How to protect electronic against moisture? 99% sealed? Or better open to air?

I will use an Arduino and some other electronics in my motorcycle.

Arduino, WS2812 LED stripes, Accelerometer, LDR, SD-Card, maybe OLED screen

I will install most of this under the pillion seat. It won’t be exposed to water (rain) but there might be high humidity. I live in Bangkok with often 30 degrees Celsius and high humidity.

I see two options:
a) Try to seal everything as good as possible, i.e. with sealed connectors, heat-shrink and hot glue.
b) Cover the parts i.e. with heat shrink or a box but don’t try to seal it.

I guess 100% sealed would be perfect. But I guess that is very difficult. So maybe I end up with 99% sealed which let’s moisture in but it takes time before the moisture get’s out again.
If I use option b then the electronic might be sometimes in high humidity. But after “the rain” is over there will be normal, not so humid, air and it will be dry again.

Any suggestions?

Edit: Previously I had another edit but that was intended for another post.
I removed it and an attachment.

The problem is likely to be condensation - due to falling night temperatures the moisture in the air
condenses to droplets. The only solutions to this I can see are complete sealing (hermetic box(*) or potting), or keeping
in a very well thermally insulated box with a small amount of constant heating (just leaving it powered on
continuously might be enough). The air flow into/out of the box should be minimal (one small breathing hole?)

(*) for hermetic sealing you need to seal in only very dry air, such as from a fridge or just nitrogen or CO2
Something like an otterbox might be a good sealed enclosure.

We used to make the electronic control boxes for a local motorcycle manufacturer. All the electronics were inside a plastic box with waterproof automotive connectors. No wires into or out of the box. After testing the box was filled with epoxy potting compound. And then the cover was put on the box. Same as your case, the box was put under the seat.

You need to decide if you ever want to modify what you have. If so, you cannot waterproof it. If you need to modify it, then the best, as suggested, is to keep a warming element in the box and connect it to the battery or power from your house AC supply.

Paul

I’m having great success with keeping stuff open to air - protected from the rain, large ventilation openings in the box, conformal spray coating on the electronics. Similar climate as yours - subtropical, so hot and very humid in summer. These electronics are on all the time, though, and even though it’s using maybe 0.5W of power it keeps the box at a few degrees above ambient. More than enough to stop condensation.

We have plenty of nights where your laundry gets wet outdoors - it’s that humid - so unpowered and unheated the electronics would be much worse off I’m sure.

100% sealing usually is impossible to achieve - and even with 99.9% moisture will find its way in, especially when the box get sprayed with water, cools down fast, pressure inside drops, and water gets sucked in. Normal atmospheric pressure changes can have a similar effect. That means you end up with water in your box. Potting is indeed the way go if you have to make it totally water proof.

Water is a mighty opponent!

The special electronic "solder-through conformal coating" looks and smells exactly like ladies' nail polish. Buy the clear nail polish and brush it on the entire PCB and the metal legs of the components.

Thanks for the information. A few follow up questions:

a) Are there other words for epoxy potting compound? I found that on ebay but not on DigiKey,

b) Where to buy this epoxy potting compound? In electronic shops?

c) If I would use epoxy potting compound with an Android and I want to still be able to use the USB connection: Should I connect a USB cable in the USB connector and seal it all? Or should i solder a wire to the USB contacts?

d) Can anybody confirms MorganS idea about nail polish? I guess what smells is the solvent but that does not say much about the real coating.

Edgar1:
Thanks for the information. A few follow up questions:

a) Are there other words for epoxy potting compound? I found that on ebay but not on DigiKey,

b) Where to buy this epoxy potting compound? In electronic shops?

c) If I would use epoxy potting compound with an Android and I want to still be able to use the USB connection: Should I connect a USB cable in the USB connector and seal it all? Or should i solder a wire to the USB contacts?

d) Can anybody confirms MorganS idea about nail polish? I guess what smells is the solvent but that does not say much about the real coating.

This is what we use for potting devices: EPOXY RESIN BLACK POTTING COMPOUND 4 CIRCUIT BOARD & ELECTRONIC MASKING SEALANT | eBay.

Until you are ready, I would really recommend a brush-on conformal coating. Polyurethane is easiest to work with.

You NEVER want to use potting or conformal coating on connectors!

Paul

A) I'm surprised you can't find it with that search term. There are a lot of subtle issues to work out if you are embedding the circuit in solid plastic.

B) boat shops will be cheaper but it might not be the right stuff.

C) either. I would go for the plug but hardwired works too. Just watch the strain releif where it exits the blob.

D) it works. It keeps out moisture but you can melt it with a soldering iron.

I would try to pot the electronics if it were me.

What about a small 12v fan maybe?

A fan just brings moisture in.

You don't have to be super-careful. Look at the electronics already on the bike: nothing is completely sealed. But you only expect the Arduino to last 10 years or less. The rest of the bike (12V or 6V) will still be going, with minimal repairs.

Loctite E60-NC is a very low viscosity epoxy specifically designed for potting. I've used the less runny E30 version to good results for an underwater project.

It's pretty expensive (about 10 USD per 50 ml tube) and only available in 50 ml packages.

For outdoor use I am using "99% sealed" box with silica gel desiccant with colored indicator. The box is common lunch box with silicone seal so it is easily opened and hole is drilled for wires entrance. So far (about half a year) it works well and the desiccant is nearly fresh:

MorganS:
A fan just brings moisture in.

You don't have to be super-careful. Look at the electronics already on the bike: nothing is completely sealed. But you only expect the Arduino to last 10 years or less. The rest of the bike (12V or 6V) will still be going, with minimal repairs.

Automotive electrics are robust, much more metal than in a PCB trace, and they still corrode heavily.
This is survivable for large blade terminals and relay modules with widely spaced connectors, but
regular condensation on a soldered PCB will corrode component legs clean away.

Yes, conformal coating is a very good idea, liberally applied to all metal contacts and the PCB both sides.

Hi,
Conformal coating,

http://www.humiseal.com/conformal-coating/

https://www.techspray.com/conformal-coating

Tom.... :slight_smile:

I just saw this with interesting answers: