Will this work as a conformal coating?

[John in CR]

I need to put a conformal coating on some controller boards that I'm ventilating. This is on some cheapie controllers that won't get repaired if they blow again, so a thin clear coating that I can get thru to replace a component isn't necessary. I just want to protect them from dirt and moisture that forced ventilation may cause.

The closest thing I could find locally is 3M 1602 red Insulating Sealer. It's an alkyd resin with a dielectric strength of 850V/mil, and the quote from the can that makes me think it will work is. Use Insulating Spray sealer to spray over insulation on wire and cable splices, as a general-purpose sealer or for touch-up insulation on motor windings and frames.

It seems like maybe the same stuff DocBass sprayed on the stator of one of his X5's.

What do you think...go for it or find something more specifically called a conformal coating?

 

[kfong]

Should be fine, you could even in case it in epoxy if you don't plan on servicing it.

 

[John in CR]

Should be fine, you could even in case it in epoxy if you don't plan on servicing it.

Thanks for the input. I'll report back if it doesn't work out. It seems like the dielectric strength is good enough, and since it's for putting on motor windings, the thermal limits must be good enough.

I'd go the epoxy route, but locally I've only been able to find epoxy for laminating fiberglass, nothing for potting. If this laminating resin gets too thick, it goes into thermal runaway while curing and bubble up. Plus it has quite low thermal limits. I have a couple of gallons, so I use it whenever I can, but I don't think it's good for this app.

John

 

[texaspyro]

Be real careful with do-it-yourself conformal coatings... they can be MUCH worse than no coating. Water, capacitor barf, etc can get trapped under the coating or wick in via hairline cracks. With no easy way out, it gets bored and hungry and starts eating away at whatever it can find. Even mil-spec electronics is seldom conformal coated these days.

Dust is almost never a problem with electronics (except for open frame switches and relays). Most outdoor type electronics is mounted in boxes with drain holes in the bottom for that nasty water to finds its way out.

 

[John in CR]

Thanks TexasPyro,

I did it already on the cheapie and hope for the best. My 24 fet will get dual small blowers, and I'll forgo the coating but make extra effort to avoid water ingress.

What do you think about vibrations being an issue? I can mount it on the swingarm with the controller near the pivot extending to about halfway between the pivot and the axle, or mount it fully sprung under the seat. I think on the swingarm will look better, but the technical plus is that the phase and battery cables would be only 1/3 or less of the length compared to the under the seat mounting. This is for road use only, so movement on the swingarm shouldn't be too much more than if the bike was a hardtail.

 

[amberwolf]

When I was at Honeywell CFSG, quite a number of things we worked with for various aircraft were either potted or conformal coated. The CC used was always this UV-dyed clear stuff that could be dissolved away with (I think) acetone. It never got really hard, but was still soft enough to mark with a fingernail, so it would flex with components and such during thermal cycling.

Potting compounds were varied, but the two most popular ones that weren't totally rigid were by 3M. One was a baby-blue silicone type, and was quite flexible, but required mixing or final setting in a vibration machine to remove all the microbubbles of air in it, or else you'd end up with sometimes component-sized voids in it. It could easily be removed by pulling and scraping, if repairs were needed. IIRC, it was a thermally-cured type, so it would remain liquid (viscous) until all the bubbles coudl be removed.

The second was black, and was harder, more like a softer epoxy, and was a catalytic-cure type. I forget the working time, but it was fairly long--long enough to again put it on a vibration table to help bubbles rise out of it to prevent voids.

I wish I knew what the 3M names or numbers for these two were, but we only ever used the internal Honeywell names/numbers, which I don't even remember anymore.

 

[parabellum]

What do you think about vibrations being an issue?

Are you fixing big caps with extra silicon or something else, normal glue (or what it is) used for usually brakes and caps jumps inside until braking of I suppose (I only got to the part of jumping inside, now I open every controller before using)

 

[texaspyro]

What do you think about vibrations being an issue?

For almost any surface mount or through-hole components, not at issue. I've shot unpotted PCBs out a "gun" at around 20,000 G's.

Big caps are probably the most problematic part on a controller. They tend to have some mass and have small leads. The usual cure is a bead of silicone around the base... may or may not help. Another potential issue is very poorly mounted PCBs that can flex. Mostly a problem when one end is rigidly attached and the other end isn't. And transformers and inductors on DC-DC converters. Basically, you want to look out for weighty things that stick out from the board.