Powering a Wi-Fi switch from intercom

leonffrench · 31-01-2018 4:08pm #1

Hi all. I plan to add a sonoff Wi-Fi enabled momentary switch to my electric gates to control it via app and alexa. I am going to do this by wiring the sonoff switch into the button of the intercom telephone which opens the gate when pressed. The sonoff is powered by micro usb 5v. The intercom telephone is a Comelit 2602 which seems to be powered by 24v. My question is: if I get a 24v to micro usb convertor will this power the sonoff switch? I'm good with the physical bits and the wiring but not sure on the theory side of things i.e whether there will be enough power or if pulling 5v from the telephone will mess up something else.
Help greatly appreciated

srsly78 · 31-01-2018 4:10pm

Find out how much current it supplies, then you can find power. Just knowing voltage tells you little.

P = V * I
Power is voltage multiplied by current

leonffrench · 31-01-2018 4:18pm

srsly78 wrote:

Find out how much current it supplies, then you can find power. Just knowing voltage tells you little.

srsly78 wrote:

P = V * I Power is voltage multiplied by current

Thanks for fast reply. The Comelit intercom phone has 24v 100mA Hmmm...now that I think about it the micro Usb puts out 5v 3A so this probably won't work?

srsly78 · 31-01-2018 4:19pm

That might be the max usb can supply, the device may actually need less. Not looking good tho.

Your intercom can supply 2.4W, while usb can supply 15W max it seems.

leonffrench · 31-01-2018 4:21pm

There is no plug nearby to plug in to switch so im looking for an easy way to power it. There is a Horstman heating controller and an IMIT room thermostat on the wall beside the phone but these seem to be powered by 230v

leonffrench · 31-01-2018 4:24pm

May just have to run an extension lead to power the switch via an old phone charger. Messier than I wanted it but looks the only choice. Thanks again for replies

TheChizler · 31-01-2018 4:25pm

leonffrench wrote: »

Thanks for fast reply. The Comelit intercom phone has 24v 100mA Hmmm...now that I think about it the micro Usb puts out 5v 3A so this probably won't work?

Those Sonoff switch typically need around 100 mA, you should be fine. 0.5 W standby.

leonffrench · 31-01-2018 4:35pm

TheChizler wrote:

Those Sonoff switch typically need around 100 mA, you should be fine. 0.5 W standby.

You reckon with a 24v to 5v converter there should be enough to power the sonoff? Would be ideal to have everything in a junction box screwed to the wall beside the phone with no cables running anywhere. Thanks for reply will give it a try

TheChizler · 31-01-2018 4:45pm

leonffrench wrote: »

You reckon with a 24v to 5v converter there should be enough to power the sonoff? Would be ideal to have everything in a junction box screwed to the wall beside the phone with no cables running anywhere. Thanks for reply will give it a try

Depends on the converter, but if you can find a 24 V to 5 V converter that's rated for 100 mA input and output current slightly above what your Sonoff switch needs then it should be fine. A tidier option would be to get a 24 V Sonoff switch.

leonffrench · 31-01-2018 8:20pm

TheChizler wrote:

Depends on the converter, but if you can find a 24 V to 5 V converter that's rated for 100 mA input and output current slightly above what your Sonoff switch needs then it should be fine. A tidier option would be to get a 24 V Sonoff switch.

Yea it would have been easier but ive already ordered a 5v one. The converter I ordered doesn't specify input current only voltage then output is 5v 3A.

Powering a Wi-Fi switch from intercom

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