Adding coolant temp gauge? (1 Viewer)

[RavenTai]

Ok I've now spent the past couple days at work refreshing up on Thevenin equivalents and I think I have the math working right. Yay I have my freshman understanding of electronics back.

Congratulations , I never got Thevenin equivalents to work right and gave up after a day or so, I completely abandoned trying to figure out the needle position besides center. And used the test bed, trying of pin down the center point was hard enough and that was for the much easier to follow math of a balanced whetstone bridge,

Thanks again RavenTai for your research and numbers. Also thanks for the gif showing the stock gauge.

I have a about 900 MB of pictures and charts that you may find useful also, maybe smaller if I compress them, If you want I can send you copies, not sure how would be the best way to get them to you though. Too large for E-mail.

I did some math on the 110 degree resistor with a wire replacing the zener diode (assuming that L1 = 95.3 ohms, L2 = 81.5 ohms, and L3 = 46.0 ohms) and I got .9140 volts across L1 at 226 degree F. This is using a resistor value of 38.4 ohms for R2. This should put the needle at above the red zone.

Ok with the 110 R1 and shunt replacing diode I got pegged hot with 226, in-fact about 224 or 225 or so the needle stopped pegged. According to the stock needle sweep (the sweep we have L1 voltages for) .9140 should have been near the top of red not pegged full hot.

I've read the actual results you obtained and it seems like this is about 10 degrees off (not unlike the value for the 110 ohm resistor). In reality .9140 volts across L1 with R1 = 110 ohms and a short for the diode is about 217 degree F.

That is true, every attempt I have made to go from paper to the gauge have been off, I would have to go back through this thread any my notes to see if there was a consistent amount they are off by, also the stock needle sweep was early, I cannot remember it that was at a good source voltage or not making the needle position per voltage across L1 suspect.

A coworker of mine mentioned that since the needle is pegged cold with a spring of some sort that this could be why the temps are lower than we expect given the resistances. The spring is biasing the sweep a bit. This may or may not be true. I think to figure out if it is we would have to divulge into the realm of differential equations (which I'm currently not up to).

I am not either, there is something in the needle movement that brings the gauge to the cold mark, It does so slowly with to me means it is fairly weak and that the needle is dampened somehow. It could be a spring or also could be a small magnet placed in the air core motor case.

I'm going to be playing with resistor values to replace the diode today to see what I get and to see how closely the math mimics reality.

RavenTai as a request, if you do any more tests can you always measure the voltage across L1? That would be awsome. To me that value is the best way to see if the math on paper matches reality. Source voltage is nice to know but seeing that it doesn't change much it isn't that valuable.

I was monitoring source voltage early on because I was working with a battery and battery charger. Had to constantly turn the batty charger on and off. To keep close to the desired voltage. When I built the DC power supply that took care of that but I was still afraid to monitor the L1 Voltage as the currents in the L1 coil are very small and I was afraid that the current the meter draws to measure the voltage (albeit even smaller) would skew the results. Also the DC power supply wanders a bit (0.1 volt or so) especially as it warmed up, I monitored and adjusted the pot as necessary to keep it close to the goal of 14.50 volts.

The more I do the math the more I would like more readings in regards to the voltage over L1 and the temperature. Right now I'm not trusting my calculations to calibrate the thermistor graph due to not being 100 percent sure on how to handle the diode in the circuit when it comes to Thevenin equivalents. As noticed in real life the temperatures and the resistances measured from the thermistor aren't exact when it comes to the circuit. The 110 ohm resistor should have created a center of 200 degrees but it seems like it was off 9 to 10 degrees. It looks like the curve is a bit off when the circuit is involved.

I would agree that the thermistor curve is off.

I did some calculations on one of the gif images and for a voltage of .200 volts across L1 I calculated that the resistor R2 should be 31.9 ohms (or 30.8 ohms depending on how I calculate it ). This corresponds to 228 degrees Fahrenheit based on the gif.

If you look at the chart 31 ohms should be between 239 and 240 degrees.

I also have some calculations on the current circuit with the 110 ohm R1 resistor and various diode replacements.

