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.
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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."
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.
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).
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!
Parts List: www.digikey.com/short/327wpp