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wiring 4 mots for 240

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sparky

Sun Feb 25 2007, 07:15AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

usually I have 500nF 5kV worth of MOT caps on either side of my quad pack. Thats 2 X 1uF 2500V rated MO caps in series. Still the current is stiff at 26.5 A - 240V service.

sparky

Tue Feb 27 2007, 03:47PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

4 120V -MOTs in series/series arrangement for 240V - 9.6kv output

jameselectric

Tue Feb 27 2007, 08:10PM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

well i tested my 4 mots of various sizes. I put 120 to the sec and measured the pri. All the voltages were 6. wich gives me a 20:1 ratio rating each mot at 2400 vac. Is this an accurate way of measuring a mot. I will wire all 4 for 240. I will try running unbalasted. I am going tomorrow to pick up more caps. here's a dumb question, I understand what happeneds to capacitance in series or parrallel but what happens to the voltage rating. I'm also thinking of a voltage doubler.

sparky

Thu Mar 01 2007, 07:26AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I too use the same method to measure potential output of the transformers - adding voltage to high voltage side of MOTs is a great way to get an accurate reading for secondary to primary ratios.

Adding secondary side MO capacitors tends to increase the voltage slightly due to capacitive inductance - If memory serves me correctly I think my 4 pack with MO caps on the secondary side was a constant 11.5 kV start - drop to 9-10 kV under load.

Just a suggestion that you might find useful:

Running a quad pack unballasted means that you will need a large power outlet, preferably one rated at 240V/40A or larger. I tripped my 30A breaker after very short runs - so I went with a 50A range outlet. Current draw was 42.5A at peak.

jameselectric

Thu Mar 01 2007, 08:04AM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

first light.

Tonight i finally got my stuff together.
2 mots wired for 120. 120 in 2400 out
2 caps ballast rated at 2 kv .955Mf on the hv side
spark gap.
4 caps at 2kv at .250Mf wired in series ( tank cap)
2 diodes for voltage doublers

I still think i do not have enough caps, i also have 2 mot caps left.

Any tips on how to optimize this system?

sparky

Thu Mar 01 2007, 06:52PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

jameselectric wrote ...

first light.

Tonight i finally got my stuff together.
2 mots wired for 120. 120 in 2400 out
2 caps ballast rated at 2 kv .955Mf on the hv side
spark gap.
4 caps at 2kv at .250Mf wired in series ( tank cap)
2 diodes for voltage doublers

I still think i do not have enough caps, i also have 2 mot caps left.

Any tips on how to optimize this system?

For a first run I'd limit the power to 1600-1800 VA to start. Put those extra Mo capacitors in series with the diodes- that way you have 4 MO caps running 800-900 watts on either leg when you short the transformer. You may also want to make a visit to Greg Hunters website: He uses charging chokes which recycle the power very quickly through a Tesla Coil circuit - you may want to look into this :)

jameselectric

Sat Mar 03 2007, 08:08PM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

first light.

I fired her up tonight. tuning was about 3 or 4 turns out. good spark gap operation. topload was a large deep dish pie pan. I played with the cap and settled on about 58nf. I did have to submerge the transformers in oil as i wasted 2 by shorting out the secondary. i also added a third mot as a ballast on the primary side. performance sounded good but visually i only got about 1/8 in sparks of the toroid.

sparky

Sat Mar 03 2007, 09:16PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

jameselectric wrote ...

first light.

I fired her up tonight. tuning was about 3 or 4 turns out. good spark gap operation. topload was a large deep dish pie pan. I played with the cap and settled on about 58nf. I did have to submerge the transformers in oil as i wasted 2 by shorting out the secondary. i also added a third mot as a ballast on the primary side. performance sounded good but visually i only got about 1/8 in sparks of the toroid.

You will loose BIG power by shorting a MOT across the primary. Don't do it... simply run the MO caps 2 in series each leg and that wil provide more than enough current control for your first light. Also run the tesla coil with a very small top load first then gradually increase the size and increase the turns on the primary. This way you'll find the sweet spot on your tesla coil...

jameselectric

Wed Mar 07 2007, 04:25AM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

fired up the coil tonight. It will light up a flourescent light like nothing about 6-7 feet away. I can only draw about a 3 inch spark though. what is going on.

...

Wed Mar 07 2007, 06:00AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Most likely you are out of tune. Try changing the number of primary turns and see how it affects the spark output.

It is also possible that you spark gap isn't quenching properly, putting a vacuum or leaf blower sucking/blowing across it can help that.

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