Switch rating - Page 1
Forum section: electronics / projects

author: Gowda1
author_rank: Contributor
timestamp: December 08, 2020, 03:35:14 pm
content: Hello,I want to have a switches from the tap of inverter legs as shown in the figure.to switch between line 1 to line 2.. The output of the inverter is 40Arms.I am looking double pole switch for this combination but I did not find any switches for this rating. Moreover I am not sure which type of voltage reading I have to consider since the PWM is neither Ac nor Dc.I am stuck with this.. Any suggestion will be helpful. Thank you

author: bob91343
author_rank: Super Contributor
timestamp: December 08, 2020, 06:50:11 pm
content: Not enough information. Do you want to hot switch? What is the frequency? What mechanical configuration is required?In the extreme you can use a knife switch. I have one that would do the job. It's open construction and so care must be exercised with it.

author: themadhippy
author_rank: Super Contributor
timestamp: December 08, 2020, 07:08:26 pm
content: this sort of thing?http://protekuk.co.uk/40A-2-Pole-IP65-Plastic-Rotary-Changeover-Switch-PSCO0240

author: Gowda1
author_rank: Contributor
timestamp: December 08, 2020, 07:55:43 pm
content: The frequency of the inverter is 85kHz..But I am not looking for the inverter switches. I am looking for the one which can be switched between two lines as seen in the figure. It should be mounted on the PCB and its better to have a small sized switch and also can hold the power rating.. I could not find the proper switches from the distributors.. Please let me know..

author: Gowda1
author_rank: Contributor
timestamp: December 08, 2020, 07:56:52 pm
content: Quote from: themadhippy on December 08, 2020, 07:08:26 pmI am looking for the one which can be mounted on PCB..Kind of Toggle switch

author: themadhippy
author_rank: Super Contributor
timestamp: December 09, 2020, 01:36:43 am
content: Quotefor 40amps?

author: Phoenix
author_rank: Frequent Contributor
timestamp: December 09, 2020, 03:47:49 am
content: Quote from: Gowda1 on December 08, 2020, 07:56:52 pmA second H-bridge perhaps?Two big SPDT relays?https://www.azettler.com/pdfs/az2501.pdfAre you going to be expecting to handle live switching?

author: Gyro
author_rank: Super Contributor
timestamp: December 09, 2020, 07:14:20 pm
content: If the inverter frequency is 85kHz then in may require a very substantial switch. Normal AC rated switches work on the basis that the arc caused by the contacts opening is extinguished at the next zero crossing, and assume 50-60Hz sinewave.At such a high frequency, particularly with a squarewave output, there may not be sufficient time for arc products (evaporated contact material) to dissipate and cool, causing the arc to re-establish on the next half cycle. It this respect, it may behave more like breaking a DC circuit, which requires a very large amount of de-rating of the switch when voltage is as high as 400V and current in the 40A region!It may help that the inverter is being switched into another load, but I suspect not (it may end up driving into both loads until arcing stops). This may be a case which requires a much more substantially rated switch is needed with some physical evaluation. I don't know. I really doubt that the switch will be anywhere near small enough for PCB mounting.The only hope of size reduction would be if the inverter could be (guaranteed to be) turned off while while switching.

author: mag_therm
author_rank: Frequent Contributor
timestamp: December 13, 2020, 04:44:38 pm
content: It might be that any conventional switch, even an off-load switch that can withstand 40A at 85 kHz will be large,( and will come with no warranty ! ).The switches I was involved with, to repetitively (and off-load) switch 22 kHz, 250 Amp, 800 V in auto production units,were pneumatic switches .These are supplied by dry air , or dry nitrogen were of a type as used in high power radio transmitters to switch antennae.They were quite unreliable and solid state switches work a lot better.But by the time you get a solid state switch to work, with two devices per leg and all the protection, you are better to just add another inverter.