PDA

View Full Version : Cooling Fan For Powerex MH-C800S


Eman
2010.03.06, 06:27 PM
I noticed my AA's where heating up quit a bit whenever I charged them. So I came up with this. It works good, but I think it could be better. I might try cutting it down an inch. Getting the fan closer to the batteries might help pull more air over the batteries. The fan is 30mm. Might try 40mm fan. I've got a 4xAA battery holder on the way (more narrow and longer than the current one). I'd rather use higher capacity AA's. I'll put an old Mini Z switch on it when the battery holder gets here. Total out of pocket about $6. The probe in the photos is about 1mm above the battery.

http://i85.photobucket.com/albums/k41/willis67017/Mini%20Z/DSCF0176.jpg

http://i85.photobucket.com/albums/k41/willis67017/Mini%20Z/DSCF0175-1.jpg

LED
2010.03.06, 07:14 PM
Are you blowing air in or sucking air out?
1 thing you need to know about aircooling. Its not the amount of air passing that gives the best result but the speed it passes with. So if you make the box as small as possible it will give better cooling with the same fan. I would try mounting the fan on 1 side and let it blow over the top of the batteries instead of blowing down on them. Now the middle ones will cool very good and the outer ones less.

Eman
2010.03.06, 07:29 PM
Its pulling the air in from the sides. So I figure if I make the inlets smaller on the sides by lowering it, it would increase the speed of the air over the batteries. A little thing called the Bernoulli <sp> principle, but in reverse. I'm not sure the theory works in reverse though. It might actually starve the fan. Its not rocket science man. Mostly trial and error. With a 15 degree difference I'd say I'm on the right track.

EMU
2010.03.07, 03:20 PM
I would blow air onto them. Using a low RPM 80mm fan at least. It would be much quieter than the 30mm high pitch sound. I rigged up a few LED fans that I had laying around to a 5v PSU... Made a huge difference.

Volume makes a difference as well, its not just speed of the air. I have done a LOT of aircooling on computers a few years back. In general, a vacuum works best, but then you are only cooling the top of the battery, not the sides between each cell, which is why I recommend a fan blowing from the top. It would then vent out the sides of the duct.

Realistically, your cells are not getting hot at all at 88f, and I think you may do more damage than good with the fan with the charger that you are using. Cells should be warm, almost hot to the touch when they are near completion of their charge. Cooling them at a low amperage could make them peak improperly, and charge too long (since they will have more resistance when they are cooler). If the cells get too hot to touch, then they are too hot. Most chargers use about 125f as a cutoff temp (Maha MH-C9000 and LaCrosse BC-900). It the cells are under 100f, I would let them be. Over 100f, then worry about cooling them. Batteries are more efficient when they are warm. Cold cells have less runtime, and dont take as much of a charge.

Eman
2010.03.10, 01:41 AM
Lowered 15mm. Temperature variance now 22 degrees. However fan sounds like it is working harder. Pretty sure I'm starving the fan. Not sure pulling the air over the cells is the best way to cool them. The temperature is only lowered above the cells where the air is moving. In between the cells where there is no air movement there is hardly any temperature variance. I think a 120mm fan blowing down on the batteries would be better at cooling the entire battery. Actually a pair of 50mm fans wouldn't obstruct my view of the display. So maybe I'll try that first. Of course I'll have to come up with a different way to mount the fans. A piece of plexi shaped like this ] (roughly) should work. Just have to make the bottom piece longer so it would extend under the charger.

EMU
2010.03.10, 03:02 AM
When cooling my chargers, I just lay the fan over the charger without a shroud. It should cool more than enough... A single 120 should cool the entire charger if placed in the center. You can also add stilts to raise the fan off the charger as well, and still see the display.