Introduction: Testing Bare Conductive Paint at Higher Voltages and Currents
I noticed the packaging for the Bare conductive paint states that it has not been tested at over 12VDC. I took this as a challenge to find out what it could do.
The materials I had on hand, only allowed for testing at 120v AC, so I decided to go for it, as we can do more testing later on.
First off, I needed a substrate. I chose some 1/8" HDF (High Density Fiberboard). It's the same material they make pegboard from.
Next, I grabbed 4 nuts, bolts, and washers to use for electrical connections.
I also needed something to supply power, so I grabbed a spare power cable for some long-lost electrical appliance.
For a load, I used a pair of woot-off lights, plugged in to a 120v usb phone charger, as well as a 60 watt incandescent bulb in a edison base to NEMA plug adapter.
I then grabbed a spare single gang outlet box and power outlet.
And last, but not least, the stuff I'm actually testing. The Bare conductive paint.
This is such a bad idea, i'm just going to say, don't do it. Not only do you have live 120v AC voltage sitting on some fully exposed bolts, but you also have that same voltage running through a line of carbon sitting on a piece of wood. If you ignore me, and actually do this, at least have a fire extinguisher nearby and do it on a circuit with a circuit breaker.
First thing I did was set up the connections. You will want to drill four holes in the substrate of your choice, large enough for your bolts.
After this, you will need to prepare your wiring. I cut the end off of the power cable, and then cut a second piece off of the cable to attach to the outlet. Wire up your outlet, by connecting each of the wires to the outlet, and mounting the outlet in the single gang box.
Next we created the conductors by running a bead of Bare conductive paint between the input and output holes on the substrate. We used a 1/8" bead of Bare. You can probably get more current carrying capability by making a wider trace with the Bare.
Now it's time to hook everything up. Strip the ends of the wires, place the bolts in through the bottom of the substrate, place your wires down on the substrate next to the bolts, put your washer down on top, and bolt everything down. This will squeeze the bare paint across the bottom of the washer, which should help make a better connection. Once everything is bolted down, let it dry. The bare paint doesnt seem to be very conductive while wet (upwards of 15KOhms).
Once everything was dry, we tested with a small load. A USB phone charger powering a set of woot-off lights. Once everything was plugged in, we powered up the circuit. At this point, we noticed something interesting. The lights would turn on and off on their own, in a consistent time frame. It appeared that we had created an oscillator by adding resistance into the circuit. The capacitors in the phone charger would charge up slowly, get to a certain point which triggered the regulator to start up, dump all the energy from the capacitors out to the lights, then shut off until it could charge up again. The paint was not yet dry.
After leaving the paint to dry a little while longer (actually, hitting it with a heat gun... ain't nobody got time for that) the lights would stay on constantly.
This was a rather small load, less than a hundred mA or so. The paint was handling it like a champ though. No noticeable heating from the traces, and the lights were just as bright as they would be when plugged in to a regular wall outlet.
Now it was time for the 60W bulb. Upon powering everything up with the 60w bulb, we had no light. Checking the voltage on at the outlet showed about 3 volts passing through, with the voltage rising slowly. We decided to keep it powered up, and noticed the voltage start rising faster. Eventually, at about 12 volts, the bulb started glowing dimly, and started getting brighter. At about 14 volts, smoke was beginning to emit from the area of the bare paint. It turns out, it wasnt the bare paint that was smoking, but the wood substrate underneath. Checking the temperature with an IR thermometer revealed that the temperature of the bare paint and surrounding wood was about 450-500 degrees Fahrenheit. The bare paint eventually started arcing. At this point we used a clamp-on current meter to see how much current was passing through the circuit, the meter read 410mA, which is about 50 watts, a bit shy of the 60 watt bulb we had as a load.
After a lot of smoke, arcing and general mayhem, it became obvious that the bare paint was no longer the conductor in the circuit, we had burned all the way through the substrate and the charred, burnt wood became the conductor. We left it running until the board finally burned enough that the circuit broke.
Well, What did we learn?
We learned that bare conductive paint is fairly resistive (about 40 ohms per cm), Will heat up quite a bit when the right amount of power is passed through it, and doesn't really like 120v AC.
We also learned that it has to be completely dry before you use it, otherwise it is way too resistive to be useful for much of anything (it wont even allow an LED to light when wet).