wiring fans up with switches, have a question?

[Rausch]

Schottky diode /ubbthreads/images/graemlins/grin.gif

 

[atc250r]

You definitely should use relays.

 

[jepherz]

Are you saying "just a switch doing the work" meaning no relay is being used? Then you shouldn't need a relay at all, right? In that case there's no coil for voltage spike to occur. Unless it is also coming from the fan?

 

[Rausch]

^ He's saying that whichever is actually doing the switching should have a flyback diode. A switch (being used alone) may see a spike from the fan motor itself. If a relay is used, the relay is actually doing the switching, and the relay would need to be protected. Basically anytime a coil of any sort is used, this is a good idea.

I will admit I never used to use flyback doides for installs like this, but usually with more serious car stereo type installs. It's a good idea, and just good insurance, if nothing else.

Edit: KC, I'm sure I have some 1N5406 diodes laying around. I'll make sure to bring a few with me to the meet.

 

[toybreaker]

Quoting VRausch4:

Nice pic!

Can someone photoshop in a diode from terminal 87 to terminal 85?

Many of the cool guy relays meant for inductive loads come with this diode already installed. /ubbthreads/images/graemlins/smile.gif

Sounds like Aaron knows what needs to be done.

 

[blacksheep]

I bought 2 40 amp relays this weekend and will try to wire up tonight - I may have questions... /ubbthreads/images/graemlins/rofl.gif

John - whats thid diode thing all about? This sh*t is getting way too complicated for me!

 

[jepherz]

You can wire diodes in with your relays, or some relays come with them wired up internally. The idea is that anything with a coil of wiring in it acts as an inductor, whos job is to maintain a constant current. This becomes a problem when you're driving a relay with electronic circuitry, because when you shut the remote wire to the relay off, the coil inside the relay tries to maintain a constant current, which results in an infinite voltage spike. When this high voltage meets complex circuitry, it can burn components out. In your case, though, since you're just controlling the relay with a simple switch, the most that can happen is the contacts will get corroded on the switch and you'll have to replace it.

BTW, a diode is just a one way door that allows current to flow one way and not the other.

 

[blacksheep]

Jeff - are those points 87, 86, 85 and 30 always mean the same thing from relay to relay?. Why those specific no's, anmyone know?

 

[Rausch]

^ YEs, and Bosch style relay will have the same numbers, with the same functions. I'll bring you a few diodes this weekend. /ubbthreads/images/graemlins/wink.gif

 

[blacksheep]

Autozone.com PL-RY2 is what I bought. It seems to have same no's as well...

 

[ktmrider]

Quoting blacksheep:
Jeff - are those points 87, 86, 85 and 30 always mean the same thing from relay to relay?. Why those specific no's, anmyone know?

Should be the same, here is a nice linky click with diode info too.

 

[blacksheep]

Got the relays all wired up last night. I tapped 12V constant power off the ignition harness and the 12V acc power to the switches off the same harness as well. I put a 20A in-line fuse holder for the switches. On a side note, working under the dash is such a pain in the neck, ass, knees and shoulders. I mounted the switches to the lower console piece. I wish I was about a foot shorter, it'd be so much easier. They seem to work as desired with key in acc1 position.

 

[vr4199]

Don't mean to jack the thread but, I was thinking about doing the same thing.

I want to wire both AC and radiator fans to a switch to run them all the time.

To keep the car really cool any ideas how to do this ?

 

[jepherz]

Look here.

 

I just got back from Radioshack and before opening up anything I want to make sure I have everything correct.

I have a bosch-style relay with only FOUR connectors. It looks like the first picture. I have two diodes that are 12 volt 21mA (current) with a max of one watt. I bought an inline fuse holder with mini spade fuses and three 20A mini spade fuses. I have 16ga wire and heatshrink. Did I get everything right? I am going to wire it to a "Normal/Sport" button and put it near my mirror switch.

Jason

 

[Rausch]

^ You want diodes that can handle a good amount of voltage. These guys will see a potential spike well over 12v.

Standard we used to use was a 1N5406 diode. Rated to 400 or 600v, I can't remember. You can get them pretty much anywhere, and they are cheap. /ubbthreads/images/graemlins/smile.gif

 

Aaron,

Thanks for letting me know. /ubbthreads/images/graemlins/smile.gif Looks like I will be bringing them back in exchange for some larger capacity ones.

 

[vtecds1]

Quoting blacksheep:
Quoting vtecds1:
Thats the same exact one that I have wired to my fan and the same exact wiring diagram. Works for me...



Confused - Which one, Mine or Aaron's post?

Jeff - I am using 22 gauge wiring? Is that too thin?

Aaron - So from my accessory source, I send +ve to acc prong on switch and then negative to pole on the relay? Confused...



Sorry for the late post...your diagram.

 

[Spyke169]

Y not do it this way? wiring is easier and if you want a reminder night just get one of those switches with the little led on it. I have done this on all my dsms no problems. Instead of running 2 wires just ground the negative to the chassis at the fuse block and and ground the switch negative inside the car.

 

[BoostedAWD91]

So the 87a pin on the relay is not used?