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What are the Characteristics of These 3D-printed Capacitors

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This is a question about 3D printers. I don't know whether it is proper to ask you questions here...I hope someone can help me out. There are conductive filament for 3D printers which seem to have between 30 and 115 ohm/centimeter resistance depending on the axis. (Proto-Pasta conductive PLA)

They can be 3D printed as a capacitor of 2 cubicly-interlacing-but-not-touching matrices as follows, with one negative and one positive:

xtK45.thumb.png.60861d61865a0421bf02f5c92c489561.png

 

Does it have useful properties? I figure probably it could already be done, but here maybe it can be done at home simply and relatively cheaply, and so I wonder what that does, if someone can figure it out. I don't have yet the equipment to try. With a cheap printer I can't imagine doing more than 2x20x20x20 cubes, inside 20 * 20 * 20cm, with 1cm per side. I know that's surely not much compared to normal caps rolled onto themselves. I tried it with normal filament. The bridging is tricky, but it can be done, so I wonder about the theory.

 

2.png.ac9496777af34912382223ebc2c2ee03.png

 

Sorry for the blurred image..An interesting thing about 3D printers is that it can create shapes of things nested one into the other. But I don't understand capacitors(http://www.kynix.com/Product/36.html) and so it's possible the effect cancels out and that it's of no use as it is, or that the standard plate-against-plate is better.


Anyway, I'll be trying it eventually, or at the least, a standard configuration.

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I don't think this is going to work. The main problem is that most 3D-printers do cause hairs or strings, when jumping from one spot to another, especially for when printing very small pillars. And in this design they have to jump a lot. So you are going to have lots of short-circuits.

 

If you would print thin full layers on top of each other (thus: layer1=pos, layer2=insulator, layer3=neg, layer4=insulator, layer5=pos, etc.) you might have more success, but still. When printing, the nozzle often gets dirty, and drags around material which is deposited somewhere else. This too could cause short-circuits. And due to the large distances between layers, you simply won't have enough surface to get a reasonable capacity.

 

Finally, the high ohmic resistance (I don't know if this is the proper English term) is going to reduce the quality of the capacitor a lot.

 

I do see the value of 3D-printed circuits for ohmic resistances, for example to power LEDs in model railroad trains or so, but for capacitors and coils, I don't think it going to work with this sort of printer, and least not in the near future.

 

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We can do a very approximate ballpark capacitance figure as follows: C = K x E0 x A / D (e.g. see http://www.daycounter.com/Calculators/Plate-Capacitor-Calculator.phtml

so put in an area of 100 mm2, a distance of 1 mm, K=1 for air is accurate enough, and yo get a capacitance of 0.885 pF. This is pretty d*m small.

Supposing you print 2x20x20x20 cubes, I'll take it that's 1x20x20x20 = 8000 cubes for one plate of the cap, so the maximum surface area you can get is 8000 x 6 cm**2 for each "plate". 1mm is my assumed distance between one plate & the nearest bit of the opposite polarity plate. so that's an area of 4800000 mm**2. Stick that in the calculator and you get 425 pF, or about 0.4 nF. But a lot of your cubes won't be able to expose 6 faces to another cube, as they will need a face to attch to the next one. End cubes will be able to expose 5 faces. So multiply than guesstimate by 5/6.

 

This formula reveals that what matters is the area exposed to the other plate, not the volume. Also halving the air gap doubles the capacitance.  So cubes are the wrong thing to be printing, you want flat sheets. And you may as well try to use both sides of any sheet you print. So what you want to aim for is rather like the tuning capacitors found on 1930s valve radios, I've knocked up a quick pic here. Yellow bits are fixed, red bit rotates, and the more red plate gets sandwiched between yellow ones, the greater the capacitance, so you can alter the frequency of a tuned circuit.

Variable Capacitor.png


You could do something similar by printing tall thin flat plates interleaved, something like this:

FixedCap.png

 

The narrower the air-gap (d) is from one plate to another, the greater the capacitance. But get it too small, a higher voltage could arc-over (say 10,000 volts/cm in air maybe might arc) and it's toast. And maybe dust accumulating might short it out a bit.

 

Edited by andywalter
typos and arrange pics.

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