amplifier cooling fan

[fasteddie]

installing a 12 volt cooling fanon mr rm 200 linear base install. i want to wire in a thermistor and mount it to the heat sink so that it turns on and off automaticly. Question is whut should be my turn on temp?

 

[mackmobile43]

Perhaps 25% less than the rated junction temperature of your output transistors.

 

[fasteddie]

 

[Toll_Free]

Dude,

Lift the fans about 3/4 of an inch above the heat sinks (makes them a LOT quieter), and put a resistor in line.

Just let them spin all the time. The trick is to lift the fans off the sink, use fans BIG enough to be able to slow down (big slow fans = quiet)..

Thermistors are hit / miss.... You would want to mount it directly on the transistors, or next to them.... Otherwise, many variables can screw with it.

--Toll_Free

 

[fasteddie]

thanks for the input i'll give that a try. doesn't get hot untill i get bucket mouthing it. I think whut i will do istead of a resistor i will put in a potentiomitor inline istead so i can adjust it hi or lo. also with a switch for the radio is always on standy and dont nead fan on all the time.

 

[Toll_Free]

I did an amplifier like your talking about. It sat behind the seat of my GMC 4x4 pickup, so I HAD to have cooling.

I mounted a fan to it, and powered it from the power switch. HOLY MOLY, that was a mistake! It was LOUDER than the AC Blower on HIGH!!!

That's when I discovered lifting the fan about half an inch to an inch above. Once I did that, A LOT of the noise went buhbye!

SO, I had to make it better. I put a half speed switch on it (electronic) that worked like this:

Power on to the amplifier, it would run the fan at half speed.

As SOON as it keyed the relay, it would bypass the resistor (or pot, in your case), and fun full speed.... I put a steering diode in the positive lead to keep the fan lead from keying the linear, and a transistor switch to short the resistor.

Shortly after that, I took the 'key' circuit out, and put in negative keying..... ground to an RCA jack keyed the amp and supplied bias.... AS WELL AS working the fan speed switch.

You COULD do the same thing with the thermostat switch you want to use... Just wire it in like normal, and put the pot ACROSS it... Then, it will short the pot out and run to full speed when the amplifier heats up.

I'd say that's a lot more work, though, for a solid state amp. If you're HELL BENT on a thermistor, I'd have the thermistor in my keying line, but backwards: IE, it would be SHORTED when the amp was cool, and open when it got hot... THEN, you can't key the amp if it's too hot

--Toll_Free