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Need a BIG 10kv DC supply

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LAN_403

Electra

Fri Aug 07 2015, 10:38PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
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Posts: 156

Don't understand much about the electron beam process your using it for, But how well regulated does the supply have to be? Couldn't you manage by controlling the primary side. If your using something like a 3 phase inverter / VFD, perhaps find one that you can get the schematics if you need to modify it, or preferably has provision for an external input to control voltage. On the secondary side a little circuit with a divider amplifier and opto coupler to give the feedback, you might have problems with the feed back loop oscillating if you have too much gain.

While a linear regulator is simple in concept, scaling things up to the power levels you need is a project in itself, also you have to design over current and thermal shut down circuits.
I seen a picture once of a big laser power supply, that used what was probably getting on for a hundred power transistors on a massive heatsink, presumably this was a regulator.

macona

Sat Aug 08 2015, 06:54AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

It needs to be pretty stable otherwise the beam will wander.

You can adjust the voltage output on the VFDs, at least most of them.

Yes, old ion lasers used massive pass banks of 2n3055s.

There are already voltage dividers onboard for monitoring the output voltage. If I could find a 3cx10000A7 I could just turn into a tube controlled supply as it was designed. I would have to remake the control board for the tube but the schematics and drawings are out there so it would not be a big deal.

Hydron

Sat Aug 08 2015, 03:06PM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

macona wrote ...

I know a guy who designs VFDs and he thinks it will be fine. Here's hoping! The windings should be OK, each winding section is epoxy impregnated.

Otherwise I will be rewiring the primaries to run in parallel and have to add a whole bunch of bulk capacitance.

I got the thing mostly re-wired. I dont have the 3CW-20000A7 tube or even a smaller 3CX-10000A7 so I am going to have to come up with a different voltage regulator. Thinking of trying to stack a bunch of mosfets. I have a w whole bunch of APT24M120L 24A, 1200v mosfets

to mess with. Capacitively couple the gate and cross my fingers. I have about 50lbs to play with:

Not sure what you mean by capacitively couple the gates and cross your fingers, but you might be able to build a regulator circuit with a whole lot of cascaded mosfet based regulators with opto-isolated control (maybe using something with linear response like this:

).

Would be complicated though, and watch the SOA of your mosfets - they may have big grunty switching ratings but at 1A continuous drain current they can barely do 100Vds (you may be better with stone age TO-3 BJTs or something more suited to linear region operation).

If you did do something like this I think you'd want most of the gain before the optos, otherwise the cascaded stages wouldn't share well.

macona

Sun Aug 09 2015, 04:28AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

I noticed the current handling characteristics after I posted. Not good.

I was thinking of doing a pwm output using something like a SG3525 to run as a CV power supply. But then I would need a output inductor too.

I am trying to find the tube for it. Not a cheap tube! I might just have to rethink my plans in general on this.

macona

Mon Aug 10 2015, 04:17AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

I hooked up a 3hp VFD to the 10kv, 1.4A transformer in the partiall gutted electron beam power supply chassis after I rewired it according to the schematic. It actually worked, I did have to up the PWM carrier frequency on the VFD from 10 to 15khz, at the lower frequency it was drawing way too much current. The output is a little low, no load it should be around 12.5kvdc and it is actually outputting about 9.5kv. If I use the 208v tap I can probably get it to 10kv. It does overload the VFD after about 30 seconds which is no real surprise, this was mostly a proof of concept.

I am not sure how much further I am going to take this on this supply. It does seem pretty stable, staying within +/-50v of 9.5kv but I have no idea what is going to happen when I put on a real load. I can probably sell the vacuum relays out of this to people that want to make flux capacitors and buy a complete power supply off ebay... ï»¿

Temescal CV-14 hooked to a VFD by Jerry Biehler, on Flickr

macona

Fri Aug 21 2015, 06:21AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

So, I have scrapped the idea of getting this supply running for the e-beam gun. Finding a tube has been very difficult so I picked up a Thermionics EBPS15, 15kw, tetrode electron beam power supply to do the job, it is good for up to 10kv at 1.5 amps. It uses a 4CX15000A tetrode for regulation. I got the power supply itself from a guy in Tennessee and the control box for it from BMI Surplus. Thermionics was able to supply me with a very complete manual so I should be able to get it going.

I do need to make the interconnecting cables and the filament transformer box. It contains the SCR controller for the filament transformer, the current sensor, and the filament transformer. Lucky for me the details of the operation of the unit are very complete and was able to figure out how to build it. I had a hall type current sensor from one of the old chassis that I picked up in california that will work for feed back and I can use the Airco filament transformer I picked up earlier. The controller uses the current sensor to detect emission current and then sends a 0-10v signal to the SSR module to control the power to the filament which limits emission. I picked up a Eurotheum 425A SCR controller off ebay which is rated for transformer coupled loads so I should have everything I need.

The control box showed up today and the power supply was picked up by Yellow Freight today and is on it's way. New price on the power supply is about $40k, with the control box and shipping it is all coming to about $1200.

Strapped down and ready to go:

Thermionics EBPS15 by Jerry Biehler, on Flickr

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