Universal Voltronics XRC-60-60N Analog Control

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Dan Knapp
Posts: 385
Joined: Wed Aug 06, 2008 8:34 am
Real name: Dan Knapp

Universal Voltronics XRC-60-60N Analog Control

Post by Dan Knapp »

A batch of the Universal Voltronics XRC-60-60N -60kV, 60mA power supplies appeared on the used market several years ago when Panalytical switched to using Spellmann supplies in their x-ray equipment and sold off their spares. Being negative polarity supplies with voltage and current suitable for fusor work, I suspect that Fusor Forum people snapped up many of these. They still appear periodically on eBay, but at increasing prices; there is one currently listed for $2500. These are very well made power supplies, but the fact that they were built to be driven by a computer limited their utility. If you are able to talk directly to their control processor, you can get 12 bit resolution on voltage and current settings. Their user interface board with a connector on the back, however, has only 8 bit DAC's giving a resolution increment of about 250 volts on the high voltage (OK for x-ray equipment but rather coarse for other uses). Universal Voltronics was bought by Unipower, and they for a while offered a version of the XRC supplies with control knobs and meters on the front panel. This suggested that it should be feasible to convert one to analog control, so I dug into the user interface board and successfully built a simple analog control with ten turn pots for the voltage and current settings. I'm posting the circuit in case others have these supplies and would like to convert them to analog control. The circuit could also be used for homebrewing computer control injecting 0-10V analog signals from a LabView or other interface board. I had not used my supply for a good while and had forgotten that they require a warmup time of ten minutes or so after powering up before the high voltage will come on. I chased this problem for a couple of days before realizing it was operator error. One must wait about ten minutes after powerup before switching on the enable control. I didn't include meters in my control box but added jacks for attaching external meters (more uses for the freebie Harbor Freight red meters!). Converting to analog control or using this circuit for computer control using a more standard interface should make these supplies more readily useable. I hope other XRC owners will find this information useful.
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vlad_klanoff
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Joined: Sun Nov 17, 2013 4:32 am
Real name: Vlad Klanoff

Re: Universal Voltronics XRC-60-60N Analog Control

Post by vlad_klanoff »

Decided to mention one thing that threw me off a bit at the beginning when I started playing with this power supply. From the control box schematics/description I got an original impression that the PS can actually work in a “Constant Current” mode as the control box has “mA enable” and “mA set” controls. So I thought (judging from the control’s names) it’s possible to set a desired current and the power supply will maintain it (basically changing output voltage).
In reality those current controls do nothing for a “normal” fusor operation. Originally the PS will maintain a requested HV current by adjusting X-ray tube’s filament current. More proper name for the “mA enable” would be “Filament on”. As a “typical” fusor doesn’t have a filament, so the current controls don’t do anything useful for a fusor operations.
I haven’t tested this with analog controls, but my PS with a digital control would provide a HV without turning a filament on at all, so those current controls aren’t really needed for this specific application…
Possibly it was clear for everyone except me, but l still decided to mention it to avoid possible confusion…
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