Radiator fan relay help...

[j par]

Long time ago I got two 12in electric fans from a member. I believe he said they came out of a 440 motorhome. Of course they work fine when I got them and then of course when I installed them one didn't LOL. No problem I just clean the contacts.
I've always just ran them off a manual power switch. They didn't like a 20 amp fuse and they seem to pull more and did fine after a 30 amp. I helped a customer install a automatic control switch for his Mustang and I went home and immediately purchased one and installed it. But I haven't hooked up the wires yet. Of course now after it's installed I start doing my research and find out it's only 20 amps.. so of course now that it's all installed I own it..
Anyways I was researching this is a little bit and someone was talking about putting it on the backside of the circuit on the ground wire? Quit possibly not taking the hint of the electricity? But you know I don't know electricity like that and it probably doesn't matter one way or the other it's just going to end up eating it up in frying the fuse. I think what I might do is I have and extra circuit going up to the front as well left over from the electric water pump. I may just split the fans up and run one manually and One automatically. I'll feel a know when the automatic one comes on. I also can go get yet another $30 actuator and mount it to the other fan?
I don't know I guess this is more of a what would you do kind of thing?
Thank you for your time and experience....

 

[Dubob]

Depending on the fan control you have you may be able to mimick the wiring for the ford contour fans. If you ignore the resistor in this picture I saved from somewhere, which is strictly there for low speed on fans, you should be able to wire up both fans off of relays. If your control is only set up for one fan with a heavy enough relay and wiring you should be able to run both automatically with the control. Just be sure to fuse both the power to the relay and power for the fans. Ignore the low speed side that requires the second relay if that makes sense.

 

[Dubob]

This would be for a single speed set up with two fans.

 

[Mike69cuda]

Just put in a 30 amp relay & let the controller drive the relay. Hook the relay contacts up where your switch was.

 

[65wgn440]

You could just go buy a 20-30amp relay for the 2nd fan, and fuse it properly, then piggyback off of the fan controller you bought to get your relay turn-on for 2nd fan.

 

[Dfr360cuda]

Maybe a Lead-Lag set up.
Fan #1 turns on at maybe 180
Fan #2 turns on at maybe 200 if fan #1 isn't keeping up.
Also a manual switch wired parallel in case something craps out.

 

[j par]

As I was looking at the electrical wires I did notice that if I used the power of the switch and used the new thermal switch as a negative on off switch if it ever went bad I could just pull the wires out and connect them together and bypass of totally?
Also I was wondering if anybody knew if it mattered whether something was on the positive or negative side? And what it did? I don't know if I mentioned it but I was thinking of putting one of these switch and maybe just running a extra long line to be able to connect another unit like this one I already have..

 

[my68barracuda]

Are you talking about wiring in the relay so that the relay supplies power to the fans when triggered vs the relay supplying a ground to complete the fan circuit when triggered?
I get what you are saying about the ground side carrying less current, so it should be a way for you to use the 20 amp relays. Using a ground triggered relay is worth a try anyway. Just remember your positive circuit to the fan motors will always be hot. Be sure to fuse them properly.

 

[j par]

Are you talking about wiring in the relay so that the relay supplies power to the fans when triggered vs the relay supplying a ground to complete the fan circuit when triggered?
I get what you are saying about the ground side carrying less current, so it should be a way for you to use the 20 amp relays. Using a ground triggered relay is worth a try anyway. Just remember your positive circuit to the fan motors will always be hot. Be sure to fuse them properly.

Yes they're completely fused and running on a manual switch. I don't turn them on that often. Just sometimes if I'm sitting at a light for a long time or a very hot day. Never on the freeway and almost never that I can think of while traveling over 30 mph....

 

[my68barracuda]

And remember that electric motors only pull peak amps at start up.
If you can get a clamp on DC amp meter you can verify exactly what the fans pull at start and when running.
For relays that run radiator fans,
If the relays are mounted under the hood, I would get ones with extra capacity, as when you use them the relays are already temperature hot from the hot environment.
I have bought and used the inexpensive relay packs of five off e bay, never had an issue with them in use.
Just be sure to go by the numbers on the relay itself, there does not seem to be a standard for the wire color coding.

 

[Mike69cuda]

Current is the same on positive and negative. The electricity flows in a circle so the current is the same at every point in the circuit.

Some prefer the relay or switch on the positive side as they consider it safer. The voltage is not supplied to the fan except when the relay is on. That is probably true in most cases, but it will work either way.

