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Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
I have two fets wired in parallel, driven with a 555 timer. When I first start it up, the arc is around 2 inches long but after a few seconds its shrinks down to about a cm and stays there, why?
Also, I have had the problem in the past where the arc is long when I play music from my BlackBerry but once I plug in my computer the arc shrinks and I get a lot of high screeching noise.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
A number of things could be happening....Do the mosfets get hot at all? Are you running it from a battery? What might be happening is your fets are overheating and thus conduct less current, so less arc length for you. Or, the power supply could be dropping depending on how heavy your load is. And, blackberries and small mp3 players have a bit of electrical noise; stuff that makes the arc all noisy, but the same problem might be happening worse with your computer, depending on its age.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
I have the fets well sinked so they don't heat up at all, currently I'm running it off of a 19.5v laptop power supply, although I have run it off a computer psu and nothing's changed. Tomorrow I will try running it off of just one fet, maybe the 555 isn't switching fast enough?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
SMPS power supplies can have some deceptive properties. I had a ATX power supply that would fold back from 12V to 7.7 v when i pulled 2 amps, out of a 10 amp channel!
Try a good battery and watch the current input and the voltage across the battery while your running your device. this should confirm or deny quickly the input power issues, after which we can move on to more complicated issues.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
The circuit is powered with a DELL computer power supply, the flyback is powered with a laptop power supply. I packed up the speaker to bring to school tomorrow, when I get home I will try the battery with the multimeter and I will post the images of the scope.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Ok I scoped it is a weird oscilloscope though and I was unfamiliar with it so I am unsure if I did it correctly... The first picture is of the actual scope, the second is when there was an arc, and the third is when the arc was on but I didn’t ‘engage’ the arc. It's a "bk precision oscilloscope 1403A" I had the "vert input" connected to the drain. The "sweep range (Hz)" was at 1k - 10k and "V. ATT" was at 1/10
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Plasma Speaker Questions
