Touch Pad Switch - Lamp Conversion Project

Introduction

In recent years, I purchased a number of lamps with touch-pad on/off switches For a while, these were ubiquitous; you could hardly find anything else at Home Depot, for example. But in all five cases, the lamps stopped working properly after a few years.

In one case, the dimmer capability no longer functioned (it should have had 3 levels but over time it only had one that worked).
In another case, the lamp wouldn't turn on anymore (switch failed in the off position).
In another case, the lamp wouldn't turn off anymore (switch failed in the on position).
In another case, the switch became randomly over-sensitive (one touch of the touch pad would go on, then off, then on, then off, in a random way).
In another case, it just quit working. Upon examination, this unit didn’t take a bulb at all, but had LEDs built into a plate, where the socket would usually be, which was covered by a plastic/diffuser. Pretty tough to replace.

These lamps weren’t super expensive, but it is still annoying to have these things break down in the course of a few years. It seems to me that old-style lamps (with regular switches) could last for decades, so what’s with these ones malfunctioning so soon? It got so annoying that the last lamps we bought were from a second-hand place (a Habitat for Humanity recycling place), with old fashioned pull-switches (cool, in a retro sort of way).

These malfunctioning units were just sitting in the garage, waiting to be thrown out. But, rather than do that, I thought I would try to salvage them, by replacing the touch pad switch with an old-fashioned switch. Since there was no easy place to put a switch on the lamp base itself, I decided to go with in-line switches, the type that is built into the cord.

These touch pad switches are solid state devices. My reading says that they are based on the fact that when a human being contacts the touch pad, the capacitance of the overall device changes, which activates a transistor(s), that is acting as a switching device. It is somewhat akin to a person adjusting a radio antenna, improving the reception, but only as long as they continue to hold it. Basically, the person becomes part of the switch or antenna, as the body can store electrical energy (small amounts). I suspect that the capacitors in these lamp switches degrade over time, creating problems with the circuit, either inconsistent behaviour or complete failure. Cheap caps are often the failure points of solid-state devices.

These days, LED lights have all the circuitry needed to for an LED light to operate, built into the bulb (i.e. diode based rectifiers to change AC to DC, power converters to step down the voltage). The lamp circuit has the transistor-based switch, and often also has a dimmer capability built into it. I tend not to have much need for dimming lights and I don’t find using an old-fashioned on-off switch to be a very onerous task. Thus, the extra electronics in the lamp itself just represents a potential failure point, and a pretty consistent failure point in my experience.

So, I decided to snip out the electronic circuitry (literally a black box) and hook the wires from the mains back up to the wires to the lamp’s socket, so that power was going directly from the house current to the bulb. Then, I installed the in-line switch.

I actually did this for several lamps. I mounted two of them on a base, side by side, to be able to throw more light on a spot, for reading or doing fine work of other kinds. It is set up so that both lamps can be on or off, or one or the other can be on while the other is off.

Installing the In-line Switches

Note: For the steps outlined below, you should (obviously) ensure that the lamp is unplugged from the house outlets and thus cannot have any current flowing.

Tools: screwdriver(s), utility knife, wire cutter and stripper, multi-meter, electrical tape, marker pen.

1) Examine the wiring. In the case of this type of lamp, the relevant circuitry is in the base of the lamp, as in the example below. There will be some type of material covering this up. In this case, that was a metal plate that covered the electronics package (in a black box that contained the transistors, capacitors, etc.) The entire base was further covered by a fabric, which acts to protect the wires and presumably also as insulation.

The plate had a couple of screws for removal and replacement, while the fabric cover was fixed with glue, and could be glued back on (you could also use electrical tape, if you aren’t too fussy about appearances.

Note also that there are various channels to house the wires, ensuring that they are kept safely off of the surface that the lamp is sitting on and that the base of the lamp is level, so that it sits nicely on a table.

2) Snip the wires that go from the bulb to the electronics package, in order to remove the latter. Snip the wires as close to the electronics package as is reasonably possible. That will give you more wire to work with, when reattaching the wire from the bulb socket to the wire that goes to the household wall outlet.

3) Snip the wires that go from the cord that plugs into the house outlet to the electronics package. As with the previous step, snip close to the electronics package, so that you will have plenty of wire to work with, when reattaching the two sets of wires.

4) Rejoin the wires from the bulb socket to the wires going to the house mains.

The light socket side:

Strip back the insulation from the wires coming from the lamp socket (where the bulb screws in). Strip them back about 3/4 inch, so that bare copper conductor is showing. You can use a wire stripper for this or carefully do it with a utility knife. But, don’t nick or damage the copper conductor beneath the plastic insulation.

The neutral in the bulb socket connects to the threads in the socket. Conventionally, the neutral wire will be coloured white. But, you can confirm that with a multi-meter, by setting it to test for continuity (that just means that current can flow from one point to the other). So if you set the multi-meter to use the resistance option, then touch the thread and the copper end of the white wire that you had previously stripped with the multi-meter probes, your meter will show some non-zero resistance between these points. There may also be an option to have it beep when there is continuity. That’s a nice feature.
The hot wire in the bulb socket connects to a screw in the middle of the socket. Conventionally, the hot wire should be black. Again, you can confirm this with your multi-meter, by testing for continuity.
If the wires aren’t colour-coded for some reason, you can mark them with a marker pen or a bit of coloured electrical tape, so you don’t forget which is which.

