I'm knowledgeable in wiring cars but wonder if, I can install a warning light for the cooler fan that will light up if....... the fan quits ? An illuminated switch (or in line light) would only show power at the switch and since you cannot hear the fan with the engine running, I'm wondering if wiring it the same way as the Alternator 61 indicator light will work. That being would the fan motor armature be actual ground if not energized ? .....Interesting huh?
Replies sorted oldest to newest
Definitely, I think, but maybe not. It all depends!
There are various types of sensors that will accomplish your goal, Alan. Optical, magnetic, and Hall-effect sensors can all detect a rotating mass. There are pro's and con's of each: cost, reliability, and general sturdiness that an engine environment would demand. You need something robust for the described application. Google rotating mass sensors or something similar and you'll find lots of examples.
The down side is that you limit your self to the single application of the cooling fan operation, as opposed to engine operating temp, but I assume you already have some kind of oil temp gauge.
I tried to attach a file that shows examples, but I may have flubbed it.
I guess you want to observe an electric oil cooler fan?
I would buy just a simple bimetal temperaturswitch in a f.e. 220 degree Version (see picture) and stick it with a two component adhesive to the outside of the oil cooler.
With this switch you simply switch on your warning light.
It will show you if the cooler overheats
These switches you can buy for some cents in an electronic shop or on ebay. I use these switches in my builds to stear the cooling fan on of. works fine since years.
best 
Those temperature switches Jan mentioned are pretty popular - we used them in computer assemblies to turn fans on and off, but they usually energized a relay to run the fan. I don't know how much current they can take, but a light would be fine.
To get a rotation mass detector, like a Hall Effect sensor, to work, you'll need metal fan blades. Plastic blades could be detected with a photoelectric eye, but the blades would have to stop with a gap where the eye sits.
As far as wiring up a lamp similar to an alternator light, my first thought is,
No...
The D+ on an alternator goes through an internal electro-magnet winding and then directly to ground. When the alternator is not turning and not generating electrical voltage/current, that electro-magnet winding is just sitting there connected to ground. The other end of that circuit goes through the dash lamp to the ignition's +12 volts. When the engine is started, the dash lamp is connected to +12V and provides a biasing circuit to that electro-magnet to start the charging process, thereby feeding +12V back towards the lamp and balancing the circuit out (+12 volts on both sides of the lamp = no ground and no light).
In order to do this with a fan motor you would need that additional biasing circuit to detect voltage output and you don't have that. Cub Cadet lawn tractors had a generator/starter motor all in one, back in the day. It would start the engine as a motor, then turn immediately into a generator, but it had dual sets of windings to make it all happen.
My best idea would be a Gene Berg Dipstick switch. When the fan stops and the oil temp rises, the switch closes and lights a separate, big honkin light on the dash to tell you something's wrong. Already designed, readily available and only $35 bucks.
I am going to take Al’s question at face value and try to answer what he asked, which was whether or not he could use an arrangement similar to an alternator light to prove the fan was running.
I don’t think so.
In my little corner of the world proving inductive loads (pumps, fans, etc.) used to be a pretty convoluted process utilizing sail switches, flow switches, hall-effect sensors, optical sensors, centrifugal switches, etc., similar to the stuff Jim was talking about.
At this point, the cleanest and easiest way to prove that something is running is with a current sensing switch. It works exactly like the name implies: when the switch detects current flow, it makes a set of contacts.
The vast bulk of what we do is proving alternating-current loads, but a very quick phone search turned up no shortage of DC current sensing switches for under 10 bucks.
I don’t know why Al wants to prove the fan is running, and a current sensing switch is not 100% foolproof (as a hall-effects sensor would be), but it’s cheap and easy and we would be sufficient unless the fan locked up .
@GORDON
these Switches are usually used in Coffee Mashines, Water cockers, electric irons, Air concitions a.s.o. They are good for 15 Ampere and have a guaranteed number of switch circles of at least 10.000.
There is no Relay needed but of cause you can use one. I switch on my fan with these since years.
About you idea with using a hall sensor: for me the disadvantage is, there are a lot of situations, the fan doesn't run anyway. For example as long as the engine is not on temperature. that means the warning light will also light up in these situations.
I think maybe get a temperatur warning of a too hot cooler is more efective, isn't it?
I think you wanted a warning if the fan fails for some reason.
I just wanted to know if the fan is on. I wired an LED so it gets power if the fan gets power.
Just came in from the garage and read these great posts.... I'll put a LED lamp in and be done with it ..... Gordon your clarified what I thought as to how the alternator works. Thanks All !
I'm a fan of this conversation and I do not intend to switch.
I just would like to ad something to this LED - idea:
I did exactly the same, a LED with a resistor... but it alwys killes the LED. The reason was, If I switched off the engine with a running fan, the fan works for a short time as an altanator. Now the electricity runs in the wrong direction (+-/-+). and kills the LED. To solve this I needed to put a diode inline with the LED or use a simple light bulb (I did so)
Best
I did almost the same a few years ago, but no LED.
The Chinese repop multi-gauge that most of us use has three red, unused indicator lamps (the fourth is blue, and usually used as the high-beam indicator). Mine even came with bulbs already installed.
Run a wire from whatever twelve-volt switch (manual or automatic) you use to turn on the fan to one of these lights, and done.
The most foolproof device for reporting if the fan is actually turning is this:
https://www.youtube.com/watch?v=krPQ1PMM00Y
That is essentially what I did. My muti-gauge has LEDs and I used one of them.
Mitch - I used one of those un-used, big honkin lights on my multi-gauge to tell when the glow plug in my heater is on. I honestly don’t really need it, but it is kind of cool to see it (and the heater) cycling on and off as it is supposed to do. 
Good idea, Gordon. I like it.
On my old car with the VDO gauges, I used the three red lights in the combi gauge. They were wired into my ignition giving me a sequential rev limiter. Something like 5900, 6100, 6300. It had a hard cut at 6500.
The new Speedhut gauges don't have those lights, so I installed 3 LEDs next to 5500, 6000, and 6500 around the tach.
I used one of those lights to tell me (when it's lit) to switch on my siren that goes on when I loose oil pressure. On a sunny day I cannot see the red oil pressure light if it comes on. The little audible electronic siren alerts me to look at it. I manually switch the siren off when starting the engine. I tried doing this for the Alternator but it wasn't that simple when you have two power sources turning off the Alt. light. My guess is that I need to put some diodes in there somewhere.
Danny...I like your rev limiter warning light idea. Also, I prefer soldering to all other connection methods.............Bruce
I am not sure how it wired (as I did not do it) but in the Dtype I have both a light and a buzzer on both electric fans. If one stops working, I know about it pronto.
I will email the guy who did it and see what he did. I do know it was a pretty simple process. Sorry - I would rather build a motor outside in the rain than deal with electrical stuff.... I suck at it.
When Bridget's radiator fan goes on the generator light glows dimly. I don't even know why. But if I see the temp gauge above 195 or so and that faint green glow isn't happening, I'll know the fan ain't working.
@Scott S I will email the guy who did it and see what he did. I do know it was a pretty simple process. ( Thanks!)
edsnova posted:When Bridget's radiator fan goes on the generator light glows dimly. I don't even know why. But if I see the temp gauge above 195 or so and that faint green glow isn't happening, I'll know the fan ain't working.
Sounds like you have a slight ground feedback into the generator. Or the load of the fan drops the rpm just enough that the alternator isn't quite at battery voltage.
If you want to get rid of that, try putting a diode in the supply for the fan relay.
Roy posted:I'm a fan of this conversation and I do not intend to switch.
So bad it was good. Had to give it a "Like".
