exceeding relay contact current rating

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strantor

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I know the cut & dried answer is probably NO, but can you get away with exceeding the contact current rating of a relay if the relay isn't making/breaking that current? For example, I use 100A relays to make an H-bridge circuit where the current will be 200A, and use 1 IGBT for the PWM. The 2 relays will be energized, and then the IGBT will start PWM once the relays have closed, and then the relays will not open until after PWM has ceased. Can it work? Or will the relays fry?
 
No, relays are current rated for carrying capacity, not make/break, that's a separate spec, and often not listed. If you try it there's a virtual guarantee that you'll weld something.
 
Contact current means when the relay is actually fully engaged... The actual switching current compared to this value is MASSIVLY derated, perhaps 10-20 times or more.
 
Last edited:
Thanks for the replies. got it. bad idea.

ronsimpson, I didn't have a specific relay in mind, just a general question.
 
Is there a cost effective (safe) way to skimp out on buying 4 expensive IGBT modules to make a high power h-bridge? BTW I'm talking 1000A+, not the 100A or 200A I mentioned previously.
 
Where will you find 1000+ amp IGBTs? I do not know of any.
What voltage?
 
Ouch 1k$ transistors. Full bridge=$4,000. Smoke=$4000.

MOSFET: IXFB132N50P3 500V 130A $18.00@1 so parallel 10 = $165 from DigiKey.com 1300A.
IGBT: FZ1200R12KE3 1200V 1200A $600@1
 
ronsimpson said:
Ouch 1k$ transistors. Full bridge=$4,000. Smoke=$4000.

MOSFET: IXFB132N50P3 500V 130A $18.00@1 so parallel 10 = $165 from DigiKey.com 1300A.
IGBT: FZ1200R12KE3 1200V 1200A $600@1
Click to expand...

I had another post where I ask asking about paralleling MOSFETS or IGBTs but I got the idea that I would need some kind of load sharing. I had given up on the idea until I read your post here, and I started searching again and found this in a nuts n volts article

So, would it really be as simple as constructing a simple H-bridge circuit, but using 10 paralleled MOSFETS instead of 1 for each of the 4 switches (40 total)? Would a MOSFET driver be able to drive 10 at a time?
Thanks
 
Might be cheaper to use another small motor and controller to drive in reverse.
MOSFETS - easy to parallel, IGBTS hard to parallel.
 
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