Using Arduino relay board outside its intended voltage

Question

I am making a multistage coilgun, with the switching of stages controlled by an Arduino Uno R3. There are ten stages total, and each stage has 5 80uf 330v photoflash capacitors. I need a way to switch that high voltage into the coils, and I have decided to use an Arduino to control that. The problem is, I don't have the money or time to use correctly rated relays, and wire them up to work with the Arduino. So I was looking at the relay boards sold for switching 120VAC, but the voltage I am switching is very far outside the rated voltage for the relays. Would it still work, at least in short term, or would it fry the relays instantly, or weld their contacts? any help is appreciated.

The relay board I am considering: http://www.ebay.com/itm/16-Channel-5V-Relay-Module-Optocoupler-Protection-Power-Supply-Arduino-PIC-DSP/252124532517?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3D167e4df2b792461f8cfaff32c63a7e26%26pid%3D100338%26rk%3D1%26rkt%3D17%26sd%3D291440146340

• Ecnerwal: No money or time to do it right, but then you have to come up with money and time to do it over (assuming you don't just throw the money and project down the drain.) So either don't do it (save money and time, make less trash), or do it right, if doing it at all.

Answer 1

Likely the contacts will weld the 1st time you use it.

2nd, the pull-in time of the relays will vary (nearly randomly), and this will degrade the sequencing of your coil gun.

3rd -- the EM pulse from the coil gun might cause the Arduino to malfunction. You'll have to shield it very well from the discharge -- the relays might not allow that.

Best to use semiconductors -- IGBTs would be well suited for this task, and can run 1000's of A

Answer 2

It's virtually impossible to tell how (or if) exactly they'll fail. No matter what the potential might be, it's a really bad idea to run any device out of spec - especially by almost 3 times.

Side note, there is no such thing as not having enough time or money to be safe and do the right thing - especially if there's a reasonably high potential for disastrous failure modes.

• MarkU: 120VAC (rms) is 170VDC peak (square root of 2 times greater), so 330VDC is effectively 200% of the rated limit. Manufacturers always include some guardband before the actual failure point (like a "baker's dozen" -- customers hate it when products break), so I could see maybe pushing a couple percent over the limit in rare cases. But 200% seems excessive, especially on a unit sold through ebay.