T-Pain Is On A Boat: Re: [Electric Boats] Encapsulating Electronic Components

Saturday, February 8, 2014

Re: [Electric Boats] Encapsulating Electronic Components

Bob

You are dead right about waterproofing. The effect you mention we would call The Diurnal Pump effect. Every night the enclosure cools, sucks in moist air, maybe some dew, condensate and dew collect. Every day the air expands leaving the water behind. Over a period of time the enclosure fills. Some desert survival water makers use this effect.

So trying to seal the enclosure may be the wrong approach, it has to breathe.

Personally, I seal the enclosure and then drill a small hole at the lowest point. Now when the air expands it blows out the water. Not perfect but better.

A more sophisticated approach is to fit a breather tube. The watertight enclosure will breathe through this tube, preventing the seals from blowing. If the length and diameter of the tube are above a certain ratio, different saturated vapour pressures can be maintained at each end. So the air in the enclosure can remain dry while the air outside is moist.

Maybe the best approach is to make the void in the enclosure as small as possible and fill the enclosure with a potting compound. But this too is a bit of an art, ensuring the differential expansion and contraction does not create stress cracks along which the moisture will track. For example, the interface between pcb and compound may separate due to thermal stress allowing moisture to creep along the pcb. Some components change size, coil cores may elengate when magnetised, capacitors may fatten when charged, they may vibrate when used with alternating voltages and currents.

Easiest solution? Seal the enclosure, drill a hole at the lowest point.

Peter

On 8 February 2014 13:08, Bob Noble <bnoble@sonic.net> wrote:

I haven't tried to waterproof anything, but have some experience working for the old HP in a Reliability Physics lab, where I did a lot of work seeing how water entered things in very tiny parts.

Most silicones are not conductive so it could help make it resistive to water.

The real problem with trying to make something water proof is this little catch.

If there are any air pockets at all, even little ones, this is what happens.

Let's say the air in those air pockets is at ambient temperature. When the part hits the water, it's much colder, which causes the air in the air pockets to cool down fast, which causes a suction. Since the part is in the water, it causes water to get sucked into the parts. It's very hard to stop this action, the greater the temp difference, the greater the suction.

When people try to waterproof a box, they try to seal it, but, there is a big air space in there and the seal usually won't hold for any length of time when submerged in cold water.

There is also a problem with condensation in a sealed box. If any water at all gets into it, it can't get out and will eventually fail because there is no place for the water to get out of the box.

It's actually easier to make something water resistant, than it is to waterproof something.

I think the silicone would make your part at lease water resistant with a good job of applying the silicone, if there are no moving parts on the part, which I don't see?

Since the part is only sixty bucks, it's worth a try and I think the part would last longer this way, than not doing it.

Bob Noble
Blog: http://www.bobseyes.net

From: tommy033107@gmail.com

Sent: Friday, February 07, 2014 3:32 PM

To: electricboats@yahoogroups.com

Subject: [Electric Boats] Encapsulating Electronic Components

I am thinking of getting a "Watts Up" meter to use on my solar canoe project. I can't seem to find a waterproof meter? So I am wondering if its possible for me to encapsulate the Watts up meter in lets say Sylgard 184 Silicone Elastomer ? I have access to it for free from a friends solar panel build.

Does anyone have any experience to share on waterproofing circuit boards etc. ???

Watts Up meter:

http://www.amazon.com/Watts-Meter-An...watts+up+meter

Kind regards

Peter Verralls  PO Box 71, Caribbean Villas, San Pedro, Ambergris Caye, Belize.  International Cell Phone:  +501 610 3155  Guatemala Cell Phone:     +502 490 46237   Satellite Phone:                 +8816 316 53280  E Mail:                               pverralls@verralls.bz  Satellite E Mail:                 881631653280@msg.iridium.com (160 characters max).  or use free messaging at  http://messaging.iridium.com/, to 881631653280 (no spaces).