Hi,

I'm in the process of choosing dual electric fans and saw something interesting at the Derale website. The instructions for one of the dual shrouded fans (in this case 16833) says the following:

WIRING OPTIONS
IMPORTANT: Due to the high amperage of each individual RAD fan on the Dual RAD Fan Assembly, each fan MUST be switched*
individually. Failure to use two different switching devices could cause damage to your vehicle and/or your new Electric Fan Assembly.
* Switched - Utilizing an automotive rated thermostat or manual switch
There are a few options on how to activate (turn on) your new Electric Fan Assembly.
1. Manual Switch - Install a switch in the passenger compartment and turn on Electric Fan as desired.
2. Electric Fan Thermostat Switch
A. Adjustable Thermostat - Allows an adjustment range for you to determine optimal turn on temperature.
B. Pre Determined Temperature - Thermostat has a pre determined temp. from the factory that determines turn on temp.
We recommend using two thermostats to activate Fan #1 at an earlier temperature than Fan #2. This will help spread the major
amp draw on your vehicles electrical system. Please visit www.derale.com for available thermostat options or visit your local
retailer.
Important: When purchasing a thermostat always consider the maximum amp draw. Some thermostats are not designed to
properly handle 25 amps.
Note: When installing the Electric Fan with a Thermostat always follow manufacturer's instructions for specific details.


What caught my eye was the instruction (highlighted in blue font) to activate the fans individually to spread the amp draw. Has anyone wired their fans like this? What temperature settings are you using for each fan?

Thanks

Seems to me you could power up both fans together if you run them through a high-amp relay hooked directly to the battery. Let the thermostat trigger the relay.

https://www.summitracing.com/parts/bch-0332002168

I'm running dual Ford Contour fans. Both on high draw 40 amps total when running, and the starting surge is an unknown amount larger. I wired them both to come on full through a large relay driven by a temperature switch.

When they'd both kick on, the extra load through the alternator would drop the idle 150-200 rpm and sometimes start to spiral in (big cam won't idle below 1000) requiring a touch on the throttle. Annoying with a manual trans when (for example) backing up...

Anyhow I'd recommend doing it the way Derale recommends - or better yet, get a beefier PWM controller from Darryl the Auto Cool Guy. I love mine, well worth the extra cost. And no high load surges either.
(No connection, just a satisfied customer).

I made this diagram as a one way to wire it, Using three relays if you got A/C, to be able to turn the secondary fan not just by the dual temp sensor, but also when A/C is on.

Having ammeter is not correct to feed them from battery, but from alternator, OR at some juntion point between ammeter and alternator

You can also feed the system with key in Ign1 ( run ) or straight from the main wring ( batt circuit ) and that will keepit working still with key off untill get the temp completelly down

The key point about running electric fans is that max current is drawn when 1st actuated....
Once the fans are running their current draw drop to a lower continuous level...
But it is still crucial to make sure the wiring and alternator are capable of supplying adequate current..

Just my $0.02...

Althought being wired from alt stud there is nothing to worry about stock wiring, aside get the propper wire to feed relays. ( 12 gauge should be quite enough for them ). Specially if setup is made to work just in RUN.

but upgrading the alt, get a nice path between alt and amm is mandatory

Thanks all for the responses. Especially Nacho for the diagram.

Think I'm going to try wiring it like Derale suggests, turning on fans sequentially. My main question what temps to turn each fan on/off?

With a 180F thermostat, I'm guessing Fan 1 - On at 185F, Off at 180F, Fan 2 - On at 190F, Off at 185F? I'm just taking an educated guess with those numbers. That's why I was asking you guys.

If this method doesn't work, I'll keep the PWM as Plan B.

