Aux Fan Indicator Lights??? - Page 2 - PeachParts Mercedes-Benz Forum

zafarhayatkhan · #1 06-16-2004, 10:00 AM

The motherboard in my computer has 3 zones and it tells me what the temperature and the rpm of the cooling fan is, in each zone.

I do not think that this information is necessary but it would be interesting to know the rpm of each aux fan. The rpm will be an indication of the fan and/or pre-resistor condition. It would also indicate which fan is weaker.

But all this can be done in a minute with a tach, without adding more instrumentation to the cockpit.

An easier check is to keep an eye on the the temp gage and it starts going over 100 C, just open the hood and check to see if the Aux fans are coming on.

If the coolant is lost completely, the temp gage will show a cold engine, so if the engine does not warm up per gage, again the hood can be opened and coolant level checked, or the low coolant level light will come on.

JimF · #2 06-16-2004, 01:29 PM

If the coolant is lost completely, the temp gauge will show a cold engine,. . . .??

If that's true, why would a car have a temp gauge?? It certainly negates anybody from looking at the temp gauge to 'see' any useful information.

Re the 12V fan: yes, you are correct but was we have 'evolved' in this discussion, 'playing' with the fan ckt is really not what we NEED to do.

I think we have decided that a high engine temperature is what we want to know. Whether it's caused by the fans not working or a low coolant level, etc. it's engine temp that we want to know. What caused it can be determined by 'inspection' as zafar said.

But if he's right, that's the end of that story! Fortunately, I believe that he's wrong. The ECT and CTS sensors, B10/8 and B11/2 on my car, will exhibit a low resistance (very low!) at high engine temperature. B10/8 drives the temp gauge, B11/2 drives the LH module for fuel.

So monitoring the temp (resistance) of B10/8 will do what we want. By the way, you can do the complete ckt with just one (1) opamp; don't need a comparator.

For the output 'alarm' how this: wire it so that if the preset engine temp is exceed, all of the panel lights flash! Cool, eh? That might get your attention. But not sure that's easily done.

zafarhayatkhan · #3 06-16-2004, 03:21 PM

Jim, you are right, the sensors B10/8 and B11/2 will work for what you are trying to do, except for the extreme case of complete engine coolant loss.

If you were designing a car engine, how would you get a temperature reading? The logical answer is that you would get it indirectly through the coolant, which circulates throughout the engine and this would be a good average reading for the entire engine.

It is very unlikely that you would loose all the coolant very quickly. So the coolant sensors for both the ECU and the Instrument cluster work fine, these sensors can give you the engine temperature only if they are immersed in the coolant.

If there is no coolant, you will still get a reading (very low) but it will not be the engine temperature.

JimF · #4 06-16-2004, 04:41 PM

since the sensors are insulated from the manifold so it makes sense that if the coolant drops below the sensor level, then they will not read correctly. Bad news!

Well, based on that 'fact', that almost kicks our idea in the head! The ckt NEEDS to work in that situation since that's the most catastrophic situation where you WANT it warn you!!

Back to the drawing board . . . . .

JimF · #5 06-17-2004, 01:09 PM

thermocouples (TC) since their output is sooo low; in the low millevolts. When you subject that to the car's high-energy ignition, leakage of tens of volts make it difficult to process the TC's output since it's over -60dB down.

A better choice would be a thermistor similiar to what is currently used in our cars except in a different form factor; you can get them packaged in a T0220 case that would attach nicely to the engine block.

Then a relatively simple ckt (opamp and bias resistors) could be used to process the signal. At trip point, it would drive a power transistor to turn on the alarm, which is still tbd.

The worst part is that some sort of pcb needs to be fabricated and 'placed' someplace in the car as well as mounting the tc. Also power must be 'stolen' from someplace convenient on the car to power the ckt. Lots of work for the purchaser which means lots of negatives with bad and/or marginal installations.

Jim Anderson · #6 06-17-2004, 01:49 PM

Thermocouples need a cold junction. They really read temperature differential.

