Filter for MOTs?
Daniel Uhrenholt, Fri Apr 06 2007, 10:00AMHi all.
I’m rebuilding my BIG MOT Tesla coil, and I have a question about RC filters on the high voltage side of my MOTs.
I have searched the internet for schematics and ideas, and I found this:
Terry Filter
(Can this be used for 4MOTs?)Terry Blake’s filter
The MOTs are external ballasted to 2KVA, the output is 9800V 200mA. And the frequency of the Tesla Coil is about 100 kHz
My coil runs with a 200bps SRSG, and 0.085uF tank cap.
I have 15 2k 75W resistors that I could use for this purpose, but I need doorknob or ceramic discs caps for it.
Is there any calculations on how big the resistance and capacitance should be in a filter circuit?
Does anybody have a suggestion or an idea for a filter?
Cheers, Daniel
Re: Filter for MOTs?
sparky, Fri Apr 06 2007, 08:07PM
What I used for my 3kVA 12kVDC MOT supply are 2 - 5 Hn chokes on either leg of the outputs and 2 - 15kVDC, 1nF rated - blue ceramic disc capacitors from ebay with a safety gap. No resistors used...
On a large power system - 4 MOTs in series - I'd just simply use a static safety gap with 15kVDC rated ceramic caps to help with any "RF" surges. Run the power supply away from the base of your tesla coil and all should run well. You should run these trannies under oil too!
sparky, Fri Apr 06 2007, 08:07PM
What I used for my 3kVA 12kVDC MOT supply are 2 - 5 Hn chokes on either leg of the outputs and 2 - 15kVDC, 1nF rated - blue ceramic disc capacitors from ebay with a safety gap. No resistors used...
On a large power system - 4 MOTs in series - I'd just simply use a static safety gap with 15kVDC rated ceramic caps to help with any "RF" surges. Run the power supply away from the base of your tesla coil and all should run well. You should run these trannies under oil too!
Re: Filter for MOTs?
Daniel Uhrenholt, Fri Apr 06 2007, 09:23PM
Hi sparky
I guess I’m safe because my MOTs stand about 2 meters from my TC, and they are under oil
I’ll take a look on E-bay after capacitors, and make the safety gap as close to the MOTs as possible.
It’s getting late here, and I have to go to work tomorrow morning. I’ll write some more tomorrow
Thanks, Daniel
Daniel Uhrenholt, Fri Apr 06 2007, 09:23PM
Hi sparky
I guess I’m safe because my MOTs stand about 2 meters from my TC, and they are under oil
I’ll take a look on E-bay after capacitors, and make the safety gap as close to the MOTs as possible.
It’s getting late here, and I have to go to work tomorrow morning. I’ll write some more tomorrow
Thanks, Daniel
Re: Filter for MOTs?
Terry Fritz, Sun Apr 08 2007, 02:48PM
Hi,
The"Terry Filter" was never meant to be used with MOTs.
Cheers,
Terry
Terry Fritz, Sun Apr 08 2007, 02:48PM
Hi,
The"Terry Filter" was never meant to be used with MOTs.
Cheers,
Terry
Re: Filter for MOTs?
HV Enthusiast, Sun Apr 08 2007, 03:10PM
You shouldn't need any filters for MOTs.
HV Enthusiast, Sun Apr 08 2007, 03:10PM
You shouldn't need any filters for MOTs.
Re: Filter for MOTs?
Daniel Uhrenholt, Sun Apr 08 2007, 06:26PM
Terry,
I thought your filter would work if I centre tapped my MOTs like an NST.
But after searching more on the internet I’d have to agree with EVR, because there aren’t many who use filters on their MOTs.
So if I set it up with a couple of safety gaps, I should be fine
My only concern is if I kill a MOT in my supply, it would be a pain in the a%& to find a new one. I can’t buy old microwave ovens at the recycling place anymore, because the municipality has made some new rules about recycling in my area
But thanks for the help.
Cheers, Daniel
Daniel Uhrenholt, Sun Apr 08 2007, 06:26PM
Terry,
I thought your filter would work if I centre tapped my MOTs like an NST.
But after searching more on the internet I’d have to agree with EVR, because there aren’t many who use filters on their MOTs.
So if I set it up with a couple of safety gaps, I should be fine
My only concern is if I kill a MOT in my supply, it would be a pain in the a%& to find a new one. I can’t buy old microwave ovens at the recycling place anymore, because the municipality has made some new rules about recycling in my area
But thanks for the help.
Cheers, Daniel
Re: Filter for MOTs?
HV Enthusiast, Sun Apr 08 2007, 08:57PM
I forget the name of the place, but there is an EBAY seller who has a ebay store which sells MOTs (new) quite inexpensively. Like $15.00 a pop. Sure, its not free from the trash, but its still relatively cheaper than a NST.
HV Enthusiast, Sun Apr 08 2007, 08:57PM
I forget the name of the place, but there is an EBAY seller who has a ebay store which sells MOTs (new) quite inexpensively. Like $15.00 a pop. Sure, its not free from the trash, but its still relatively cheaper than a NST.
Re: Filter for MOTs?
Terry Fritz, Mon Apr 09 2007, 12:30AM
Hi,
The Terry Filter was only made to handle less than 1/4 amp of current. A MOT can hit 2 amps and would just burn it up. I would just use a safety gap and for sure fuses on the input side. MOTs have very low secondary resistance so the high frequency noise should not be a problem there. I really am not sure a safety gap would do much good, but that might depend on exactly how it is setup. Fuses will be the main protection so definitely use them.
If you system is ballasted to 200mA, then the Terry Filter might be OK and might not really hurt anything. I just have never considered using it with MOTs at all before so I don't know for sure. I know that odd things can happen, so I hesitate to say it is OK without really knowing for sure.
Cheers,
Terry
Terry Fritz, Mon Apr 09 2007, 12:30AM
Hi,
The Terry Filter was only made to handle less than 1/4 amp of current. A MOT can hit 2 amps and would just burn it up. I would just use a safety gap and for sure fuses on the input side. MOTs have very low secondary resistance so the high frequency noise should not be a problem there. I really am not sure a safety gap would do much good, but that might depend on exactly how it is setup. Fuses will be the main protection so definitely use them.
If you system is ballasted to 200mA, then the Terry Filter might be OK and might not really hurt anything. I just have never considered using it with MOTs at all before so I don't know for sure. I know that odd things can happen, so I hesitate to say it is OK without really knowing for sure.
Cheers,
Terry
Re: Filter for MOTs?
sparky, Mon Apr 09 2007, 08:46AM
I had my 17KV rated diodes die from RF kickback into the power supply - using safety gaps with some added inductance took care of the nasty surges and sent them to ground. The gap fired once every 3 seconds.
sparky, Mon Apr 09 2007, 08:46AM
I had my 17KV rated diodes die from RF kickback into the power supply - using safety gaps with some added inductance took care of the nasty surges and sent them to ground. The gap fired once every 3 seconds.
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