Terry,
My ARSG control assembly is set up pretty much the way you’ve described yours, and I had that very same issue with my coil when I grounded (mains, not RF) the outer metal casing of my FWB rectifier (also rated @ 1kv/50 amps). My FWB rectifier worked perfectly fine in this arrangement when only driving the motor, as long as the coil wasn’t ‘sparking’. However, once I turned the voltage feed variac to my transformer up enough to break down the spark gap and initiate sparks from the top load, the FWB rectifier shorted out almost immediately! I believe I let the magic smoke out of two or three of them in this manor! Once I replaced the blown out FWB rectifier with a fresh one AND removed the ground from its outer casing and just allowed it to ‘float’, it worked flawlessly throughout coil’s active sparking range of power throughput (and the voltage input range for the motor) and I had no more problems.
David
Sent from my iPhone
> On Jul 27, 2020, at 6:54 PM, shaun <snoggle@xxxxxxxxxxxxxx> wrote:
>
> Does the motor case and variac share the same ground.
>
> -----Original Message-----
> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Terry Oxandale
> via Tesla
> Sent: July 27, 2020 4:52 PM
> To: 'Tesla Coil Mailing List'
> Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier issue
>
> Blows only under higher powers, and could be related to ground strikes or
> strike rail strikes. There is a lot going on when I bump up the power, and
> the death of the rectifier or fuse has some component of time delay before
> the obvious slowing of the rotor disc is noticed. I do know that I've had
> ground and rail strikes that did not result in this issue, so no definitive
> or observed issue that I can find that has an obvious direct correlation.
>
> Terry
>
> -----Original Message-----
> From: Tesla <tesla-bounces@xxxxxxxxxx> On Behalf Of shaun
> Sent: Monday, July 27, 2020 1:20 PM
> To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>
> Subject: **External Email** Re: [TCML] DC motor fuse/rectifier issue
>
> I use about the same setup with a 3hp dc motor and not blowing fuses, the
> bridge does get warm. Can you just run the motor on the floor by itself.
> Also does the fuse blow right away or ever time. Sounds like you have an
> short in the wiring.
>
> -----Original Message-----
> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Terry Oxandale
> Sent: July 27, 2020 1:51 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] DC motor fuse/rectifier issue
>
>
> I'm using a permanent magnet DC motor for my ARSG. Power is through a
> variac, to a diode bridge, and then out to the motor under the coil. The
> issue is that I can't keep the fuses protecting this circuit, nor rectifier,
> intact. I use a 10 amp fuse at the control cabinet for protection (just off
> the 120vac hot leg of a 240vac source), and the DC supply cable for the
> motor is surrounded by grounded braided copper. I have an ammeter to monitor
> the motor, which indicates proper draw during runs (2-3 amps depending on
> speed), yet the cheap bridge (50 amp/1000 v) gets warm fast, and also does
> not endure an extended run on the coil. A while back I created a filter of
> sort to smooth the full-wave pulses (cap/reactor), but that made things
> worse, so that was removed. I don't have a sufficient understanding of the
> induced currents associated with these coils, and hoping someone here can
> help. I have yet to determine if a failed bridge is the cause of the fuse
> blowing, so I may insert
> some fuses at different points of the circuit to find out. My assumption
> is the rectifier (very cheap ebay item) could be at fault, but there is a
> lot of knowledge I lack about what impacts of these coils on
> surrounding/supporting circuits. Any thoughts on what can do to resolve
> this?
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