Dual Fan Wiring

[TomG]

Hi

On my radiator, I have a Mondeo dual fan setup switched by an X-Fan. Currently i have it working that the first fan starts at the lower temperature then the second joins in at the upper temp.

It strikes me that when one fan is running, some air could be sucked in backwards through the blades of the stationary fan so not totally efficient.

I was wondering how it would be possible to wire it so that at the lower temp, both fans are running in series (half speed) then both fans wired parallel at full speed when the upper temp is reached.

I've tried to figure it out on paper.. and failed. Something tells me it involves diodes and relays, then I got really confused

Anyone got a circuit diagram?

[Bowie69]

5 mins with Paint and I came up with this:

Uses two relays and a shed load of spade connectors, but it can be done without diodes..... at least I think... I have been staring at this PC toooooo long today

Excuse the quality of the schematic, I lost my electrical CAD program a while back and not replaced it yet. Oh and the bottom line is of course earth, but I forgot to mark it as such

Hope that helps,

Bowie.

[simonb]

Hi

On my radiator, I have a Mondeo dual fan setup switched by an X-Fan. Currently i have it working that the first fan starts at the lower temperature then the second joins in at the upper temp.

It strikes me that when one fan is running, some air could be sucked in backwards through the blades of the stationary fan so not totally efficient.

I was wondering how it would be possible to wire it so that at the lower temp, both fans are running in series (half speed) then both fans wired parallel at full speed when the upper temp is reached.

I've tried to figure it out on paper.. and failed. Something tells me it involves diodes and relays, then I got really confused

Anyone got a circuit diagram?

Don't need diodes just relays, not sure its worth the faff though. At 6v per fan there isn't going to be much blow, or suck...

For most effiency the fans need to be as close as possible to the rad core, if they are, not much air will be pulled through from the "off" fan. The running fan should be drawing a "disc" of air throught the rad in front of it which should be enough. To be honest unless you are doing hard off road stuff one fan will suffice, if not ur rads shot!

[TheRecklessEngineer]

^^^Wot bowie69 said...just finished drawing same thing, but his is much smarter!

Just because they are getting half the voltage doesn't mean that the motors will turn at half the speed....

If you were looking for a really overcomplicated clever solution, I'm sure you could make a microprocessor based P controller...(or even PID if you are feeling really sad clever)

[Bowie69]

Also agree about the 6 volts not really being enough, I would expect 9V to be a closer figure to acheive half the air throughput.

To acheive that.... well yes... there's various ways, most reliable being thyristors.... but you didn't want diodes... so I guess you don't want full-on semiconducotr devices in there

[Mark90]

There is a very good wiring diagram that does the series/parallel switching that was done by Bull Bar Cowboy on here. Had a quick look in the tech archive but couldn't see it.

However I never had any problems with twin mondeo fans on a 4.2 V8 wired up as you have, the second fan very rarely came on, one fan was usually sufficient even off road.

[FridgeFreezer]

Bull Bar Cowboy did a very nice version which I've just cut-n-pasted here. Mine runs this circuit and it works really well - 99% of the time "slow" mode is enough to cool it and is much quieter than fast mode, also drawing less power from the vehicle.

Here's the full article with big up massive respeck to Ian for an excellent solution:

Application Description

Although this article applies to the Rover V8, you can easily adapt it to any engine if you know the normal operating temperatures.

When the V8 EFI was transplanted into the 90, it quickly became evident that the Rover standard fit of a junior propeller had to go and be replaced by an electrical fan arrangement.

The fans are Vauxhall Astra MkIII. The fans are laid face down and the triangular mounting parts of the fans are cut away, this then allows the two fans to be bolted to give a twin fan setup. The top and bottom of the fans are then joined using a short strip of stainless steel with a thickness of 1.5mm. This assembly is then mounted on the rear of the radiator using stainless steel "L" brackets. The built in cowls of each fan are in contact with the radiator thus providing a very good thermal air path. You can use any pair of fans you wish, though.

Control of the fans is achieved by the use of a dual thermal radiator switch (Intermotor 50091), which is mounted into the top hose. These switches are a standard fit item on many models and thus easily sourced in a variety of different temperature characteristics.

Note: This bit is kinda superseded by the X-Eng fan switch but I've included it for completeness:

The "splice" fitting for the top hose is constructed from a short length of 38mm diameter thick walled brass tube. The tube is machined (or drilled and filed) to take a standard 22mm temperature switch radiator fitting. These can be obtained very cheaply from most good radiator specialists. Alternatively a 16mm brass compression pipe fitting can be used as this has a 22mm internal thread (not to be confused with the standard 15mm pipe fitting that has a BSP thread).The fitting is then soldered into the brass tube which is mounted close to the radiator.

