How to build multi-low-voltage stacks

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.
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ian_krase
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How to build multi-low-voltage stacks

Post by ian_krase »

The standard fusor just needs a single high to very-high voltage negative-output power supply.

But there are a lot of other instruments in the world (and also, there are ion guns in some fusors) that need a series of low-voltage power supplies... at various different voltages...

For example, you might have a high-current 6 or 12 volt supply for a hot cathode filament, with both ends of this offset to some voltage between 50 and 200 volts, a series of other extracting, separating, and accelerating electrodes at various voltages within 500 volts of ground and each other (all low current), and then the high voltage if needed.

And one wants all of this to be adjustable and reconfigurable on a whim.

Rapp Instruments seems to have a good way to do this (used on his mass spectrometer and beam-on-target reactor), but between the foreign language and my limited electronics skill I don't feel very confident of my understanding of it. I see that you can get reasonably priced DC-DC converters with outputs of 48 to over 150 volts, and all isolated -- would chaining a series of these together be viable?
John Futter
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Re: How to build multi-low-voltage stacks

Post by John Futter »

ian
It is much easier than you think
At work we call this "terminal"
ie a local earth somewhere between 10kV and 12MV away from real earth
Many differnet ways to produce this
The easiet is a car battery, inverter and what you want "local earthed" at terminal voltage.
then motor generator with the shaft made of insulator between motor alternator to produce isolated mains at terminal potential
The least easy is the isolation transformer which go up in price exponetially with increasing voltage

The easiest adjustment method is insulating sticks on the control pots ( I do this up to 140kV) then fibre optic control which needs much more electronics both ends to make a good system.
Blue tooth zigbee are also options--I have done the bluetooth one for controlling an x-ray psu again this is more complex than the other options
ian_krase
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Re: How to build multi-low-voltage stacks

Post by ian_krase »

These sound like great options for high voltages. What about medium voltages no more than 200V? Good all-electronic options?
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Rich Feldman
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Re: How to build multi-low-voltage stacks

Post by Rich Feldman »

Yes, what John said about powering and controlling equipment whose local "ground" is offset by 5 or 6 digit voltages.
Long ago I made (and reported here) an isolated filament supply using the motor-generator approach -- an un-natural coupling between a blender and a cordless drill. One reply included pictures from some accelerator lab, where a nonconducting drive shaft delivered some horsepower to an isolated booth at 500 kV. The booth's metal shell was rounded like an Airstream trailer.

If Ian is just talking about hundreds of volts, or low thousands, ordinary power supplies might come with enough isolation. Look up the specs. They are supposed to pass HiPot testing at the factory.

This fusor thread reminded me that the ubiquitous Ethernet ports for 10base-T, 100base-T, etc. include tiny transformers for galvanic isolation.
8P8C_but_not_RJ45.PNG
8P8C_but_not_RJ45.PNG (82.97 KiB) Viewed 3900 times
In a discussion at https://electronics.stackexchange.com/q ... ly-coupled, one Olin Lathrop says:

Once transformer coupling was decided on, it was easy to specify a high isolation voltage without creating much of a burden. Making a transformer that insulates the primary and secondary by a few 100 Volts pretty much happens unless you try not to. Making it good to 1000 Volts isn't much harder or much more expensive.

"Given that, ethernet can be used to communicate between two nodes actively driven to significantly different voltages, not just to deal with a few volts of ground offset. For example, it is perfectly fine and within the standard to have one node riding on a power line phase with the other referenced to the neutral."
All models are wrong; some models are useful. -- George Box
John Futter
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Re: How to build multi-low-voltage stacks

Post by John Futter »

Ian
I didnt realise you only wanted low voltage ie below 1kV
optocouplers digital and linear ( the linear ones have two Photo transistors one you put in the TX feedback the other for recieve) these do up to 3kV but relatively slow 100kHz max unless very special and expensive
Transformers if you can get away with AC coupling home made with triple insulated wire will get you 6kV isolation easily
Fibre optic link using the cheap plastic fibre
27MHz radio control using servos to control pots etc

There are some esoteric linear ones that go to 10kV using transformer /ultrasonic coupling in DIL 28/ 40 package

Rich
I remeber your Blender beast
ian_krase
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Re: How to build multi-low-voltage stacks

Post by ian_krase »

Yeah, I'm happy for the high voltage suggestions as well. But I'm trying to avoid needing any precision to cross HV boundaries. (maybe just filament heater current)

With thermionic emission much can be done at low voltages.
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