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Snubber for 250V ac/dc
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Jester:
I'm looking for an affordable way to switch a 20A, 250V ac/dc resistive load .

Obviously relays exist for this, however they are big and expensive.

When switching high currents the voltage will be low, less than 50V
When switching 250V, the current will be low, 5A max

One thought was to use an inexpensive relay like this: https://www.mouser.com/ProductDetail/TE-Connectivity-PB/T9AP1D52-12?qs=sGAEpiMZZMtSzCF3XBhmW%2fHkUL8cHIexYxdlOkSBp0I%3d
that is not rated for DC and help it with an active snubber, for example:

https://www.mouser.com/ProductDetail/IXYS-Integrated-Circuits/CPC1968J?qs=%2fha2pyFaduggqnz%252bdP%252bTMHGhYnLgauQSBn6kv3xcIxY%3d

This SSR has a 10ms, 25A peak rating, so if I turn it on for say 10ms, 5ms after disabling the relay, in theory the SSR will be doing all the work with respect to breaking the DC arc.

I should also have a RC snubber to help out.

Thoughts on this, do you think it will work?   Is there a better approach?



T3sl4co1l:
What drive is available?

What budget?

Size?

Transient ratings?

Yes, double-switching would seem likely to work.

Snubber value is unclear, presumably you want it smaller than would be irritating for AC operation.  So, not, like, >10uF and 1 ohm or something, roughly.

The low voltage operation doesn't buy you much, the switch still needs to be rated for full V and I.  Or more, if transients are expected (the 250V is mains-connected).  A normal "250VAC" relay includes that in its UL rating, AFAIK (the '250V' is a type rating and the actual breakdown is some kV?).  Or hmm, maybe not, that would be something a disconnect would need to be rated by, but not necessarily a relay?  Or contactor?  Look up the standards to be sure.

If you need absolute least cost, and safety is not a concern, then just [ab]use whatever relay and be done.  If you need UL approval, buy the 250V AC/DC relay and be done.

If this is one-offs, what are you even worrying about, you've already spent the $10 difference thinking about it!

Tim
Jester:

--- Quote from: T3sl4co1l on January 14, 2019, 05:15:50 pm ---What drive is available?  12Vdc or 120Vac

What budget?  about $20

Size?  the relay in my link would fit; 1.1" x 2" x 1.1"

Transient ratings?  the above are the worst case.

UL not required, but replacing burned up relays, unless that occurs > 10,000 operations

Yes, double-switching would seem likely to work.

Snubber value is unclear, presumably you want it smaller than would be irritating for AC operation.  So, not, like, >10uF and 1 ohm or something, roughly.

The low voltage operation doesn't buy you much, the switch still needs to be rated for full V and I.  Or more, if transients are expected (the 250V is mains-connected).  A normal "250VAC" relay includes that in its UL rating, AFAIK (the '250V' is a type rating and the actual breakdown is some kV?).  Or hmm, maybe not, that would be something a disconnect would need to be rated by, but not necessarily a relay?  Or contactor?  Look up the standards to be sure.

If you need absolute least cost, and safety is not a concern, then just [ab]use whatever relay and be done.  If you need UL approval, buy the 250V AC/DC relay and be done.

If this is one-offs, what are you even worrying about, you've already spent the $10 difference thinking about it!

Tim

--- End quote ---

This relay is close, https://www.mouser.com/ProductDetail/Phoenix-Contact/2908044?qs=%2fha2pyFaduhG2tsweHCXD2XrOo%2fLGBsP%2fANbF9f62x8%3d
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