Switch 6kV between two terminals - Page 1
Forum section: electronics / beginners

author: gus789
author_rank: Contributor
timestamp: July 18, 2016, 11:03:37 pm
content: Hi all,I'd like to switch 6kV/~1mA (from a potted brick HV PSU) between two terminals. This is only a temporary arrangement for testing. I was thinking of using a modified relay mechanism (from a broken, line power rated relay) as in the schematic below. The teflon piece is attached to the relay swing arm to both extend the swing range and to isolate the relay mechanism from the 6kV.Is there any reason not to try this? I am mainly concerned with inductive kickback from the switching destroying my 6kV PSU. Is that likely to be a problem in this scenario?Thanks!Gus

author: uncle_bob
author_rank: Unknown
timestamp: July 19, 2016, 12:03:54 am
content: HiWell, you likely will get a cute looking arc when you do it. Don't make the contacts out of anything you care about. They will be vapor pretty soon ....Bob

author: JoeN
author_rank: Frequent Contributor
timestamp: July 19, 2016, 06:34:12 am
content: Seems to me that there are actually parts to do this. All I did was a parametric search for relays at Digikey and grabbed the ones that have the highest rated voltages. They aren't cheap, but I wouldn't say they break the bank either if you need a part to actually do this. Reading one of the datasheets, one of these relays is rated for 10^6 actuations at 10KV under load, which is impressive to me, at least. Tungsten contacts to make this happen. I guess it arcs but the tungsten just doesn't care.http://www.digikey.com/product-detail/en/cynergy-3/DAT72410/725-1034-ND/752013http://www.digikey.com/product-detail/en/coto-technology/5501-12-1/306-1010-ND/301645

author: Molenaar
author_rank: Regular Contributor
timestamp: July 19, 2016, 07:59:19 am
content: Tubes can easily switch this and at this current, gas filling is not even needed.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 19, 2016, 11:01:59 am
content: Quote from: gus789 on July 18, 2016, 11:03:37 pmThere are several reasons, to use a proper and intended-for relays, instead of your DIY solution:1. 5kV will quickly destroy usual low voltage relay contacts. Use HV reed relays with gas filling, instead2. Proper HV separation between HV contacts and your steering circuit is required, at least for safety reasons.Otherwise, the HV will arc over to your circuit and destroy it, and may as well also harm the user, that is YOU.3. Take handling of HV very serious, please.. so don't do such experiments, only to save cost!The HV PSU will not be affected by induction, where should that come from?? The inductivity is on the steering side only.I remember, that these old HV reed relays (inside the FLUKE 335 calibrator) are still available, so look for one of these, they are really huge, but are able to switch 5kV, 7.5kV, 10kV at reasonable power figures, so 1mA should be no problem. The outer switching coil is available for 5V, 12V and 24V.They come from MEDER, COTO, and others. Price maybe on the order of 20..50$, but your life is worth the price, I think.Frank

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 19, 2016, 02:39:03 pm
content: What load? Is it capacitive?Shouldyou be expecting inductive kick?If so, you may want to invest in a few series resistors, on the order of 100k 2W or more. Or there are HV types rated for that in a single part.Tim

author: Synthetase
author_rank: Regular Contributor
timestamp: July 19, 2016, 03:03:45 pm
content: Sorry I have nothing constructive to add except that I saw the thread title in the beginners section and laughed

author: HighVoltage
author_rank: Super Contributor
timestamp: July 19, 2016, 03:11:51 pm
content: Quote from: Dr. Frank on July 19, 2016, 11:01:59 amYes, I would suggest the same manufacturer...I have used a Meder Standex HM24-1A83-08 beforeIt is rated 10,000V DC and 3A (50 Watt limit)

author: joeqsmith
author_rank: Super Contributor
timestamp: July 20, 2016, 12:35:04 am
content: I was going to mention the power rating for the contacts. Most of these HV relays are not rated to switch with the supply active. So pay attention to the power and how many cycles they are rated for. You may be surprised how poor some of them are..OP, maybe a couple of microwave diodes if you are concerned about the supply.

author: Assafl
author_rank: Frequent Contributor
timestamp: July 20, 2016, 11:04:33 am
content: The inductive kickback will only come from whatever is connected to the contacts T1 and T2. Not from the relay coil on the control side. Tesla coils?

