Temp sender resitance

[GrahamFountain]

Anybody got a correct temp/resistance profile, or even just a couple of values, for the NTC sender. I found mine only shows about 7/8ths of scale when it boils. However the fuel guage just full when the tank is full and for 30 miles or so. So the stabilizer voltage can't be that far off.

Graham

[GTS290N]

Check the thread a few down from this, Dolomite Sprint Cooling system.....

[MIG Wielder]

Back in 2011 I did a complete analysis of what the temperature gauge on my old Sprint read versus 2 variables .
1. Stabiliser voltage. ( Using a good psu at 9.00 V ; 10.00V, & 11.00V
2. Temperature sensor actual temperature in an oil bath. ( So I could go >100 deg C)
They are large files even with .jpgs
The results were in a 2011 issue of Dolly Mixture but are also available on a DVD " TDC DVD Articles from 25 years of the Club Magazine, 1986 - 2011."

Look for Section 0: Index ---> section 5: Electrical ---> SE 0052C Temperature readings.jpg and SE 0052d Page 2.

I have very recently done an update to indicate ( surprisingly !) how good the standard mechanical voltage stabiliser ( 2 samples) is, when used with the standard gauge at a constant temperature. ( Contrary to some of the stuff you read on the www. ) This is where I derived the value of 68 ohms to ground instead of the temperature sender giving you "N" on the gauge if the voltage stabiliser is good and the gauge is good and the input voltage to the stabiliser is O.K.
I know there is quite a backlog of articles to be printed in Dolly Mixture in the future so look out for it perhaps in the New Year.
HTH,
Tony.
Edit ... Have a look at viewtopic.php?f=6&t=29903

[GrahamFountain]

Thanks for the data.

So I should be looking for a sender that gives 900 ohms at NTP and 68 ohms for N on the guage (85-90?) if I had the standard electo-mechanical stabalizer set right. A value for full scale on the guage would be usefull, but I can get that by experimentation - I must have a ww 1k linear pot somwhere.

However, what I think I probably want is a variable voltage stabalizer, so I can adjust it to get the guage to read full hot when the engine is, whatever sender I actually get. That mighn't give a reading bang on center for normal, but as long as it's between about 1/4 to 1/2 ish, and stable, that's less important than being about right when there's a problem. Right now, it reads 1/4 normal, 1/2 when the leccy fan comes on, and 3/4 for seriously hot.

I might get a better result just with a different sender, but if there's such a variation in what's being sold, being able to use what's available seems to make sense to me. This looks like it might fit in the space for 99p - http://www.ebay.co.uk/itm/LM2596-DC-Buc ... SwZVlXoVBH - though it doesn't say what the minimum drop is. Hopefully it's less than 1.5 v.


Graham

[GTS290N]

I take it you don't care what the fuel gauge says?

Robsport do the sender that is closest to the originals, standard slant at standard temperature and a 10v regulator reads a bit below the half way mark on the gauge. The sender isn't overly sensitive, land rover replacements are.

[MIG Wielder]

Yes, < 1.5V drop-out voltage looks like a good value. "Typically 1.16V ".
http://www.ti.com/lit/ds/symlink/lm2596.pdf

I still have that Dolomite temperature gauge set-up in the workshop.
I'll see if I can get you some more resistance / indication points later today.
Tony.

[GrahamFountain]

I take it you don't care what the fuel gauge says?

Robsport do the sender that is closest to the originals, standard slant at standard temperature and a 10v regulator reads a bit below the half way mark on the gauge. The sender isn't overly sensitive, land rover replacements are.

I aren't that worried about how close to full it reads and the stabalization voltage won't much affect when it reads empty.

Is that with a solid state 10v reg or one of the electro mechanical ones.

BTW, has anyone tried adjusting the adjuster on the back of one of the electro-mechanical ones?

Also, I've ordered one of those adjustable regs and wondered if anyone has an original reg can or a broken one. No rush, the reg is comming from China.

Graham

[Galileo]

My sender stopped working (actually massively under reading) so I bought a generic combined sender with overheat switch, which was quite a bit out fro normal, so used a simple pull up resistor to earth to make it match the gauge.

I did initially fiddle with the gauge adjustment slots (they move left/right rather than turn) but the adjustment is quite small, might be good enough for you. This was my guide http://www.triumphexp.com/phorum/read.php?9,1405143

[GrahamFountain]

My sender stopped working (actually massively under reading) so I bought a generic combined sender with overheat switch, which was quite a bit out fro normal, so used a simple pull up resistor to earth to make it match the gauge.

