackerMechTech
10-12-2008, 11:56 PM
Hi Al:

80V with respect to ME! :), and other machines. I thought the run caps should be isolated. Sigh.... Well there's nowhere else it can be coming from, those caps are the only non-plastic, non-wood pieces of matter attached to the mounting plate. It has to be coming from the caps. I'll isolate them on a non-conductive mounting plate and be done with it.

Andrew

Al_The_Man
10-13-2008, 10:13 AM
If there is 80v appearing on the enclosure it means it is not grounded adequately.
If you are placing a lead on the enclosure and grasping the other lead, it is possible to get a reading on an electronic meter, this is due to the fact that the meter input is very high impedance and there is radiated/capacitive effects in play, If this is the case and the enclosure is adequately grounded, this voltage is not capable of suppling any kind of appreciable current.
Measure from the enclosure to a good ground point and it should be zero.
Al.

HackerMechTech
10-13-2008, 10:28 AM
Hi Al:

If the case voltage is induced as a result of eddy currents in the run caps then yes, it should cause no harm. However a voltage reading relative to GND will read similar as it does when read relative to me or one of the other machines. There's still no place for the case currents to short to. We could be wrong there, and I'd hate for me to find out the hard way. I'll isolate the run caps today after work and sometime this week, I'll put in that grounding system I knew I always needed. I only have neutral coming into my garage, not a real ground. That will change.

I never had any issues with my single phase systems, this is a new game.

Andrew

Al_The_Man
10-13-2008, 10:52 AM
I'll put in that grounding system I knew I always needed. I only have neutral coming into my garage, not a real ground. That will change.

I never had any issues with my single phase systems, this is a new game.

Andrew

I would say there is your problem right there, or at the very least an adequate ground conductor should always be present in a workshop, and if not practical, an Earth Leakage Trip where it enters the shop.
Al.

HackerMechTech
10-13-2008, 10:15 PM
Okay did my first full up test. It runs pretty damn SMOOOOOTHHH! I ran the three phase shaper I picked up a few months back. Beautiful! No hichup on startup, just nice smooth motion on the machine and the idler.

L1 = 240V
L2 = 240V
L3 = 235V Generated.

I'm happy. ....

..... Now that grounding system......

Andrew

TOTALLYRC
10-14-2008, 08:16 AM
Okay did my first full up test. It runs pretty damn SMOOOOOTHHH! I ran the three phase shaper I picked up a few months back. Beautiful! No hichup on startup, just nice smooth motion on the machine and the idler.

L1 = 240V
L2 = 240V
L3 = 235V Generated.

I'm happy. ....

..... Now that grounding system......

Andrew

When I ran the 100 amp service from the main house to the workshop subpanel, it was required that I put in a seperate grounding rod and "Not" use the bonding screw inside the new subpanel. I would double check with an electrician to be extra sure.

Mike

HackerMechTech
10-14-2008, 10:31 AM
Hi Mike:

Thanks for the heads up. I just assumed I'd have to use a new grounding rod. I'm starting to prep the campaign now. My local codes says 8ft down.

Andrew