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Half speed thermo fan wiring schematic

Started by _judgelj_ , Dec 19 2013 09:05 PM

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45 replies to this topic

#1 _judgelj_

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Posted 19 December 2013 - 09:05 PM

Hi,

Hoping someone could throw a few ideas at me as I am trying to work out a way to wire in a relay to split voltage to two fans, have the, run at half speed 6 volts each, until temperature is reached and they return to full speed. Any ideas of where to start?

Cheers

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#2 _The Baron_

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Posted 19 December 2013 - 09:27 PM

EF/EL used a number of speeds from 2 fans and a bunch of relays.

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#3 Rockoz

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Posted 19 December 2013 - 10:46 PM

What will you be using to sense the temp change?

2 temp sensors?

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#4 Oversteer

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Posted 19 December 2013 - 10:55 PM

Get a 2 speed fan(many factory cars use a 3 wire fan)

But the question is why do you want to 2 speed the fan.? do you have a proper thermostat controlling the on/off of the fan/s ?

You could use relays to series the fans then switch back to parallel but this requires at lease 3 relays.... and feeding most fans low voltage will burn them out ! Proper way to speed control dc motors is pwm with a controller...not such a hard thing to find, look on fleabay.

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#5 Rockoz

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Posted 19 December 2013 - 11:12 PM

Have worked out a circuit that will have no fans running until low temp sensor activated.

Then will run fans at 6 volts each until high temp activated. Then both fans full voltage.

Uses 4 x standard single pole headlight relays.

Could do it with less but using cheap readily available stuff.

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#6 _judgelj_

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Posted 19 December 2013 - 11:20 PM

What will you be using to sense the temp change?
2 temp sensors?

Well the idea was to use one sensor to control the on/off of full speed and run both fans at 6v all the time.

Get a 2 speed fan(many factory cars use a 3 wire fan)

But the question is why do you want to 2 speed the fan.? do you have a proper thermostat controlling the on/off of the fan/s ?

You could use relays to series the fans then switch back to parallel but this requires at lease 3 relays.... and feeding most fans low voltage will burn them out ! Proper way to speed control dc motors is pwm with a controller...not such a hard thing to find, look on fleabay.

The reason being as I'm having trouble cooling my engine and I put it down to a combination of shitty fans and no cowl to direct airflow. I thought if I could run the fans at half speed it would stop the temp from climbing so quickly and give the fans a better chance at cooling when they hit full speed?

Is my theory silly?

P.S I already have a thematic switch with 2 relays.

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#7 _The Baron_

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Posted 20 December 2013 - 07:35 AM

Again......go and have a close look into the EF/EL setup. From factory they just use relays to get 2 (EL) to 3 (EF) fan running configurations (subject to model and fan types) with relays alone.

And yes they series up 2 fans to attain one of the speeds. No Pulse Width Modulation (PWM)stuff.

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#8 _judgelj_

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Posted 20 December 2013 - 08:24 AM

Yeah so I was thinking one relay switched by ignition to split 12 volts in half for each fan, but it has to somehow cutout when the temperature cut in is reached and fans resume full speed

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#9 Rockoz

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Posted 20 December 2013 - 08:57 AM

Just a suggestion.

Why not run 1 fan permanently and the second cut in at temp.

Would be a whole lot simpler.

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#10 S pack

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Posted 20 December 2013 - 09:04 AM

Yeah so I was thinking one relay switched by ignition to split 12 volts in half for each fan, but it has to somehow cutout when the temperature cut in is reached and fans resume full speed

You will need a resistor or transformer to reduce the voltage from 12 volts to 6 volts. Relays don't reduce voltage.

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#11 Rockoz

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Posted 20 December 2013 - 09:12 AM

Transformers dont reduce DC voltage either.

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#12 S pack

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Posted 20 December 2013 - 12:49 PM

Transformers dont reduce DC voltage either.

I'm not a sparky so wasn't completely sure about using a transformer. Thanks for the clarification.

Cheers

Dave.

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#13 RallyRed

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Posted 20 December 2013 - 01:05 PM

hi....just had a 2 second think about this......personally I'd probably try the 2 fans , supplied by 12v , that are staged depending on the temp.
but regardless, this circuit might work.
I have not shown detail of fuses, temp. controller etc, just the basic concept.
All care, but no....well, you know..I'm not even sure the fans would like having only 6v applied to them.
But regardless, the question was ...could anyone post a circuit...,.

Attached Files

6v 12v fan bodgey.jpg 378.13K 8 downloads

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#14 _Bomber Watson_

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Posted 20 December 2013 - 01:51 PM

Now that thats done, my brayne seriously doubts your idea will help.

Cheers.

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#15 S pack

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Posted 20 December 2013 - 02:26 PM

Been looking at some thermo fan wiring diagrams. Do your thermo fans each have 3 wires, two power wires (high & low speed) and one earth?

