50kV 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.
Joe Gayo
Posts: 123
Joined: Mon Jan 07, 2019 2:34 am
Real name: Joe Gayo
Location: Los Angeles, CA

50kV Supply

Post by Joe Gayo » Thu Jan 17, 2019 10:27 pm

Often you can find a high voltage power supply that maybe has a failed or no driver section. The high voltage transformer and multiplier section is the greatest technical challenge in the power supply needed for a neutron producing fusor.

I used the multiplier section of AHV Glassman supply (https://www.ebay.com/itm/GLASSMAN-High- ... 4055921785) and a half bridge driver.
1291087766_3414_FT101843_glassman.jpg
Example half bridge: http://www.loneoceans.com/labs/sstc2/

The half bridge driver can be open loop control without feedback (i.e. use a potentiometer to control duty cycle, but I keep the frequency and duty cycle constant). I power the circuit with a variac to control the output voltage.

Cristiano_Machado
Posts: 34
Joined: Fri Aug 24, 2018 1:03 pm
Real name: Cristiano Machado
Location: São Paulo - Brazil

Re: 50kV Supply

Post by Cristiano_Machado » Fri Jan 18, 2019 12:43 am

Hello Joe,

Thanks for the information. It is not clear to me how do you connected the parts. Do you have any block diagram? Do you have any schematic of your half bridge?

I am not an expert in HV, but I would like to learn how to assembly this HV source.

Regards,

Cristiano

Joe Gayo
Posts: 123
Joined: Mon Jan 07, 2019 2:34 am
Real name: Joe Gayo
Location: Los Angeles, CA

Re: 50kV Supply

Post by Joe Gayo » Fri Jan 18, 2019 1:31 am

Take a look at this thread for more guidance: viewtopic.php?f=11&t=4852&p=68616&hilit ... man#p68616

I purposely provided information that would require a basic understanding of electronics to complete. Attempting to build a high voltage supply is extremely dangerous!

Rex Allers
Posts: 377
Joined: Sun Dec 30, 2012 8:39 am
Real name:
Location: San Jose CA

Re: 50kV Supply

Post by Rex Allers » Fri Jan 18, 2019 5:25 am

Joe -- Interesting stuff, but for this crowd, maybe a bit more cryptic than necessary.

I'm fairly familiar with the circuits of a few Glassman HV supplies. Never saw this particular one (your shared ebay listing), though.

In your Images du Jour post...

Joe Gayo's Fusor
Sun Jan 13, 2019 7:07 pm
viewtopic.php?f=18&t=12618#p81937

In one of the pictures of your nice, clean fusor apparatus, I thought I saw on one side, a "High Voltage"-labeled white-ish box that looked like a Glassman HV multiplier section assembly. You weren't very specific about your HV supply, but I had assumed you got a Glassman multiplier and built your own driver to feed it. I was interested, but never asked for details.

Is the ebay listing thing the basis of your fusor supply?

The one on ebay has the P/N: AHV1IRT50N06-11, which per Glassman part numbers would be Negative 50kV 6mA, and one ebay picture of the label does say that (-50KV, 6MA). It also says "INPUT 115V 48-63HZ 1PH".

The 50KV top end is higher than many have used for fusion but the 6 mA seems a bit low to start a plasma and sustain fusion. HV switcher supplies typically shut down if current spikes above rated. Is this what you are using succesfully?

The Input spec (115V) on the label seems to imply the ebay box has its own driver section. You shared a schematic image of a typical Glassman multiplier section. As shown, one of these is typically a full-wave multiplier that takes, as input, opposite phases of about 5 KV at a 10's of kHz frequency with a grounded center. Does this ebay box with its 115V input have some driver inside it for making the low KV input to the multiplier?

On the ebay box I don't see any standard AC mains connector. I assume that big circular multi-pin connector supplies everything, including 115VAC and controls.

So, clarifications on the following would make this thread much more helpful.

-- Is the ebay item what you used to make your fusor HV supply?

-- Is there a driver in the box? Did you use it or something different with the multiplier section.

-- Are you monitoring current? Does it exceed 6 mA? If so how do you avoid shutdown? Are the diodes in the multiplier rated for more than 6 mA? The 6mA rating seems low for a fusor.

I'm not saying that there is anything wrong with this post or what you are using, just that you haven't shared many details and factoring what I know about Glassman stuff, I am puzzled by the things above.

Not asking that you should provide exact answers for each of my questions, but I'd really like to hear some clarifications on the themes of my post here and what you have used.

