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Re: Differential triggered gap
Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
Daniel: The RF choke is to protect the diode so it must be between the diode
and the capacitor. This cuts the surge of the capacitor on the diode.
Robert H
> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Sat, 10 Aug 2002 21:44:40 -0600
> To: tesla-at-pupman-dot-com
> Subject: Re: Differential triggered gap
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Sat, 10 Aug 2002 21:46:55 -0600
>
> Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <dbarrett1-at-austin.rr-dot-com>
>
> Hi Robert!
> Thanks for the response. I probably should have mentioned that I have
> capacitors before the choke as well. I put these in after the first couple
> of diode arrays fried ;). They are not as big as I'd like, but 'parts are on
> order'. They do a reasonable job of killing the worst of the transients *so
> far*
>
> (per side) 9mH
> --------------D|--------^^^^^-----------|
> | _ 1/2 of MMC (90nF)
> - _
> - .002 / 20kV |
> | |
> -----GND-------------------------------
>
> -circuit is mirrored below ground for negative rail.
>
>
> But a smaller choke would have less of a trisient supressing effect,
> wouldn't it?
> I'm finding that my rectifiers were dying not of overcurrent but from high
> dv/dt on their cathodes when reverse-biased. We really need fast-recovery
> rectifiers here...
> db
>
>
>
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Saturday, August 10, 2002 9:13 PM
> Subject: Re: Differential triggered gap
>
>
>> Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <rheidlebaugh-at-zialink-dot-com>
>>
>> Daniel: Having used DC to power and charge the spark I see you used an 18
> mh
>> choke. I found I lost rectifiers due to surge current at the time the SG
>> fires. If the choke is not fast enough to stop that surge your diodes will
>> smoke. I used a much smaller choke. 15T 1" od 8" long of #12 wire air
> core
>> coil in series with my DC supply powered with a 15/60 nst&rectifier. After
> 2
>> years of use I lost no diodes due to surge. The coil must be fast.
>> Robert H
>>
>>> From: "Tesla list" <tesla-at-pupman-dot-com>
>>> Date: Sat, 10 Aug 2002 06:46:50 -0600
>>> To: tesla-at-pupman-dot-com
>>> Subject: Differential triggered gap
>>> Resent-From: tesla-at-pupman-dot-com
>>> Resent-Date: Sat, 10 Aug 2002 07:02:39 -0600
>>>
>>> Original poster: "Daniel Barrett by way of Terry Fritz
> <twftesla-at-qwest-dot-net>"
>>> <dbarrett1-at-austin.rr-dot-com>
>>>
>>> Hi List!
>>> I have been trying to bring up an 8 inch by 36 inch DC powered coil
>>> designed around a dual-MOT power supply and triggered gap and have had
>>> limited success. I have an idea about the spark gap and wanted some
> feedback
>>> from some of you gurus ;)
>>> About the design:
>>> Secondary is resonant at 140kHz with topload.
>>> The gap trigger is a microcontroller driving the usual
>>> capacitive-discharge ignition coil circuit. I'm running this thing at
> about
>>> 5 BPS until I can convince myself that the power supply won't crater. I
> have
>>> burned through about 250 1N4007's this week :)
>>> The power supply is 2 MOTs, one modified to float the ground connection.
>>> These drive seperate pos and neg doublers, with approx +/- 10kV out. My
> tank
>>> cap is a center-tapped 45nF geek-cap array (3 string of 5 per leg). This
> is
>>> charged through a couple of 18mH inductors. Since the power supply is
>>> bipolar, it seems to make sense to me to keep the primary circuit as
>>> symmetrical and bipolar as possible. Because the power supply is
> reasonably
>>> well decoupled from the tank via theses charging inductors, Im
> connecting
>>> the gap as follows:
>>>
>>> GAP
>>> +10kvdc-------[18mH]----------O O-----------
>>> | ^ |
>>> - | |
>>> 90nF trig |
>>> - >
>>> | >
>>> Tesla coil
>>> power_gnd---------------- > Primary
>>> | >
>>> - >
>>> 90nF |
>>> - |
>>> | |
>>> -10kvdc-------[18mH]--------------------------
>>>
>>> Gee. Someone needs to write an ORCAD-to-ASCII schematic converter ;)
>>>
>>> Ok, this works, but I'm having a lot of trouble finding a gap spacing
>>> that (a) fires reliably on each trigger, and (b) doesn't power arc or
> fire
>>> muliple times per trigger. This is proving to be difficult. So now for
> the
>>> question: Would it be advantageous to build a tripple-gap as described
>>> below? The idea is that the center gap fires (via the trigger circuit),
>>> which raises the potential of the entire primary coil to
> +some_high_voltage,
>>> which should cause the bottom gap to over-volt and fire, pulling the
> primary
>>> to -10kv, which overvolts the top gap. Now the main discharge happens.
>>> That's my theory anyway.
>>>
>>> GAP #1
>>> +10kvdc-------[18mH]----------O O-----------
>>> | |
>>> - |
>>> 90nF |
>>> -
>>>> TC primary
>>> | >
>>> power_gnd---------------- > ------O
>>> O--[igncoil]
>>> | >
>>> GAP #3
>>> - >
>>> 90nF |
>>> - |
>>> | GAP #2 |
>>> -10kvdc-------[18mH]-----------O O----------
>>>
>>> Does this sound reasonable? Would this help increase the margin between
>>> reliable firing and spontaneous firing? Any comments?
>>> Thanks!
>>> db
>>>
>>>
>>>
>>>
>>>
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