Max's High Voltage Supply

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Post Reply
MaxfieldFrancis
Posts: 20
Joined: Wed Sep 01, 2021 9:22 am
Real name: Maxfield Francis

Max's High Voltage Supply

Post by MaxfieldFrancis »

After much trial and error I believe I have constructed a supply that is up to snuff in regard to powering a functional fusor. I have a variac running current through a rectifier, which is powering a ZVS driver. The low voltage high frequency is then stepped up by an ignition coil that drives a voltage multiplier.

The supply managed to create some enormous arcs. I measured them reaching up to 7 cm. I have measured my output voltage and am seeing at least 30kV out @ 25v-30v 20 amps in. Today I will be working on fixing the ZVS driver's cooling system as well as using a Kill-A-Watt meter to verify that I am supply ample power for fusion. The system has yet to be pushed past 40v input so I am optimistic.

Please let me know if there is anything I have missed.
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: Max's High Voltage Supply

Post by John Futter »

max
I'll be surprised that you can get enough power through an ignition coil you need at least 200 watts of power at better than 30kV continuous
ie 6mA 30 kV. Most successful fusors here have current capabilities in the 20 to 40mA region.
Measuring input power to yoursetup is not going to give you anything useful except that the output power is going to be much less
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Max's High Voltage Supply

Post by Matt_Gibson »

I’d ditch the ignition coil and go for a few very beefy flyback transformers. I think that Mark Rowley pretty much pioneered this :-) Look up what he did. I’m pretty sure he’s using a zvs driver also.
MaxfieldFrancis
Posts: 20
Joined: Wed Sep 01, 2021 9:22 am
Real name: Maxfield Francis

Re: Max's High Voltage Supply

Post by MaxfieldFrancis »

Originally the ignition coil was going to be a temporary "burn it up and toss it" sort of solution, however this coil has held up quite well. They can be pushed at surprisingly high voltages. My variac supplies up to 2 kW and I highly doubt I am losing 90% of my power, but its better to verify it than just guess. I am waiting on a high power bridge rectifier to arrive on Wednesday, then I will be measuring the output current on the high voltage side of the power supply.

I am on the lookout for better transformers. I did see Mr. Rowley's system, I may take some ideas from that. Thank you for all the help. I will update everyone later this week when I can test the output current.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Max's High Voltage Supply

Post by Richard Hull »

I have always been against ignition coils. Their advantage is that they are intrinsically unsaturable with a super heavy gauge primary winding. This means if you have the input energy and limit your frequency with some coils, you might do an interesting 30-40kv fusor. Accel racing coils are famous for being beefy and expensive but a close look at them might be in order for those at the lower end of fusion who have the chops and desire to monkey with them. These are not your Dad's old ignition coils!

https://www.summitracing.com/parts/acc- ... KIQAvD_BwE

Make sure to click on the "more info" specifications on this coil. A 0.7 ohm primary would burn out most points on a car and they supply a special ballast resistor for the primary circuit in the car. You will not need this as you have no points to burn up, only your drive circuit is needed to be beefy!!! Classically, a 6000rpm, an 8 cyl. race car, at red line, would pulse this puppy at 48khz. Even at a struggling idle of a radically cammed race engine of 2000rpm you are at 16khz. As the coil is expected to handle this, fusion power filtering might be easy with a good driver circuit.

Now to the secondary: Ohmically, it is in the 11K ohm level and 300 watts out would mean the base secondary current would be 300 = I^2 X 11,000. Meaning about 17 ma continuous would have to be produced by the secondary at what ever voltage it could muster. 300 watts into a stable fusor load at 30kv would be 10ma for a fusor impedance load of R= E/I = 3megohm load. This is light loading related to the coil if you can hold the voltage up to the 30kv level. Naturally there are all manner of issues related to the supply coil being reactive and not purely ohmic. The load is horribly variable and ohmic in a fusor, as we all know. As such, a supply output ballast resistor may or may not be needed in a successful coil supply.

The key for the would-be experimenter is to have a real ohmic load of about 3 megohms that could absorb 300 watts to act as a test bed for a voltage and current curve related to performance of their effort. One would also need and a bag full of Harbor Freight $7.00 DVMs and a good DSO to play the game intelligently.

I would not fiddle with more than a doubler on the output under load, but would, first, try a simple direct full wave system. In the end, if you have to put in 500 watts at15-20 volts pulsed, (25 amps or more) to get 300 fusion watts out and the coil can take this for some suitable run time, you are in the fusion biz.

Still other issues are grounding. Never forget grounding as all ignition coils are auto-transformers. Guys with the chops who are also fusor guys, to do this, will figure out what I mean here. Nuff said.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Max's High Voltage Supply

Post by Matt_Gibson »

One drawback to those ignition coils could be the secondary resistance and the I^2R losses, no? Maybe a few in parallel (Like what Mark is doing with his beefy flyback style transformers) would work out pretty decently?
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Max's High Voltage Supply

Post by Richard Hull »

Re-read the post as I have been adding to the first pass until the moment I hit send here. (approx 1 hour!) Paralleling is an option related to IR losses, as you suggest.

Paralleling is possible with auto-transformers but make sure the primaries have the minus or base of the secondary coils are connected properly. As I note watch the supply and system grounding here. The beauty of paralleling is you might not need to double or triple the output of the coils for lower end fusion work.

The draw back might be you can't operate at 70khz like flybacks.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
MaxfieldFrancis
Posts: 20
Joined: Wed Sep 01, 2021 9:22 am
Real name: Maxfield Francis

Re: Max's High Voltage Supply

Post by MaxfieldFrancis »

Sorry for the very late reply. I decided to take your advice and bite the bullet and purchase a proper ferrite core transformer (1:625 turns) from amazing1.com. Right now the supply seems to be pretty much completed, I just need to put a resistor between the wall and the variac to stop the variac's fuse from being blown. It blows at 55v so Im only getting 27 volts (variac output is halved from rectifying) into the ZVS driver. If I can get 60v into the ZVS driver I could theoretically get 37.5 kV out of the transformer, obviously that doesn't take losses into account, but it is still more than I think I need. Later on I may try parallel ferrite autotransformers, but Ill save that for after I have completed my reactor.

I have acquired a chamber, flanges, a feedthrough, and a turbomolecular pump. I also have the supplies for deuterium electrolysis, so I believe I am nearing completion. I hope to test my fusor on April 1.
User avatar
Joe Gayo
Posts: 404
Joined: Sun Jan 06, 2019 9:34 pm
Real name: Joe Gayo
Location: USA

Re: Max's High Voltage Supply

Post by Joe Gayo »

I don't know what ZVS driver you are using, how many turns you have on the primary (remember faraday's law and make sure the core isn't saturating), or the VA rating of the variac, but the behavior you mention could be troubling.

Here is a ZVS driver I designed/built/tested many years ago that decouples the input for the high-frequency transformer from the MOSFET gate drive to allow for higher voltage and more robust operation.
HV-ZVS.PNG
MaxfieldFrancis
Posts: 20
Joined: Wed Sep 01, 2021 9:22 am
Real name: Maxfield Francis

Re: Max's High Voltage Supply

Post by MaxfieldFrancis »

Thank you Joe! I'll look into your ZVS design. I have 4 turns on the primary. I believe I will need a ballast resistor on the transformer, I found a 40k ohm wirewound resistor for a decent price on ebay.
Post Reply

Return to “High Voltage - Fusor Input Power (& FAQs)”