# Tech Forum

March 2017

### Getting Started With High Voltage

I would like to experiment with high voltage projects, but all my experience in building power supplies is for low voltage (typically 5 or 12 volts). I’d love a schematic for a high voltage power supply that could produce between 0 and 250 volts safely. Also, any safety pointers for getting started would be appreciated.

#3171
Ed Warren
Everett, WA

It is my understanding that "Variac" type transformers do not provide isolation from the input power. They are basically tapped coils. In order to safely provide isolation they must be connected through a 'true" transformer. Depending on output stability requirements, you may be able to use a Cockroft-Walton voltage multiplier circuit through an isolation transformer. Check Wikipedia for "Cockroft-Walton" and "autotransformer."

Bay Saint Louis, MS

You want to be extremely cautious experimenting with high voltages as they are lethal and can be fatal. Rather than trying to construct a high voltage supply, which could be dangerous, you might consider a variable transformer such as the Volteq #1KVA_110V/250V (www.volteq.com), which costs about \$70. This transformer plugs into a standard 120 VAC outlet and provides an adjustable output from 0 to 250 VAC, and provides isolation from the AC power grid. If you want DC voltage, you can construct a simple bridge rectifier circuit. However, there are many more interesting projects that use 5 - 12 volts, and I suggest you pursue some of them instead.

Bob Stewart
Mancos, CO

Correcting Bob Stewart's answer: The variac he mentioned "VOLTEQ 1KVA VARIABLE TRANSFORMER VARIAC 1000VA 0-250V 110V INPUT" does NOT provide insulation from AC, as confirmed by Volteq. I suggest connecting such a variac only to an outlet with a Ground Fault Interruptor (GFI).

Oskar Leuthold
Santa Cruz, CA

You didn’t indicate how much current you are expecting from the supply? Searching the internet I found the referenced schematic for a 300 VDC variable voltage supply that will deliver up to 100 ma. Circuit is for 220 VAC mains but we can substitute a step up transformer for operating with a 120 VAC mains. I have attached a parts list reference from Digikey that should do the trick. Due to the high voltage involved, you should put the components inside an enclosure, such as a Bud Industries box and bring the output up to a couple of banana type jacks or terminal block. You can also mount the pot on the outside of box and add a knob to it. Transformer is the most expensive component and can be sourced from other suppliers if you need to reduce costs. Hope this helps!

Doug Foreman
Warren, MI

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