Testing Proto Pasta Conductive PLA with Snap Circuits

3D printed Snap Circuit pieces
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In a previous blog I wrote a review of Proto Pasta’s Conductive PLA filament. For that review I just looked at the printing properties of the material.
I liked how Conductive PLA printed, and it had a smooth matte black finish. Texture wise it does feel silkier than normal PLA. When I discovered that the filament can be used as a pencil, I realized that the silky texture was due to the graphite in the filament.

Electrical Properties

According to the companies site it has the following electrical properties.
• Volume resistivity of molded resin (not 3D Printed): 15 ohm-cm
• Volume resistivity of 3D printed parts perpendicular to layers: 30 ohm-cm
• Volume resistivity of 3D printed parts through layers (along Z axis): 115 ohm-cm
This material has the potential for use in electrical applications. I can see variable resistors 3D printed with this conductive filament. I can also see this possibly as a low temp resistance heater for use in on 3D printer beds. For cosplayers, this would be a good way to embed wiring and LED’s into a prop.

Testing

For this I wanted to test it with a multi meter to see all of its properties. Then I remembered what happened to my last multi meter (It died a horrible electronic death, totally my fault, don’t ask).
So to test this, I decided to think outside the box and use another tool set I did have.
As a science teacher, I used Elenco Snap Circuits to show students the concepts of electronics.

3D printed Snap Circuit pieces - conductive PLA

The original Snap Circuit pieces in blue, the 3D printed ones in black.

I also remember that we lost a few pieces, and I am curious to see if I can 3D print them in Conductive PLA.
I made my own Snap Circuit pieces in TinkerCAD  to test with. However as I test fitted them to the original Snap Circuit pieces, I hit my first issue.
The thermal expansion on this seems to be more than normal PLA. Nothing I printed fit with the dimensions of the original Snap Circuit pieces. It looks like everything Printed in the Conductive PLA had shrunk by 0.5 – 1 mm from the original dimensions.
In spite of this, I found that the graphite in Conductive PLA also makes it softer and easier to work with. I was able to press fit the pieces I wanted together.

Test 1, Light Test

For this, I wanted to see how the resistance of Conductive PLA would affect the brightness of a standard flashlight bulb.

origional light test - conductive PLA

Light Test with the original snap circuit kit.

I build the light setup shown here with the pieces in the Snap Circuit kit.
While the regular setup worked, the Conductive PLA piece that I replaced a snap with  provided too much resistance to power a 2.5 V / 0.3 A bulb.

No light. - conductive PLA

With the printed piece (black) the resistance was too much.

Test 2, Motor Test

In this test, I wanted to see how Conductive PLA would work in powering a small DC motor.

working motor - conductive PLA

Original Snap Circuit setup.

With the normal set up, the motor turned the fan at a good speed. With the 3D printed piece, the motor did not turn at all.

3D peice keeps motor from turning. - conductive PLA

With the printed piece (black) the motor would not turn.

LED Test

With this test, I built a simple LED circuit. While the normal circuit worked fine,

LED - conductive PLA

Normal LED setup in snap circuits

adding the printed piece to the 10K ohm resistor did drop the brightness of the LED down.

Dim LED - conductive PLA

With the black piece and 10 K ohm resistor, there was almost no light from the LED

When I changed out the Snap Circuit resistor with just the printed piece, the LED did light up with a medium brightness.

printed resistor. - conductive PLA

LED setup with just the printed piece acting as the resistor.

Meter Test

I wanted to see how much resistance the piece offered. With the standard Snap Circuit setup, a 10,000 ohm resistor will show as 10 mA on the meter.

10 mA -conductive PLA

Normal Snap Circuit setup, with 10 mA reading.

With the printed piece in place, I had to switch to the 100 mA setting on the meter. I got about 50 mA with this setting.

50 mA reading -conductive PLA

50 mA with the printed piece in place

If we use Ohms Law to find the resistance , we get R = V / I.
When you plug-in the numbers, R = 3 V / 50 mA = 60 ohms.
The piece used is 6.3 mm wide, so if we take the following value;
Volume resistivity of 3D printed parts through layers (along Z axis): 115 ohm-cm
We get that the theoretical values of this piece should be 72.45 ohms.

Now the piece was printed with only 5% infill, so it makes sense that the resistance is less than the predicted value.

Reflection

Proto Pasta’s Conductive PLA is a material for experienced 3D printers.
With the thermal expansion I experienced, you will have to design parts with a very loose tolerance to get the conductive parts to fit to your other prints. You will have to play with this filament on your printer if you want to get a super tight fit.
If you want to integrate this into your 3D print, this would be a great project for a dual extrusion head printer. I can see cosplay props with integrated LED wiring, as this filament also acts as the resistor. I can see other applications where you can save time and assembly by using this as your wire and resistor.
I know my testing in this was not super scientific, and in the future I’ll hopefully have a working multi meter to better test these pieces.
If you’re an electrical engineer, this would be an interesting material to test and develop a guide for. As more 3D printers play with this material, it would be nice to see the results of integrating Conductive PLA with other print material.

AUTHORS NOTE: Due to Copyright restrictions, I can not release the .stl files for the test pieces I copied for this test.

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