Hi Scott,
You know, that was one of my next ideas because now that I think about it, I believe the exterior housing of the original FWB rectifier assembly was in fact "floating". It was a Radio Shack purchase and I believe only the bottom side of it was actually metallic, for heat transfer. The remaining exterior surface was black molded plastic. I had mounted the metallic bottom to a flat piece of copper for heat transfer but I do not believe that I had actually grounded the copper mounting plate. And of course I have been grounding the exterior metal case of the FWB bricks that I keep smoking.
I would say that almost has to be the problem, as that is the only thing that is infact different about my current vs original setup, now that I have reinstalled the electrolytic capacitor. If that is the reason, that would make for a pretty easy fix. Hoping and praying that is all that's going on. I just reordered 10 additional 10/50 FWB bricks and they are due to arrive next Tuesday. I will wait till the "reinforcements" arrive defore doing another live spark-off test, as I am down to my last functional FWB in my circuit now. Unfortunately, I discarded the original RS FWB but it shouldn't be that difficult or expensive to replace with that particular one if it comes down to that. Hoping that Jim's suggestion of an internal HV breakdown inside the motor is NOT the problem :-/ but I'll keep you updated. And yes Mark, I've systematically tried to put everything back like it was originally, minus Scott's floating the FWB suggestion.
David
Scott Bogard <sdbogard@xxxxxxxxx> wrote:
>Hi David,
> That is most unfortunate, Green Monster is one of my favorites! As a
>point of curiosity are you bolting your FWR brick to something, or is it
>free floating? If I had to guess, and others are probably of more use here
>as I am just a mechanical guy, but I would say the metal case of the FWR
>brick is picking up EMI from the coil and shorting. Did you try swapping
>the old diodes back in? You could try bolting it down if it is not, but it
>sounds like you had it electrically grounded. At any rate if it were my
>green monster, I'd start by putting everything back as it was and
>introducing new components one at a time; it might even be a cable or
>connector... Best of luck, wish I could be of more assistance.
>
>Scott Bogard.
>
>
>On Fri, Mar 7, 2014 at 11:03 AM, David Rieben <drieben@xxxxxxx> wrote:
>
>> 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 elec
>> trolytic 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 run
>> ning 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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