PLa and ABS as insulators

[John Stevenson 1Participant @johnstevenson1]

[John Stevenson 1Participant @johnstevenson1]

Seeing as we have some very clever people on here and also two Google Childs

What out of the two materials, PLA or ABS would make the best printed distributor cap.

Usual high voltages associated with spark plugs but no extremes of heat to be overcome.

[Anonymous]

Posted by John Stevenson on 11/05/2014 12:07:33:

Seeing as we have some very clever people on here……………..

That's as maybe, but it's not going to stop me replying.

Most plastics have very high dielectric strengths (V/m), so in that sense I don't think it'll make much difference which is used. However, the other two important factors in voltage isolation are creepage and clearance. Clearance is what it says, the clearance between conducting parts through the medium in which the item is placed, usually air. The clearance breakdown depends upon the configuration of the conductors and the properties of the medium, not on the material of the item. Creepage is the distance over the surface of the item between conductors, and is therefore affected by the material, as well as any surface pollution.

I would think that creepage is most important factor in this case, and given that the water absorption of PLA is rather worse than ABS, I'd go for ABS.

Regards,

Andrew

[FatgadgiParticipant @fatgadgi]

Yep, agreed, ABS would get my vote as well.

PLA absorbs more water yes, which is bad for resistance, but worse, PLA is biodegradable. I have this vision of you bounding out one morning only to find a puddle of goo on the floor. Good compost for the garden though.

And I know you say that temperature is not a problem, but if it's going on a hot engine, neither materials are particularly good at temperature. It's the softening temperature (not the melt temperature) that you need to watch – PLA is lowest and can soften in a hot car, for example.

I would suggest that you take time to get the parameters dot-on to make sure you have no porosity in the build otherwise it will track through the cap.

You need to check which, if any chemicals are going to come in contact with the ABS – some greases and oils are a problem, as well as acids and acetone. The acetone is a good to wipe on the outside surface to melt it and improve the surface finish …. and solve the problem with your porosity, perhaps

Nice idea to try though – can't wait for the results ….

Cheers – Will

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