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I'm struggling to find any relay or contactor even close to the specs I need, and I've contacted many manufacturers. This is controlling a large contactor, so draws a 30A 24DC inrush current. It then settles to a 250mA hold current. It seems any relay large enough to handle the 30A inrush, then also has minimum current ratings well above 250mA. I can not seem to find anything to handle both, and I can't suppress the inrush.

Does anyone know of any such device? My only other potential idea is to use a number of small relays and split the current through possibly upwards of 12 contacts, so as to put a small current through each and be looking at more like a range of 20mA to 2.5A per contact. Even still, this is bad practice and will lead to failure anyway. Surely there must be a better way.

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  • \$\begingroup\$ Is there a reason you don't want to use a MOSFET or SSR? 30A is not a problem for solid state switches. \$\endgroup\$ – Spehro Pefhany Aug 28 '15 at 20:14
  • \$\begingroup\$ Why is it a problem to have one with well above 250mA rating? \$\endgroup\$ – PlasmaHH Aug 28 '15 at 20:18
  • \$\begingroup\$ @PlasmaHH Contacts that can reliably switch 30A may not be reliable at 'only' 250mA. \$\endgroup\$ – Spehro Pefhany Aug 28 '15 at 20:21
  • \$\begingroup\$ @SpehroPefhany I have little to no knowledge on SSR's. I have never worked with them before. Is price the only reason they're not permanently used instead of electromagnetic relays? Will this DC100D40 get the job done? crydom.com/en/products/catalog/dc_ip20_100.pdf \$\endgroup\$ – C.J. C Aug 28 '15 at 21:48
  • \$\begingroup\$ Yes, I'd be very confident about that one. You wouldn't need a heatsink unless it was seeing that surge frequently. There are other reasons to use relays- more resistant to abuse such as short circuits which blow a fuse, and to surges. And price, of course. You could make a SSR function including isolation for much less money. \$\endgroup\$ – Spehro Pefhany Aug 28 '15 at 22:32
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That wide range between min and max current is a problem for most relays.

You have a couple of options.

  1. Use a solid state device. MOSFETs are good at low potential and high currents.

  2. Use two different relays: one for the pull-in, the other for holding.

You will have to control both relays individually - the smaller holding relay will pin much faster than the large relay.

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