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For my first thread, an extreem mot power supply !

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LAN_403

Vigh holtage

Sat Dec 09 2017, 01:55AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
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Posts: 44

Ok guys this is my first thread here but no stranger to you tube, anyway i built a huge 4 pack mot power supply all self contained in a big mark 19 grenade launcher ammo can !

I am looking for some help basically judge it and let me know what you think and if i am on the right track with balasting .

Any help on a suitable balast that will handle 4 kva or more and not over heat ? I thought of 2in pvc filled with an iron bars and wrapped in 250ft 12g wire or even 2 mot E cores and 4 primary windings ?

Vigh holtage

Sat Dec 09 2017, 02:03AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
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Posts: 44

Ok here are the videos on my youtube channel explaining everything and drawing arcs!!!

Vigh holtage

Sat Dec 09 2017, 02:28AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
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Posts: 44

Here is the begining of the build, i may run it balasted at 15-20 amps and full wave rectified to 13,000 vdc into a smoothing bank then 4 to 5 charging chokes of around 5 henry each with decoupling diodes and an asynchronous rotary gap.

End result should be around 26,000 volts into the tank capasitor !!!!!

profdc9

Sat Dec 09 2017, 11:52PM

Registered Member #58522 Joined: Tue Mar 15 2016, 08:33PM
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Posts: 50

A higher voltage primary may not necessarily be better. I built a switching power supply for my Tesla coil that produced 30+ kV and it was very difficult to prevent the RF spikes from feeding back into my transformer and destroying it. Preventing arcing from primary to secondary was also more difficult as well. I was using a custom ferrite transformer, but any diodes in your voltage doubler might be damaged by RF spikes. Something to consider. Each of the MOVs I used is rated from 1.4 kVDC, so you'll need 20 or more of them in series to absorb the RF spikes, as well as a very high voltage cap bank for a Terry filter if you decide to use one. You will also need higher voltage primary capacitors, but a lower capacitance, and a higher impedance primary in general, so you will end up getting the same voltage on the secondary anyways. There may be less spark gap loss though with the smaller current with the higher voltage, but it seems to me once one has 10 kV or more, the spark gap can fire fairly reliably and higher voltage is probably not going to help that much.

Dan

Vigh holtage

Sun Dec 10 2017, 01:14AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
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Ok so i suspected as much anything over 20 KV is probably just too difficult to insulate and deal with.

I have (10) 20kv 2a diodes, and (100) 1kv 6a fast recovery diodes FR607 's soo...

My secondary idea was to just connect a full wave rectifier to a smoothing Bank for 13.5kv ish, and run that to an asynchronous Gap but ... I am not sure how the parallel smoothing Bank before the asynchronous gap will affect the series connected tank capacitor.
I'm not sure if the Transformer will see the Gap firing into the tank cap as a short circuit.

If this doesn't work out then I can still full wave rectify it which would provide me with 13.5 KV of 120 hertz pulses which is a reasonable voltage at twice the line frequency which would allow me to still use a synchronous rotary Gap
I have (4)1/2 horsepower induction Motors from polishing machines, these run at 3450 RPMs and can be modified with just two Flats to be synchronous at 3600 and I have four to play with , along with three 1500 W vacuum motors for an asynchronous gap

Lastly i can just push the 9800 vac into a multie static spark gap if all else fails but that would mean a massively expencive maxwell 100 nf pulse cap and be difficult to quench. I only have a 20nf 45kv maxwell to play with, i could add an mmc in parrallel i guess but still cost prohibitive, (10) 12nf bucket caps in parralell mabey roflao ???

I am a machinist so i have acsess to infinity 1/4 shank tungsten bits that are dull and no longer get used, they have 2inches of perfect shank on them so i cut them to 2in and bring them home, i can machine any kind of gap nessasary for this

Aso i will be pouring the oil tomorrow to cover those mots, i am going to use generic full synthetic motor oil that has a light wieght and will be thin not thick and viscous, i may actually add mineral oil in a 1:1 ratio to make it even thinner so it can get in and between everything if nessasary.

This transformer will be painted nicley and be a permanat fixture in my lab wich is half my basement , so i want it done RIGHT form the start. 13.5 kv dc pulsed, or smoothed dc, or 9800 vac and it must be compleatly self contained in that grenade launcher ammo can, balast and all, so all i have to do is run cable to a spark gap mounted in a base with a tank cap and the coil on top, or just hook it whatever HV crap i dream up.

