USB powered relay for mains voltage?

[mattbatt]

So I have a small LED light and a pair of amplified speakers that I only want turned on when my computer is on. I'm thinking that there must be a way to trigger a relay when USB power comes on. I just want to make sure I build it correctly. I would imagine there should be a transformer or something to isolate the Computer side from the mains power side.
Am I crazy?
Is there already a product like this? I haven't been able to find one.
Thanks Guys.

[joshnz]

Re: USB powered relay for mains voltage?

Very easy.
U will need a 5v relay that is sutibale to switch mains,
a diode,
a usb cord,
wire sutiable for mains,
Mains Plug and socket,
A case to hold relay and connections.
Two cable grips to fit the enclosure.
Good wiring practices and the relay provides the isolation.

[budm]

Re: USB powered relay for mains voltage?

Or get smart outlets:
Something like this
https://www.amazon.com/TrickleStar-O...dp/B00JPDYYSM/

[stj]

Re: USB powered relay for mains voltage?

or just grab an SSR from ebay.
http://www.ebay.co.uk/itm/252999774991

and build it into the speakers if you have room!

[joshnz]

Re: USB powered relay for mains voltage?

or just grab an SSR from ebay.
http://www.ebay.co.uk/itm/252999774991

and build it into the speakers if you have room!

I was thinking same but he mentioned led desk lamp or somthing like that.

[joshnz]

Re: USB powered relay for mains voltage?

Or get smart outlets:
Something like this
https://www.amazon.com/TrickleStar-O...dp/B00JPDYYSM/

Nice

[mattbatt]

Re: USB powered relay for mains voltage?

Thanks guys that's exactly what I was thinking of. Solid State Relay I thought those were more expensive. I have some more research to do.
Thank you.

[goontron]

Re: USB powered relay for mains voltage?

If you are real anal about isolation, a triac, and opto-isolator are cheap.

[sofTest]

Re: USB powered relay for mains voltage?

or just grab an SSR from ebay.
http://www.ebay.co.uk/itm/252999774991

and build it into the speakers if you have room!

One might want to be careful with what SSR one buys.

Teardown

One thing is overrating, but with that isolation distance, hardly CE compliant, if one care for such things.

[goontron]

Re: USB powered relay for mains voltage?

^ Seems to be China Export compliant to me....

That european lab thing on the other hand....

[sofTest]

Re: USB powered relay for mains voltage?

Clive also tested running a LED lamp from the SSR, as per OP requirement. Look what happened here. Speakers and blinking light, and you got a disco! ;-)

[stj]

Re: USB powered relay for mains voltage?

i did see the teardown, the 25A bit is unimportant for most people,
and it's fine at 5v and with a decent load.

it's pretty stupid to use something like that for a few W.

[Curious.George]

Re: USB powered relay for mains voltage?

I would imagine there should be a transformer or something to isolate the Computer side from the mains power side.
Am I crazy?

Why bother with the AC mains at all? Will you remember to switch the hot and not the neutral? Will your gizmo get plugged in "backwards" (thereby moving the switch onto the neutral leg where it doesn't belong)? etc.

Chances are, your speakers are powered by a wall wart (which is what you were initially hoping to control by gating the mains). Insert a relay in the low voltage supply from the wall wart (instead of in the mains supply to the wall wart).

Note the output rating on the wall wart when sizing the relay contact(s) to ensure the load represented by the speakers can be handled. Note, also, that DC current switching capabilities of relays differ from AC loads. But, unless you're powering something "sizeable", this should still be an easy fit.

Depending on the speakers' power requirements, you can also just salvage a "PC power supply" to power the speakers and control it via your USB device (i.e., using the soft power-on control lead)