Posted: 3/9/2011 5:20:24 PM EDT
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Ok... I'm staring at my dillon 1200 trimmer. It needs cooling. It get's too hot to touch for more than a second after ~25 minutes of operation.
It's a 5k rpm motor. The body is a cylinder about 3 inches in diameter by 3.5 inches tall. I was thinking I might try to fab a heatsink for it out of 1/8" thick plate aluminum. The plan is to take two pieces 3.125" wide and 12.8125" long (half the circumference + 3" for fins/mounting tabs) and bend them into little Omega symbols. Probably in a press around something 2.75" diameter or so (for springback). Then drill through the wings to clamp them together around the body of the motor. How much airflow should I have to keep it cool, tho? I don't know how many amps the motor is drawing, but I can find out with a meter. What's a rough ballpark in CFM I should shoot for? I'm thinking a couple of these little PC case fans aren't going to cut it, am I right? |
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Quoted:
Duh. Call Dillon first thing in the morning. They have techs who do nothing but deal with calls from guys like you about stuff like this. They live for it. They'll probably tell you you need a new frammis, and send you one for free. I already called them and the guy said he only runs his trimmer 30 mins at a time, that the overheating was normal, and that trying to cool it would not help. Personally, I think that 30 mins is a little generous. Mine got really hot after 25. |
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ok, it's drawing between .98 and 1.06 amps.
116.6(3.414) = 398 btu per hour, right? The circumference of contact between the aluminum heatsink and the motor housing should be slightly less than the circumference of the motor. Call it 9" Then I'll have another 3 inches on either side extended out as fins. 3 inches wide means 15(3) = 45 inches squared to dissipate heat, correct? I'm really not sure how to figure this problem further, as I'm sure the speed at which it can transfer heat away depends on how fast the air around it can absorb heat, which I think is in turn dependent on the difference in temperature between the air and the heatsink... |
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Seems to be working.
After about 30 minutes and 580 pieces it was hot, but still cool enough that I didn't have to take my hand away from the top of the motor where there was no heatsink contact. Down on the body, it was only warm to the touch. Even 1/8" plate aluminum (softest allot available) is pretty hard to bend by hand with just a bench vise and clamps. 
If I were going to make another one, (or a bunch) I'd use a hand brake for the two wings and build a press jig for the center half circle. For the top, I might try some kind of flat, circular cap with a cutout for the power cord. |
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Quoted:
Just go down to Wall-Mart or Target etc and get one of those PRC-made desk fans and using a bit of "Yankee" ingenuity, reg up a little mount to blow air on it. That should it keep it cool, if you have a concern. I put a fan blowing across it, too. Haven't tried it with just the fan and no heatsink, tho. I know the heatsink is helping tho, because the fins are getting warm. |