The battle against moisture

Baoshi — Mon, 20 Aug 2012 13:51:50 +0000

Singapore, a tiny little island at the tip of Malay peninsula, is probably one of the world’s most humid country. The average relative humidity (RH) level is 84.2% according to NEA, with thunderstorms occur on 40% of all days when RH can shot up to 100%.

As you may wonder how does this relate to electronics, look at this chip I dropped in my drawer 3 years ago.

Rusty chip

For information purpose I list the storage humidity requirement for various items here:

RH%	Items
50-60%	Painting, Antique, Currency notes, Stamp, Book, Musical instrument, Jewellery, Leather products
40-50%	Camera, Camcorder, Lens, Digital products, CD, Binoculars, Film, Video tape
30-40%	Metal, Semiconductor products, PCB, IC, Battery, Precision equipment, Optical equipment
20-30%	Raw medical, Dye, Seed, Pollen
<20%	Special chemical products, Precision electronics components, BGA, LCD

Buying a dry cabinet is obviously the best approach. In fact I already have a small one for the cameras. But to store all my electronics and computer stuff I need a pretty big one, which costs a bomb, and I simply do not have the luxury of floor space. During a recent house cleaning exercise I decided to convert one of my wardrobes into a dry cabinet. Here is the victim:

Wardrobe in my room

There used to have a horizontal bar at the top for hanging clothes but I removed it. There are no shelves. A trip to IKEA brought me these wire baskets:

IKEA KOMPLEMENT basket

These baskets are not cheap (S$19/pc), but very sturdy and well below the cost of custom made shelves. I draw some marks in the wardrobe and start the irreversible modifications.

Markings inside the wardrobe

Here comes the main actor – the drying controller. I bought it from China taobao.com at RMB258 (S$52).

Dry cabinet controller

It is rated 6W/42W(max), control RH range 25%-55% with drying volume of 200L. I studied for a while and roughly figured how it works: the dry element is very similar to those we saw in “Thirsty Hippo” packet. There is a metal door in the controller. During drying operation the door opens inwards to let the dry elements suck the moisture from inside the cabinet; after a certain time the metal door closes, an electric warmer heats up the dry elements and dispels the moisture to the outside environment. The whole process repeats again and again until a pre-set humidity level is met.

To increase the effectiveness of drying, rubber strips are installed around the door frame.

Rubber strip along door frame

And here come the final product :

Finished dry cabinet

During day time when my room humidity reads 69%, here is what inside the cabinet:

RH reading inside dry cabinet

It doesn’t reach the advertised 25%. Maybe because the cabinet is not enough airtight and the total volume is larger than rated 200L.

I spend two weeks sorting all my components into plastic boxes. So far I’m pretty satisfied

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The battle against moisture