These are the numbers I get for the R2 resistance when the voltage across L1 is .740 volts which should put the needle at the bottom of the red zone (i.e. the bottom of the needle is touching the bottom edge of the red zone):

D1: 100 ohms R2: 32.9 ohms
D1: 75 ohms R2: 34.5 ohms
D1: 50 ohms R2: 36.9 ohms
D1: 90 ohms R2: 33.0 ohms

Ok taking the 50 ohm D1, R2= 36.9 and crossing to the thermistor curve that should be approximately 229F but in reality bottom of red is 213 (using top of needle sighting) so there is defiantly something amiss

I also thought some about a replacement zener diode but the smallest break over I could find in the Mouser catalogue was 2.4 volts which is larger than the 2 volt break over of the stock component. I'm guessing a 1 volt break over would shrink the dead zone to only 20 degrees but I haven't calculated that nor is there much point if we can't find a diode to meet that requirement. Also with a diode the resolution would be harder to modify.

Correct me if I am wrong ( I very well may be) but I think a 2.4 ZD would actually give 3.1 volts total dead time, as there is .7 v (or .5) on the foreword bias side that is added to the reverse bias break over when working with both foreword and reverse bias as we are here.

I do not think any dead spot is desirable no matter how small, it leads to surprises.

I would love for someone to work on the theoretical model side of this, I have given it about all the metal energy I could muster at the time. It needs fresh eyes.

So do you think the thermistor curve is the major source of flaws in the model? It very well may be and is actually probable that the thermistor reacts differently when under load, the thermistor curves I have are direct unloaded meter readings.

so
Is it the load that is causing the change?
What is the best way to get very accurate loaded thermistor curve?

First thought would be put a load on it, might as well be the same load it experiences, 110 ohm resistor in series with R2, apply 14.5 volts across both. Wile you cannot directly check the resistance of R2 wile it is electrified you can check the voltage between the two resistors, since source and R1 are known you should be able to calculate for the resistance of R2 based on the voltage between them.

But what of the current To/From L1? Is it better to measure R2 wile experiencing this current (ie measure with in the entire circuit) or is that double dipping when you drop these numbers into the Thevenin equivalents? I have an very early cook that did something similar to this

 

[Darwood]

I have a about 900 MB of pictures and charts that you may find useful also, maybe smaller if I compress them, If you want I can send you copies, not sure how would be the best way to get them to you though. Too large for E-mail.

This would be great. I'll PM you with the access to my FTP site so you can upload it if you would like to.

Ok with the 110 R1 and shunt replacing diode I got pegged hot with 226, in-fact about 224 or 225 or so the needle stopped pegged. According to the stock needle sweep (the sweep we have L1 voltages for) .9140 should have been near the top of red not pegged full hot.

I think the problem with this calculation is I was going off the thermistor graph and calling 38.5 ohms 226 F. As noted later this relationship probably doesn't hold.

That is true, every attempt I have made to go from paper to the gauge have been off, I would have to go back through this thread any my notes to see if there was a consistent amount they are off by, also the stock needle sweep was early, I cannot remember it that was at a good source voltage or not making the needle position per voltage across L1 suspect.

After doing some calculations based on the stock needle sweep, the values I get for R2 vs temp seem to be more accurate compared to real life which is encouraging. I really need to do more comparisons. I too have yet to compare the values enough to give a good answer on the consistency of the variance in temperatures, though it kind of appears that the higher the temperature the greater the amount that the temps are off.

Ok taking the 50 ohm D1, R2= 36.9 and crossing to the thermistor curve that should be approximately 229F but in reality bottom of red is 213 (using top of needle sighting) so there is defiantly something amiss

Actually I was calculating the resistance here based on a L1 voltage of .740 v which should be bottom of red using bottom of needle sighting which I think due to your experiments should be 217, so it's a little closer. I'm really curious to see if we could pin 36.9 ohms to 217 F. If there was a run where the voltage across L1 was measured with the temperature being 217 F then I could calculate whether or not this always results in 36.9 ohms. Hopefully it will, otherwise my math is wrong.