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#16 madtoranajzedded

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Posted 20 December 2013 - 04:03 PM

i still dont get why you are having overheating problems jacob,you have two thermos,i had an 186 45 dcoe webbers 35/75 camshaft etc and had the old 2 core radiator with 12 inch thermo no shroud with the sensor in top hose with adjustable temp,no fan on motor ,had it set on 190 and never had probs,if the tanks have been takin off and cleaned ,and thermostats the right one and timings right,and carbs are tuned,hoses fine etc,i cant see why its overheating ,are the thermos hard up on radiator?

maz

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#17 RallyRed

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Posted 20 December 2013 - 05:31 PM

aaw come on Bomber.....at least give me 4/10 for trying....

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#18 _hutch_

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Posted 20 December 2013 - 09:30 PM

I had twin thermos on the HZ with 3.3 black engine fitted I had it wired to run one fan with the AC and 2 off the temp sensor worked as good as gold

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#19 _judgelj_

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Posted 20 December 2013 - 11:14 PM

Just a suggestion.

Why not run 1 fan permanently and the second cut in at temp.

Would be a whole lot simpler.

Probably be the same amount of stuffing around as two at 2 speeds at different times.

You will need a resistor or transformer to reduce the voltage from 12 volts to 6 volts. Relays don't reduce voltage.

Cant i just split 12v into 2 fans?

Been looking at some thermo fan wiring diagrams. Do your thermo fans each have 3 wires, two power wires (high & low speed) and one earth?

These have two wires

i still dont get why you are having overheating problems jacob,you have two thermos,i had an 186 45 dcoe webbers 35/75 camshaft etc and had the old 2 core radiator with 12 inch thermo no shroud with the sensor in top hose with adjustable temp,no fan on motor ,had it set on 190 and never had probs,if the tanks have been takin off and cleaned ,and thermostats the right one and timings right,and carbs are tuned,hoses fine etc,i cant see why its overheating ,are the thermos hard up on radiator?

maz

To be honest its not overheating, its just getting hot. But then again i haven't actually driven it yet properly to see it overheat. It did spew a bit of water out of the overflow when i got to the roadworthy joint, and then again at home. But, the probe was not set up yet. After setting up the probe in the top hose and running the engine with a digital thermometer to adjust it, i found that the temp was spiking at times and siting idle around 95, before dropping very slowly. In essence the fans were on for 3 minutes off for 1, instead of on for 1 minute, off for 3, if that makes sense. I still think they need a shroud as they are pushing a lot of air out of the gaps. Timing is good, carbs were a bit rich when testing, so probably wont help that i leaned them out now.

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#20 S pack

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Posted 21 December 2013 - 07:12 AM

Cant i just split 12v into 2 fans?

These have two wires

Running two fans off one 12v supply wire won't split the voltage in two. Both fans will still receive 12 volts. What will happen is you will double the amps load on the single 12v supply wire.

It appears that thermo fans capable of two speed operation have 3 wires going into to the motor, one high speed circuit (12v) one low speed circuit (6v) and one earth wire. Most likely the resistance to drop the voltage down to 6v for the low speed circuit is built into the fan motor.

So you will need to install a suitable sized resistor into the low speed power circuit to drop the voltage down to 6v.

You will also need to get rid of the radiator hose mounted sensor and get a two stage thermo switch to run dual speeds.

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#21 RallyRed

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Posted 21 December 2013 - 09:06 AM

the circuit I posted above -
- splits the 12v across the 2 fans when the relay is off.
- supplies 12v to both fans when the relay is on.

If not, either i'm wrong, or someone better get on the blower to Mr Ohm, cause his Law is wrong.

Weather that actually results in the fans running at 1/2 speed in the first case, prob depends on the actual fan motor design.

Edited by RallyRed, 21 December 2013 - 09:09 AM.

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#22 _judgelj_

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Posted 21 December 2013 - 09:55 AM

Problem is id like to retain the existing thematic switch and have the half speed as an addition.

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#23 S pack

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Posted 21 December 2013 - 10:09 AM

Problem is id like to retain the existing thematic switch and have the half speed as an addition.

Forget it then unless your existing thermatic controller is dual speed capable.

Easiest and neatest option would be to use a two stage thermo switch mounted in the thermostat housing or cover and have one fan cut in at the switches lower temp setting then the second fan cuts in at the higher temp setting.

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#24 _Bomber Watson_

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Posted 21 December 2013 - 11:15 AM

I must still be missing something, what exactly is this to achieve again?

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#25 _The Baron_

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Posted 21 December 2013 - 11:24 AM

aaw come on Bomber.....at least give me 4/10 for trying....

Nothing wrong with your idea really, just needed extra detail like an upstream common relay (Rp) to apply initial power to your whole circuit and maybe we should split the function of relay R1 to two relays (R1a/b) because a double pole, double throw relay would be rare and probably expensive.

Maybe change relay R1a/b connections such that when you power the circuit up intially you get low speed (2 fans in series). When you power up R1a/b with Rp you get both fans in series.

Thats the "power" wiring sorted, now control cct will need a little work where the low speed fan setting say as used with an AC application (whether already on or off) will always be over ridden by a high temperature sensor and or a manually operated switch (these can function in parallel).

I will give this some more thought but the basic concept is close.