Pantry Cabinet Lights

I wanted to put lights in a pantry cabinet without spending lots of money and preferably no batteries. The no battery criteria removes many remote switch and motion sensor options, but I had a plan.

As to lights, I liked 2W (~200 lumen or 20W incandescent equivalent) LED disc lamps that could be attached using double sided tape above each shelf. They are powered by an AC to DC converter so no worries about replacing or recharging batteries. Yes, a small wire running from each one, but not too obtrusive. They can be gotten for a couple dollars a disc these days.

I was stuck on a door switch option but I didn’t want the door switch to be operating on AC line voltage. There are some smart house options that you can put together for $150 that will also give you WiFi or Bluetooth control. I really didn’t need that for this and I certainly didn’t want to pay for that.

What I did find was a really cool and inexpensive AC Relay from Digital Loggers (http://www.digital-loggers.com/iot.html). It was designed to allow a Raspberry Pi or the like to control an AC outlet and has several useful features, namely:

One: Compact and easy to use module with power switch, including circuit breaker, and surge suppressor.

Two: Has both normally ON and normally OFF outlets. The usefulness will become more evident later.

Sadly, the control input is not self powered which could lead to a complicated control circuit. I really just wanted to use some magnetic switches like you might find on windows for a security system.

That brings us to #3: the module is easy to modify. Remove 6 screws and it easily opens up. There is no internal 3.3V or 5V DC source in there. Turns out driving the input needs less than 1 mA. There is an isolated (capacitive coupled) bridge rectifier in there but it is very current limited, enough to drive the AC relay but not much more. Temped as you might be to use it, don’t. It can work but I found it unreliable as a source. When the AC relay is activated it pulls down this voltage by 2/3rd.

I suggest adding another rectifier after the power switch. You will loose out on isolation inside the module but that is okay as the magnet switches should still make it an isolated circuit. Add about 10 uF across the input, that would be enough to ride out a half period should you not want to put in a full bridge. 75 kohm is enough for current limiting, use at least 1/2 w (assuming US residential line voltage). One more hint, place all the components top side of the circuit board as it makes it easier to put the board back in the case. Connect the current limiting resistor and rectifier to the + input with neutral as the other. This will give you about 3V across the input, enough to saturate the opto-isolator they use to drive the AC relay. You could just reuse an old 5V phone charger, but they are not as easy to take apart.

Get normally open magnetic switch (they are open when the magnet is away from the sensor). You can get a bunch of them cheap from Amazon (ASIN B0011W4YNK for example) which have nice recessed wire terminals and double sided tape already on the bottom. My pantry had more than one door so I needed more than one switch.

Wire them in series to get any door to turn on the lights. I had a spool of some shielded two conductor wire, the kind used on old (really old) fashioned phone system. Any insulated wire should work. 22 AWG is fine.

Plug the lights into the normally OFF AC outlet. Then they will turn on when the door opens (magnet switch goes to normally open which allows the control input to charge up switching the normally off AC outlet to on).

If you got, for some reason, NC switches then you can still make it work. Wire the switches in parallel and swap the lights to the normally ON AC outlet – why having both types of outlet is useful.

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One Response to “Pantry Cabinet Lights”

  1. Laura Fields Says:

    You need some pretty pictures of our fancy new cabinet.

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