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MEXICOWANDERER's avatar
MEXICOWANDERER
Explorer
Nov 30, 2015

Blinking 12 volt LED With 120 vac Power Supply?

I have lots of items I wish to monitor via eyesight at night. Like power to a pump 200' distant with bare rock in between. Power to the gen shed with 300' in between me and the devices. Yeah I could do it with relays, voltage buckers, etc. etc. But some of these things are outside and I don't feel like spending a fortune on larger project boxes and wiring stuff up.

I can see a 3.2 volt 20 ma blinking green LED at night even at 300' The BREAKERS are a 70' walk sometimes through driving rain to a NEMA 4 enclosure. The gen shed has it's own service service drop.

A power outage monitor is easy to configure for inside. But not so easy for the outside stuff. And I have indeed lost service multiple times to several critical outside devices. And not known it.

That's the justification for the work...

I would like to use plastic handy boxes, sealed up, with nylon blank plates drilled for a 5 mm LED holder.

Also inside the box would be a 7K 5-watt ceramic resistor. I have a bunch of everything listed here and a chance to order whatever and get it down here next month. I do not want to spend a King's Ransom on this.

Is there any problem with the ceramic resistor / enclosed 12 volt blinking LED combination?

Call it a wireless power outage indicator.

23 Replies

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  • DrewE's avatar
    DrewE
    Explorer III
    Nov 30, 2015
    As alluded to in the marcspages link, a blinking LED often wouldn't like the applied voltage going to zero periodically and has a nonuniform power consumpotion. With the mains dropper resistor approach, you'd still likely need a rectifier and capacitor and zener or other crude regulator to give it something resembling continuous power.

    Do the LEDs work on 5V? If so, I'd be mighty tempted to hook up a generic cell phone/USB charger doohicky as the power supply (probably with a fuse to ease the paranoid mind).
  • allenm's avatar
    allenm
    Explorer
    Nov 30, 2015
    Not sure what kind of load you're going to have on that 5 watt resistor, but a few years ago I enclosed a 4 watt night light in a 4" x 6" x 8" wood box to protect an alarm circuit box from sub-zero temps out in a remote shed.

    To my surprise it failed because it got too hot in the box. I couldn't tell exactly, because it pegged a 120 degree thermometer. I ended up leaving the lid about half open. That still gave me a 30 degree temp boost, which was all I needed.

    Another project - right now I'm using a 1/2 watt 1K resistor in series with a 12V flashing LED connected to a 12 5AH battery. The battery lasts about 6 weeks with the resistor or less than 2 weeks w/o the resistor. Can't really tell any difference in brightness either way.

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