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Short (1ms) high current (~200A) current pulses - relay rating?

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Smokey:
Altran AEV250 Series:
https://www.digikey.com/en/products/detail/altran-magnetics-llc/AEV250-M/9748544
https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/3717/AEV250_2.pdf

900V, 500A.

If you put big holes in your PCB, you can screw the studs right through the board, so I guess that's "PCB Mount".

T3sl4co1l:

--- Quote from: Smokey on April 23, 2024, 09:34:20 pm ---Altran AEV250 Series:
https://www.digikey.com/en/products/detail/altran-magnetics-llc/AEV250-M/9748544
https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/3717/AEV250_2.pdf

900V, 500A.

If you put big holes in your PCB, you can screw the studs right through the board, so I guess that's "PCB Mount".

--- End quote ---

The fun part about test equipment is, it's a one-off, we've collectively spent orders of magnitude more labor / project timeline discussing candidates, when a worst-case option is readily available for hardly an hour of shop time. :)

Tim

Smokey:

--- Quote from: T3sl4co1l on April 24, 2024, 04:33:10 am ---
--- Quote from: Smokey on April 23, 2024, 09:34:20 pm ---Altran AEV250 Series:
https://www.digikey.com/en/products/detail/altran-magnetics-llc/AEV250-M/9748544
https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/3717/AEV250_2.pdf

900V, 500A.

If you put big holes in your PCB, you can screw the studs right through the board, so I guess that's "PCB Mount".

--- End quote ---

The fun part about test equipment is, it's a one-off, we've collectively spent orders of magnitude more labor / project timeline discussing candidates, when a worst-case option is readily available for hardly an hour of shop time. :)

Tim

--- End quote ---

You could have just asked me from the beginning :)

Berni:

--- Quote from: max_torque on April 23, 2024, 02:02:37 pm ---Update: Change of plan! 

Going to use a crowbar relay that is not is series with the output, but in parallel with it. So when the Estop is hit (or power is removed from the device), not only will i de-power the switch mode convertor that generates the 250Vdc, i'll drop a crowbar across the output capacitor to ensure it is discharged and cannot be charged.  As the device will be connected to DUTs that run at up to 33vdc, i'll probably use some big 40V TVs diodes and a low value power resistor to quickly drop the output voltage below 50Vdc (as required by the Low Voltage directive)

This means my output path from the pulse caps is now just across the output control switch which is a semi-conductor switch

--- End quote ---

That is indeed a better solution.

Tho the thing to watch out for is closing that relay while the capacitors are still very full. Be it because a wire going to your DUT fell off, or the DUT failed open quickly. Closing a relay directly across the charged capacitors has a very high chance of welding relay contacts with the huge initial pulse current. The relays are most vulnerable to being damaged during switching (due to switch bounce), once it is fully closed, it can handle very large peak currents.

Perhaps it is adequate for your solution to have the relay connect a low value resistor across the capacitors. Then pick a value that will discharge the capacitor with a few 10s of Amps just below what a regular small relay might survive without welding, yet have the resistor be low enough in value that the charging circuit is not powerful enough to charge up the capacitor to any meaningful voltage with the resistor applied.

Nice thing is also that if the relay welds, it fails stuck into the safe state

max_torque:
Yup, looking to use something like a 40V bidirectional TVS (to prevent current flow when the output is connected to the DUTs normal supply voltage) and say a 10ohm power resistor (or resistor array).  Should limit peak discharge currents to 20A or so.  I'll also put  a high value discharge resistor across the caps that is permanently connected, and normally, the shut down / turn off will be handled by the control micro, that can turn off the boost converter and just wait a bit till the output cap has mostly discharged across that fixed R.  Only on the occasion where the Estop is pressed during normal test running or during supply failure (ie someones tripped over extension lead and yanked the kettle lead out the back........) will the crow bar circuit operate with the output cap charged.

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