The house outlet side:

Cut the insulation in the middle of the wire, so that you can separate the neutral and hot wires on the power cored.
Strip back the insulation from those wires (coming from the plug-in side), in the same way as above.
The neutral wire should have a rough surface on the side of the insulation, compared to the smoother surface of the insulation covering the hot wire.
The neutral wire will connect to the ‘fat prong’ on the plug-in. The hot wire will connect to the skinnier prong.
If your cord wire isn’t too twisted, you may be able to trace back from the plug-in to the end of the wire, to identify the neutral and hot wires at that end, as a check against the ‘rough insulation’ rule.
You could also check with your multi-meter.

Joining the wires:

Now that you are certain about which wires are neutral and which are hot, you can connect them, so that current flows from the house outlet to the light bulb.
- Take the copper conductor wires that you exposed previously and twist them together. As you will observe, the wires are actually composed of many strands of thin wire.
- Take a wire-nut (also called a marrette). Lamp wires are generally 18 wire gauge, so you want the smaller orange wire-nut, for a proper fit. Twist together the neutral from the bulb side and the neutral from the plug-in side. Then insert that into the wire nut, and turn the wire-nut clockwise nut to tighten everything down.
- You can test the connection by pulling on it, to make sure it is a good solid connection, with no copper showing. You want a good fit, so that no stray current can leak out of this connection and cause a short circuit, which could result in an electrical shock for a user, which you really don’t want.
- Do the same to connect the two hot wires.
- Test the connections for continuity. Putting probes on the fat prong on the plug-in and the threads in the socket should show continuity with your meter. Same thing for the connection between the skinny prong and the center screw in the bulb socket.
- Now that you have connected all these wires and tested for continuity, you should put them in a protected space. In this case, you can stuff everything back into the void space that previously held the electronics package (the black box that you removed earlier).
- There may be another narrow yellow wire (a ground wire). Stuff that into the void space as well. That wire is to ensure that if there is a short on the body of the lamp, it will go to ground through the wires in the house, and not through you.
- Then, cover that up. In this case, you can screw that plate that had covered the electronics package back into place. You could also put the fabric cover back over the base of the lamp.
At this point, you could put a bulb in the lamp and plug it in. It should light up.

5) Now, put in the in-line switch.
First, locate the section of the cord where you want the in-line switch to be. That might be close to the body of the lamp or somewhere along the length of the wire - someplace that might be convenient from which to operate the switch. You might want to mark that spot with a marker pen.
Use your wire cutters to cut the cord. Then split it down the middle to separate the neutral and hot sides (use a utility knife, carefully so as not to nick the wires). Strip back the insulation on both sides about 3/4 of an inch or so.
Twist the strands of copper conductor together, so that they can be nicely tightened down.
Identify which side is the neutral side and which is the hot side. Again, the neutral side will have a rough edge. You can also confirm which side is neutral and which is hot, by testing for continuity with the multi-meter. Mark the wires so that you can easily identify them later.
Open up the in-line switch, by removing the screws that keep the two sides of the switch together.
Note that the next few steps can be a little fussy.
Looking at the picture:
- At the top and bottom are some screws and a plastic housing, used to hold the wires tightly to the switch, once they have been properly placed into the body of the switch.
- If you look carefully in the gap between the two sets of screws, you can see some lettering. In the picture, on the left side it says N (for neutral) and on the right side it says L (for load, or hot wire side). The neutral wires from the cord will be tightened under the left, or neutral (N) screw, while the hot wires will be tightened under the right, or load side (L).
- Next are some screws that will be used to tighten down the copper wire and make the electrical connections to the toggle button part of the switch. The mechanical part of the switch mechanism is in there, though not visible.
- Take those screws out and remove the plastic piece. Then put the insulated wire through the gap. Spread the neutral and hot sides of the wire out. Then flip the plastic piece and place it back over the wires, aligning the holes in the plastic piece with the holes for the screws. Then screw that down tightly, so that the wires are held firmly in place.
- Then, maneuver the copper conductors under the screws (you will have to loosen and raise the screws). Wrap them snugly around the screws and then tighten the screws down (this part is tricky).
- Take care that there are no stray copper conductor wires that might touch any stray wires on the other side of the switch, which could short out the connections in the switch.
- Then do the same for the wires that will enter the switch on the other side. Remember to ensure that the neutral wire goes on the neutral (N) side of the switch and the hot wire goes on the hot (L) side.
- Put the top and bottom halves of the switch back together and screw it up tightly.
- Test the connection, by tugging on the wires one either side of the switch, to ensure that they won’t come loose.
Test for continuity. If the switch is in the on position, there should be a connection from the threads of the light socket, through the switch, and back to the neutral (fat prong) of the plug. Similarly, there should be a connection from the hot central screw in the light socket, through the switch, to the skinny prong of the plug.
If you put the switch to the off position, there should be no continuity.

6) Test the lamp. You could test the lamp for a short circuit. Put your multi-meter on DC voltage and place one probe on the body of the lamp (a metal part) and the other on a location of the house that is connected to ground (e.g. a water pipe). There should be no voltage drop showing up on the meter. As an extra safety check, you could get someone who knows this stuff to double-check it (I have a brother that is an electrician).

If everything went well, you should be able to put in a bulb (use an LED bulb since they don’t draw much power), plug in the lamp and turn it on from the switch. Then you can enjoy a lamp with a trouble-free switch.

7) The Fancy Two-lamp model. I actually put two of them on a common wooden base, with cable raceways to cover and protect the wires, then added a power bar to the side of the wooden base structure. Wrap the wires up neatly with some ties and staple them down and you have a unique bit of industrial art. :)

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