Diesel Fan PCB

FrenchMike · 31st July 2015, 13:36

Hi all,

I have had the opportunity to look closely at this small 3 speed PCB.
I have "rebuilt" the drawing in order to understand how that works.

Here it is:

The system is constructed around a quadruple comparator without sensible components.

Comparator one generate a continous voltage on C9 according to the
PWM ratio:
at a battery voltage of 12 volt,we get around

1.6 volt for this:

5 volt for this:

and 8 volt for this:

That voltage is compared in each of three remaining comparators to three
different thresholds.
produced by 3 resistor dividers .

R8/R6 for Low
R11/R5 for Medium
R13/R12 for High

In addition the Medium threshold is forced low when A/C trinary input is earthed.
forcing the medium relay to be activated.

It is noticeable that in low speed,only the low (biggest ) relay is active
In Medium speed ,Medium+Low are active
In High speed all the three are ON

For tests a tiny PWM generator is easy to make:

HOWEVER,by simply earthing the PWM input (red/blue wire)
a voltage ramp is produced on C9 and if all is correct ,one can hear successively the three relays clicking.(half a second rate)

LOW ....LOW+MED....LOW+MED+HIGH
Idem in reverse

(Better removing the 80 Amp fuse before)

Have good funs

Mike

Arctic · 31st July 2015, 16:11

Hi Mike.
Is the set up above for a Four wire 3 speed fab/PCB as the two wire 2 speed does not have a purple wire as in your drawing please.

RayH · 31st July 2015, 16:18

Quote:

Originally Posted by FrenchMike

Hi all,

I have had the opportunity to look closely at this small PCB.
I have "rebuilt" the drawing in order to understand how that works.

The system is constructed around a quadruple comparator without sensible components.

Comparator one generate a continous voltage on C9 according to the
PWM ratio:
at a battery voltage of 12 volt,we get around

1.6 volt for this:

5 volt for this:

and 8 volt for this:

That voltage is compared in each of three remaining comparators to three
different thresholds.
produced by 3 resistor dividers .

R8/R6 for Low
R11/R5 for Medium
R13/R12 for High

In addition the Medium threshold is forced low when A/C trinary input is earthed.
forcing the medium relay to be activated.

It is noticeable that in low speed,only the low (biggest ) relay is active
In Medium speed ,Medium+Low are active
In High speed all the three are ON

For tests a tiny PWM generator is easy to make:

HOWEVER,by simply earthing the PWM input (red/blue wire)
a voltage ramp is produced on C9 and if all is correct ,one can hear successively the three relays stick.(half a second rate)

LOW ....LOW+MED....LOW+MED+HIGH
Idem in reverse

(Better removing the 80 Amp fuse before)

Have good funs

Mike

Thanks Mike for your work on this, I don't pretend to understand all of that but I'm sure others will.

Ray

FrenchMike · 31st July 2015, 17:16

Quote:

Originally Posted by Arctic

Hi Mike.
Is the set up above for a Four wire 3 speed fab/PCB as the two wire 2 speed does not have a purple wire as in your drawing please.

Yes Steve,

Your picture looks like the one i have tested.

I think the PCB schemes are the same for both types .it's simpler to play
with the power external circuits .

Basically at each relay closing corresponds a PWM ratio and so a engine temperature
The only important thing .IMO

Low=100 degrees
Medium=106 degrees
High=112 degrees

Mike

SD1too · 31st July 2015, 19:17

Mike; could you just clarify a few things for me please?

Quote:

Originally Posted by FrenchMike

Comparator one generate a continous voltage on C9 according to the
PWM ratio:
at a battery voltage of 12 volt,we get around ... 1.6 volts ... 5 volts ... and 8 volts ...

So are you saying that the period of the waveform shown makes no difference? It's only the amplitude which matters?

Quote:

In addition the Medium threshold is forced low when A/C trinary input is earthed .. forcing the medium relay to be activated.

Thank you Mike. I had wondered how this works.

Quote:

It is noticeable that in low speed,only the low (biggest ) relay is active
In Medium speed ,Medium+Low are active
In High speed all the three are ON

Yes, it's the same for the petrol engines with the 3 speed system, but no PCB thankfully!

Quote:

... by simply earthing the PWM input (red/blue wire)
a voltage ramp is produced on C9 and if all is correct ,one can hear successively the three relays stick.

What do you mean by "stick" Mike? Do you mean "energise"?

Quote:

Originally Posted by FrenchMike

I think the PCB schemes are the same for both types ...

It isn't Mike. On the 2 speed PCB D1, T3, T6, R13 and R19 have not been fitted by the PCB manufacturer (there may be others, please advise).

Simon

Mike Noc · 31st July 2015, 19:18

Mike excellent work.

Always good to understand more about how our cars work.

rovertone · 31st July 2015, 19:48

There are clearly experts on this thread that understand fan electrics. Could I pose a question on this subject.
Is it possible to have a 2 speed fan on a diesel that works on both speeds but fails to kick in on the 2nd speed when the coolant temp ?110/112deg calls.
Background is I have had problem with overheating earlier this year when towing up long climbs in Spain. although it wasn't very safe on one climb I did manage to check the fan and although traffic noise was high I am sure that at 118 deg the fan was only on 1st speed.
It definately works when I carry out the demist/trinary switch test, I have had it on a T4 which triggered both speeds ok simulating a signal as if from the coolant sender/ecm. The fan will have been changed from a 3 speed at some stage.
I did have a new radiator fitted in Spain which has subsequently led to fitting gold resistor and new aircon condenser. I just wondered if there could possibly be a wiring problem that could create such a scenario.
Any thoughts would be very welcome. Thanks