author: Back2Volts
author_rank: Unknown
timestamp: July 20, 2016, 02:03:05 pm
content: Quote from: Synthetase on July 19, 2016, 03:03:45 pmYes. It makes you wonder what is the skill level.

author: gus789
author_rank: Contributor
timestamp: July 21, 2016, 02:51:57 am
content: Thank you all for the suggestions. This question seemed appropriate for the beginner's section, BTW, other than the HV involved.I will give one of the HV relays a try. Just ordered it in fact.http://www.digikey.com/product-detail/en/cynergy-3/DAT71210F/725-1031-ND/752006The load is not inductive (an electrospray) but I've put some resistance in series just in case.Cheers

author: MarkF
author_rank: Super Contributor
timestamp: July 21, 2016, 03:26:59 am
content: One reason not to........

author: Brumby
author_rank: Unknown
timestamp: July 21, 2016, 04:55:40 am
content: Quote from: Synthetase on July 19, 2016, 03:03:45 pmI look at it this way....People who have worked for years in battery to mains powered equipment could still be classed as beginners in HV.I've never had experience working with anything more than mains (if you ignore CRT EHT - which I never actually worked on directly - just kept my distance) - and if I was going to venture into it, I would have to class myself as a beginner 'who has done pre-requisite reading'.If somebody starts their electronics interest in HV, they are going to need some fundamental (safety focussed) guidelines VERY quickly.

author: Assafl
author_rank: Frequent Contributor
timestamp: July 21, 2016, 06:05:42 am
content: Quote from: Brumby on July 21, 2016, 04:55:40 amI don't know about beginners in HV.One of my majors was power electronics and control, and worked with huge HV capacitor banks that discharged to hydrophones. Friends worked as linesmen for high tension (and Ultra High Tension) and to this day bus bars and high voltage insulators and capacitor banks (especially the ones that look like huge pickle cans) terrify me.If I have to - and usually as an engineer I can depend on the dielectric safety of pen and paper (actually keyboard keys and mice) - I will work on devices, but even at home wiring the supply cabinet scares me. I always feel like a beginner since to err is maybe to die.I remember the linesmen friends - every project they treated like they were in high school. Going over the rather simple drawings and what they were going to do and triple verifying the power was down and then shorting the lines just-in-case.I cringe at those with Tesla coils (or capacitor banks) in their attic. I just don't get it. There are many good reasons to go up in volts, amps and joules - foolery isn't one.

author: Brumby
author_rank: Unknown
timestamp: July 21, 2016, 06:12:16 am
content: You'll love this guy....https://www.youtube.com/user/Photonvidshttps://youtu.be/Oyl8F23uXHc

author: uncle_bob
author_rank: Unknown
timestamp: July 21, 2016, 11:40:39 am
content: Quote from: gus789 on July 21, 2016, 02:51:57 amHiKeep in mind that resistors with 6KV ratings are not real common. Even when they are rated, there are issues with keeping things clean and properly separated. It is not uncommon to see significant derating.A switch or relay is a "millisecond" sort of device. Unless you have > 1H of inductance (you likely have 1/100000 of that) there isn't going to be a "kick" relative to the ~ 6KV you already have.Bob

author: Synthetase
author_rank: Regular Contributor
timestamp: July 21, 2016, 02:27:16 pm
content: Quote from: Brumby on July 21, 2016, 04:55:40 amI agree with you. I just thought it was kinda funny is all...

author: Assafl
author_rank: Frequent Contributor
timestamp: July 21, 2016, 06:17:58 pm
content: Quote from: Brumby on July 21, 2016, 06:12:16 amHe seems to know what he is doing, apart from being a fire hazard (actually - an all around hazardous individual).

author: gus789
author_rank: Contributor
timestamp: July 21, 2016, 09:41:05 pm
content: QuoteThanks, I ended up using 12 x 1MOhm (3W) in series enclosed in a thick silicone tube. It turns out the spray requires a lot less current than I initially estimated.

author: uncle_bob
author_rank: Unknown
timestamp: July 21, 2016, 11:57:08 pm
content: Quote from: gus789 on July 21, 2016, 09:41:05 pm