DRSSTC Interrupter Frequency.
gentoo_daemon, Fri Mar 23 2007, 03:48AMHello
After testing out my interrupter, I see that it's capable of all sorts of frequencies from low as 500 Hz to 10kHz. Even though I am limiting the duty cycle to less than 8%, could operating the interrupter at the lower frequencies be catastrophic for my bridge? And as for your own coils, what interrupt frequency was optimal for the coil?
-Thanks.
Re: DRSSTC Interrupter Frequency.
Steve Ward, Fri Mar 23 2007, 05:41AM
Your range is way off for producing long sparks vs input power. You should have a sweep on the range of 50hz to 500hz. The pulse width should be from 50uS to 250uS, or thereabouts. My DRSSTC-1 runs well at 200bps (200hz) and 110uS pulse width. My DRSSTC-2 runs well at about 180bps and 180uS.
Steve Ward, Fri Mar 23 2007, 05:41AM
Your range is way off for producing long sparks vs input power. You should have a sweep on the range of 50hz to 500hz. The pulse width should be from 50uS to 250uS, or thereabouts. My DRSSTC-1 runs well at 200bps (200hz) and 110uS pulse width. My DRSSTC-2 runs well at about 180bps and 180uS.
Re: DRSSTC Interrupter Frequency.
Steve Conner, Fri Mar 23 2007, 11:32AM
Yeah, generally around 100-200Hz PRF and 150-300us on-time seems to be good for DRSSTCs. I have run mine at 10Hz and 3ms on-time, though, which gives some pretty spectacular effects. My interrupter goes from single shot to around 300Hz, and from 10 to 300us on-time, with a x10 switch that changes the range of on-times to be 100us to 3ms.
Steve Conner, Fri Mar 23 2007, 11:32AM
Yeah, generally around 100-200Hz PRF and 150-300us on-time seems to be good for DRSSTCs. I have run mine at 10Hz and 3ms on-time, though, which gives some pretty spectacular effects. My interrupter goes from single shot to around 300Hz, and from 10 to 300us on-time, with a x10 switch that changes the range of on-times to be 100us to 3ms.
Re: DRSSTC Interrupter Frequency.
HV Enthusiast, Sat Mar 31 2007, 02:26AM
Actually, yes. One thing i see quite commonly is people running successful DRSSTCs at 100Hz, and when they go down to say 50Hz or even lower, the bridge blows. This occurs because at lower PRFs, the interpulse droop is much less so you get a much higher voltage being pumped into the primary which also means more current as well.
But as the Steves said, the modulator should be set optimally between 50Hz and 300-500Hz maximum. 10kHz is way too high, especially if you want to maintain reasonable duty cycles in which case the pulsewidths would be extremely short.
HV Enthusiast, Sat Mar 31 2007, 02:26AM
wrote ...
could operating the interrupter at the lower frequencies be catastrophic for my bridge?
could operating the interrupter at the lower frequencies be catastrophic for my bridge?
Actually, yes. One thing i see quite commonly is people running successful DRSSTCs at 100Hz, and when they go down to say 50Hz or even lower, the bridge blows. This occurs because at lower PRFs, the interpulse droop is much less so you get a much higher voltage being pumped into the primary which also means more current as well.
But as the Steves said, the modulator should be set optimally between 50Hz and 300-500Hz maximum. 10kHz is way too high, especially if you want to maintain reasonable duty cycles in which case the pulsewidths would be extremely short.
Re: DRSSTC Interrupter Frequency.
Steve Ward, Sat Mar 31 2007, 06:35AM
I never really thought too much about that one. I figured the failure mode was due to higher currents needed to re-initialize the breakout, since when the arc extinguishes, starting from no ion cloud near the toroid causes the voltage to go higher (implying higher primary current).
My coils dont have any problems with one shot mode, of course.
Steve Ward, Sat Mar 31 2007, 06:35AM
Actually, yes. One thing i see quite commonly is people running successful DRSSTCs at 100Hz, and when they go down to say 50Hz or even lower, the bridge blows. This occurs because at lower PRFs, the interpulse droop is much less so you get a much higher voltage being pumped into the primary which also means more current as well.
I never really thought too much about that one. I figured the failure mode was due to higher currents needed to re-initialize the breakout, since when the arc extinguishes, starting from no ion cloud near the toroid causes the voltage to go higher (implying higher primary current).
My coils dont have any problems with one shot mode, of course.
Re: DRSSTC Interrupter Frequency.
Steve Conner, Sat Mar 31 2007, 11:12AM
Yay, I found a picture of one of my 3ms single shots.
The ion cloud explanation kind of makes sense too. When I was trying to get the absolute longest spark from that coil, I found I could get much further before it flashed over and started burning itself up, if I gradually raised the voltage. If I just flipped the gate drive on with the DC bus caps already charged, a spark would shoot from the middle of the secondary to the strike rail. Of course the transient in DC bus voltage that EVR mentioned could be part of the explanation, too.
Steve Conner, Sat Mar 31 2007, 11:12AM
Yay, I found a picture of one of my 3ms single shots.
The ion cloud explanation kind of makes sense too. When I was trying to get the absolute longest spark from that coil, I found I could get much further before it flashed over and started burning itself up, if I gradually raised the voltage. If I just flipped the gate drive on with the DC bus caps already charged, a spark would shoot from the middle of the secondary to the strike rail. Of course the transient in DC bus voltage that EVR mentioned could be part of the explanation, too.
Re: DRSSTC Interrupter Frequency.
Tom540, Sat Mar 31 2007, 04:59PM
It kinda sounds like the current lag and voltage spike in your secondary made it jump from the middle. Like it didn't have enough time to charge up the toroid. Then again I don't know.
Tom540, Sat Mar 31 2007, 04:59PM
It kinda sounds like the current lag and voltage spike in your secondary made it jump from the middle. Like it didn't have enough time to charge up the toroid. Then again I don't know.
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