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Re: Mercedes fan upgrade
[Re: Andrewh]
#838290
12/02/10 01:47 AM
12/02/10 01:47 AM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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The sensor is a resistor that changes resistance with temperature. I'd put it in a voltage divider so I can read the voltage, and from that calculate the resistance and the temperature. Without the sensor hooked up, the voltage will read higher than it would with the sensor, so I can detect that. I can also detect if it's shorted to ground.
The problem is I have no way of knowing, if the sensor input is high, if it's because the sensor isn't hooked up, or if it's waiting to be grounded. Adding another 'grounding' input would require a jumper or resistor put in place of the sensor.
So I think the only solution would be a dipswitch to change modes. Unless we get rid of the no sensor fail safe (which I don't really want to do).
If you ever find yourself in a fair fight, your tactics suck.
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Re: Mercedes fan upgrade
[Re: Andrewh]
#838292
12/02/10 12:21 PM
12/02/10 12:21 PM
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Joined: Jan 2003
Posts: 28,068
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,068
Irving, TX
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Andy, the sensor should supply a ground. No sensor, no ground. That means the controller thinks the car never gets up to temperature and the fan never comes on. Engine go *poof*  A fail safe would mean no resistance to ground (missing sensor) turns on the fan. The other plan would be to supply a ground via manual switch to trigger the fan. See the problem? One says no ground turns on the fan. The other says no ground, no fan. It would require logic to be added that determines what to do when either switch goes to ground or remains open and which to ignore. A dipswitch would tell the controller which program to follow.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Mercedes fan upgrade
[Re: feets]
#838294
12/02/10 03:30 PM
12/02/10 03:30 PM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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Quote:
See the problem? One says no ground turns on the fan. The other says no ground, no fan. It would require logic to be added that determines what to do when either switch goes to ground or remains open and which to ignore.
A dipswitch would tell the controller which program to follow.
Exactly! Said much more elegantly than I could come up with 
Quote:
two, I was wondering if short to ground is a failure mode for temp sensors in gneral.
That is I understand open, IE no resistance at all, but what if it shorts to ground instead?
or is that a high resistance reading?
I'm not sure what a normal failure mode for the sensor itself would be. If it shorted to ground internally, the voltage I read would go to 0v, which would never happen normally, so I can turn the fan on. If it failed open (same as unplugging it), the voltage would go high, which would also never happen normally, so I again can turn the fan on.
The failure I was more concerned about was if/when the wiring got disturbed and the sensor came unhooked from the controller, assuming it's set up to look for the sensor. In that case I need to turn the fan on.
Using a switch to turn the fan on implies one of the above failure modes, so I need some way to know why a sensor isn't detected.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Mercedes fan upgrade
[Re: Andrewh]
#838297
12/02/10 04:25 PM
12/02/10 04:25 PM
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Joined: Jan 2003
Posts: 28,068
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,068
Irving, TX
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Andy, you're making my headache worse.
A ground would show a full circuit. The controller is looking for a ground through the sensor.
Think of the sensor as a variable ground. The hotter the sensor, the stronger the signal. Get it hot enough and it'll act like a wire going straight to ground.
A cold sensor has a weaker signal.
An unplugged sensor reads the same as a frozen sensor. There is no appreciable circuit. The fan will never come on because the controller is waiting for the engine to build heat.
It's either/or.
Run a switch and forget that a sensor ever existed.
Use a sensor and forget you ever heard of a switch.
Pick one.
No doubt you're going to ask for a sensor with a manual override for tinkering purposes.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Mercedes fan upgrade
[Re: feets]
#838298
12/02/10 04:52 PM
12/02/10 04:52 PM
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Joined: Feb 2003
Posts: 8,684
Andrewh
master
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master
Joined: Feb 2003
Posts: 8,684
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that isn't what I asked.
