Cooling Fan, Yet another question.

Papa · December 14, 2013, 09:35:29 PM

Following on Bills comment about cooling the Northstar I got out my two cooling fans. They are from a computer power system.
They are brushless motors, 12V, 0.72A. The fan diameter is about 35mm and the plug has three wires. Black, Red and Blue. I tried hooking them to a LiPo but I can't get them to run. How could I fix them so they would run when I hooked up the power battery?

jack.

pmackenzie · December 14, 2013, 10:05:47 PM

Normally black would be negative and red positive. 3rd wire is RPM feedback.
However no guarantee that they have used the normal colours.

If the connectors are still on then this page might help:

http://pcbheaven.com/wikipages/How_PC_Fans_Work/

Pat MacKenzie

Papa · December 14, 2013, 10:58:12 PM

I think this is a dead issue as I need a tach generator on the 3rd wire to make them run.

jack.

Ededge2002 · December 14, 2013, 11:01:39 PM

There are many small 12V computer style cooling fans available. Sayal has them and I have a couple If you needed one.

Papa · December 15, 2013, 12:21:53 PM

I have the fans my problem is I can't get them to run because they have an rpm feed back. What I wanted to do was turn them into a straight dc motor that would run at a fixed speed when I hooked up the battery.

Jack.

Ededge2002 · December 15, 2013, 01:02:52 PM

Yes. The fixed speed ones are available.

Wingnutz · December 15, 2013, 04:02:18 PM

I'm not sure how much a cooling fan would do unless it could pull cool air from outside of the model and push the warmed air out. That involves holes of some kind...same kind which would allow water in.
The Polaris gang have gone to a heatsink thermal-greased(cemented?...I can't remember) to the ESC with the finned (actually spined) surface outside the model and no large holes to allow air...or water in. The ESC(s) mount on the inside of the fuse skin and the heat sink protrudes through into the air flowing over the fuse. Silicon can be used to seal the heat sink to the fuse. I don't think this would stand up to immersion for long but it would keep most of the spray out, protect from a quick immersion, is simpler and probably lighter than fans and motors.
My oldest Polaris still has one of these but I've cut cooling holes in the others...so far so good.
My Seawind has no heat sinks or cooling holes at all...I just used a bigger ESC and it doesn't get very hot!

Papa · December 15, 2013, 04:24:57 PM

My idea was to put a backward facing covered opening, for air intake, on top just before the hatch. Then I would exhaust any hot air from the area through the fan high up on the fuselage just behind the hatch.

Jack.

pmackenzie · December 15, 2013, 04:59:41 PM

Quote from: Papa on December 15, 2013, 04:24:57 PM
My idea was to put a backward facing covered opening, for air intake, on top just before the hatch. Then I would exhaust any hot air from the area through the fan high up on the fuselage just behind the hatch.

Jack.

Backward facing vent would tend to draw air out.
A fan right on the ESC could help a lot if there is little or no airflow.
It would end up warming up all the air in the fuse, but that is much better than nothing.

Papa · December 15, 2013, 05:14:17 PM

Maybe that's the answer. The backward facing vent drawing air out. A forward facing vent on top bringing cool air in. It would be as far from the water as possible. No need for a fan in that case.

Jack.

pmackenzie · December 15, 2013, 05:19:54 PM

Simple is better most of the time.
If you duct the air with some simple baffles to direct the airflow it will be even better.

Look at a Piper Cub.
Even with the jugs hanging out in the breeze they still put on baffles to direct the airflow through the cylinders rather than just let it flow around them

https://www.google.ca/search?q=piper+cub+engine+baffles&source=lnms&tbm=isch&sa=X&ei=1yquUpn3JIixqgGlzYCwDg&ved=0CAcQ_AUoAQ&biw=1536&bih=787

Wingnutz · December 15, 2013, 07:30:35 PM

I subscribe to the keep it simple school of thought and simply cut many cooling holes in the top of my EDF powered Polaris...(translates as small depron copy of the North Star). It's a 60A ESC in a 1-1/2 lb model. If I flip it in the water, the ESC is probably done but since I usually fly it off the grass or snow, that's infrequently a concern
The model has survived my dumb-thumbing for several water flights at Rob's Fantasy Lake, with the Scugog Float Flyers at...Lake Scugog and at Frenchman's Bay. As long as I keep it right-side up, I think the ESC will survive. Good thing as there's no pilot figure to blame if things go wrong!
I attached the photo to show the NACA/NASA duct in front of the hatch, the scoop in the top of the hatch and the exhaust holes behind the ESC. Some variation of of one of these should work for the North Star, especially if it's baffled.
"Hoover" is a hoot to fly...not as peppy as the propped version which most people build but I enjoy the leaf blower whine and the scale take-offs as the model catches up to the EDF...grass, snow or water
But Jack's contra-rotating is way cool!
Good luck with the build Jack! I'm fascinated! I like your non-mainstream approach!

Ededge2002 · December 15, 2013, 08:00:07 PM

The "hoover" sticker cracks me up Bill!

wollins · December 16, 2013, 12:43:05 PM

I love this discussion ... I was thinking I may have to implement some version of cooling system as well so this outcome is going to be so helpful. Thanks for being somewhat of a guinea pig Jack!

Colin

wollins · December 16, 2013, 12:49:23 PM

Quote from: Ededge2002 on December 15, 2013, 01:02:52 PM
Yes. The fixed speed ones are available.

Hey Ed ... how does one differentiate between the two? I putter around at Active Surplus (on Queen street) from time to time and they have all sorts of fans there but are not categorised etc.

Colin