I'm trying to put a switch on two sides of a battery. +36V and -36V, pulling 6+ amps. Thought it would be easy to find a power relay in a small PCB package, but so far, all the DC ratings for every one I've seen are only up to 30V at 8A max. Are there no power relays in the world for this level application?

Realestate is scarce on the board and they can't be too tall either, ~ 1/2".

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BSEE

 

Can you use MOSFETs?

 

That was our first idea...then we ran into complications trying to deal with the negative side MOSFET switch. To have adequate protection and clamping it's usually necessary to use a mosfet switch high-side or low-side driver that has a charge pump built into it to keep the fet enhanced with protection. High side was no problem, but when we wanted to do low side topology for the neg. line, we ran into all sorts of voltage shifting schemes we had to use to keep our CMOS enables working with the driver, etc. blah, blah, it just became too complicated with too little board space.

Long story short, we're going with relays...thought about reed switches but they're all low power...and now it looks like there is some strange bound to the contact voltage rating in ALL power relays in the world: namely, 30V.

It's weird, but it's starting to seem like no one in the world has ever had to switch a 36V+ battery with PCB mount relays.

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BSEE

 

I just read my catalog and found one: FUJITSU FBR 56 N D12-W 50VDC 20A, 14.5*20*16.2mm case.

 

Thank you...but I looked at the data sheet and the D12 doesn't have a 5V coil. I couldn't find the 50V, 20A contact rating either. Are you sure it's FBR 56?

http://www.fcai.fujitsu.com/pdf/fbr56.pdf

I've found a relay from Potter & Brumfield/Tyco that is rated at 16A 30V. So I figure 6A 36V shouldn't be a problem for it. Thanks for the info, though.

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BSEE

 

Fujitsu guarantees the 6 volt coil will operate at 4.5v @ 85C, and the Maximum Break Capacity graph says it will handle 36v at around 10 amps.
Looks to me like it would work.

Ron