Convert HVPS from Pos to Neg

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Dennis P Brown
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Convert HVPS from Pos to Neg

Post by Dennis P Brown »

Well, after having this for many years - I bought it surplus for $5 (shipping, $10) on e-bay, this working 40 kV Glassman power supply was positive output - so a 'no-go' on a fusor. It claims it can output up to 10 ma but that would only be the low range voltage operation. Still, I considered it useful since in theory one can reverse the diodes and make it a negative supply.

Well, was rewiring the old section of my house and realized that I needed some parts; after thinking on it, I decided that since I didn't want to drive a long way to get the needed parts (local store closed Sunday) I decided to wait till Monday. In the meantime, I decided to start doing one of my long ago projects that is still on my 'other' to do list - i.e. not a "Honey-do" project ;)

So, taking the unit apart - rather easy - I discovered that the diode multiplier is mounted in the open inside a plastic housing! So, luck would have it that switching the diodes will be 'trivial' :) Of course, soldering isn't totally trivial but compared to digging these out of a binder - well, no comparison

Both sides of this assembly has nearly identical cap arrangements (15 kV and 0.015 mfd (7) and just one 8 kV and 0.01 mfd.) I guess after the other project is done this week, I'll finish this one and report on the results - hopefully, still works :) No idea if it can hold up powering a fusor.

I am including various images of the unit and the HV multiplier assembly.

If anyone can pick up an old Glassman for cheap (and working), and its the wrong polarity, well this is a rather easy fix to convert these very old units.
Attachments
Disassembled Glassman Unit (empty HV case on left)
Disassembled Glassman Unit (empty HV case on left)
High Freq. PS circuit board
High Freq. PS circuit board
Diodes
Diodes
One Cap side (all 15 kV, 0.015 MFD)
One Cap side (all 15 kV, 0.015 MFD)
Resister system (no idea why this is required)
Resister system (no idea why this is required)
Cap Odd-ball side (3: 15 kV and 1: 8kV)
Cap Odd-ball side (3: 15 kV and 1: 8kV)
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Richard Hull
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Re: Convert HVPS from Pos to Neg

Post by Richard Hull »

Don't forget to reverse the metering leads.

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
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Dennis P Brown
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Re: Convert HVPS from Pos to Neg

Post by Dennis P Brown »

Oh - missed that completely! That would have been a silly & confusing mistake - thank you, Richard.

So, as I understand this - I need to locate the sensing wires on the circuit board and switch them on the multiplier box inputs. I assume the meter will then respond properly and the system will not cut out due to the opposite polarity.
JoeBallantyne
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Re: Convert HVPS from Pos to Neg

Post by JoeBallantyne »

There was a post from Wilfried Heil back 15 years ago or so, who also reversed the diodes in his unit, and he had a schematic, and in addition to reversing the diodes, there were 3 jumpers he needed to change the state of on the board.

There might be jumpers on your system that also need switching.

See viewtopic.php?p=92967#p92967

And also this one (this is the one I saw recently from about 15 years ago). viewtopic.php?t=4622

The above thread actually has the schematic attached as a PDF. May not be the same unit as yours, but might still be somewhat helpful.

Joe.
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Richard Hull
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Re: Convert HVPS from Pos to Neg

Post by Richard Hull »

If there are jumpers they may just reverse the metering as well. Electronics in some supplies can be confusing. Manufacturers do what they want, sometimes just to confound and confuse aftermarket alteration. (keep the money in shop)

A good design should be simple. Make a fully controlled high frequency switcher to pump RF AC out. Next, make a rectifier/multiplier system as a separate board. Finally, make the metering a simple electrical hookup to the output. There is little need for grossly complex electronics beyond making the customer appreciate the $$$$ they have to pay for the supply. Most of the complex electronics are devoted to various current limiting and shutdown electronics, RS232, GPIB, USB control, or other computer apps so loved by modern users. This is sometimes important as less than adept people might be using the system. Add a few more $$$ for dunderhead protection.

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
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