An alternative method is to use the thermostat housing from an export or "air-con" model as this is designed to take the thermal switch (the air con models have a 100°C switch fitted). However, the housing is in the order of £45 +VAT. As the coolant is some 6°C to 8°C cooler at the radiator entry point than the engine block , a switch fitted in the thermostat housing will need to reflect this difference (use a 50174).

The dual speed switching came about as it was found that both fans running at normal speed were too efficient - @ tickover, the fans were set to come on at 100°C and would cool the engine coolant to thermostat temperature in 15 seconds. Unfortunately that amount of heating / rapid cooling is bad news for the expansion and contraction stresses of the radiator and engine components. To overcome this it was decided to run the fans in series (a bit less than half speed) when the engine temperature rose to circa 95°C and to run them on full speed if the engine temperature further rose to 100°C. In practice the fans only come on when sitting in stationary traffic (the slow speed gently cools the engine down to 90°C and keeps it there) or when towing (on hills). Only once have I had the fans come onto full speed - the radiator was completely clogged with mud and I had driven from Wiltshire to Devon with the fans on slow most of the way, but at telegraph hill the engine temp rose to the magical 100°C. However the fans did the trick and the engine temp dropped back sufficiently.

Much of my work is in the design of Radio systems for Public Safety (mainly Fire and Ambulance related) where any single point of failure is designed out - hence two fans, dual switching etc - get the picture!

Diagram Description

The master switch controls the supply to the thermal switch (s). In its off position it turns on one of the spare dash lights (amber, in the bottom right hand corner). Closure of the first thermal switch at 88°C (engine temp of 95°C - remember the 6°C - 8°C temperature difference between coolant in block and coolant in top hose) operates relay A. This completes the circuit of --- supply to Fan 1, via normally closed relay D contacts to Fan 2. This connects the fans in series and under normal circumstances will give more than adequate cooling.

If you are giving the engine a hard time and the temperature rises to 100C the second thermal switch will close and operate relays B and D. Relay D contacts will change over and a supply via the relay B contacts will be directly applied to Fan 2 The closure of Relay B contacts causes relay C to operate and apply an earth to the negative side of Fan 1. Relay C also ensures an appropriate delay in applying the earth (if this feature was not included there was a possibility of intermittent fuse blowing dependant upon relay timing). This arrangement now allows the fans to run at full speed (parallel operation). A further feed is also taken back to the dash lights as a warning that the fans are on full (I used the spare green light - top row centre)

The supplies to the fans should come directly from the battery (Starter motor in most cases, as this in the shortest run). I run the feed to the main switch as a direct fused live, because having the fans remain on when the engine in switched off (and they then come on intermittently as thermo siphoning takes place in the cooling system) causes less long term engine bay problems due to heat soak.

Attached is a list of INTERMOTOR switches that are readily available for this application (I have listed all types, but the M22 switches are of most interest)

Intermotor switches:

Part No. A/F Size Thread Temp °C

50480 19 3/8" BSP Taper 50-46 N.C.C.

50471 19 3/8" BSP Taper 77-74 N.C.C.

50460 27 3/8" BSP Taper 90-85

50370 27 3/8" BSP Taper 95-90

50372 27 3/8" BSP Taper 100-95

50010 25 3/8" x 18 NPTF 79-74

50080 21 3/8" x 18 NPTF 88

50172 22 M14 x 1.5 87-82

50042 24 M14 x 1.5 90-85/98-93

50041 22 M14 x 1.5 95-90

50173 22 M14 x 1.5 100-95

50040 22 M14 x 1.5 103-98

50481 21 M16 x 1.5 50 OFF N.C.C.

50475 17 M16 x 1.5 60 OFF N.C.C.

50430 17 M16 x 1.5 85 ON

50320 27 M16 x 1.5 85-80

50420 21 M16 x 1.5 85-80

50432 21 M16 x 1.5 85-80

50476 17 M16 x 1.5 85-80 N.C.C.

50300 27 M16 x 1.5 87-80

50317 22 M16 x 1.5 87-82

50321 22 M16 x 1.5 88-79

50310 22 M16 x 1.5 88-86

50301 22 M16 x 1.5 90-83

50474 19 M16 x 1.5 90-83 N.C.C.

50461 21 M16 x 1.5 90-85

50421 21 M16 x 1.5 90-85

50470 17 M16 x 1.5 90-85 N.C.C.

