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Re: resistors
From: Gary Lau 14-Nov-1997 1413[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Friday, November 14, 1997 12:21 PM
To: tesla-at-pupman-dot-com
Cc: lau-at-hdecad.ENET.dec-dot-com
Subject: Re: resistors
>>>From: Peter Electric [SMTP:elekessy-at-macquarie.matra-dot-com.au]
>>>Sent: Wednesday, November 12, 1997 1:33 AM
>>>To: Tesla List
>>>Subject: Re: resistors
>>>
>>>I am using fairly large ferrite core chokes (around 30mH) with a string
>>>of 3 by 1K, 10Watt resistors in each leg. Transformers are 15Kv 60Ma.
>>>These used to run stinking hot with the forced air quench gap I ran
>>>previously but something interesting happens with my new sync rotary. If
>>>the rotary is not phased right, the safety gap sparks and the resistors
>>>run very hot. If the sync is spot on, the safety gap stops sparking and
>>>the resistors run noticeably cooler, but the output streamers get
>>>longer!
>>>
>>>It would seem from this that much of the heating in the resistors is
>>>power being reflected back into the transformer.
---------------------------------------------------------
>>From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
>>Sent: Wednesday, November 12, 1997 6:58 PM
>>To: Tesla List
>>Subject: Re: resistors
>>
>> Gary, Peter -
>>
>> If you have a scope it would be interesting to check the waveforms. The
>>rotary, properly phased, should show quench at the first notch. This would
>>indicate the enegy (power x seconds) is being dissipated in the longer
>>streamers.
>>
>>The forced air gap should show several transfers and notches before
>>quenching. This condition would indicate the energy is being reflected back
>>to the primary circuit and would be causing the overheating of the resistors.
>>
>> The probe for voltage waveforms could be a 1000 ohm resistor across the
>>scope leads held a safe distance from the coil.
>>
>> John Couture
>>
>From: Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
>Sent: Thursday, November 13, 1997 1:25 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: resistors
>
>Interesting. I am using a 12 kv 60 ma neon transformer for power. The
>resitors get hot but not red hot. I have no inductance in series with them.
>
>Ed Sonderman
My coil (with 15K/60mA and hot (not red-hot) 50W 750 Ohm R's, 14mH
ferrite chokes, 600 pF bypass caps) uses a RQ static gap with vaccuum
motor. When I last scoped things, it definately did not quench at the
first notch (don't recall exactly when it was). I understand that
failing to quench at the 1st notch implies multiple pri-sec power
transfers and loss of efficiency therein. But I would think that the
hefty chokes employed in my xfmr protection network would pretty much
keep HF current from flowing into the R's and xfmr beyond. Isn't that
why chokes are used in the first place? At 290 KHz, my choke's Xl is
25.5K. This would attenuate the voltage across R by a factor of 750/
(25500+750) = 0.029.
Also, while the 60 Hz current flowing through the R's is continuous, the
duty cycle of the HF tank oscillations is probably less than 1%, so I
find it hard to believe it's the HF component that is heating the R's.
But having said this, I still have no alternate explanation for Peter's
rotary-phase-dependant resistor heating.
Could it be that ferrite chokes are saturating? Mine are pretty beefy at
about 5" OD.
Gary Lau
Waltham, MA