As secretly hoping to use our carbon fiber parts as a common ground for overall power distribution, I thought it would be good to actually measure how it is doing in a context of our other options. The plan is to measure the material resistance and voltage drop for copper wire, aluminium bar and our CF tape on 1 m of material.
Our first testing subject is 25A 2 Core Tinned DC Power Cable from Jaycar.
Running it through a nice cable calculator, we should be seeing following readings – expected resistance to be 5.8 micro-ohms.
Now to our actual measurement.
Well, we measured 0.3 ohm. That doesn’t seem to be correct as this would be 100 times higher value than what calculator shows. Voltage drop was 5.87 mV.
Our second testing subject is Metal Mate 20 x 1.6mm 1m Aluminium Flat Bar from Bunnings warehouse.
Running it through our nice cable calculator again, we should be seeing following readings – expected resistance to be 0.8281 micro-ohms.
Now to our actual measurement.
Well, we measured 0.4 ohm. That doesn’t seem to be correct as this would be again 50 times higher value than what calculator shows. Voltage drop was 0.6 mV. This value is lower than with copper as we have more much more cross-section area here (10 times more).
Carbon Fibre tape
Our last testing subject is 12k 200gsm 4″/10cm width Carbon Fiber Uni-directional Cloth UD Fabric Tap High strength Repair material Tensile strength 3400Mpa from AliExpress.
Unfortunately our calculator doesn’t know Carbon Fibre material, but as it didn’t help much for that copper and aluminium before we’ll just go ahead. Seb prepared aluminium clamps so we have something to connect to.
First reading came with 8 ohms resistance, what seems to be roughly 20 times higher value than for the others. As were trying to measure the voltage drop, we needed to put weights on those clamps to improve connectivity. Still, we measured quite high 1.2V drop just on that 1 meter!
So putting it all in a table:
|Material||Resistance [Ohms]||Voltage drop [mV]|
Honestly I am not sure what to make out of this. Does this still qualify to be used as our common ground? I suppose someone with more insight into electricity needs to have a look. It is not a big deal if this is not ok, but we’ll have to count with additional weight for doubling our power cables.
Update from Richard 2023/1/23
You can connect it to GND, but you can’t use it for electrical GND for return currents. So you really want to be using:
So if 2A flows P=32W
Update from Chris 2023/1/23
Resistance is different in different directions on carbon fiber as well – and almost none between layers. CF threads are “wet” with a chemical which helps the resin absorb – if you’re wealth enough to grow carbon nanotubes on the CF to use as the wetting agent, you then get excellent conductivity in all directions.
Or the opposite of that technology – when you don’t use nanotubes, conductivity is poor. Multi-Functional Carbon Fibre Composites using Carbon Nanotubes as an Alternative to Polymer Sizing – what’s the ground for? If it’s the high-current for the motors, perhaps some copper tape laid along with the fibers when you make the tubes like below?
There’s been also big comment from Adam, see in comments below.
Thank you guys!