He states that
If it shorted to ground internally, the voltage I read would go to 0v, which would never happen normally, so I can turn the fan on. If it failed open (same as unplugging it), the voltage would go high, which would also never happen normally, so I again can turn the fan on.
so, I infer that if it went to ground, it would show infinte resistance, giving him a return of 0 volts.
which would work for the ground check instead of a sensor.
however, the problem occurs when the ground goes away, ie open circuit.
This too would trip the fan on due to the returning 12 volts.
which is why there needs to be a switch to determin if you are reading from a sensor or a ground.
IF I understood correctly.
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Re: Mercedes fan upgrade
[Re: Andrewh]
#838299
12/02/10 05:06 PM
12/02/10 05:06 PM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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Quote:
so, I infer that if it went to ground, it would show infinte resistance, giving him a return of 0 volts.
Incorrect. Infinite resistance would look like an open circuit (no sensor). Interesting side note: at -40F, the sensor has a resistance of ~100,000 ohms. This will give a voltage very close to the no sensor voltage. So, if you start up at -40, the fan may run for a minute until it warms up a little more 
Quote:
however, the problem occurs when the ground goes away, ie open circuit.
This too would trip the fan on due to the returning 12 volts.
which is why there needs to be a switch to determin if you are reading from a sensor or a ground.
IF I understood correctly.
Correct 
If you ever find yourself in a fair fight, your tactics suck.
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Re: Mercedes fan upgrade
[Re: feets]
#838302
12/09/10 03:07 AM
12/09/10 03:07 AM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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 So I was able to do some more testing today. I think this gauge is more accurate than the one in the dash   It seems to read about 10*F cooler than the one in the dash. It is on the other side of the thermostat housing coming from the other head, which could explain some of the difference. A month or two ago I replaced the 180* thermostat with a stock one (192* or 195*?). Right at 195 on the fan controller, it dropped back to 190* as the thermostat opened, then creeped up to 194ish. Meanwhile the gauge in the dash was sitting at 205*. Anywho, the temperature reading seems to work great. I'm very pleased with the resolution and apparent accuracy I'm getting. I have a 175A alternator coming so I can test the fan without killing any batteries. ( )
If you ever find yourself in a fair fight, your tactics suck.
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Re: Mercedes fan upgrade
[Re: gtx69]
#838304
12/09/10 11:11 PM
12/09/10 11:11 PM
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Joined: Jan 2003
Posts: 12,157
Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,157
Benton, IL.
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While we're waiting for the controller, I would like to ask a basic question. Do you recommend locating the temp switch for the controller on the w/p housing or in the radiator?
And, if you prefer the radiator, how important is it's place in the radiator?
I think I would prefer to put my guage sender in the w/p housing and then put the sender for the fan controller in the radiator.
Thoughts, opinions?
Master, again and still
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Re: Mercedes fan upgrade
[Re: Andrewh]
#838306
12/21/10 03:53 PM
12/21/10 03:53 PM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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A week and a half later, apparently my alternator finally shipped. On the phone they said they could turn it around in a day. It'll probably take another week going ground from Connecticut to Oregon.  Ohwell, I'll have another update once it shows up
If you ever find yourself in a fair fight, your tactics suck.
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Re: Mercedes fan upgrade
[Re: hooziewhatsit]
#838307
12/21/10 04:01 PM
12/21/10 04:01 PM
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Joined: Jan 2003
Posts: 28,068
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,068
Irving, TX
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Cool. I should have shipped you my alternator just to play with it. It's back on the hot rod now.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Mercedes fan upgrade
[Re: feets]
#838308
12/21/10 04:05 PM
12/21/10 04:05 PM
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Joined: Oct 2007
Posts: 3,896
Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,896
Oregon
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Nevermind  For some reason Summit's system cut off the last half of the tracking number when they emailed it to me. After a quick live chat, it should be here on the 24th (just in time for christmas  )
If you ever find yourself in a fair fight, your tactics suck.
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