RayH · 31st July 2015, 20:10

Quote:

Originally Posted by rovertone

There are clearly experts on this thread that understand fan electrics. Could I pose a question on this subject.
Is it possible to have a 2 speed fan on a diesel that works on both speeds but fails to kick in on the 2nd speed when the coolant temp ?110/112deg calls.
Background is I have had problem with overheating earlier this year when towing up long climbs in Spain. although it wasn't very safe on one climb I did manage to check the fan and although traffic noise was high I am sure that at 118 deg the fan was only on 1st speed.
It definately works when I carry out the demist/trinary switch test, I have had it on a T4 which triggered both speeds ok simulating a signal as if from the coolant sender/ecm. The fan will have been changed from a 3 speed at some stage.
I did have a new radiator fitted in Spain which has subsequently led to fitting gold resistor and new aircon condenser. I just wondered if there could possibly be a wiring problem that could create such a scenario.
Any thoughts would be very welcome. Thanks

I can't see how to be honest.

If you were monitoring the temperature from the instrument panel then the sensor must be working.

You know the high speed is working from the trinary test, and from T4 simulation.

From T4 simulation the fan PCB and ECU must be working correctly

Therefore any possibility of a wiring fault can be excluded.

"although it wasn't very safe on one climb I did manage to check the fan and although traffic noise was high I am sure that at 118 deg the fan was only on 1st speed"

I now have visions on you sliding out onto the bonnet whilst cruise control is engaged, and your passenger steering, to peer into the grill

FrenchMike · 31st July 2015, 21:26

Quote:

Originally Posted by SD1too

So are you saying that the period of the waveform shown makes no difference? It's only the amplitude which matters?

What do you mean by "stick" Mike? Do you mean "energise"?

It isn't Mike. On the 2 speed PCB D1, T3, T6, R13 and R19 have not been fitted by the PCB manufacturer (there may be others, please advise).

Simon

Well Simon,

-It's essentially the ratio Time HI/Time LO which makes the difference
See the waveforms above (Pulse Width Modulation)

-Sorry,i wanted to say click (in silent environment)

It isn't Mike. On the 2 speed PCB D1, T3, T6, R13 and R19 have not been fitted by the PCB manufacturer (there may be others, please advise).

-Possible costs cutting but the principle is the same ,i guess.
you can send me a 2 speed version

Mike

FrenchMike · 31st July 2015, 21:29

Quote:

Originally Posted by Mike Noc

Mike excellent work.

Always good to understand more about how our cars work.

Thanks Mike ....
I think the lines PWR and Trinary are crossed in your drawings
Red/blue versus grey wires

Mike

31st July 2015, 13:36	#1
FrenchMike This is my second home Rover 75 Saloon Join Date: Aug 2007 Location: Avignon Posts: 4,466 Thanks: 94 Thanked 661 Times in 554 Posts	Diesel Fan PCB Hi all, I have had the opportunity to look closely at this small 3 speed PCB. I have "rebuilt" the drawing in order to understand how that works. Here it is: The system is constructed around a quadruple comparator without sensible components. Comparator one generate a continous voltage on C9 according to the PWM ratio: at a battery voltage of 12 volt,we get around 1.6 volt for this: 5 volt for this: and 8 volt for this: That voltage is compared in each of three remaining comparators to three different thresholds. produced by 3 resistor dividers . R8/R6 for Low R11/R5 for Medium R13/R12 for High In addition the Medium threshold is forced low when A/C trinary input is earthed. forcing the medium relay to be activated. It is noticeable that in low speed,only the low (biggest ) relay is active In Medium speed ,Medium+Low are active In High speed all the three are ON For tests a tiny PWM generator is easy to make: HOWEVER,by simply earthing the PWM input (red/blue wire) a voltage ramp is produced on C9 and if all is correct ,one can hear successively the three relays clicking.(half a second rate) LOW ....LOW+MED....LOW+MED+HIGH Idem in reverse (Better removing the 80 Amp fuse before) Have good funs Mike Last edited by FrenchMike; 31st December 2016 at 13:33..

31st July 2015, 19:48	#7
rovertone Gets stuck in Rover 75 Conne SE Auto CDTi Join Date: Nov 2012 Location: Redditch Posts: 674 Thanks: 185 Thanked 135 Times in 109 Posts	There are clearly experts on this thread that understand fan electrics. Could I pose a question on this subject. Is it possible to have a 2 speed fan on a diesel that works on both speeds but fails to kick in on the 2nd speed when the coolant temp ?110/112deg calls. Background is I have had problem with overheating earlier this year when towing up long climbs in Spain. although it wasn't very safe on one climb I did manage to check the fan and although traffic noise was high I am sure that at 118 deg the fan was only on 1st speed. It definately works when I carry out the demist/trinary switch test, I have had it on a T4 which triggered both speeds ok simulating a signal as if from the coolant sender/ecm. The fan will have been changed from a 3 speed at some stage. I did have a new radiator fitted in Spain which has subsequently led to fitting gold resistor and new aircon condenser. I just wondered if there could possibly be a wiring problem that could create such a scenario. Any thoughts would be very welcome. Thanks __________________ 2003 Mk 1 Connie SE CDTi Auto Monogram Mirage 2/Sandstone Leather 511th CDTi out of 4744 produced 9th in Mirage 2 out of 17 produced Also 2004 Rover 25 SXi CVT, 1999 Megane Cabriolet and still missing my 800 Fastback.

31st July 2015, 19:18	#6
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,579 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Mike excellent work. Always good to understand more about how our cars work.