I see this potting all the time in HID ignitors and some electronic halogen PSU's and they are fine for many years. The ignitors sometimes are exposed to extreme heat (straight above th ereflector of HID lamp), moisture (leaking fixtures) and still work fine

The trick is that te polyester or epoxy or whatever hey are potted in is not completely hard, its a bit like acrylic sealant so it can flex for thermal expansion etc

The potted ignitors contain four components in total (not counting terminal block and the case), so do not have to use P.C. board, the components are soldered together "in the air", the assembly is put into the canister and filled by the plastic.

What work quite well is close the electronic into a sealed box (or can), but with the air inside and use the plastic only to form a kind of seal. That I've seen used on many electronic devices, e.g the exposed electronic modules (HID ballasts, engine ECU,...) in cars.

And what work the best (and it is used in aircraft industry for simpler and critical electronic devices) is to use a metal canister (with glass isolators to pass lead wires), solder it shut and before sealing, fill it with some inert gas (or at least nitrogen) under pressure. The result look more like an oil filled metal can capacitor, but with way more lead wires.
This really could ensure complete weather protection and it is still feasible to check the seal quality (the fill gas pressure - if it dis not leaked, no foreign matter could be inside; as a "pressure gauge" is usually used one of the can wall, what become deformed by the inner pressure, so the extend of the deformation tells, if the inner pressure is OK/NOK, sometimes even equipped with an internal warning contact). But something like that is not feasible in more "normal" applications, even the car industry does not use that.

Again, the board itself is kept clean, without any lacquer or so.

We used to seal our medical battery packs in this way, the two lead-acid gel batteries and charger/monitor board were assembled into a plastic case which was then sealed with acetone, using a syringe with electronic driver. The boards were not coated in this case.


BG

We used to seal our medical battery packs in this way, the two lead-acid gel batteries and charger/monitor board were assembled into a plastic case which was then sealed with acetone, using a syringe with electronic driver. The boards were not coated in this case.


BG

The battery and electronics in one common sealed compartment?
That does not sound too reliable: The battery emit some (small quantity) of H2SO4 fumes when becomes fully charged, what tend to corrode everything around.
Moreover completely sealing the SLA is considered as an unsafe practice, as you in fact defeated the safety purpose of the pressure valves...

It does not look very reliable to me when there is an "air bubble" around the circuit... Give it 1 thin way in (imperfection around some wire seal, water soaking into the strands of stranded wire entering the enclocure....) and it'll sip in every drop of water it can get just by thermal pressure changes of the air in the enclosure

It does not look very reliable to me when there is an "air bubble" around the circuit... Give it 1 thin way in (imperfection around some wire seal, water soaking into the strands of stranded wire entering the enclocure....) and it'll sip in every drop of water it can get just by thermal pressure changes of the air in the enclosure

Indeed, but the liquid (what causes the problems is only liquid water, as it is the only form capable to carry ions) water would remain on the canister wall, so out of the reach for the electricity. And as during operation the board become warmer than the enclosure, the water won't condense on the board (provided itis clean, so no resin flux residues,...), so it won't doany damage to it. Moreover the condensate on a clean surface made of material not soluble in thewater mean, the water would be free of any dissolved content, so electrically not conductive. And when remain not conductive (and it most likely would at least till theboard warm up and the water evaporate), it can not cause electrolysis corrosion.

But of course, when the hermetic sealing is not necessary (e.g. IP69 immersible equipment,...), it is way better to keep drain and steam vent holes in the enclosure, so the water could go out (in both liquid and vapor form)...

The hole may happen to be located in such a way that it'll pull in liquid water, and let out air. In this case, the box will fill up with water untill the water level reaches the circuit...

Also, watre pulled into stranded conductors will cause corrosion ofthe conductors in that spot - it doesnt even need to reach the enclosure, the enclosure only supply the vacuum to pull the water

The hole may happen to be located in such a way that it'll pull in liquid water, and let out air. In this case, the box will fill up with water untill the water level reaches the circuit...

Also, watre pulled into stranded conductors will cause corrosion ofthe conductors in that spot - it doesnt even need to reach the enclosure, the enclosure only supply the vacuum to pull the water

But that is not about "filling or not filling", but about generally bad design...