Installing Cooling Fans

A fact of life is that amplifiers give off heat. Heat sinks help amplifiers get rid of this heat safely, before it damages electronic componants in the amp. Nowadays, function follows form, as many amplifiers look nice at the expense of a good design, and heat sinks are shaved off.

The purpose of a heat sink is the take heat away from the transistors inside an amplifier. The easiest way to do this is to use large metal fins. The more surface area on those fins, the more exposure to air, and the better the cooling. However, the one fatal flaw of this method is that air must move over the fins. If the air stagnates, then the efficiency of the fins is reduced. Simply adding a fan is enough to keep the air moving over the fins, improve cooling, and save your amplifier from sizzle-frying.

Mounting of the fan is simple. Most fans have a frame already, and that frame will have holes into which you can drive screws, or bolts. The fan should blow onto an amplifier in the direction which the heat sinks are lined.

Always use a 12 volt DC brushless fan. Brushless fans are much less likely to introduce noise into your electrical system.

For wiring the fan, there are two ways: The simple way, and the hard way.

The simple way is to merely use a relay. Connect 85 to your remote turn on lead, and 86 to ground. Use 30 to connect to the fans 12 volt wire, and 87 should go to a fused 12volt source. Ground the fan. Now, whenever you turn on your radio, it will activate the relay, which will turn the fan on. Incidentally, if you have a multiamp system, you can use the 30 wire as the remote turn on output. Generally, any more than three devices in a system is stressful for the remote output on most decks, so using a relay anyway can help avoid failure of the remote.

The problem with this method is that the fan will always come on with your amps. This can be a problem. For many amplifiers, running too cool is as bad as running too hot. Engineers know that their amplifiers are going to have an optimum operating temperature. Look in your amplifier users manual to find the optimum operating temperature. Then, obtain a thermistor. A thermistor is like a transistor, but instead of using one current to control another current, a thermistor uses heat to control a current. As temperature rises, a thermistors resistance drops. Place a thermistor inline between the 12 volt source and 85 on a relay. If you can't find a thermistor that changes at the maximum operating temperature of your amp, then get a thermistor a few degrees lower (but as close as possible). If it several degrees lower, you can put a variable resistor inline to adjust the temperature.

Using silicone heat sink grease, attach the thermistor to the hottest part of the amplifier (this is where the output transistors are most likely going to be).

This method will allow your fans only to come on when the operating temperature begins to be exceeded.

by: Andrew Krause