High voltage switching - Page 1
Forum section: electronics / projects

author: Christopher
author_rank: Frequent Contributor
timestamp: May 07, 2013, 05:36:04 pm
content: Replacing a design which uses the output of a HiPot tester (1500Vdc, 100uA max).This is fed into a 10 throw, 2 pole rotary switch which then switches the output accordingly. Obviously this rotary switch is only rated for 50Vdc... The technical manager says it has to be replaced with something more safe.I was thinking something like the following (with only two throws not 10..):The outputs are connected together to the 1.5kV hipot output in weird combinations, so the output of the Rotary s/w would be connected to a PIC input and the fet gates would be connected to the PIC output, so I can control which inputs the 1.5kV is connected to.https://www.circuitlab.com/circuit/8gb84j/unnamed-circuit/#postsave_link_and_shareBut obviously there are no high voltage FETs or Relays which can be had for cheap...Sorry if you can't understand what it is i'm trying to do...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 07, 2013, 05:59:05 pm
content: HV reed relays may be a fairly cheap option

author: Christopher
author_rank: Frequent Contributor
timestamp: May 07, 2013, 06:15:27 pm
content: Cheapest reed relay rated for over 1.5kV on Farnell is ~£8. So that's £80 overall.Any cheaper solutions?

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2013, 06:16:45 pm
content: You are right Mike, they are available up to 14kV at 1A. What will also work are industrial relays, as these are tested in many cases to have a 2kV withstand voltage between contacts and case, and also are available in a 4 pole option, with optional NC blocks, so you can use them to either provide the output or to connect it to ground. Cheaper than the reed relays, but a lot larger, and you will need 24VDC at around 300mA for each one.

author: Rufus
author_rank: Super Contributor
timestamp: May 07, 2013, 06:27:56 pm
content: Quote from: mikeselectricstuff on May 07, 2013, 05:59:05 pmSomething I might also have suggested but something cobbled together with a PIC doesn't sound 'more safe' to me.'Only rated for 50v' on the switch is pretty meaningless. If it is currently handling 1.5kV the 50v isn't likely a useful or realistic rating. It is probably a contact live switching rating. Presumably the 1.5kV isn't supposed to be switched live so the important rating would be between contacts and between contacts and the operator.Apart from isolation of the switch operator the switch shouldn't be relevant to safety, the grub screw on the knob gets loose and someone is electrocuted because the switch wasn't in the position he thought it was? - give me a break. (100uA not really being enough to kill anyone without some capacitance to charge up somewhere).If you want safe the switch isn't the problem. It might be part of a problem of making something safe work.

author: IanB
author_rank: Super Contributor
timestamp: May 07, 2013, 07:52:03 pm
content: Regarding the original rotary switch, can't you bond all the exposed and metal parts of the switch to a safety ground? That should protect the switch operator from coming into contact with any dangerous voltages.