PDA

View Full Version : DIY 2-speed fan control



albersondh
07-03-2010, 01:09 AM
This is how I did mine. Its not as good as a full on IC logic controller but it gets the job done. Why its good.

- When the hi side adjustable fan switch kicks on, it kills power to the low side fan switch. Only one set of the fans windings can be active at a time. This may extend the life of the fan, and will certainly lower the continuous current draw.

- Its full adjustable. You decide when low kicks in and when high kicks in, and you set the low to high overlap.

- Adjusted correctly it will overlap from low to high. This means the fan is already moving and the inrush current requirement to get high moving is much lower than if the fan were not moving. I run a 40A fuse on high and it has never blown.

- My low is on at 180 off at about 187. The only time high comes on is in traffic on a 90*+ day in traffic with the AC on blast (5.2L OE radiator).

- Its cheap. Shouldn’t run over $100 in parts.

BOM:
qty 2 sealed standard automotive relays 30A rating. $8.75 x2 http://www.wiringproducts.com/contents/en-us/d36.html (http://www.wiringproducts.com/contents/en-us/d36.html)
qty 1 BWD S672 80A continuous duty Solenoid $29 http://www.oreillyauto.com/site/c/detail/BOR0/S672.oap?pt=N0791&ppt=C0218 (http://www.oreillyauto.com/site/c/detail/BOR0/S672.oap?pt=N0791&ppt=C0218)
qty 2 Hayden pn# 3653 (or higher quality equivalent). $23 x2 http://www.summitracing.com/parts/HDA-3653/ (http://www.summitracing.com/parts/HDA-3653/)

Miscellaneous:
Appropriate AWG wire and qty 2 30A fuses, qty 1 40A fuse.

Notes:
I get power from the fuse/relay box main power lug and ground to appropriate chassis grounding points. I tapped the main OE harness coming from the fire wall on the PS for my ign 12V (make sure its a circuit that can handle 10 or more amps for powering the relay coils). The cheapo thermo-switches close circuit when they get wet so mount them high. I seal them up with liquid electrical tape and mount them high, never had an issue with them closing when wet. Bathroom silicone caulk would work as well, just seal the shit out of them and no worries. You could easily integrate a "fan on" light and a fan kill switch into this mess if you were so inclined, mounted in the cab. Kill switch would be for fording, ect. The two relays fit nicely in in the existing fuse/relay box and the lid closes just fine.


http://i151.photobucket.com/albums/s150/albersondh/fan/Fancurcuit1.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/DSC03449.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/DSC03451.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/DSC03452.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/Fanswitch.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/Fanswitch2.jpg

http://i151.photobucket.com/albums/s150/albersondh/fan/Fanswitch3.jpg

albersondh
05-17-2011, 11:17 PM
Update with a note/caution. I have run this system for a few years now and never had an issue untill last night. I decided to swamp my POS and the fan switches got VERY wet. So as I pointed out in my original post, they both stuck shut, and as the system is designed to do, the hi-side over-rode the low and stayed on for longer than I have ever had it run before. The fuse holder and wires to the hi-side main soleniod got pretty hot and the 40A fuse blew. The way I designed the circuit you can loose the low side and high will still work fine, but if high craps out you loose low. Ill have to look at my circuit and post a revision.

Im going to make a waterproof project box for housing the switches. Also going to step up to a 60A interupt breaker. If you do this I would recommend you do the same.

After this incodent I decided to look at fan controllers (again), same as before, nothing on the market is designed to carry the kind of current this bish needs on high. So without basicaly building a high current DC controller yourself I still think this is the way to go.