Thanks

that's basically what I'm saying and why I made the diagram on the way I did. Just including the A/C compressor signal to turn on the secondary fan having reached or not the temp... because eventually will reach it anyway and will add more cool to the A/C system


Here is a thread where I initally posted that diagram and the dual temp switch varieties with temp ranges available from the regular market... thread sizes and all. Mostly sure would require thead adapters. Most of these are from European cars such as Fiats, Mercedes, Alfa Romeos. Sure the temp rates are in celsious ( the website I found was from Italy ), but the Farenheit conversion is easy and I'm pretty sure some of these should be available from Mopar dealers being Chrysler now FCA ( Fiat )

http://www.dodgecharger.com/forum/index.php/topic,137696.0.html

several interesting temp rates from those.

It took me HOURS ( if not days ) untill find those switches options on the web with PNs

I ALLWAYS FORGET TO INCLUDE FUSES OR BREAKERS ON MY DIAGRAMS, sorry.

As mentioned the diagram was made based on a guy not using ammeter, but if using ammeter, relays MUST be sourced from alt stud

Plugs for these temp switches should be available from auto parts just like switches itself

AAAAAAAND, YOU CAN ALLWAYS INSTALL AN OVERRIDE SWITCH somewhere down the dash, for one of the fans ( either one ) with just ground signal spliced into the 85 terminal of any of the fan relays ( usually, the secondary fan ), or even spliced into the 87 terminal of the fan clutch signal relay

honestly, reading what Derale offers... aside the PWM controlers, the regular relay system they offer are not more than what I made on diagram but single stage... with another difference, they use a positive signal to trigger the relays and I used negative ( ground ) signal to trigger them throught the temp sensor/switch, which in any case IMHO is more versatile and easier to wire up. No need for wire from ignition system ( neither diodes ) except if you want to keep fans off when key is off. Modern cars use to keep fans on with key off

and they have the option of the probe system if you don't want to insert the sensor into the water system, but they offer single stage sensors anyway. You could get a probe and try to fit them with adaptors on to a dual stage temp sensor/switch too.

You can also use 2 adjustable thermostat switches with the probe to trigger the relays instead the dual stage temp sensor/switch.

i always like to activate relays with the ground. it seems safer to me, and if using a toggle switch [or other type], i believe it's easier on the switch itself.
if i'm thinking wrong, someone please correct me.

Nacho, very interesting read at the Charger site! Also good to know that there are thermal switches for multi speed fans available.

I converted the temp settings on the first switch to F and found the following: LO - 180F ON, 170F OFF HI - 190ON, 180OFF. That's fairly similar to the values that I took a guess at.

FYI, I ran across a controller that might fit the bill. It has the ability to control the ON/OFF temps of single or dual fans and it doesn't need a separate sensor (only possible if you have a Dakota Digital dash). The P/N is PAC-2800BT. Since I already have a Dakota Digital VHX dash, I'm considering this controller instead of wiring something myself.

But I do appreciate your diagram and your input!

There are several rates, not just that, for all three switches posted there. To each own

And sure, if a computer controled system can be afforded and you like, go for it. I just meant the "analog" system Derale website offers is not diff from what I posted being home made and cheap, and even more, my diagram is way better than what Derale suggests LOL.

I think will make some other adds on the diagram I made, like the override switch. I will post here for future references.

NEW DIAGRAM about WHAT I would do on my own car if I was to install a dual fan setup fully analogic and cheap system ( not PCM or PWM controled ).

I hope it works for many of you if wished

Thanks for the completed diagram!

I think it should be made a sticky or be put into the tech archives so that anyone who wants to wire their own dual fans has this guidance.

Mounted on fuse relays can be used for simplicity... they are available without the 87A terminal ( 4 prongs ), which is not needed on this case

just now this sentence took my attention... why Delare instructions gets worried about that ? the load is handled by relays not straight for the thermostat/temp sensor switch!!! not even being activated by positve from the thermostat/temp sensor switch.

just as a reminder... My diagram shows it being triggered by negative from thermostat/temp sensor switch, opposite to what Delare shows.