[TCML] Terry Filter Caps
FIFTYGUY at aol.com
FIFTYGUY at aol.com
Tue Aug 26 20:25:00 MDT 2008
In a message dated 8/26/08 9:57:24 P.M. Eastern Daylight Time,
yurtle_t at yahoo.com writes:
>BTW, I just blew up my second VFD :-(((.
I killed two of my VFD's as well. They were old Motortronics units,
nothing I was too excited about, but they were perfectly fine pulls until I used
them to run the ASRG.
I thought the first one was on it's way out, since it kept tripping its
upstream MCP on power-up. It worked fine until I started tuning the coil and
getting more power out of it. Gave a nice flash and stopped working. Did a
power cycle and got a *BANG*. The other one (identical) didn't trip the MCP, so
I thought it would do better. Nope, lasted all of 20 seconds. That's when I
stuck the SISG under there!
Autopsy revealed not only was the power module blown, but the driver
IC's were vaporized off the board! At that point I swore I wouldn't pay more
than $50 for a drive that I would sacrifice on the altar of Tesla, and I set off
to improve the transient protection of the control system.
I built the Terry Filter. I also put common-mode MOV's at the jack for
the cable going out to the RSG motor. I had also run the RSG motor cable in
the same flexible conduit as the two hots from the pig. Despite the RSG cable
shielding, that probably wasn't the best way to do it!
I bought a *really* cheap VFD. Apparently Dart Controls, who makes a lot
of fractional HP DC drives, did a stint of little inverters! Discontinued
now, and they just don't get more cheaply built than this thing! I've got a
*tiny* Mitsubishi as a back-up, but I'll be darned if that Dart hasn't died yet!
It really does take 1/2 HP to accelerate a 12" RSG with a 3/4" G10
8-electrode disk to 3600 RPM in 20 seconds. It takes 2/3 of that to keep it
spinning at that speed!
At least one good thing about running a series/parallel Y motor off 240
is it gives some headroom for transients. Running them off 480V with an
inverter gives little room for noise in normal applications - it's usually the
first few windings that die when the switching spikes burn out the insulation.
I'm still undecided as to how to ground the motor frame and cable
shield, so I've just left them floating. :)
Center for the Advanced Study of Ballistic Improbabilities
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