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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
What does it take to get a smooth HV DC from a MOT? On the VTTC FAQ it said you would need 10's of uF but, thats a bit impractical at the voltages in use. The reason I want to do this is to audio modulate a VTTC.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
cduma wrote ...
What does it take to get a smooth HV DC from a MOT? On the VTTC FAQ it said you would need 10's of uF but, thats a bit impractical at the voltages in use. The reason I want to do this is to audio modulate a VTTC.
Clearly, this depends on the current required, but in general you would have to use large can HV electrolytics in series. Eight 4700μF 400V electrolytics - each larger than a soft drink can - would give you an effective capacitance of about 600μF @ 3200V, a costly proposition.
Why not use cathode modulation using an audio transformer?
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
how about using a pulse discharge capacitor? the kind weighted more towards capacitance than voltage. (ie. would probably be cheaper than lytics that big. or would they not be suitable for a smoothing application?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Forty wrote ...
how about using a pulse discharge capacitor? the kind weighted more towards capacitance than voltage. (ie. would probably be cheaper than lytics that big. or would they not be suitable for a smoothing application?
That capacitor would do very nicely if it were not "untested as is" with a "corroded" case and did not cost $200. Someone might themselves decide that they were preapred to take the risk of such a part exploding, or causing a fire, but I would not be the one to recommend anyone to use such a doubtful part at several thousands of volts, when the energy stored in a 460μF capacitor would be almost 1000 joules.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
cduma wrote ...
From what I have read the 60HZ buzz is very prominent without filtering.
Prominent is an understatement!
This is what half-wave rectification looks like without a smoothing capacitor:
Can you not build a bridge rectifier from four MO diodes?
This would require a lot less smoothing, it may even be possible to use MO capacitors in parallel for smoothing?
One end of an MOT secondary is Earthed to the laminated core.
Someone here is bound to say that you could un-Earth the cold end of the secondary, and perhaps you could, but the insulation is not designed for that, and no serious person would ever suggest it.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
oh, no. I didn't mean buy that exact one. i just meant it as an example of the discharge caps that have a higher capacitance versus the types that have maybe 1uF at 25kvdc.
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HV DC Filtering
