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Re: Gap Dwell Times (formerly: Beating S




Have you tried putting varistors (series) across your mosfets to eat (clamp) 
the spikes?
Barry

 ----------
|From: "tesla-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|To: Benson Barry; "Tesla-list-subscribers-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|Subject: Re: Gap Dwell Times (formerly: Beating S
|Date: Friday, September 27, 1996 3:53AM
|
|<<File Attachment: 00000000.TXT>>
|From MALCOLM-at-directorate.wnp.ac.nzThu Sep 26 22:18:09 1996
|Date: Fri, 27 Sep 1996 08:13:59 +1200
|From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
|To: tesla-at-pupman-dot-com
|Subject: Re: Gap Dwell Times (formerly: Beating Solved)
|
|In reply...
|
|>   I did some research this weekend, pouring through a Corum brothers
|> monograph and some old posts to this newsgroup and found out that the
|> optimal dwell is 1/(k*Fr), *not* 1/(2*k*Fr). In other words, the spark
|> gap should conduct for only 1/2 of the superimposed beat-frequency
|> envelope. Primary current peaks at that point, and maximum energy is
|> transferred into the secondary.
|
|I started from k approx dF/F, and ringup time = 1/2dF so you can see
|how I derived that. The problem when cutting the gap off (if you
|could) when Ip is maximum is that with k<1, most of the primary
|energy is coupled to the primary. I tried doing exactly this with the
|MOSFET gap and the spikes hit the roof. Virtually none of that energy
|was coupled to the secondary. The spikes in a real gap would have re-
|ignited it anyway. I wonder if they have actually tried doing this?
|I found the ideal dwell to be when the secondary was fully rung-up
|and the primary had virtually nothing left. Even then, quenching at a
|primary zero-crossing is a no-no because of spike generation. I sent
|some photos I took of this process to several people.
|
|Malcolm
|