 | Home > Technical > Td5 dials in non-TD5 temperature sensor |
 
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237   
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All,
My V8 project is using TD5 dials. I made the modification to the temperature gauge wiring behind the binnacle so that the sender runs through the internal resistor in the speedometer. However, once I connected this up, i decided to bench test the setup. Connecting the sender connection directly to earth only allows the gauge to read just a fraction over half! Therefore no matter which sender you use, the gauge will never read over half even if the engine is boiling over. I have currently connected the dials upto a black 300tdi sensor which barely registers on the gauge at <50degC and gets upto about 1/3 when reading nearer 100degC with the connection made via the speedometer resistor (as per ROW spec). When i bypass the internal resistor in the speedo and connect the blacktop sensor directly to the gauge input, temperature readings are just over half at ~80degC and close to the red zone and 'H' at 100degC. This seems much more sensible readings. I do not have a green top sensor to test, but it is still impossible that , with one fitted, the gauge could read over 1/2 if connected as per the online guides. Really, what i am looking for is for anyone who has TD5 dials in a non-td5 to connect directly earth the temperature sender connection directly to the block/earth and see if the gauge only reads 1/2way please? If it does, i might suggest an alternative sensor and wiring arrangement. Cheers, Steve 02' 110 TD5 Double Cab Rebuild Thread |
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21st Jan 2019 3:18pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610 
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I've not done this but my understanding is:
You use the AMR1425 green top sensor as the AMR3321 black top sensor has a different response curve which does not match what the speedo head is expecting. A direct connection to earth is a zero Ohm condition which might be being detected as an error state rather than "really really really really hot"   1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 3:36pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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Interesting info cheers Martin.
I didn't really pay any attention to the circuitry within the speedo between the two temp sensor pins when I had it open. I assumed it was simply a resistor or Potential divider pair rather than an ADC and DAC to modify the temperature profile. I might have to get a green top sensor to experiment, do you happen to know what the green top temp profile is (resistance/temp) by any chance? [EDIT] Found this https://www.aulro.com/afvb/90-110-130-defe...olour.html, will check it out this evening in more detail Cheers, Steve 02' 110 TD5 Double Cab Rebuild Thread |
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21st Jan 2019 3:40pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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Remember the Td5 temperature gauge is not a typical voltage drop measurement gauge, it is driven by a PWM signal generated by the engine ECU.
My assumption is that the speedo generates a PWM signal from the sensor resistance, but as I say I have not done this nor investigated it. As part of the Puma gauges controller development I generated response curves for loads of sensors. I'll drop you a PM with some data. 1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 3:47pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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With regard to your edit
Defender 300 Tdi with pre-Td5 gauges (up to and inc. 1998 model year) use the AMR3321 black top sensor Discovery 300 Tdi use the AMR1425 green top sensor Defender 300 Tdi with Td5 gauges (1999 model year on) use the AMR1425 sensor as per http://www.retroanaconda.com/landrover/200...tdi300tdi/ 1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 3:52pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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You can get an AMR1425 for less than £4 delivered off eBay (e.g. eBay Item No. 370890433656)
Edit: possibly genuine take-off here: eBay Item No. 170342490120 1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 4:00pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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Thanks Martin,
Have ordered a green top off ebay to experiment. In the mean time I will experiment with fixed value resistances. I agree with your theory of the speedo generating a pwm signal to begin with. However the gauge is internally the same as the fuel gauge which looks for a path to earth on the sensor pin. If the speedo/TD5 ecu does output a pwm signal then it must do it to between ground and floating (i.e. as a sink) rather than 5v or 12v and floating (i.e. as a source). Cheers Steve 02' 110 TD5 Double Cab Rebuild Thread |
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21st Jan 2019 5:39pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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Certainly the Td5 ECU output is open collector (floating/ground switched).