How about inside/outside(remote) thermometer?

zafarhayatkhan · #7 06-17-2004, 03:31 PM

We would like to know:

1) What the fans are doing
2) What the engine temperature is

ABS sensors give the ECM rotational speed information for brake application, power retardation.
A similar sensor could give us the RPM of the aux fans. Two gages can be mounted on the A pillar to show the rpm for each fan. So, that solves the problem of what the fans are doing, whether they are rotating or not.

For the second problem, we could continue to use the temp gage.

This is how it would work, you are driving around and the temp needle goes to 107 C, you look at the rpm gages for the left and the right aux fans to see how fast they are rotating. If the rpm is low, you will know that they have not gone into high speed mode.

Another feature can be added. If the engine temperature goes above a certain temperature, an Led lights up above the aux fan rpm gages. The existing temp sensor resistor could be utilized.

For the coolant loss situation, the low coolant light will turn on and the AC will not provide any heat.

wjm · #8 06-17-2004, 04:45 PM

You guys are killing me... this is great! I computer saavy... but electronics is not my thing (at least not the advance stuff).

I'm holding off on my white guage upgrade, as I may have the guy doing the upgrade drill and add a couple of LEDs (or whatever) while he has the dash open.... in preperation for whatever the end result of this great debate is! :-)

JimF · #9 06-17-2004, 05:40 PM

This started out to be simple, cheap and, most of all, practical!

With all respect, zafar's solution is just the opposite! ABS sensors??? Mounting gauges on the 'A' pillar?? Not easily done, not cheap and not practical for the average MB owner. Nuff said.

Also the low coolant scenario has a problem: in my car it's possible to have the CTS (B10/8) with no coolant flow but the coolant low sensor be ok! It's about 6" below the CTS and there could be coolant in the overflow reservoir.

This would give you a low(er) temperature reading but could still do damage to the engine because of low coolant but not enough to give an alarm.

Willy, how many people would want to take their IC out so they can drill some holes for mounting LEDs??? And even if they do, how many could actually do that and wire LEDs (what the hell are those?) to my fan sensor ckt?? How about "NONE"!

wjm · #10 06-17-2004, 06:44 PM

I'm taking my cluster out and sending to someone to have the guages changed to white, needles painted, and some chrome bezels put on (which I got from a source on ebay).

My original idea was to add two LEDs to the dash (possibly inside the cluster like I've seen done many times in the past on other cars by auto alarm companies). These LEDs would then get lit up by whatever mechanism can be designed to determing an alarm state. In this case, alarm state means aux fan is not working (1 LED per fan).

I'm open... just a thought

myarmar · #11 06-17-2004, 07:56 PM

Coolant pressure switch would help in case of a coolant loss.

JimF · #12 06-19-2004, 01:29 PM

. . . at least ONE!

I replaced the schematic with a version that will do what you want: indicate a fan(s) failure when told to come on.

The ckt operates in conjunction with the relay the activates the fan. It supplies ground (to "GND" pin) to the fans AND my ckt. So when the fan(s) are not called, the ckt 'idles' (no power); LED off.

When the relay activates, calling for the fans, the ckt is also supplied with power. If the fan(s) turn ok, the LED will remain out. If they don't turn, the LED will light.

Need a ckt for each fan so you can tell if one is working and one is 'dead'. The current sensor is wired in the lead that comes from the relay to the fan 'return'. This way you can separately sense the current for each fan. The ckt is cheap, simple as it can be, and does not effect or unbalance the existing fan ckt.

As you know, the fan ckt impedance is very low and the use of a resistor as a current sensor (which would make it VERY simple) cannot be done without effecting the fan speed.

JimF · #13 06-20-2004, 04:12 PM

embedd into your IC, but the LED shown in the schematic is a Radio Shack 276-307. It has a CLEAR lens, lights up "red" and can take up to 20ma.

But maybe you would prefer a RED lens. That part number is 276-209 and it only requires 10ma. The choice of LED may change the dropping resistor, shown as 100 ohms in the schematic.

I've simulated the ckt in PSpice and it works as advertised. If you're interested in the plots (charts), let me know.

JimF · #14 09-03-2004, 02:56 AM

where did you go?????

wjm · #15 09-03-2004, 01:41 PM

Sorry,

I was layed off at the end of July, so you can imagine how busy I've been. Luckily, I'm back at the same company now (just started this week). Remember, you still have my email address.

What's up?

Willy