What kind of a relay to use for auxiliary cooling fans?

[ClydesdaleKevin]

Okay...I know I should use a relay with my OEM auxiliary cooling fans, and I'm also installing a bigger transmission cooler with its own fan.  I know its a bad idea to run them right through the toggle switch on the dashboard because of how much juice they draw through the tiny switch.  I'm going to go with lighted toggle switch so I don't forget to turn the fans off.

That said, I really want them to run off the same switch...the OEM fan will come on thermostatically, but I like to be able to control it from the dash.  So I'll need a pretty significant relay to power all three fans from 1 lighted toggle switch.  And I know it has to be a continuous duty relay.

So, any suggestions on what kind of relay I can use?  I don't want to pay a fortune, so is there a relay that would work, say a headlight relay, that would do the job and not burn out?  Or should I go with the same type of battery relay they use on old RVs, the ones that look like the robot from Lost In Space?  I'm looking for the cheapest option that will also work reliably and have longevity.

Also, and suggestions on the wiring?  Here are my thoughts...smaller gauge wires going from an ignition on source to the lighted toggle, and then down to the relay...then heavy wires direct from the battery to the relay, and from the relay to the fans with heavy gauge wires.  Do I need 2 wires coming from the toggle, positive and negative, going to the relay, or is does one wire go to ground, and the relay itself gets grounded?

If anyone can draw up a diagram, that would be awesome!  I'm way more a visual person when it comes to wiring.

Thanks ahead of time guys!

Kev

[DaveVA78Chieftain]

First thing you forgot is fuse (or a CB) in the battery to relay path.  Size will depend on total fan amperage.

Relay size is based on total fan amperage.  The standard aux relay available in the auto supply electrical section has 40 amp capacity and runs about $15-20.  If the total amperage of your fans is more than that then use a RV aux battery isolation solinoid  (http://www.ebay.com/sch/i.html?_sop=15&_sacat=0&_nkw=battery+isolator+solenoid&_nkwusc=battery+isolator+solinoid&_rdc=1)

Dave

[ClydesdaleKevin]

Thanks Dave!  Didn't even think about putting a fuse in. 

Hmmmmmm...now, how do I figure out the amperage of the OEM fans already in place?  I'll look for a label, but if I can't find one, then I'll assume they draw the same amps, per fan, as the new one that fits over the larger transmission cooler.

Hopefully whichever relay I get has some sort of diagram telling me which wire goes where...lol!

Kev

[DaveVA78Chieftain]

a clue to the answer -

What size fuse (or fuses) did GM or the coach mfg install for them?

Dave

[ibdilbert01]

Do you have a multimeter capable of reading amps?

[ClydesdaleKevin]

Okay...they each draw 5.5 amps, and the new turbo fan draws 6.5, so I went with a Ford truck style starter relay...heavy duty, and is probably overkill...lol!  I bought a lighted toggle as well.  Change of plans on the mounting though...my AC system is still pressurized, albeit not enough to work, so its fixable, and I'm not going to remove or alter anything.

That said, I bought a 16x12 transmission cooler, easily 3 times larger than the one that is on here now, and a 12 inch high output fan to mount over it as a "push" fan, as opposed to behind it as a "pull" fan (you can use it either way, but it has its own grill, and will work better the way I'm going to mount it than trying to mount it behind the cooler.

I also bought an inline fuse to go between the battery and the relay. 

The cooler is going to be mounted below the OEM fans, so it will get a significant amount of its own uninterupted airflow just from the air scoop below the bumper...it angles up and will blow pretty much right on the cooler.  Already have the mounting brackets designed and the materials for it, so tomorrow I'm attacking this project.  SWEET!

Kev

[ibdilbert01]

Are Ford truck style starter relays continuous duty?

[Elandan2]

Hey Kev,

Wiring up a relay is quite simple.  Here's a link to a diagram.  Unlike Dave, I can't draw on the computer (at least anything anyone would be able to understand).  The spades on the relay are numbered with standard numbering to make it easy.

http://www.ado13.com/techs/relay.htm
 
The relay you can get from any parts store. They may be available at Harbor Freight.  In Canada, they are at Princess Auto for about $7 including a plug and pigtails making for a real simple installation.  Rick

[Elandan2]

Here is a picture from the Princess Auto site

[ClydesdaleKevin]

Hey guys...its actually a Ford Truck starter solenoid.  Which is essentially just a great big relay:



Very heavy duty, and very easy to wire in.

Not sure how "continuous" the duty is rated for, although the parts guys were pretty sure it would be more than adequate.

And remember, I'm only going to be putting the fans on for short periods of time up huge elevations to keep the temperatures down...so this should work just fine.

Kev

[TommyM]

My name's not Dave, but I vote for a different relay.  You'd do just fine with the generic automotive relay like somebody posted a photo of above. 

The Ford starter relay is meant to be operated long enough to start an engine, maybe 15 seconds at a time.  10 minutes IS continuous, by comparison.

Tommy

[DaveVA78Chieftain]

Like Frank said, 15 seconds max.  You said 5.5 + 5.5 + 6.5 amps = 17.5 amps.  One of the smaller 30 to 40 amp aux headlamp relays in the pegboard electrical section will do fine.  They only run $15 or so.  Rick gave you a wiring diagram for them (http://www.ado13.com/techs/relay.htm)



BTW - Sorry about slow response.  Been hectic both at work and at home.

Dave

[ibdilbert01]

VEHICLE RELAYS - Operation & Diagnosis

http://www.youtube.com/watch?v=Mru8BbTGDwM&feature=pyv

[ClydesdaleKevin]

Okay folks...I erred WAY on the side of caution...lol!  After a trip to the auto parts store for another relay, I got really frustrated with them at Autozone, since not a single person in the store could look up a continuous duty relay, and even with an automotive square relay, they don't carry pigtails for them, or brackets.  A quick trip to Tractor Supply showed the same thing...no one new if any of the relays they carried were for continuous use.

Solution?  Earl's RV!  Earl hooked me up with a RV battery select solenoid...definitely made for continuous use...for 24 bucks, with a built in bracket.  Its the metal can type (like the robot from Lost in Space...lol).  Its the 3 terminal model, 2 big ones, battery in and out, and one small one that goes to the toggle switch.  It grounds itself when bolted down to metal, which is what I did.

Its all hooked up, the cooler and fan is in place, the lighted toggle is in place, and it all works great!  I left it running, all 3 fans, for about a half hour while letting the oil warm up for an oil change, and the relay only got warm...not hot!  SWEET!  Definitely the easiest way to go, and way overkill...so it will last a long time.

Thanks for all your help guys, and for steering me away from the Ford starter solenoid!

Kev

[gadgetman]

Another easy relay to use is any old chrysler/dodge starter relay like for a 70 truck. They were high amp rated and screw down easily. Now for a smaller relay use a bosch style 4 or 5 pin relay. Ebay would have them with a pigtail harness too very common relays.

[DaveVA78Chieftain]

gadgetman,
You should not use starter relays for this sort of application.  The coils are not designed to be kept energized for extended periods.  You have to have a relay that is designed for constant duty service.

Dave

[gadgetman]

that Chrysler relay will run full time no trouble its not like a ford solenoid. Its just a relay and can be run full time. I use them everywhere and have for years. foglights. horns.fog backup lights, ac fans  ect.