50390 17 M16 x 1.5 90-85 N.C.C.

50316 22 M16 x 1.5 92-82

50330 22 M16 x 1.5 92-82

50453 24 M16 x 1.5 92-85

50315 22 M16 x 1.5 92-87

50341 24 M16 x 1.5 92-87

50342 24 M16 x 1.5 92-87

50371 27 M16 x 1.5 92-87

50373 24 M16 x 1.5 92-87

50450 21 M16 x 1.5 92-87

50340 29 M16 x 1.5 93-86

50374 24 M16 x 1.5 93-88

50479 17 M16 x 1.5 93-88 N.C.C.

50332 22 M16 x 1.5 95-85

50477 17 M16 x 1.5 95-88 N.C.C.

50455 22 M16 x 1.5 95-90

50454 22 M16 x 1.5 95-90

50380 17 M16 x 1.5 97-92 N.C.C.

50478 17 M16 x 1.5 98-91 N.C.C.

50375 24 M16 x 1.5 98-93

50472 17 M16 x 1.5 98-93 N.C.C.

50473 17 M16 x 1.5 98-95 N.C.C.

50431 17 M16 x 1.5 100-95

50331 22 M16 x 1.5 102-97

50100 29 M22 x 1.5 82-68

50101 29 M22 x 1.5 84-79/88-83

50250 29 M22 x 1.5 86-76

50012 29 M22 x 1.5 86-77

50090 29 M22 x 1.5 86-81

50120 29 M22 x 1.5 88-79

50295 29 M22 x 1.5 88-79

50296 29 M22 x 1.5 88-79/110-102

50271 29 M22 x 1.5 88-83

50272 29 M22 x 1.5 88-83

50275 29 M22 x 1.5 88-83

50217 29 M22 x 1.5 88-83/92-87

50091 29 M22 x 1.5 88-83/92-87

50212 29 M22 x 1.5 88-83/92-87

50213 29 M22 x 1.5 88-83/92-87

50216 29 M22 x 1.5 88-83/92-87

50221 29 M22 x 1.5 88-83/92-87

50219 29 M22 x 1.5 88-83/92-97

50240 29 M22 x 1.5 90-80

50110 29 M22 x 1.5 92-82

50111 29 M22 x 1.5 92-82

50112 29 M22 x 1.5 92-82

50113 29 M22 x 1.5 92-82/95-80

50218 29 M22 x 1.5 92-82/97-92

50170 29 M22 x 1.5 92-87

50200 29 M22 x 1.5 92-87

50210 29 M22 x 1.5 92-87

50211 29 M22 x 1.5 92-87

50220 29 M22 x 1.5 92-87

50230 29 M22 x 1.5 92-87

50231 29 M22 x 1.5 92-87

50235 29 M22 x 1.5 92-87

50260 29 M22 x 1.5 92-87

50270 29 M22 x 1.5 92-87

50280 29 M22 x 1.5 92-87

50281 29 M22 x 1.5 92-87

50285 29 M22 x 1.5 92-87

50290 29 M22 x 1.5 92-87

50215 29 M22 x 1.5 92-87/97-92

50011 29 M22 x 1.5 93-88

50102 29 M22 x 1.5 93-88/97-92

50035 29 M22 x 1.5 95-85/102-92

50130 29 M22 x 1.5 95-86

50030 29 M22 x 1.5 95-90

50033 29 M22 x 1.5 95-90

50061 29 M22 x 1.5 95-90

50062 29 M22 x 1.5 95-90

50160 29 M22 x 1.5 95-90

50092 29 M22 x 1.5 95-90/100-95

50174 29 M22 x 1.5 95-90/100-95

50104 29 M22 x 1.5 97-92

50282 29 M22 x 1.5 97-92

50103 29 M22 x 1.5 97-92/101 -96

50214 29 M22 x 1.5 97-92/102-97

50190 29 M22 x 1.5 100-95

50195 29 M22 x 1.5 100-95

50196 29 M22 x 1.5 100-95

50197 29 M22 x 1.5 100-95

50198 29 M22 x 1.5 100-95/110-105

50000 29 M22 x 1.5 103-98

50013 29 M22 x 1.5 103-98

50014 29 M22 x 1.5 103-98

50191 29 M22 x 1.5 120-115

[TomG]

Thanks all for the replies, excellent info there!

Fan blades are approx 15mm back from the rad and completely sealed in the mondeo cowling. Will give the PID semiconductor approach a miss but I like the look of the relay setups.