Power for cooling fan

[rcav8r2]

I have an old timer that I converted to electric. There really isn't a convenient way to provide cooling for the batteries, so I was thinking of adding a cooling fan. I did a few searches here, but found too many hits to be useful.

Anyway, I have quite a few 12v fans I can use, so I'm sure I can find one the right size, but I'm not sure how to power it. I'm running 18 cells in the plane. a 10 cell pack, and a 8 cell pack. Can I tap into the 10 cell pack? The problem I see here ( besides more than 12v) is that as the power is used, the voltage to the fan will drop when it is needed the most.
Can I use a linear voltage regulator for the fan and use all 18 cells, or would this be too much for the regulator?

Also would it be better to put the fan before the pack to blow cool air over, or put it after the pack to suck the warm air off the pack? Or even use one on each end? Right now I have plenty of entry and exit opening area, but no way to direct the air flow. Batteries are rather hot after a flight. They discolored the thermal label paper I put on the packs ( turned the whole lable black) . I use the same label paper on other packs that get better cooling, and they haven't turned, so I'm assuming this pask is getting too hot.

Thanks in advance.

[Comatose]

Tapping off the 10 cell pack might work okay if you charge the two packs separately. It may cause cells to overcharge and die if you charge all 18 in series. If your fan draws less than 100 mA or so then you can probably try a linear regulator.

I'm not sure that a well placed air scoop would't solve the problem more effectively, with less weight and complexity though. Or perhaps some internal baffeling to direct the flow from the scoop.

[TMetalMan]

You could probably just use a 7812 chip. Very simple, and it can handle 1amp.

They should sell them at your local electronics store.

[rcav8r2]

Comatose: Yea a scoop would be easier, but there really is no good place to put it on the plane without spoiling the look of an old timer.....

TMM; Thanks for the info on the 7812. I'll look for it around here, but I'm guessing I'll have to send away for it as there are no real electronics stores around here. I take it I can ask Mr. Google for the schematics?

BTW here is a pic of the plane.

[Andy W]

7812 is available at Radioshack. Also, tapping off 10 cells will work just fine. The fan only draws 150mA or so..
..a

[Chamkeeper]

If you are planning on using 2 fans, make them do the same thing, either force air in or draw air out. One going each way only gives you the benefit of one fan.

[rcav8r2]

7812 is available at Radioshack. Also, tapping off 10 cells will work just fine. The fan only draws 150mA or so..
..a

I'll check out the local radio shack. The ones around here don't even have resistors anymore :( I was thinking the current draw would be minimal, but I was worried about the speed of the fan at the end of the pack as that is when it needs to draw the most heat.

Cham.... yep one pushing, one pulling. Just not sure if the 2nd one was needed. There certinally is the room and with an 8foot wing I don't think the extra weight will matter.


THANKS for the feedback.

[Chippie]

if weight isnt too much of an issue, why not just use a cheap lipo pack(3 cell) to power the fan?

Looking at the model( very nice btw) could you put an air scoop underneath where it would be inobtrusive.....?

[AndyOne]

[QUOTE=rcav8r2] I take it I can ask Mr. Google for the schematics?QUOTE]

rcav8r2

Look at...

http://lorca.umh.es/isa/es/temas/micros/doc/datasheets/7812.pdf

Fig 1 page 13 is all you need.

Andy

[siberia37]

How about a heatsink for the battery? It might do the job a lot quicker and easier- and no power loss.

[Warske]

...12v fans...running 18 cells in the plane...better to put the fan before the pack to blow cool air over, or put it after the pack to suck the warm air off the pack? Or even use one on each end?

If you do use 2 fans, they should work fairly well if wired in series (24 v) and connected directly to the battery pack (about 21.6 v to 25.2 v). The 2 fans should be the same for this to work.

Warske

[olmod]

Comatose: Yea a scoop would be easier, but there really is no good place to put it on the plane without spoiling the look of an old timer.....

TMM; Thanks for the info on the 7812. I'll look for it around here, but I'm guessing I'll have to send away for it as there are no real electronics stores around here. I take it I can ask Mr. Google for the schematics?

BTW here is a pic of the plane.

Its been my experience that fan exhausting hot air have to be a larger capacity than fan drawing in cool air as hot air is less dense,
I personally would opt for a small square of expanded alluminium mesh with the louvres facing forward ,over a hole in the front bottom of the fuselage and a corresponding one behind the trailing edge of the wing, with the louvres facing the tail painted white to blend in,plus air circulation holes where needed in the bulkheads. i must add it looks a spendid model and i would imagine a gracefull flyer. :) cheers.

[Acetronics]

Hi, rcav8r2

And What about running two smaller 12 v fans connected in series ... you can find some from 1 1/2 " to 5 " ( ! ) in electronics and computers shops.

No additionnal circuits needed ...

Alain