You could put a relay on each fan and tie the control lines together if you are worried about current.

 

[j par]

Oh forget it, I just went down and got another one and an adapter to get the electricity from my water pump switch and I'm going to run them on their own switch and their own thermostat. That way I can have them staggered.

 

[j par]

$29.99 thermostat has now turned into $70 + LOL....
I LOVE THIS CAR.....

 

[my68barracuda]

Current is the same on positive and negative. The electricity flows in a circle so the current is the same at every point in the circuit.

Some prefer the relay or switch on the positive side as they consider it safer. The voltage is not supplied to the fan except when the relay is on. That is probably true in most cases, but it will work either way.

You could put a relay on each fan and tie the control lines together if you are worried about current.

Mike 69 Cuda,, I don't wish to clog J Par's post, however I am more of a mechanical engineering guy, although I do my own EE stuff I stay well within the bounds because electricity is not my forte, perhaps you can help here, I believe you when it is said that electricity flows in a circle, current is the same on the + and - side....
So why do we put battery disconnect switches on the negative terminal to eliminate sparks? Why can I make a spark or start a fire off a grounded hot wire, but not make a spark or a fire off a grounded ground wire on a energized circuit? If the current is the same on both sides of an energized circuit. This is not a trick question.
thanks

and J Par, I have used these typical e bay relays on several vehicles with over 5 years of service without any issues. I do tend to up size the relay capacity. And the wire colors tend to vary among all the manufacturers, pay attention to the terminal number coding on the relay itself. Less than $12.00 for five relays and free shipping, got to looove those Chinese even if they point nukes at us, the Russian never give us deals on car hobby parts. I can't think of one NATO ally that gives us a discount on performance parts either.

(10 pc) 12 VOLT 40 AMP BOSCH STYLE RELAYS & SOCKETS CAR WIRING SPDT RELAY 40A | eBay

 

[Mike69cuda]

Sparks aren’t the issue with disconnecting the negative first. You are right, you can make sparks anywhere in the circuit.

The reason folks disconnect the negative first is safety. If your wrench slips and hits the fender when unhooking the negative, nothing happens. If your wrench slips and hits the fender when unhooking the positive, then the sparks fly. I did that once and welded the gears in a ratchet. No more ratcheting.

I know of incidents where batteries have exploded from shorting.

 

[my68barracuda]

Sparks aren’t the issue with disconnecting the negative first. You are right, you can make sparks anywhere in the circuit.

The reason folks disconnect the negative first is safety. If your wrench slips and hits the fender when unhooking the negative, nothing happens. If your wrench slips and hits the fender when unhooking the positive, then the sparks fly. I did that once and welded the gears in a ratchet. No more ratcheting.

I know of incidents where batteries have exploded from shorting.

"hits the fender when unhooking the negative, nothing happens"

again, just trying to understand, if the electrical path is truly a circle, why does nothing happen when an energized ground circuit is grounded?

 

[kursplat]

"hits the fender when unhooking the negative, nothing happens"

again, just trying to understand, if the electrical path is truly a circle, why does nothing happen when an energized ground circuit is grounded?

try it on a car with positive ground, you'll get sparks. it has to do with potential, the body and battery neg on a neg grounded car are at the same potential. the pos side isn't. if you want something to spark when hooking up the neg side, make sure everything is turned on when you put the neg cable back on the battery

 

[Mike69cuda]

The negative battery terminal the same as the fender, so no potential difference. The battery negative is already connected to the fender with a big wire.

If you unhook the negative battery cable, the battery is no longer grounded to the frame. That way it is safer to take the positive off, since if you touch you wrench to the frame there is no circuit.

 

[j par]

Separate 12v switches with their own separate fuses going to two separate adjustable thermal sensors.
Done for the day..
All connected and tested with the wife's hairdryer.
Now I need to get everything pulled back apart wraps, zip-tied, tucked, and generally spiffed all up with that alternator put back on as well. Then I can warm it up test drive it and set the fans probably staggered. So I'll check back with test drive still to come and I can always switch this around as well I put everything with Spade connectors....

 

[65wgn440]

Is your engine under boost ?

 

[j par]

Is your engine under boost ?

No..

 

[j par]

I got a little time into it after work and I'm gonna try and get it finished after dinner.
I want to be able to start on another fun project tomorrow.
Maybe some finished pictures later...

 

[j par]

It would be odd to see any other wires than the spark plug wires, all done.
Clean mess in the morning and get started on my next project...