Need a BIG 10kv power supply

[macona]

OK, I will give the MOTs a try. There seems to be a lot of talk about the risks of the transformers breaking down but I have not seen a report of one actually breaking down. I have a whole bunch of 1/2" acrylic sheet I can mount them to and then stick that in a box made from the same. If I have to I could fill it with mineral oil.

I suppose I could also put some MOVs across the lines feeding the transformers with some sort of ground fault detection to kill the supply and crowbar it. If a transformer shorts to one of the primaries it ought to try to go to ground since the positive of the supply will be tied to ground.

I wonder if it will be fine to run it off of 240 instead of using a 240 to 480 transformer, that is a pretty sizable transformer at 6+kw.

Now I need to find some 8GA wire that can handle 10kv, the filament on the e-beam gun runs at 6-8v @ 40A.

[planters]

I don't understand the concern about these MOTs breaking down. They are robust and if good when delivered then use them at or below spec and they should last a long time. I suspect that some experimenters will try to series the secondaries and not the primaries and attempt to exceed their 20:1 step up. You don't need oil. Just space each MOT at least 1/2" from its neighbor and you will be several times further than breakdown in air.

The issue with 240 vs 480 is that the 20:1 ratio needs 480 or you will need to exceed the rating of the MOT. Then, you might get into trouble.

http://www.mcmaster.com/#high-voltage-wire/=xl5m1q

I actually like the left hand wire better if the gauge is right. It just handles better.

[macona]

Ahh, I see what you are saying about the 480. But in the scheme of things thats just another 240v of differential. I would do a series-parallel setup.

Egad, $8 a foot! Better make sure I mount the filament transformer close! Oh, wait, with silicone I dont need as heavy wire. Lucky...

[planters]

Ahh, I see what you are saying about the 480. But in the scheme of things thats just another 240v of differential. I would do a series-parallel setup.

I'm not sure what you mean. If each MOT is operated within spec and so @ 120V AC then 4 MOTs in series will split the 480V AC input. Their series output will be 9600V AC. This can then be rectified or as I have done, used this AC to drive a voltage doubler.

http://www.allaboutcircuits.com/text...e-multipliers/


I also paralleled two strings of these MOTs to split the load and reduce heating.

If you want to save some money you can run some conventional wire within silicone tubing or even vinyl tubing. Isopropyl alcohol makes a nice lubricant for inserting and leaves no residue.

[macona]

I was thinking the primaries of two MOTs in series and then two sets of those in parallel so they all are running at 120v on the primary, assuming even loading.

Not worried about the wire, it is be about $50 for 10 feet so no worries there, that should be enough to connect the filament to the transformer.

[planters]

I was thinking the primaries of two MOTs in series and then two sets of those in parallel

How do you achieve the 10kV with the two 4,800V pairs? Do you use a doubler like I linked to?

[macona]

Only the primaries are in series/parallel. The secondaries are all in series.

[absolom7691]

I suspect that some experimenters will try to series the secondaries and not the primaries and attempt to exceed their 20:1 step up.

This is why my stack is in oil. Parallel primaries and series secondaries. That's also why I have my 6 secondaries "center tapped", 3 on each side of ground. Still no mishaps in over 10 years. Then again, I'm probably only running them at about 400~500mA. I'm not pushing them too hard.

[planters]

That's also why I have my 6 secondaries "center tapped"

This is also why I stayed away from NST's. I need one polarity to be tightly coupled to ground. I'm using huge energies. The cathodes on my lamps need to be safely grounded to isolate the gas handling from high potential. The pump chamber also has to be grounded to protect the user from stray voltage.

The problem with the oil technique is that if a transformer fails due to over voltage, it is more likely an internal arc over and I'm not sure about the oil penetration between tightly wound components. Also, if a MOT fails in this bath how do you diagnose it and moreover fix it? I suspect this would create quite a mess.

Step up transformers can be positively huge and are inexpensive (relatively). Furthermore, You can pursue this staging much further.

http://www.ebay.com/itm/50-KVA-1-Pha....c100005.m1851

I also saw this. Just saying.

http://www.ebay.com/itm/ISOREG-41031...=LH_DefaultDom

[absolom7691]

My problem with NSTs was that they were just too fragile. Even with a safety gap, I burned through a couple. They are a horrible choice for anything demanding, much less, a Tesla coil. One secondary out of the two would always fail.

I can imagine that the equipment you're running would need very stable and clean power. For a Tesla coil, it doesn't matter too awful much. I have never had an MOT fail yet but you're probably right, the oil bath has probably done little to protect them. At the time I built it, I think I was more interested in how it looked, over the function. The Tesla coil group I was in a long time ago ended up turning into a #$@& waving contest so.... If I had it to do all over again, I'm sure I would have gone a more practical route.