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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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.
- XRC Analog Controller.Rev3.pdf
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