MOT for Tesla Coil and Magnetic Shunts
thedatastream, Fri Aug 31 2007, 03:33PMI'm going to build a small SISG coil using a single MOT to power it (Terry's Pirahna design) and I was wondering whether or not to de-shunt my MOT.
I've looked on the web (unfortunately Pupman is blocked on the work computer) and what I can find suggests that removing these increases potential output current by removing the partial flux path formed by these bits of iron.
Anyone have any idea what sort of current / voltage output increase can be gained by de-shunting a MOT?
Is this conventional practice for MOTs used for Tesla Coils?
Thanks
James
Re: MOT for Tesla Coil and Magnetic Shunts
CT2, Fri Aug 31 2007, 06:48PM
I don't think you should remove the shunts. A mot will run untill it burns itself up/blows fuse. So I don't think you can squeez any more power out without killing it.
CT2, Fri Aug 31 2007, 06:48PM
I don't think you should remove the shunts. A mot will run untill it burns itself up/blows fuse. So I don't think you can squeez any more power out without killing it.
Re: MOT for Tesla Coil and Magnetic Shunts
Garry Neeley, Fri Aug 31 2007, 09:36PM
CT2 is right. A MOT is not a current limited transformer. If you short the secondary on a MOT it will continue to draw more and more current until the breaker flips. I would suggest you leave the shunts in place as well.
Garry Neeley, Fri Aug 31 2007, 09:36PM
CT2 is right. A MOT is not a current limited transformer. If you short the secondary on a MOT it will continue to draw more and more current until the breaker flips. I would suggest you leave the shunts in place as well.
Re: MOT for Tesla Coil and Magnetic Shunts
sparky, Sat Sept 01 2007, 02:46AM
No ,Garry
MOTs are current limited by nature. I've done tests to prove that a 1000 watt MOT will draw 1700 watts when run in a short circuit operation. Remove those shunts and the transformer will burn up - and the
secondary voltage will climb radically.
So if you are wanting to run higher power you might check the local repair shop and see if you can get one of those 2500 watt - 1900V rated industral MOTs. These guys weigh in at 20 lbs and can short over 3 amps! They do run 240V....
sparky, Sat Sept 01 2007, 02:46AM
No ,Garry
MOTs are current limited by nature. I've done tests to prove that a 1000 watt MOT will draw 1700 watts when run in a short circuit operation. Remove those shunts and the transformer will burn up - and the
secondary voltage will climb radically.
So if you are wanting to run higher power you might check the local repair shop and see if you can get one of those 2500 watt - 1900V rated industral MOTs. These guys weigh in at 20 lbs and can short over 3 amps! They do run 240V....
Re: MOT for Tesla Coil and Magnetic Shunts
thedatastream, Sat Sept 01 2007, 08:07AM
Now I'm at home, I've found some Pupman stuff on this subject
- OK to remove shunts so long as you ballast
- OK if ballasted
- OK if ballasted
The question is, do the 100R series resistors in the secondary of Terry's Pirahna provide enough ballasting for me to remove the shunts?
Thanks
James
thedatastream, Sat Sept 01 2007, 08:07AM
Now I'm at home, I've found some Pupman stuff on this subject
- OK to remove shunts so long as you ballast - OK if ballasted - OK if ballastedThe question is, do the 100R series resistors in the secondary of Terry's Pirahna
provide enough ballasting for me to remove the shunts?Thanks
James
Re: MOT for Tesla Coil and Magnetic Shunts
Steve Conner, Sat Sept 01 2007, 09:15AM
Hi guys,
I believe the shunts are there to improve the power factor and deliver a less peaky current waveform to the magnetron. When I was simulating the supply for my Tesla-2, the power factor was much better with the shunts than without. It delivered plenty of power even with the shunts: I was blowing 5 amp fuses on the 240V line when I got my bigger tank capacitors.
In newer MOTs, I doubt they are big enough to ballast the transformer into a short circuit. The cross-sectional area of them is much smaller than the cross-section of the core, so they are bound to saturate quite early on.
Older MOTs, and industrial MOTs, were built much more heavily than the ones you get at the kerbside nowadays, and may have had more generous shunting. Sparky probably tested one of these. If nobody believes me I will test some modern MOTs for you and post my own results here.
As for the 100 ohm resistors, ask Terry
Steve Conner, Sat Sept 01 2007, 09:15AM
Hi guys,
I believe the shunts are there to improve the power factor and deliver a less peaky current waveform to the magnetron. When I was simulating the supply for my Tesla-2, the power factor was much better with the shunts than without. It delivered plenty of power even with the shunts: I was blowing 5 amp fuses on the 240V line when I got my bigger tank capacitors.
In newer MOTs, I doubt they are big enough to ballast the transformer into a short circuit. The cross-sectional area of them is much smaller than the cross-section of the core, so they are bound to saturate quite early on.
Older MOTs, and industrial MOTs, were built much more heavily than the ones you get at the kerbside nowadays, and may have had more generous shunting. Sparky probably tested one of these. If nobody believes me I will test some modern MOTs for you and post my own results here.
As for the 100 ohm resistors, ask Terry
Re: MOT for Tesla Coil and Magnetic Shunts
sparky, Sat Sept 01 2007, 05:05PM
If you want large easily obtained MOTs, try looking for old 1980's early 90's Kenmore, Sanyo or Amana microwaves (800-1000watt units) The MOT units that where placed in these guys weigh about 10-12 lbs and can short up to 23A with shunts! Secondary voltage tends to be 2300-2400V AC.
sparky, Sat Sept 01 2007, 05:05PM
If you want large easily obtained MOTs, try looking for old 1980's early 90's Kenmore, Sanyo or Amana microwaves (800-1000watt units) The MOT units that where placed in these guys weigh about 10-12 lbs and can short up to 23A with shunts! Secondary voltage tends to be 2300-2400V AC.
Re: MOT for Tesla Coil and Magnetic Shunts
Terry Fritz, Sun Sept 02 2007, 04:15AM
Hi,
PIRANHA uses standard MOTs "as is" without modification. It is a complex voltage tripling resonant thing where the circuit "plays" with the shunt's limiting... Maybe a better circuit could be made without shunts... but for now. leave the shunt in for sure
The value of the resistors is indeed "100 ohms"... Lots of modeling there... Those resisters prevent shorting of the whole gap and all... I did a lot of work on that since it killed my coil at first... So until some "Einstein" comes along to knock me out... The resistors need to be 100 ohms...
Cheers,
Terry
Terry Fritz, Sun Sept 02 2007, 04:15AM
Hi,
PIRANHA uses standard MOTs "as is" without modification. It is a complex voltage tripling resonant thing where the circuit "plays" with the shunt's limiting... Maybe a better circuit could be made without shunts... but for now. leave the shunt in for sure
The value of the resistors is indeed "100 ohms"... Lots of modeling there... Those resisters prevent shorting of the whole gap and all... I did a lot of work on that since it killed my coil at first... So until some "Einstein" comes along to knock me out... The resistors need to be 100 ohms...
Cheers,
Terry
Re: MOT for Tesla Coil and Magnetic Shunts
thedatastream, Sun Sept 02 2007, 08:45AM
Thanks Terry, I'll definitely take your advice!
FWIW, my resistors are 101.1 ohms (oh no it won't work!)
thedatastream, Sun Sept 02 2007, 08:45AM
Thanks Terry, I'll definitely take your advice!
FWIW, my resistors are 101.1 ohms (oh no it won't work!)
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