Cooling fans wired serially?

[maurtis]

Still working on my wife's bike, and I am looking to put her controller in a small, custom leather saddlebag (and her batteries in a saddlebag on the other side). These will be made by me, my first leather project!

Since the controller will be enclosed, I planned on using four 40mm computer fans, two intake and two exhaust. She will be running 15s lipo. Can I wire the four 12v fans in series to have them run off the main battery pack? That would really simplify things and help keep the build clean.

 

[wesnewell]

63/4=15.75V each. Might burn 12v fans up.

 

[maurtis]

63/4=15.75V each. Might burn 12v fans up.

Would using those cheap $2 12v voltage regulators work? One wired with each fan?

http://www.radioshack.com/product/index.jsp?productId=2062600#

I read online that overclockers have run the larger 80mm fans at 17v 24/7 for extended periods, but not sure how well these smaller ones would take it. I have an extra 4s lying around, I could always hook one to that for an hour. If one can handle 4s, then 4 wired serially should be able to handle 15s, right? Plus, they were only $5 each, so replacing them every now and then would not be too bad.

 

[wesnewell]

4 40mm computer fans shouldn't draw more than 10W total. A 5ah 4s pack is 74Wh. Just wire them in parallel to it and they will run a long time. But I think you can find a small 63V to 12v converter for next to nothing and then run them off the main pack. There's probably better ways, but put 2 of these in series stepping to step from 63V to 12v. 63 to 40v then 40V to 12V. Don't try 63V to 12V with just 1 module. It'll burn it up.
http://www.aliexpress.com/item/5-PCS-LOT-LM317-Low-Ripple-DC-Converter-Buck-Step-Down-Linear-Power-Supply-63V-4/851434313.html

 

[maurtis]

Those are neat looking converters, I might have to go with 2 of them should things not work out with wiring them serially. Tonight I tested one of the fans at 4s and it ran without any problems. I let it run for an hour and no magic smoke or funny smells.

So I am going to try running the 4 fans in series against the 15s pack and if one or all give out quickly, then I will spring for those DC-DC converters (and replacement fans, of course).

 

[Ricky_nz]

be careful running the fand in series directly accross the main pack voltage. If one of those fans is obstructed or jammed for any reason or the fans are not identical the voltage of the full pack will not share equally across the fans. Meaning some of the fans could be over volted by significantly more the the small amount that 4s does.

 

[Drunkskunk]

Since you're building these bags your self, why not design in vents for the controller instead?
I did something similar on my first bike. I had a rack bag that had an open bottom and back with a path for air to flow over 4 sides of the controller. The way I had the bag mounted, the openings were invisable to anyone unless they lay on the ground or stood directly over the bike and looked down between the battery bag and the controller's bag.
With some planning, you could make large holes in a saddle bag that let the air flow freely, while not letting the controller be visable

 

[maurtis]

I was planning on making them similar to these I saw online, with wood sides due to the ease of construction and unique look (my wife is very fashion conscious, so wanting to make the bike as clean as possible):



So the plan is to make the bags as small as possible, right now I am looking at about 7.5" tall x 8.5" wide and 3" deep. But I can always adjust those numbers as needed, I do not plan on building them until later this week when I get some more time.

I am planning on mounting the controller sideways, with the intake fans below the controller (with the holes through the bags facing the rear wheel) and the exhaust fans above the controller, exhausting through holes again facing the rear tire so hidden from plain sight.. I figured just having vent holes alone would not be enough, so I opted for the four small fans.



Here is how I was planning to mount the saddlebag contents, the batteries in the right side bag mounted to a sliding board so I could easily remove the pack for charging and the controller, fuse, fans, and battery quick disconnect (acting as an on/off switch) in the left saddlebag with the upper exhaust fans closest to the fets. I am planning on drilling a hole in the wood sides only for the red "key" to stick out, so she can turn it on and off without opening the saddlebags. I already mounted the CA on the handlebar stem for monitoring purposes