Gosh Jim, I hope that's not what my problem is, as that would pretty much make that nice motor useless for my coil. ;-( Now that l've read Scott's reply about whether or not the external metallic case of my FWB was grounded or floated, that makes the most sense, as upon recollection, I believe my originally FWB was indeed floating and I have indeed been grounding the case of my FWB bricks that keep biting the dust. Like I was replying to Scott, when my 10 new 1050 FWB bricks arrive next Tuesday, I'll give her another try with the sparks on and let you guys know the outcome. BTW, there is a 10 amp Corcom line filter between my FWB and the motor and the electrolytic cap is in parallel with the input leads of the motor, downstream of the filter. Although I'm not sure how effective line filters are on rippled DC as opposed to plain AC, I was thinking that filter should help prevent HV spikes from getting back into the ARSG drive motor. I know from my past experience that installing a simple line filter at the inputs to previous RSG and fan motors in Tesla coil control circuitry (including the fans that are currently inside my control panel) has consistantly prevented them from suffering a premature death.
David
Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:
>On 3/7/14 8:03 AM, David Rieben wrote:
>> Hey guys,
>>
>> Bumfuzzeld,
>> David
>>
>
>You need a fuse or circuit breaker in your ARSG power..that, at least,
>will protect the control panel's variac.
>
>but, to why it's shorted..
>
>Is there a short from winding to case in your motor? Does it fail only
>after turning on the sparks? There could be a hole in the insulation
>and it doesn't short until you actually have HV transients running around.
>
>I had some 10HP 460V motors running off 3 phase PWM motor drives.. they
>kept tripping with a fault after a while, and it was because of the
>spikes from the drive which had punctured the insulation on the
>windings. They ohmed out fine, and ran fine at full speed with the
>motor drive out of the circuit, but would trip instantly with the drive.
>
>Doing a hi=pot test on the motor afterwards showed that it would fail hipot.
>
>If you have access to someone who can hipot test your ARSG that would be
>convenient. You can also rig one up a test set using a NST and a
>variac.. (you want only a few kV.. not the full 15kV)
>
>What might be happening is a transient causes a breakdown (at HV) which
>then provides a conductive path to ground that carries enough current to
>kill the diodes.
>
>The other thing is whether you're getting inductive kickback from the
>motor into the bridge.. but that would have killed your bridges in the
>past..(although the electrolytic might have damped that out too..
>
>
>
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