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From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Garmin Edge 830 elevation issues
Date: Fri, 02 Aug 2024 07:32:05 -0700
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On Fri, 2 Aug 2024 11:34:05 +0200, Rolf Mantel <news@hartig-mantel.de>
wrote:

>Am 02.08.2024 um 04:39 schrieb Frank Krygowski:
>> On 8/1/2024 6:54 PM, Jeff Liebermann wrote:
>>> > It's possible to "pump" water into an allegedly waterproof enclosure.
>>> Heat the GPS with hot air to about 45C.  Then dump it in a bucket of
>>> 10C cold water.  The air inside the GPS will contract and create a
>>> partial vacuum, which then sucks the water into the enclosure (if
>>> there are any leaks). 
>> 
>> It's a bit interesting that the same problem can apparently happen with 
>> hub dynamos. Supposedly, the SON hub dynamos (from Germany) have a 
>> pressure compensation gizmo built into them to prevent that mechanism 
>> from rusting the insides of the hub.
>
> From the mechanism, it can happen with any bicycle hub: park the bike 
>inside (20C) in winter, use the bike in the wet around 0C.
>It's just that SON is IIRC the only hub expensive enough to have 
>detected and offered a fix to this problem.
>
>Rolf

I ran into the problem in the marine radio business.  Obviously, the
marine environment is very wet (and corrosive).  Humidity is high and
the difference between air and water temperatures can be large.  Any
enclosed box will eventually collect condensed moisture.  In general,
there are two ways to deal with the problem:

1.  Seal the enclosure and pressurize it to be slightly above
atmospheric pressure using dry air.
2.  Design a safe path for the water to exit the enclosure and do
something to reduce corrosive effects.

Neither are a complete answer to the problem.  A pressurized enclosure
works nicely, but make service and repairs difficult.  Just opening
the enclosure in a high humidity environment will produce
condensation.

Adding drain holes is worse.  Bicycles usually have drain holes on the
bottom of the bottom bracket to drain any condensed water from the
frame.  That's fine until someone hangs their bicycle vertically on a
wall or parks it inverted on the handlebars.  The hole also tends to
become plugged with greasy dirt.

There are plenty of other solutions (desiccants, inert gases,
conformal coatings, oil baths, immersion in oil, regular teardown
maintenance, etc).  They all work but also need to be designed into
the product.  Randomly drilling holes in your hub to drain the water
isn't going to work very well.

For electronics and sensors the problem is more complicated.  Air
pressure sensors require open access to the atmosphere.  Some SMD
(surface mount devices) such as clock crystals are sensitive to air
pressure.  To equalize the pressure, the manufacturer drills a
microscopic hole in the case.  That works, except the clock frequency
changes while the air is slooooowly leaking though the hold.  Apple
had that problem on some iPhone models.  I suspect that Garmin and
others are aware of such problems and settled on the most reasonable
protection solution that doesn't involve complex and expensive
solutions.


-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558