The ebay listing is very cheap if it can really be made to work as a fusor HV supply.
Rex Allers

Joe Gayo
Posts: 123
Joined: Mon Jan 07, 2019 2:34 am
Real name: Joe Gayo
Location: Los Angeles, CA

Re: 50kV Supply

Post by Joe Gayo » Fri Jan 18, 2019 6:21 am

The EBay listing is the basis for my supply. AHV1IRT50N06-11 is only the high frequency transformer and multiplier section. You can see in the pictures I posted that I removed the cover and added a separate custom board. The green board with black electrolytic capacitors (among other parts) is a half bridge driver I designed that runs unregulated at 75kHz and 45% duty cycle.

I control the available energy for the plasma discharge with a variac on the input. (i.e. I start at 20VAC which at open load the output approaches the 50kV, then once the gas breaks down I ramp the variac to supply the necessary energy to support the plasma current. I monitor the output voltage and current using the divider and sense resistor built-in the Glassman multiplier. I learned long ago that the max current can easily be exceeded (For how long, how often? I don't know)

Rex Allers
Posts: 377
Joined: Sun Dec 30, 2012 8:39 am
Real name:
Location: San Jose CA

Re: 50kV Supply

Post by Rex Allers » Fri Jan 18, 2019 7:08 am

That helps.

I ordered one from your ebay link even before I posted to you here. Seems worth it to check out. Good to learn there are HV / HF transformers in there. Those are not common and good ones tend to be expensive if found.

At that price even the diodes and capacitors of the multiplier well laid out seem reasonable.
Rex Allers

Chris Giles
Posts: 46
Joined: Mon May 14, 2018 10:46 pm
Real name: Chris Giles

Re: 50kV Supply

Post by Chris Giles » Fri Jan 18, 2019 8:35 pm

EBay listing ... is only the high frequency transformer and multiplier section
.. although these parts are hard to find, constructing a complete PSU from this is not an easy path for most. It requires quite significant expertise and working with dangerous voltages even on the "low" side.

This post has some schematics from what may be a similar PSU. The input to the stage with the transformer and multiplier circuit consists of:
- a rectifier which converts the line voltage to approx 1/sqrt(2) of that, DC (i.e. dangerous voltage/current)
- a high frequency, high power oscillator which chops the DC to around 50kHz square-wave
- control circuitry, typically uses PWM to alter the control signals (gates) to the oscillator

Note that you cannot use low frequency (i.e. 50Hz) AC on one of these transformers; you need a circuit like the above. An ingenious electronics engineer (like Joe :) ) may be able to hack another switch-mode PSU to use as the driver.

Isn't the current a bit too far off what is required anyway? I wonder it may be possible to pair two in parallel to get higher current but that may require some modification to the output circuit to prevent one sinking current from the other. I will stick with my 30kV unit!

Good luck!

User avatar
Richard Hull
Moderator
Posts: 11549
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: 50kV Supply

Post by Richard Hull » Fri Jan 18, 2019 11:58 pm

As Joe mentioned, the "stack" is the thing. If you have a negative multiplier you are 80% there. The tough stuff is done for you. Provided you are a good bit electronic savvy. There is no such thing as a 50kv, 6ma stack.(multiplier) There is only a 50kv, 6ma "power supply".

Who here, when talking electronics, think they are using 6ma diodes in the multiplier stack. I would imagine 100ma fast diodes are the norm in the stack of a 6ma "power supply". If you have the juice to design the driver, you need not heed the 6ma nameplate on the original driver as it is self- limited based on the manufacturers original driver limitations. We are assuming the 6ma rating is due to the capacitors in the stack being designed to deliver ripple free HV at 50KV, 6ma. You can over drive the stack to 20-50ma with high frequency and still have usable DC with ripple peaking near 50kv or a bit less. No problem...

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Joe Gayo
Posts: 123
Joined: Mon Jan 07, 2019 2:34 am
Real name: Joe Gayo
Location: Los Angeles, CA

Re: 50kV Supply

Post by Joe Gayo » Sat Jan 19, 2019 4:02 pm

All true.

I tested the multiplier at various resistive loads and driver frequencies and at 45% duty (90% interleaved which gives sufficient cross conduction dead-time) I found that ~75kHz gave the best output performance. Using the internal fan of the Glassman stack, 700W is no big deal.

Especially with the SSTC movement all the necessary driver information is readily available.

Dan Knapp
Posts: 281
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: 50kV Supply

Post by Dan Knapp » Sat Jan 19, 2019 7:13 pm

Disregard my question.

Post Reply