Sealed spark gap
uzzors2k, Mon Feb 26 2007, 05:29PMI've been using a more or less sealed spark gap for testing my mini sgtc, but I'm not sure how it will work over time. The gap has worked fine so far, but I want it to last as long a possible. I'm using a peice of 1.5 cm diameter PVC plugged with paper in both ends, and after no more than 5 minutes of running the paper and PVC are fairly brown. Would the build up of NO2 and other gasses affect the breakdown voltage of the gap?
Re: Sealed spark gap
J. Aaron Holmes, Mon Feb 26 2007, 07:58PM
Generally speaking, I would tend to think that sealed is bad unless by "sealed" you mean "evacuated", which does not appear to be the case (and even in that case, I'm not aware of many positive experiences with evacuated gaps, e.g., vacuum interruptors and such, though I know one or two people have tried them). Otherwise, blowing the hot air and metal vapor and other bad stuff out of your gap is probably going to help performance a lot and make it more consistent. Having that stuff accumulate inside the gap during a run is definitely going to affect performance.
Is the main reason for sealing the gap to deal with noise, or...?
Regards,
Aaron, N7OE
J. Aaron Holmes, Mon Feb 26 2007, 07:58PM
Generally speaking, I would tend to think that sealed is bad unless by "sealed" you mean "evacuated", which does not appear to be the case (and even in that case, I'm not aware of many positive experiences with evacuated gaps, e.g., vacuum interruptors and such, though I know one or two people have tried them). Otherwise, blowing the hot air and metal vapor and other bad stuff out of your gap is probably going to help performance a lot and make it more consistent. Having that stuff accumulate inside the gap during a run is definitely going to affect performance.
Is the main reason for sealing the gap to deal with noise, or...?
Regards,
Aaron, N7OE
Re: Sealed spark gap
Sulaiman, Mon Feb 26 2007, 09:09PM
A truly sealed spark gap can (I've read) be a very GOOD thing because
after a while all the oxygen is used up in oxidising the electrodes etc.
after which the gap should quench quickly
since nitrogen quenches MUCH faster than oxygen.
In your case I see only bad points
- fire hazard
- no cooling
- poor quenching
Sulaiman, Mon Feb 26 2007, 09:09PM
A truly sealed spark gap can (I've read) be a very GOOD thing because
after a while all the oxygen is used up in oxidising the electrodes etc.
after which the gap should quench quickly
since nitrogen quenches MUCH faster than oxygen.
In your case I see only bad points
- fire hazard
- no cooling
- poor quenching
Re: Sealed spark gap
uzzors2k, Mon Feb 26 2007, 09:43PM
I've had no problems with quenching yet, and the coil only draws 20-30W so the spark gap doesn't heat too much. I'll try a sealed gap and keep a regular one around just incase. I choose to seal it because of the noise, it's table top size and having a loud buzzing come from it would get annoying. Thanks for the advice.
uzzors2k, Mon Feb 26 2007, 09:43PM
I've had no problems with quenching yet, and the coil only draws 20-30W so the spark gap doesn't heat too much. I'll try a sealed gap and keep a regular one around just incase. I choose to seal it because of the noise, it's table top size and having a loud buzzing come from it would get annoying. Thanks for the advice.
Re: Sealed spark gap
Electroholic, Mon Feb 26 2007, 10:10PM
UV can breakdown PVC.
Electroholic, Mon Feb 26 2007, 10:10PM
UV can breakdown PVC.
Re: Sealed spark gap
J. Aaron Holmes, Mon Feb 26 2007, 10:20PM
Yeah, I thought that might be the case. A small, ventilated wooden enclosure, optionally lined with "sound-proof" insulation, would probably be a better way to go, though. At least it would be less likely to be attributed to poor gap performance. Even where lack of air flow doesn't immediately impair quenching, you may find that the cooling of the electrodes keeps the gap breakdown voltage from straying too far (down) during a run.
Optionally, you could replace your gap with Terry's "SISG", making it totally silent (except in the event of catastrophic failure, I expect
)
Yeah, but unless you're using tungsten electrodes, I'd bet on the electrodes eating themselves to death long before you have to worry about this. Maybe I'm wrong, though...
Regards,
Aaron, N7OE
J. Aaron Holmes, Mon Feb 26 2007, 10:20PM
uzzors wrote ...
I choose to seal it because of the noise, ...(snip)
I choose to seal it because of the noise, ...(snip)
Yeah, I thought that might be the case. A small, ventilated wooden enclosure, optionally lined with "sound-proof" insulation, would probably be a better way to go, though. At least it would be less likely to be attributed to poor gap performance. Even where lack of air flow doesn't immediately impair quenching, you may find that the cooling of the electrodes keeps the gap breakdown voltage from straying too far (down) during a run.
Optionally, you could replace your gap with Terry's "SISG", making it totally silent (except in the event of catastrophic failure, I expect
)Electroholic wrote ...
UV can breakdown PVC.
UV can breakdown PVC.
Yeah, but unless you're using tungsten electrodes, I'd bet on the electrodes eating themselves to death long before you have to worry about this. Maybe I'm wrong, though...
Regards,
Aaron, N7OE
Re: Sealed spark gap
..., Tue Feb 27 2007, 03:46AM
I tried a sealed spark gap (really small, 1/2" pvc pipe plug/cap stuck into eachother) and 2 woodscrews wound into it with my small 20w coil, and it seems to wok ok, but I let it sit for a week and when I came back whatever gasses in there rusted the crap out of my screws, and it was completly shorted out. The pvc was a little brown, but not all that bad.
..., Tue Feb 27 2007, 03:46AM
I tried a sealed spark gap (really small, 1/2" pvc pipe plug/cap stuck into eachother) and 2 woodscrews wound into it with my small 20w coil, and it seems to wok ok, but I let it sit for a week and when I came back whatever gasses in there rusted the crap out of my screws, and it was completly shorted out. The pvc was a little brown, but not all that bad.
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