I want to rectify and step up a UK mains supply for a hobby xenon flash project.

I have a good knowledge of the rest of the circuit design, but I want to know more about the power I can get before I start buying components. I am planning on designing the rest of the circuit around the power input I can get.

Most flash tubes have a nominal voltage around 500V so I'm going to have to step up the mains source. I also need a fast recycle (recharge) time, so I need to draw a lot of current.

I considered using a voltage doubler (voltage multiplier) as this will both rectify and step up the supply, but I can't find one with a high enough rated power, and I don't know what components to buy to build one myself that will be sufficient.

I want to charge about 800uF of capacitance rated at 500V in about 1 second. If I am using a voltage doubler, conservation of energy suggests that I will be drawing twice as much current on the supply side, so this is something to consider.

I can draw 32 amps from the mains before I trip the circuit breakers, but obviously I don't want to get too close too this as there will be other devices plugged in to the house running on the same circuit.

Where can I find a suitable voltage doubler, or alternatively, what are the requirements for the components if I was to make my own voltage multiplier? Or alternatively again, would it be better to use a transformer and a full wave rectifier?

I apologise for my lack of knowledge in this area. I was never very good at power electronics.

  • 2
    \$\begingroup\$ The fact that you seem to be guessing at some of the parameters I would strongly recommend against trying to use the mains to power your circuit. Use at least a good isolation transformer. You also shouldn't need such a large value capacitor or current draw, (unless you plan on signaling someone across the pond). Find a known working circuit design (just google xenon flash circuits) and work from there. Working with any high voltage (especially from the mains) requires a great deal of respect and care. \$\endgroup\$ – Nedd Nov 10 '15 at 0:15

I suggest you do a little more research first. I notice that you have not specified the energy your flash is going to dissipate, nor the maximum flash rate you want.

The energy of an 800 uF cap at 500 volts is easy to calculate, right? You've done it, right? You understand that it's about 100 Joules, right? And that this will be a reasonably hefty tube, right?

But let's say we're going to give it a try. You do understand that charging a 500 uF cap to 500 volts is not a great idea, I hope.

With a nominal 40 to 50 joules being provided to the cap in 1 second, I'd suggest a transformer rated for at least 100 watts, and 250 will be better.

Now, if you value your health and do not want to be seen as a candidate for the Darwin Award, you are going to need a transformer - connecting any homebrew circuit directly to mains is a very bad idea. I'd recommend using a 1:1 isolation transformer, and using 230 as your AC. Charging your cap via a full wave rectifier will give you about 350 volts, which will provide a bit less than half the energy of 500 volts, and for photographic purposes will only cost you about 1 f-stop. A 200 to 250 ohm limiting resistor will allow charging in about 1 second.

  • \$\begingroup\$ An old flourescent lamp ballast inductor would be good for current limiting . The type thats used on a switch start 230Vac 40watt 4 foot tube would be a good start. \$\endgroup\$ – Autistic Nov 10 '15 at 3:05

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