I do also have a 15kv 120ma nst bank with emi protection, filtering, and pfc, but that is part of a dedicated AC tesla coil i bring to the high scool for demos so i dont use it for anything else period, i cant risk frying an expencive nst bank for my hobby experimenting and then not even be able to run my demo coil as a result ! That is why i am building this supply, i can get mots at my salvag yard for 5$ a piece ! They have a huge bin full so replacing a fried mot is kiddy work, replacing a 15kv 60ma nst or 2 is out of my budget !

profdc9

Sun Dec 10 2017, 03:03AM

Registered Member #58522 Joined: Tue Mar 15 2016, 08:33PM
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Posts: 50

I think your idea of using 4 MOTs is a good one. I am using 2 MOTs with doubler because I don't want to have to worry about arcing from the secondary of the MOT to the primary and have to cover it all in oil. That makes me a little nervous, but others seem to have done it successfully and certainly you can get a lot of power that way.

I just built a static spark gap with two tungsten rod gaps, 1/4" rod diameter. I think especially for that much power you will need an extremely strong blower to keep the gap cool and quenched. I could not get it quenched correctly and I was thinking of buying a cheap electric leaf blower to blow on the gap! Rotary gap sounds like the way to go. I have read that for very high power like pole transformers, a static gap is added in series with the rotary to help quenching as well.

For 60 Hz rectification I have used microwave oven diodes in series (4 of them) but for switching power supplies I think you need a fast 100 ns-type diode. I have used UF4007 in series and it works ok. I have two-part epoxy I bought from Amazon in a big container and I insulate using that.

Why are you using smoothing? Does it help make the arcs longer? It might make the pulse energy more even I suppose, rather than peaking in the AC cycle. You won't get the 60 Hz buzz to the arcing, which may be an advantage or disadvantage.

I do not think you can use iron bars for a high permeability core for an inductor, because the eddy current losses are too high. This is why laminated steel is used in transformer cores, because it is a high permeability but the flux loops are broken by the laminations to minimize the eddy currents.

Anyways that is nice work. Make sure the ammo can case is safety grounded!

Dan

Vigh holtage

Sun Dec 10 2017, 08:27PM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
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Posts: 44

Smoothing rectified mots make compleatly insane and deady powerfull blue arcs that hummmm and growl at you !

Its compleatly unnessasary for a tesla coil that uses a syncronous gap but with an asyncronous gap it will fire at any rpm because there is no space in between pulses.

I have about 4lbs of 1/4 tungsten carbide and (4) 1/2 hp induction motors i can make syncronous soo....

I want to know if i should just leave it 9800 volts ac and go multie gap / sync gap combo

Or

Rectify it and sync the motor to the unsmoothed dc pulses, ether half wave 60hz or full wave 120hz

And has anyone rectified and smoothed a tesla power supply for asyncrous operation.... i know the charging choke design stores energy as a magnetic field and acts like a smoothing cap / doubler, i dont want to use a charging choke though because i do not want to double the 13.5kv comming out, hence the smoothing cap as an energy storage device to replace the charging choke doubler.

Vigh holtage

Tue Dec 12 2017, 01:51AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

Here are some arcs with a 9.6 mh balast installed,

After balasting the voltage dropped from 9800 to just over 8,000 and short circuit current measured 18.5 ma at 12vac soooo 185 ma at 120vac

1513043472 61739 FT180951 20171211 194252

1513043472 61739 FT180951 20171211 194325

Vigh holtage

Sat Dec 16 2017, 01:20AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

Okay here is the capacitor bank for my voltage doubler circuit it consists of 15 microwave oven capacitors wired in a series of three and 5 strings in parallel this gives 1.5 microfarad and I can probably handle around 15 thousand volts maximum, I'm going to use the typical microwave oven doubler setup using a 20000 Volt 2 Amp diode

1513387226 61739 FT180951 20171215 201204

1513387226 61739 FT180951 20171215 201228

GrantX

Sat Dec 16 2017, 07:54AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Is there any insulation between the metal cans of each capacitor? If they're in direct contact you might have a risk of internal flashover once the voltage is high enough. I'm not sure how much internal clearance they have around the terminals and can, it might be fine, or you might kill a whole string.

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