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Re: [TCML] **External Email** Re: ARSG bridge rectifier failures


Actually, I have a single 400 VDC, 3900 uFd 'lytic run in parallel with the motor's input leads. Don't think it really "smooths" anything though, as the the motor's rotor, along with the G-10 disc and the flying tungsten electrodes provides plenty of inertial mass for 'filtering' the ripple.

Actually, I had been running my ARSG motor assembly trouble free for a good while, then I got a 'wild hair' and decided to change out my relatively small phenolic block FWB with one of those nicer looking metal cased units that were rated at an impressive 1 kV at 50 amps. (These units sure do seem fragile for such a monstrous rating, though)! Since grounding the outer case of the old smaller phenolic block exterior of the original FWB assembly wasn't an option, I never had that problem beforehand. However, once I installed the new metal block exterior FWB, it only seemed natural to ground the outer metal case (mains ground, NOT RF ground). The RSG motor still ran fine UNTIL the first moment I engaged the coil to produce sparks, then the FWB quickly failed as a short and actually caused my control variac to catch fire, seeing as I did not have this segment of the circuit adequately protected from over-current (only the main 100 amp throw breaker for the entire coil system)!! As soon as I replaced the FWB assmbly, SAME THING!

At this point I started scratching my head and finally figured that the only thing that I had done electrically different from my original setup was the grounding of the external metal casing of the new FWB unit. Once I removed the ground (and installed yet another new FWB unit), the problem was solved. Fortunately, I ordered a bag of 10 of these FWB units. (I also placed better 20 amp overcurrent protection in the circuit to my motor, too). BTW, I run the supply line from the variac in my control panel to the coil's FWB rectifier and ARSG motor assembly via a metal clad (MC) 14/2 AWG cable, with the outer metal armour naturally grounded. My FWB assembly is mounted on small strip of copper as a heat sink and to a poly cutting board (and of course, I have left out grounding the outer metal casing of the FWB assembly).

As you and James were discussing, and since my motor as well as the FWB rectifier unit are mounted directly underneath my primary coil support assembly, there must be a ton of high RF voltage that is induced into the low voltage wiring and frying the sensitive silicon of the unit, and all that I can figure is that grounding the outer casing gives these induced voltages a short path to dissipate their energy. One has to wonder where these induced high voltages are dissipated without the ground, though? Well, I have on occasion noted sparking inside my control panel, too and have tried to add additional filtering of the low voltage mains inside the control panel cabinet to combat this :^o - may have answered my own question.

Merry Christmas to you and yours as well,

----- Original Message ----- From: "Terry Oxandale" <Toxandale@xxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Wednesday, December 13, 2017 2:55 PM
Subject: Re: [TCML] **External Email** Re: ARSG bridge rectifier failures


Just curious if you've got an Cap/Inductor filter on the output of your bridge? I don't think I have had any problems prior to adding this to the output of the bridge, but couldn't imagine that the ripple filter would be a cause to the problems, especially if everything runs fine without the high discharge performance.


-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of David Rieben
Sent: Tuesday, December 12, 2017 5:25 AM
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: **External Email** Re: [TCML] ARSG bridge rectifier failures


I had pretty much the same problem with my big coil. I, too, am using a DC motor designed for a treadmill, that is rated at like 130 VDC for the drive of my ARSG. I was using those 1 kV, 50 amp rated FWB 'blocks' for the rectification of the 120 VAC mains, through a 120/140 volt, 10 amp rated variac for speed control. When I grounded the outed metallic casing of the FWB rectifier in question, it would almost immediately get fried once I even started to produce a spark output from my coil! Fortunately, I had ordered a bag of 10 of these FWB units, and I discovered that when I removed the ground from the outer casing and just allowed it to 'float', the problem was solved.

Maybe you could explore this solution for your setup?

David Rieben

----- Original Message -----
From: "Terry Oxandale" <toxandale@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, December 10, 2017 9:22 PM
Subject: Re: [TCML] ARSG bridge rectifier failures

    I'm having an issue with the bridge rectifiers I'm using to power a
variable speed DC motor for the rotating spark gap. When the coil is not
energized (but motor is spinning), the diode stays cool, and appears to be
reliable. As soon as I energized the coil sufficiently to operate with
breakout, the rectifier gets a little warm, but appears to remain
reliable. With more coil performance, I notice more heating of the
rectifier. It appears, after some testing, that the lifespan of the
rectifier is inversely proportional to the power put into the coil. I have a voltmeter and ammeter to monitor the power to the DC motor, and there is nothing to indicate a problem (but these are analog meters, and may not be
sensitive enough to see everything I'm looking for).
So far, the only variable is the coil's output (performance), so that
leads me to believe something is back-feeding or being induced into the
motor's power cord and back to the rectifier. The motor only draws about 1
or 2 amps through 90 VDC at speed, yet the rectifier is rated at 30 amps
and 600 volts. I don't run the motor at the full 90 VDC because the coil
operates best at a lower RPM, and hence a lower voltage to the motor. The
rectifier is fed through a small variac, whose output then passes through
the rectifier. The rectifier does have an LC filter to dampen the full
wave output of the rectifier. I don't know if it's the cheap Chinese Ebay
bridge rectifiers or not, but am considering building one out of some
robust diodes that I've had for years.
Any thoughts please?

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