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  #1  
Old 06-09-2004, 07:47 PM
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Aux Fan Indicator Lights???

Friends,

For fun, educational purposes and possibly for good use also, I'd like to add a couple of Aux Fan indicator lights on my vehicle (I have 2 fans).

Ideally, I'd like them to go on when the system is calling for the fans to come on but the fans don't come on... ie.. fans are faulty.. get it?

I could easily hook it up directly to the fans power plugs somehow, but all the lights will tell me is that the fans are supposed to be on... it won't necessarily tell me if they actually came on. For that, I'd have to test for current draw.

Anyone have any ideas on where I can start?


Last edited by wjm; 06-15-2004 at 10:32 AM.
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  #2  
Old 06-09-2004, 07:52 PM
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Pull the fuses on top of relays [ high and low -K9 ,K10] and put amp-meters in series.....
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  #3  
Old 06-09-2004, 09:16 PM
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If your engine's not overheating, your fans are working

Sixto
95 S420
87 300SDL
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  #4  
Old 06-10-2004, 11:08 AM
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I've done that with other cars and for other stuff too. The first step was the hardest step, running a wire through the firewall. I ran a couple while I was at it. And most of the time is was connected to a voltmeter. For the fan I think the easiest would be to connect it to the half speed limiting resistor.
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Old 06-10-2004, 11:18 AM
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<>

That's it , T...
Piezo sensed LED... like a knock sensor circuit
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  #6  
Old 06-11-2004, 12:15 PM
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Probably the best and easiest way. . . .

to accomplish Willy's idea is to use a Hall Effect (HE) device. This device, for those who may not know, produces a voltage output proportional to the current flowing 'by' the Hall Effect sensor. You don't have to break into the wiring to sense the current flowing in the fans.

So use of the HE sensor and a few external parts (LED, etc) will show as a proportional glow in the LED as the fan(s) change speed. Nice device if it can be done cheaply.

I've never seen current flowing when an aux fan 'dies'. When they fail to 'turn', with eveythjing else being ok, you'll find that the brushes are 'bad'. Somtimes giving the fan a 'bang' will start it going.

If the controlling relay's contact 'welds' which is a realistic failure mode, the fans will continue to turn. But the LED will show that.

I'm thinking more about it . . . . . . .
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Old 06-11-2004, 01:02 PM
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Great Jim... Thanks!. Can't wait to hear your next response!
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  #8  
Old 06-14-2004, 07:03 PM
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Here's a ckt that uses a Hall effect . . . .

device showing the connection to sense current in an external wire.


But being a "current" device, you need to convert it into a large enough voltage to drive a LED. So here's the ckt config to do that. Any "SINGLE RAIL" opamp will work in this ckt.


The web site;
http://www.gmw.com/electric_current/Sentron/CSA-1.html Click on the 'accessories' to see the AN-109KIT.
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Last edited by JimF; 06-19-2004 at 12:15 PM.
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  #9  
Old 06-14-2004, 10:17 PM
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Thanks Jim... but...

I don't expect you to do all the work for me... but how exactly would I used this for my project?
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  #10  
Old 06-15-2004, 01:12 AM
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Willy, I haven't but there's . . .

alot yet to do! This is just the 'germ' of the idea but, as you probably can tell, it needs a printed circuit board (pcb) to mount the opamp and other components. The HE sensor is mounted on a board that will 'plug-in' (most likely solder) into the second pcb.

All I've done is designed you a ckt that will work but you need to build it and make it 'practical'. Right now it's a 'science-project'. But it will do what you wanted: something to show when the fans are 'on' and how fast they're turning.

The nice feature of this ckt is that you do not have to 'break-into' the fan wiring so it takes no power or disrupts the fan ckt. But you probably figured that out!
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  #11  
Old 06-15-2004, 10:57 AM
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I gave a quick look at that site. Did it say it uses a flux capacitor? Does that mean it measures how much current its going to draw?
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  #12  
Old 06-15-2004, 06:22 PM
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Not sure what you mean. . . .

by "its"???? (and it should be "it's" !!!) Anyway, it (the chip) cannot measure its own current, only the current flowing through the (red jacket) wire.

The C1 cap shown is simply a decoupling element used to remove line effects from the power going into the CSA_V1 chip.
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  #13  
Old 06-15-2004, 07:44 PM
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I'm being silly

I glanced at it and saw "flux concentrator" .
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  #14  
Old 06-15-2004, 08:13 PM
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Now you made it really more . . . .

complex! And probably so have I!!!!

Willy asked for a "light" to come on. He said "Ideally, I'd like them to go on when the system is calling for the fans to come on but the fans don't come on ... ie.. fans are faulty.. get it?

I believe the fans are switched on by supplying "ground" through a relay. If that's all he wanted, you could use an LED with the common side supplied by the ground action of the relay. The LED would LIGHT!

But the second part of the statement (in RED), is the kicker! The fans DON'T come on. To do that you NEED to measure CURRENT. That's the only way to know; VOLTAGE is ALWAYS present but current only flows if the fans 'work' and the relay engages.

Measuring VOLTAGE does nothing to help you learn about the fan's operation or non-operation.

Tkamiya ideas:
1) Voltage tells you nothing!
2) Coolant temp sensor measurement means you have to "tap" into that ckt which MAY load it and change the trip points if YOU ARE NOT REALLY CAREFUL. As you know these 'trip points' are not that well defined meaning that your ckt would have to be adjustable to 'fit' it to the car. Now having this information still doesn't do anything toward knowing what the fans are doing.

However, this is not to say that I don't see your point: You want to AVOID a disaster such as an overheated engine. So maybe this would be a 'last ditch' warning system, probably audible, to tell you that something is about to burn up!!!

That type of system, upon second thought, could be built relatively easily. Very similar to the concept of my Cool Harness except that it has an audible and/or visual alarm. Humm. . . . . have to think about that.
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  #15  
Old 06-16-2004, 12:55 AM
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Well, we differ but . . .

but I think you are incorrect about 'voltage'.

If the fan is turned on by switching "ground", battery voltage will always be present at the fan terminals. So measuring voltage gets you nowhere. If it's always there, you learn nothing.

The killer here is that even if the fans NEVER come on, you will probably NEVER burn up the engine. There's many MBs whose fans are not working and they survive quite nicely.

But forget about fans per se; your last idea is still probably the best. We are REALLY interested if the car's engine temp gets to dangerous point. A ckt could be implemented relatively easily.

By setting a trip point for, say 110C, assuming that's a 'good' point, it could be implemented by an opamp with a "fixed" bias point. That, in turn, would trigger an alarm device; could even be a BRIGHT FLASHING LED. Just something to alert the driver to stop the car.

Now one steps back and asks . . how many times is this needed? I think the answer is not very often. At my tech's shop, I've only seen one car in 8+ years where the engine burned up. And even it was because the driver, a young teenager who had never driven an MB, didn't watch or even look at the gauges of his aunt's car. He had the radio on full blast!

I suppose this device we are talking about MIGHT have alerted him but not sure he would have paid attention even if he saw it! He certainly couldn't have "heard" it if it was audible.

Good idea but probably not very saleable. Nor useful.

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