Re: [TCML] Treadmill Motor Question

[Stan Gray <wsmg@xxxxxxx>]

I've been using a simple half wave 2 metal stud diode rectifier with a I think 3300mfd electrolytic cap. 24 volt 20 amp supply with a 10 amp variac wired for the boost on the input of the p/s to run a 28 volt DC pm motor propeller gap for years without fail for Sparky Matic. The wire to the motor on the gap mounted under the primary is just 14 or 16 ga speaker wire that was laying around.


Stan



________________________________
 From: "pterren@xxxxxxxxxxxx" <pterren@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> 
Sent: Tuesday, September 10, 2013 7:06 PM
Subject: Re: [TCML] Treadmill Motor Question
 

I've seen DC rectifiers blow repeatedly on a museum coil.
My take on this is that there is likely to be differences in potential between the RF earth, HV feed and the mains feed to the ARSG motor.
This can be simply due to capacitance from the HV (the spark gap is very close to the motor), or voltage drop during spark events giving potentials across the small inductance leading to the RF earth for example.
It will only take a 500V transient to blow the diodes. So, how to prevent it? Not so easy.
My suggestions:
1 Completely shield the ARSG motor supply ie shield the mains cable to the motor and earth the shield to mains earth.  I have used adhesive aluminum tape over the motor mains cable for mine.
2 Use a microwave oven phi filter after the diodes. Cheap (free) and meant for AC but has caps, MOVs and inductors and will allow stray stuff to go to mains earth.
Maybe just the latter would be sufficient too.

Peter
tesladownunder.com
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