Need Relatively High Current (20A DC) MicroSwitch

[Noggin]

Anyone know of a high DC current micro-switch? It needs to be rated for about 20A. All of them I have found are under an amp. Height needs to be under an inch tall.

 

[PatM]

Better to use a relay that is controlled by the micro switch.
No micro switch that I am aware of, could carry that much current.

 

[Reloadron]

I use a good number of micro-switches (snap action) and you don't mention the actuation type? Anyway, good luck finding one rated for 20 Amps DC current. Even 20 Amps AC is hard to find.

I agree with PatM in that your best bet would be to slave a high DC current relay to a switch.

Ron

 

[dknguyen]

As far as relays go, I quite like this one:
SparkFun Electronics - Relay SPST-NO Sealed - 30A

Also easily available at Digikey. Had to search high and low for it.

 

[Noggin]

The problem with a relay is that the only voltage source available to drive the coil is the AC line (which is perfectly fine for a relay) but the customer doesn't want to tap into the AC line for that purpose.

I'm flexible on the actuation type of the microswitch (I'm assuming you mean push-button, lever, etc). It should be a normally open momentary switch. By snap-action, you mean that it opens and closes quickly, kinda like a schmidt (sp?) trigger equivalent in the uSwitch world?

dknguyen, that relay is rated for 30A AC, not DC. The problem with DC current is that when the switch opens, it can arc. With AC, there is a zero crossing that will come within a few mS to stop the arcing, but with DC it could take much longer. There are similar issues for using relays, but I did find two that were rated for the job. However, as I mentioned, we don't have anything capable of driving the coil.

I think that we've found a not-so-great workaround though.

 

[ericgibbs]

hi N,
Look at this link, 26A uSw
Your Search Results | Farnell United Kingdom


EDIT:
Or this type ref the pdf

 

[Noggin]

Thanks, but still no DC rating on it in the datasheet

I should probably start emailing manufacturers asking them to approve the switch for DC current.

 

[dknguyen]

Yeah, it's super hard to find a relay with DC rating, particuarily a high current relay. I had to settle with this relay oversized AC relay for lower current DC purposes. What of a solid state relay?

But still no driving source...So the customer wants a big metal switch that takes little microswitch force to activate? There are limits to physics...maybe...leverage? Why doesn't the customer want to tap into the AC line for that anyway? What does it matter? The switch is going to be connected to the line already, what difference would it make? If they think it's more difficult to wire up...well, it would still be a two terminal device, not a 4 terminal one. Sometimes clients specify things unware that achieving said specification will take extra cost and compromise functionality.

 

[Noggin]

The solid state won't work because like you said, there's no driving source for it.

They don't want to tap into the AC line because what they're doing is basically designing a box around an existing product. Their box has a hole in it, and the existing product's panel is viewable through that hole. You'd plug the AC cord into that panel. If we were to gain access to the AC line to switch it, instead of the DC output, it would require moving the existing device away from the hole and the end customer would lose access to the panel.

I've found about a dozen switches rated for 10 amps at 125vDC now. They use a permanent magnet to deflect and dissipate the arc when the contacts are opening/closing. If we can convince them to reduce the output power, I can probably use one of those relays.

 

[crutschow]

Can you get the switch in a 2-pole configuration and parallel the poles?

 

[dknguyen]

Won't that cause problems with different switching times though?

 

[Noggin]

I think paralleling switches wouldn't be a good idea. One of them would probably open before the other, which would then put the full current through the other leg at which point it would then be arcing as it opened.

I think I'll be able to lower the output current to 10 amps and still make the customer happy.

 

[colin55]

26A AC is about 4-5A DC.

At DC the microswitch will have a much shorter life. Try putting a large capacitor across the points.

 

[Noggin]

The customer found one on McMaster-Carr that was rated at 20 amps, 480Vac/250Vdc max, so he's taking that to mean that it'll work. I explained to him that I doubt it is actually rated for 20 amps at 60v DC, but that it'll probably work for quite a while. I added that part to the BOM as the primary part at his request and set the 10 amp magnetic blowout switches as alternates. If they switch to the 10 amp version they'll reduce the output current. It isn't an ideal solution, but they're paying for it and my boss was on the call when they requested it so I'm shielded.

 

[dknguyen]

I was rather curious about something but haven't been able to work through it completely...wouldn't putting an RC snubber in parallel with the primary contacts reduce the damage done to the arcing contacts when they go open?

Of course...there would be leakage.