# How fast can relays get?

I am in need of a really fast relay, and I was wondering what the state of the art for DIYers is? (Microseconds or preferably nanoseconds would suffice)

Can't use a mosfet or triac?

As long as it acts as a switch, I don’t particularly mind.

AC or DC?

DC, but at very high voltages and low current (between 30-50 kilovolts, and only a couple of milliamps)

I think it may be very tough to get anything that fast for those voltages. Sorry I can't be more help. I SSR is probably around 750µs response time. Probably not fast enough for you.

Regardless of the voltages I need for my purpose, how quick could I (as a hobbyist) get a switch to act (with a budget of around \$500 for the switch)?

I've seen some high voltage relays/mosfets but never that high, can you switch the supply to the high voltage source instead? That'd be alot easier

winner10920: I've seen some high voltage relays/mosfets but never that high, can you switch the supply to the high voltage source instead? That'd be alot easier

I'm not sure I follow? The circuit is high voltage but the switch can operate on a voltage as low as possible (I basically want to switch from ground to nothing very quickly).

The max vgs for mosfets or the max voltage for relays usually aren't that high, I've used a nchannel mosfet that can control up to 120v with 3v trigger, but if im interpreting it right you want to control 50kv off say 5v, I don't think you can directly for cheap maybe a circuit diagram can clear some things up?

What's the application? If you need pulses of 50kV at a few mA, it's easier to generate pulses at a lower voltage and step them up using a transformer. If you need to interrupt an otherwise continuous 50kV supply, you could derive the supply from an inverter and switch the inverter off to interrupt the supply, if you don't mind the supply taking a few milliseconds to turn on and off.

Narwhal: DC, but at very high voltages and low current (between 30-50 kilovolts, and only a couple of milliamps)

You need a thermionic or cold-cathode valve, nothing else will cope with fast switching of that sort of voltage.

dc42: What's the application? If you need pulses of 50kV at a few mA, it's easier to generate pulses at a lower voltage and step them up using a transformer. If you need to interrupt an otherwise continuous 50kV supply, you could derive the supply from an inverter and switch the inverter off to interrupt the supply, if you don't mind the supply taking a few milliseconds to turn on and off.

I am doing an experiment that involves the timed switching of ground terminals before the charge reaches the terminal (making it go in a circle until it runs down the voltage due to resistance). I need the high voltage for other applications, but a big plus to it is the electrostatic field it generates on uninsulated wire allowing me to measure it during the process.

Obviously the charge is going extremely quickly, so a switch with around a 100 ns response time would be good.

Narwhal:

dc42:
What’s the application? If you need pulses of 50kV at a few mA, it’s easier to generate pulses at a lower voltage and step them up using a transformer. If you need to interrupt an otherwise continuous 50kV supply, you could derive the supply from an inverter and switch the inverter off to interrupt the supply, if you don’t mind the supply taking a few milliseconds to turn on and off.

I am doing an experiment that involves the timed switching of ground terminals before the charge reaches the terminal (making it go in a circle until it runs down the voltage due to resistance). I need the high voltage for other applications, but a big plus to it is the electrostatic field it generates on uninsulated wire allowing me to measure it during the process.

Obviously the charge is going extremely quickly, so a switch with around a 100 ns response time would be good.

25kV on uninsulated wire is going to cause corona discharge and flash-over - I’m confused, electrostatic levels of voltage are not as easy to measure as low voltages, yet you seem to imply they are necessary. If you can avoid 25kV you’ll make everything easier (and safer).

For fast switching at low voltages there are transistors and MOSFETs and these are simple to use and cheap. At 25kV you’re talking exotic high-voltage valves as far as I know - the sort of device that can drive a large Kerr cell perhaps?