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Submarine Watertight Compartment Drying Fan

by Bob Warburton, March 2006

For those with less than perfectly tight WTC's on submarines, a good idea is to ventilate the compartment between runs in order to prevent condensation problems from causing corrosion and moisture damage to installed equipment. Here is my cheapie solution.

Ever wonder what to do with that burned out PC power supply? Well, assuming the cause of the failure was not a dead fan, it is a good source of a fan to start this project. Simply extract the fan and its wiring and also cut out the grill from the back of the case to provide a finger guard for the assembly. File off the rough edges of the grill and clean the fan (almost certainly necessary if it is used).

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Be sure to save the screws from the fan mounting, they are the easiest way to remount the fan.

Obtain a suitable easy to work with case of your choosing. I used a plastic margarine tub of the 454 gram (1lb) size. Instructions for that assembly follow:

Place the fan on the lid and mark the location of the screw holes with an ice pick or other slim pointed device. Also trace around the inside of the fan case with a permanent marker (marks easily on plastic).

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Cut out the lid (roughly) and punch holes for the four corner screws and a hole for the wires. Mount the fan to the underside of the lid with the grill on the outside. Make sure the fan is facing in the proper direction to blow air into the container. (on a PC, it blows out of the power supply case) Lead the wires out through the other hole in the lid.

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Trim around the inside edge of the grill with a hobby knife and punch or cut a hole in the side near the bottom edge to accommodate a small hose which you can lead into your WTC through a service port. The air hose should not be too long, or airflow will be severely restricted. I found that about 2 feet of 3/8" OD X 1/4" ID tubing was ideal for my application in an AKULA model.

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I just thread the hose through the access bottle cap hole, push it to the far end of the WTC, and hook it up to a 12-volt power supply.

Warning: these fans will typically not take voltages over 14 volts, so hook it up to a regulated supply, not just an automotive battery charger, the peak voltages will likely burn out the fan. A simple 3 terminal regulator IC such as an LM7812 would do just fine as the current draw is typically only about 0.2 amps at 12 volts. The fans are not reversible by switching the wire polarity, and may even burn out if reverse connected, so be careful.

Bob Warburton

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