Hey guys,
I'm in somewhat of a dilemma over a recent problem that has started plaguing me when I fire off my big SG coil (Green Monster). Let me expand. I recently decided to redo the wiring from the 120 VAC twist lock receptacle for the ARSG motor all the way back to the treadmill duty, DC drive motor, purely for a cosmetic upgrade. There is about a 50 ft umbilical "tri-plex" looking cable, consisting of two x-ray type HV cables, for the pole pig's ouput, and a Romex with the 3-wire 120 VAC wiring for the ARSG motor supply, with male/female quick disconnects on both ends, that runs from my control panel to the tank circuit assembly. Well, obviously, I have a FWB rectifier to convert the incoming AC from the control panel to DC for the motor. Well, while doing the "cosmetic upgrade" I simply removed and replaced the original Radio Shack, soldered in FWB with a 1 kV, 35 amp rated FWB "block" with the male quick-connect input/output terminals. I also originally had a 400 VDC, 3900 uFd rated electrolytic capacitor in parallel with the input leads to the motor, which I just omitted and left out on the upgrade. Other than that, I placed the FWB and the input line filter to the motor inside a metal electrical junction box, but with the exception of the omitted 'lytic cap, it was electrically identical to the previous setup.
Now here comes the problem. I pulled out the beast for a show and tell for some local school kids in a scientific club and the first thing it did when I started the spark show was to promptly burn out the new FWB bridge to a dead short! I figured out what the problem was reasonably fast but not before actually catching my ARSG control panel variac on fire (120/140 volt, 10 amp rated). Fortunately, I just so happened to have a spare variac of the same flavor that I was able to replace it with while the kiddies waited. However, it became apparent that there was indeed a dead short at the FWB and I was not able to remove and replace that in as timely a manner to allow for a second try on the spark show :-(
Well, my first thought was to reinstall that lytic capacitor, as that was the only thing that had electrically changed from my previous setup. I got a chance to try it again last night, with the lytic cap back in place and with a replacement FWB of the same type that had originally bitten the dust. Well, it only sparked for about 30 seconds or so and then that same sickening loud 60 Hz hum in the control panel indicative of a circuit fault on the ARSG control variac. I was quick enough on the E-stop mushroom switch to kill the power before the variac was damaged this time but whatever the cause of this new problem is had obviously still not been resolved. I then removed that dead soldier FWB and replaced it with one of a brand new pair of recently acquired 1 kV, 50 amp rated FWBs and tried removing the wire between the FWB and the line filter to the motor from the Romex shielding, that covered the leads from the J-box with the FWB and the J-box with the line filter and then tried running the coil again. (The original setup had no grounded shielding around this stretch of wiring underneath the tank circuit assembly). It ran a bit longer this time, maybe a full 60 seconds but sure enough, I got that sickening hum once AGAIN! Diagnosis showed that this time instead of going dead short, this FWB lost all rectification and was simply passing AC on to the motor and lytic cap! (Also a BAD thing!!). And as a side note, I could run that ARSG motor all day through any of the aforementioned FWBs without any issues, until I decided to start running the sparks! And I did not have any of these FWB issues while sparking with the previous Radio Shack special FWB (1 kV @ 10 amps, maybe?) and the "cosmetic upgrades). I get the feeling that I should've left well enough alone and I am totally bumfuzzled! BTW, my control panel had and still has filtering out the wazzoo, too! Sorry for the lengthy post but any suggestions would be most greatly appreciated!
Bumfuzzeld,
David
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