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Impres Multi Unit Charger Mod - Dual Quiet Fans
v1.0 06/02/2008

Introduction

Many people in the Motorola radio community are aware of the Impres Multi Unit Chargers:

Figure 1: Impres Multi Unit Charger (Typ.)



Those that have had occasion to be around while it is operating, for any length of time, know how bleedingly annoying the always-on fan can be. I am one of those people, as my Impres MUC sits on a counter in my kitchen, which is in the middle of my apartment, and the fan noise is universally pervasive.

Well, I decided to look into seeing what could be done. I considered placing a potentiometer inline with the fan, or getting a quieter/slower fan, but I did not want to sacrifice the cooling capability and have my nice IMUC turn into electronic toast.

I had occasion to crack open the charger and to my surprise, I noticed that although there is only one fan installed, there are two mounting points for fans in the upper housing. Aha says I! What if I find a fan of approximately half the capacity of the stock fan, and install two? There's a fan hookup on each board (6 total), so no problem there. And thus was born the Impres MUC Dual Quiet Fan Mod.

Specifications

The stock fan that came with my Impres MUC is defined as follows:
I found a similarily sized 12v fan at my local electronics component warehouse, but which ran at only 1800rpm, and had correspondingly lower values for other metrics. Most of these kinds of fans come with bare leads, so you'll need a Molex type two pin fan power connector.

I assembled and mounted everything, and put the charger back together. Whisper quiet! What a difference. Plus, having some redundancy in cooling (in case one of the fans goes out, at least there's another one to maintain some cooling). Below are some pictures of the modification:

Figure 2: Impres MUC Upper Housing with both new fans installed



Figure 3: Old fan (left) with new fans



Figure 4: Closeup of the old fan prior to dismounting and the new fans mounted




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