Cooling Fan in iMac G3

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anthony1987 Author

Level 1

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Cooling Fan in iMac G3

Hi,

Yesterday my 600mhz iMac G3 Snow overheated twice. And yes, it is properly ventilated and in an air conditioned room. I went on ebay and bought a fan, some wire, a toggle switch and two nine volt battery clips. I am going to power the fan using the batteries because I want to keep the whole fan setup seprate from the internal components. I plan to hang the fan from the top handle vent holes, with wire suspending it from the vent holes. The wires going to the toggle switch will run through the vent holes, outside the unit, and the toggle switch will be on top of the unit. I need to know if I should use the fan in an exaust or an intake setup.

Any answers are appreciated.

iMac, Mac OS X (10.4.11)

Posted on Sep 5, 2011 7:22 AM

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Answer 1

WZZZ

Level 6

13,238 points

Sep 5, 2011 7:40 AM in response to anthony1987

You want to maximize the airflow over the top case vent. That's where the PAV board is located and where overheating usually occurs.

You'd be better off running the fan from a transformer. Find one with a DC voltage output at whatever the fan needs. Probably minimum 1 Amp. Bear in mind that if you aim the air directly inside the vent, instead of across, there will be a significant buildup of dust inside, which will eventually make things run hotter. Also you don't want to interfere with the Mac's convection cooling by obstructing this vent.

Don't even think about opening the top of the Mac to locate a fan there. There is dangerously high voltage at the PAV which can kill you, even if the Mac is shut down.

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Answer 2

anthony1987 Author

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Sep 5, 2011 4:30 PM in response to WZZZ

Thank you very much for your concern, but I feel comfortable opening it, and as a matter of fact I did open the top yesterday, to take some measurements. While I do have some transformers laying around, I really don't want to commit them to one use. I feel that whatever air I can move will be good, just to aid the convection cooling. So which direction should the air flow through the top vent, in or out?

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Answer 3

rccharles

Level 6

13,037 points

Sep 5, 2011 7:07 PM in response to anthony1987

Hot air raises, so the air is coming out the top. I'm no expert.

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Answer 4

anthony1987 Author

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Sep 6, 2011 5:21 AM in response to rccharles

That's what I was going to do, but I don't know now if I want air blown over the parts or if I want their heat to vent out the top. Thanks

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Answer 5

anthony1987 Author

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Sep 8, 2011 4:35 AM in response to anthony1987

Anyone have any ideas?

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Answer 6

WZZZ

Level 6

13,238 points

Sep 8, 2011 6:16 AM in response to anthony1987

No one's done this, so you won't find any expert opionion. (But I don't see how you can keep running the fan on a 9V battery, alone. Especially, as the battery drains and the fan slows down.) Just go with what you think will work best. Heat rises. I just use a small AC clip-on fan mounted to a bracket about 2 1/2 feet away, to avoid magnetic field interference to the CRT. It blows enough air across the upper vent to move away the hot exhaust enough to keep things reasonably cool. When it's insufferably hot, I just don't use the G3 or sleep it more often.

It's maybe not a very good proxy for the PAV area, since it's located much lower, but it's all that's available; there are no sensors on the G3: I have Bresink's Temperature Monitor (lite), which finds the temp from the SMART of the drive. With the fan, I don't often see the drive getting much beyond the low to mid 40s C and in the winter it doesn't often get above 40C. Maybe it will work with your drive.

http://www.bresink.com/osx/TemperatureMonitor.html

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Answer 7

anthony1987 Author

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Sep 8, 2011 2:36 PM in response to WZZZ

I guess I'll go with heat rises, so I'll make it an exaust fan. As for the batteries, I figure that any aid that I can give to the convection cooling will do nothing but help. The machine itself is not used all that much, at most maybe a half hour- 45 minutes a day. I'll probably open it up to clean every 2 months or so, and I'll change the batteries then. I wish that I could run it off the power supply, but at ten years old (and I've heard these power supplies are always under a load) I really don't push it too far. I'll check out the site too.

I'll let you know how it turned out when I put it together.

Thanks

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