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Cooling fan warning light and switch


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On 3/30/2022 at 11:29 AM, RobH said:

If you do that the thermal switch will only operate when the ignition is on but the manual override will always work.  Since you are going to rely on the battery master switch you might as well just leave both switches in parallel and forget about the diodes, like this, which will give automatic overrun.  The light will come on if either switch closes.  Its pretty obvious from the noise, when the fan is running and the ignition is off :

1936087937_fancircuit.jpg.8cfa058fbccbe9c8a06dfa87e4082769.jpg

 

Sorry if the diagram is getting. bit scrappy looking - I'm doing quick mods to the original to save time in replying. 

Hi Rob,

Is it not better to have the switches on the earth side, ie switching off 86? And having the supply feed onto 30 and 85?

Many thanks

David

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2 hours ago, qkingston said:

Is it not better to have the switches on the earth side, ie switching off 86? And having the supply feed onto 30 and 85?

Many thanks

As I said at  the beginning David, there are a number of ways to arrange things.  Whether there is an advantage of the switches being in the earthy side as per my first drawing is a moot point; it really comes down to what is more convenient with the wiring.  Both ways work perfectly well but the circuit you linked to is arranged that way because the internally-illuminated switch will only work on the power input side, since the lamp needs the full supply voltage.  

 

 

 

Edited by RobH
clarification
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Thanks Rob, I've got this to work correctly with my illuminated switch ( as attached - can't get the image orientation to behave!)

Best Regards

David

switch wiring.JPG

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28 minutes ago, BlueTR3A-5EKT said:

The warning light for my engine cooling fan ‘glows’ above 30 mph, when not switched on.  

The fan is being wind blown and acting like a generator   - could this be the answer to global warming.

 

Roger

 

 

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1 minute ago, RogerH said:

The fan is being wind blown and acting like a generator   - could this be the answer to global warming.

 

Roger

 

 

So why does my head not glow when I drive with aeroscreens?

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29 minutes ago, BlueTR3A-5EKT said:

The warning light for my engine cooling fan ‘glows’ above 30 mph, when not switched on.

To stop that, you need to connect the warning lamp on the coil side of the relay ( supposing you have a relay that is ) instead of direct to the fan motor.

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Just a little word of caution regarding lamps that are part of the switch, as is the case with mine.  I know it is obvious and is covered indirectly by the discussion above but the lamp comes on to indicate that the switch has been operated, not that the supply has been connected to the device.  This was made very apparent to me when stuck in a traffic jam in France on a very hot day (not a little embarrassing).  No matter how many times i operated the switch, the fan didn't come on and the temp gauge refused to indicate lower.  The reason was that the blade style fuse carrying the current to the fan had fallen out of its holder at some time - at least fault finding was easy once the steam had dispersed.

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29 minutes ago, Alfrom said:

the lamp comes on to indicate that the switch has been operated, not that the supply has been connected to the device.

That is usually true for any indicator lamp.  They generally only show that supply is present, not that the thing being supplied is actually working.

 I suppose Peter's windmilling 'generator' (posts above) does actually show that the motor is connected and electrically live.... 

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Yes Rob.

As a result of this thread, I've already decided that a lamp across the fan contacts is what is needed to give a little more assurance, although checking the temp gauge is the always the fall back, even if potentially a little late. 

Pierre

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If you had a simple way to sense the current flow in the rad fan wires then that gives a pretty good idea that things are working or not.

My simple way -   have a reed switch.+12V in one end and the other connected to an LED that then goes to ground.

Wrap around the glass reed switch body an enameled  copper wire as many times as can fit. One end to +12v the other end to the fan.

When the fan is powered ON the magnetic field around the outer wire will close the reed switch and the LED will illuminate.

 

Roger

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1 hour ago, RogerH said:

If you had a simple way to sense the current flow in the rad fan wires then that gives a pretty good idea that things are working or not.

My simple way -   have a reed switch.+12V in one end and the other connected to an LED that then goes to ground.

Wrap around the glass reed switch body an enameled  copper wire as many times as can fit. One end to +12v the other end to the fan.

When the fan is powered ON the magnetic field around the outer wire will close the reed switch and the LED will illuminate.

 

Roger

Unfortunately Roger that still doesn't tell you if the fan is actually functioning, it only tells you that it has power, which isn't hugely different to my indicator bulb from the supply.

Rgds Ian

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3 hours ago, RogerH said:

Wrap around the glass reed switch body an enameled  copper wire as many times as can fit. One end to +12v the other end to the fan.

 

A typical reed switch will require somewhere between 10 and 60 ampere-turns (AT) to operate it. The number is usually quoted in the data sheet.  (e.g. see here:)

https://uk.rs-online.com/web/p/reed-switches/2293658

 If we assume the fan motor draws 10 A then you would need a minimum of 6 turns of wire to achieve 60AT, so there is no need to overdo the winding though more would be good to be on the safe side and ensure reliable switching.  It would be best to use wire of suitable c.s.a.  for the current, and it doesn't matter if it is PVC covered provided the turns fit on the switch. A double-layer of winding is fine too if the number won't fit in one layer. They could be wound on a small cardboard tube and the reed switch inserted later. 

 

 

Edited by RobH
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