7moore7

Ok, so this should be a pretty straightforward question for some electrician to help me out.

a) I am in the process of setting up a custom undertail radiator à la member Kai Ju

b) I have two fans set up, and think it would be best to set it up so they both just turned on when the fan temperature switch decides that it wants to. I don't want to mess around with having one kick on at a higher temperature (as in AZ this will probably happen anyway. Currently, the fan switch is not working properly (engine temp is at 235 and it's still inactive) but this is a separate problem that I am in the process of troubleshooting.

c) My question is: How do I wire the fans so they both switch on? One is the VTR fan and is currently hooked up to the wiring harness just as it would on a stock bike. The other is from a different bike, and has a two pronged plug- both fans work correctly. When I look at the system, it looks like I can just split the current switch wire, and basically splice in the other fan... In other words, the switch will cause both fans to turn on b/c it has created a current flow through the other fan.

Is this breaking any series/parallel rules? Will the fans be under powered or the wires be over taxed? My brain hurts and it usually gets these things wrong when it does that...

Thanks in advance!

CrankenFine

You can drive both fans motors from the same connection, 12volts across 2 or 10 DC motors will drive them with no problem so long as the current capacity of the 12 volt supply is adequate.

What you may want to investigate is where and how they are fused. The primary fuse for that circuit may need to be slightly larger to handle 2 motors. Also, if one would fail due to physical impediment, it could stall and create a higher current draw, and take out that single fuse protecting both motors giving you no fans instead of one. So if you fuse each fan motor separately with smaller fuses after your temp switch, the larger main fuse would not fail for a single motor problem. Not a big deal, just a little more security.

Hawkrider

+1

Very well explained!

scooter72

Well explained indeed. The only thing i'd add to that is that you may want to think about stepping up to a larger gauge wire to the fans from the fuse box in addition to a slightly larger fuse. The stock wiring was only intended for one fan, so 2 may overheat the wire due to less current carrying capacity and cause you some problems. If you want you can go to that same gauge for the ground side on the switch to the fans as well, it always helps when your power and ground wires are matched as it creates a better balance for current to flow.

7moore7

Cool, Cranken, I'm pretty sure I got it- I sketched what I think you described to make sure:



The way I was describing was the top way (excuse the non-electrical symbols, heh)
I think for best results you are saying the bottom way, and possibly upping the fuse in the fuse box to handle the extra amperage...

7moore7

Urgh, break open that wiring harness? I've got some work ahead of me.

Thanks guys- Hawkridester, it seems that I have a bit to learn about me shawk- I'm looking through the posts and you seem to have to correct my diagnosis of some of the questions, hah!

calitoz

Also I would suggest to add a relay

7moore7

Hm, if I up the gauge of wire I may not need a relay, correct? I just crash coursed on relays, but I think you're suggesting having the fan switch activate the relay, which turns on the fans...

calitoz

See #13 below - Better solution

CrankenFine

After reading the subsequent comments I have to agree with the others, especially if you're in a climate where your fan runs a lot the addition of a slightly larger wire size and a relay would increase the effectiveness and the life expectancy of fan motors & temp switch.

If wire size is marginal then resulting undervoltage operation shortens motor life thru increased current draw at lower RPMs, and the original temp switch was meant to turn on one fan, not 2.

Your bottom sketch does reflect pretty much what I had originally described.

7moore7

Cool, I knew I asked for a reason...

So, again, excuse the improper symbols as I am just emulating what I remember, but something like this?

scooter72

You got it. That's exactly how it should be done, and all you'll need to do is run dedicated power and ground to your fans and use the stock wiring to control the relay. The setup you've sketched should give you trouble free operation with a good degree of reliability due to separate fusing on each motor. I'd suggest running at least a 12 gauge wire for your power supply and ground, that will leave you with a good amount of current carrying capacity to those fans when its needed, and like CrankenFine said, it'll extend the life of the motors as well.

calitoz

I'd would do this:

Numbers are representation of relay. 87A remains unconnected.

Fan Switch--->85*
Ground------->86*
Ground------->30
Fan (-)one---->87
Fan (-)two---->87

Fan one (+)--->Fuse(10)--->Battery
Fan two (+)--->Fuse(10)--->Battery

*if fan switch is 12V then follow above and no fuse is needed since the switch fuse via OEM.
if fan switch is Ground, then 30 becomes 12v and add a fuse(5) since it is for the relay only and not powering the fans. Essentially, you are providing Ground connection to the fans. The fans actually getting power directly from the battery. Additionally, if you add a switch to ground, you can manually switch on the fans if the relay malfunction or that you want the fans running all the time.

7moore7

Haha, it's been wired for a couple weeks, man (and working great!).

Any reason you suggested running the (+) of the fans to the battery rather than the relay, and then the relay to the battery? The relay is rated to 30A, and I have 10 gauge wire running from it to battery and grounded everything properly.

BTW... the fans are working really well so far. I swapped in the 100 degree C fan switch for a 90 degree one and that seems to keep things running a little smoother. What I really need now is a hotter day to test this hot Arizona weather.

calitoz

The way you did above is what I had originally suggested but after thinking about it over, I think the latter is cleaner and you don't need a 30 Amp fuse....Either way will work but the latter is better IMO

7moore7

Alright, so as I get a better understanding of electricity (aka little magic dudes running round inside copper wires) and looking over your recommendation, this is starting to make more sense...

Calitoz, the most recent wiring suggestion that you had only requires two (10A) fuses. The way I did it requires these plus a (20A) fuse going to the relay. It's rated to 30, but I figured I should never need more than 20A for the two 10A fans, right? But now that I think about it, that fuse is just for the relay, and really has no relation to the fans (other than if it pops: no fans!) So by preventing a surge in current to each individual fan by doing it your way, you have already protected the relay, and no third fuse is needed...

Ok, this is cool! I swear I learned stuff like this in high school, but damned if I cared about it's application then. It's going to stay wired like it is, cause it's really only one extra in-line fuse that's pretty sealed up, but thanks for the suggestion. It helped me understand the process better.