I did initially fiddle with the gauge adjustment slots (they move left/right rather than turn) but the adjustment is quite small, might be good enough for you. This was my guide http://www.triumphexp.com/phorum/read.php?9,1405143

Problem with putting a resistor in parrallel with the NTC resistor in the sensor is that it has more effect on the low end of the guage (when the sensor resistance is high) than the high end. So it reduces the sensitivity where I'd like the guage to be most sensitive. I think. Whereas, reducing the voltage should have the same percentage effect on the current for all readings. And so, as all these guages are actuially ammeters internally, the same effect on the readings. But, if the variable stabalizers were expensive - a lot more than 99p - it might be the way to go.

Graham

[Galileo]

Not in series, in parallel from the sender to earth to 'pull' the output.

I did start typing loads of equations, 1/Rt=1/R1+1/R2 etc then got bored so here's a calculator! http://www.sengpielaudio.com/calculator-paralresist.htm

Decide what your mid-point 'normal' temperature resistance should be and then choose a value to suit the sender.

[GrahamFountain]

Not in series, in parallel from the sender to earth to 'pull' the output.

I did start typing loads of equations, 1/Rt=1/R1+1/R2 etc then got bored so here's a calculator! http://www.sengpielaudio.com/calculator-paralresist.htm

Decide what your mid-point 'normal' temperature resistance should be and then choose a value to suit the sender.

Yes, I did understand you ment in parrallel:

The other way to write the equation is Rl = Rs*Rp/(Rs + Rp); where Rl is the load on the guage, Rs is the sensor, and Rp is the parallel shunt.

Exagerating the change in the resistance of the sensor to show the effect: At the hot end, the resistance of the sensor, Rs, is small compared with Rp. In which case (Rs + Rp) is nearly equal to Rp. Hence Rl is nearly equal to (Rs*Rp/Rp)), and Rl is nearly equal to Rs. In which case the shunt makes little difference to the guage reading.

But at the cold end when Rp is small compared to Rs, (Rs + Rp) is nearly equal to Rs, so Rl is nearly equal to Rp, and the sensor makes less difference to the guage.

And that means, at the cold end, changes in the sensor have less effect on the guage than without the shunt, but at the hot end, the shunt hardly makes a difference: so the guage is less sensitive at the cold end.

Yes, I exagerated the change in Rs, but it is more than 2 decades by the data given, so there will be a decernable effect.


Putting a series resistor in would only reduce the reading, though (I think) obviously it would reduce the hot end reading more than the cold end ones.

Graham

[Galileo]

I could have sworn that I read you said in series, mea culpa.

You are of course right about the results not being linear, with a differing effect across the full range of values, but for my own purposes I was only interested in deviations from the 'normal' position, and less concerned about the extreme ranges.

[GTS290N]

A +
B =


C.

Or, to substitute real values into the equation £0.29 + £5.40 = £5.69

[GrahamFountain]

A=L7805? I see your 5 volt regulator and raise you a 10 volt L7810.

And don't tell me all plastic T220s look the same. That's devicist (deviceist?).

Graham

[MIG Wielder]

Anybody got a correct temp/resistance profile, or even just a couple of values, for the NTC sender. I found mine only shows about 7/8ths of scale when it boils. However the fuel guage just full when the tank is full and for 30 miles or so. So the stabilizer voltage can't be that far off.
Graham

Question : What does the water temp gauge read in terms of sender resistance?

1. A set of data points relating water temp; gauge reading to the simulated temperature sender resistance with constant 13.5V in to the mechanical voltage stabiliser ( nominal 10V output) with a simulated load of 150 ohms for the fuel gauge.

First indication : 180 ohms.
"1/4" on the gauge : 100 ohms.
"1/2" = N on the gauge : 68 ohms.
"3/4 on the gauge : 47 ohms.
Full scale : 22 ohms.
So, very non-linear

2. The other question asked earlier was " Can the Water temp; gauge be re-scaled as a dashboard Voltmeter ?

The gauge was scaled as a voltmeter with a 91 ohm series resistance to give 1/2 scale reading = 12.5V. The input d.c. voltage was then varied.

First indication = 6.0V
" 1/4" scale = 9.5V
"1/2" scale = 12.5 V
"3/4 " scale = 15.0V
Full scale = 18.0V .

Again very non-linear so Mr Smith's Gauge designer must have used a similar (but different) method to get the 11V to 15V voltmeter reading.

HTH,
Tony.