1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 5:56pm |
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| Romadog Member Since: 07 Jul 2011 Location: Powys Posts: 1749 |
Or save the faff and spend the cash
Cheapest I've seen below 
https://www.firstfour.co.uk/temperature-ga...nuine.html |
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21st Jan 2019 6:05pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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So a bit of tinkering tonight. You are right about the speedo using a PWM output with a floating/ground connection:
Click image to enlarge Using fixed value resistors in place of a sender, 91ohms: Click image to enlarge 45.5ohms: Click image to enlarge 30.3ohms: Click image to enlarge 23ohms: Click image to enlarge So in summary, even a sender reading 100degC the needle cannot move beyond 1/2! I think the Speedo is only able to get to 50% duty cycle. I am going try and map gauge readings to resistance a little more accurately using both the green sensor and speedo circuit and just the black sensor. Steve 02' 110 TD5 Double Cab Rebuild Thread |
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21st Jan 2019 9:21pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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That’s the same as the Td5 though, it’s not a linear conversion at all. There’s a massive flat spot in the Defender’s temperature (resistance) to PWM pulse width table. The engine has to be VERY hot for it for show hot.
One option for you could be a custom mappable resistance to PWM driver (basically a replacement for what’s in the speedo). Good work tonight and nice to see my hunch confirmed - I know a lot of people say it is just a resistor in the speedo 1988 90 Td5 NAS soft top
2015 D90 XS SW |
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21st Jan 2019 9:26pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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Yeah always good to see a theory confirmed. Its not so much the mapping that concerns me. More the fact that the gauge is not able to show more than 1/2 it seems. There is no difference it seems between 46ohms right down to 3ohms which was the lowest value i have. Like i say, will confirm tomorrow when i have a bit more time.
I have a feeling that once i have mapped the black sensor to gauge position with it connected directly to the gauge terminal, it might actually be about right. Cjeers! Steve 02' 110 TD5 Double Cab Rebuild Thread |
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21st Jan 2019 9:36pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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So a little more progress last night. It seems that with the gauge connected through the speedo circuit the needle is able to go to the fully hot position but there is a 2-3 second delay before the needle moves up to the red. This delay only seems to exist once per ignition cycle. If you simulate and overheat condition, then normal temp, then back upto overheat; the delay does not appear second time.
There are no intermediate positions for the needle between half way and full hot and the switching point for the gauge to move to full hot seems to be somewhere between 110 and 115deg based on the resistance profile of the green top sensor. This seems to be a stupid system (as per TD5 temp gauge control) as you could be running at over 110deg for ages without even knowing it. 110-115deg is far too hot for a tdi or v8. I have mapped the gauge position vs. resistance with it connected as a normal instrument (i.e. not via speedo) and its a fairly linear profile. I have put together a spreadsheet to try and calibrate it but the green sensor's response curve is just too rubbish in the most important range! Temporarily i am going to run with green sensor with a small calibration resistor in series which will mean that 80deg is at the halfway point on the gauge. At least i then know that anything over this is getting too hot. The needle will not reach the full hot zone though sadly. Ultimately i will do as you suggest Martin and knock up a standalone PWM controller which controls the temp gauge with a sensible mapping of needle position vs. temp. I shall probably use the black sensor as the response is a little better in the 80-100deg range. It is worth noting that the fuel gauge is also controlled via PWM from the speedo on the td5 dials. The speedo damps the needle position (so it doesnt waggle around under cornering) and operates the low fuel light. I do not know if this has any hidden profile for resistance but as the speedo is the same on 90/110 and the tank different shapes i guess not. If i am going to build a pwm controller for the temp gauge, i might as well do it for the fuel gauge too so i can calibrate it to my 90s side tank. Steve 02' 110 TD5 Double Cab Rebuild Thread |
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23rd Jan 2019 7:35am |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6610
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Good work Steve
I'm sure you've got it covered but if you need any help give me a shout  1988 90 Td5 NAS soft top
2015 D90 XS SW |
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23rd Jan 2019 9:38am |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2237
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Cheers Martin
,
I might use this as an opportunity to have a fiddle with an Arduino as my usual go-to of an old 8051 microcontroller isnt well suited to this. Although I have some versions with analogue input channels, i dont know of a version with a preconfigured PWM output. It would mean messing with interrupt timers and things. I will update this thread as I go but probably wont progress it for a month or so. Cheers, Steve 02' 110 TD5 Double Cab Rebuild Thread |
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23rd Jan 2019 9:59am |
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