Correct me if I am wrong ( I very well may be) but I think a 2.4 ZD would actually give 3.1 volts total dead time, as there is .7 v (or .5) on the foreword bias side that is added to the reverse bias break over when working with both foreword and reverse bias as we are here.

I actually didn't think about this but I believe it to be correct. To get the needle to move up the voltage on the inductor side needs to be at least .7 volts great than the voltage on the resistor side. I did take this into account in some of my calculations so I guess I did think about this somewhere.

I do not think any dead spot is desirable no matter how small, it leads to surprises.

You're probably right. I was just thinking a 10 to 20 degree dead zone might not be a horrible idea. Now if you used two regular diodes in parallel with their inputs reversed you should get a tiny dead zone of .7 or so volts both ways, however the resolution would probably be too small and the red zone would be up in the 240 to 250's.

I would love for someone to work on the theoretical model side of this, I have given it about all the metal energy I could muster at the time. It needs fresh eyes.

For some reason this has become horribly fun for me. I can't remember the last time I had so much fun with math.

So do you think the thermistor curve is the major source of flaws in the model? It very well may be and is actually probable that the thermistor reacts differently when under load, the thermistor curves I have are direct unloaded meter readings.

so
Is it the load that is causing the change?

I think the thermistor curve is probably accurate but the resistance of the inductors changes, which throws off the thermistor curve. I don't think the load effects the thermistor so much as the inductors aren't that constant which throws off the math when it's assumed the inductor's resistance doesn't change. By "fixing" the thermistor curve we should be able to assume the inductor's resistance doesn't change. It's not true to life but it should be "good enough".

What is the best way to get very accurate loaded thermistor curve?

First thought would be put a load on it, might as well be the same load it experiences, 110 ohm resistor in series with R2, apply 14.5 volts across both. Wile you cannot directly check the resistance of R2 wile it is electrified you can check the voltage between the two resistors, since source and R1 are known you should be able to calculate for the resistance of R2 based on the voltage between them.

This would be an interesting test. I'm skeptical that we would see a difference but I could be (and often times am) wrong.

But what of the current To/From L1? Is it better to measure R2 wile experiencing this current (ie measure with in the entire circuit) or is that double dipping when you drop these numbers into the Thevenin equivalents? I have an very early cook that did something similar to this

I like voltage readings from L1 the best partly due to the fact that I have an equation that will give the resistance of R2 based on this value (and a bunch of other knowns). I think the readings of R2 should be the same as the voltage across L3 since they are in parallel. Also I my go as far to say that you won't see a voltage change across R2 at all. I think at a 14.4 source voltage, you should get 5.195 volts across both L3 and R2, though I say this with full rights to retract this statement given that I was stupid and was assuming something I should have been.

I should add that the voltages across L3 and R2 would be different in the cases where the diode was blocking current from flowing in the bridge (hopefully that will save me in the early cook with the double dipping). If I'm wrong I'll have to reevaluate what I think I know (yet again).

 

[Darwood]

Thanks Raven for the pictures!

I've been doing some math to find out various values of R2 vs temperature. To do this I've compared photos of the voltage across L1 and the needle position to photos of the gauge with the 110 ohm and 50 ohm resistors at 14.46 source voltage. I get the voltage across L1 in the first photo and compare it to the temperature in the 2nd photo when the needles in both photos are in the same position. As you can guess this does give a little error since I'm comparing the needle position in both photos visually to get a match. Anyway I've found the following numbers:

Temperature F/ Resistance Ω

228.0 30.8
227.0 31.4978
220.1 35.7284
218.0 36.8199
212.0 41.038
208.0 44.0578
200.0 50.6317
194.0 56.094

Most of the numbers come out to be about 10 degrees lower than the thermistor chart, which is interesting.

I've also calculated different values for the gauge based on different resistor combinations. For me the red zone is to low and I'd like to lower it so that when the needle is just below the red line the gauge is reading 218-220. With R1 =110 and the diode replacement =50 this area reads 212. I'd like the lower the value because I don't want to become immune to the fact that the needle is approaching the red line. When the coolant is 208 the needle looks dangerously close to the red line, but 208 is an OK temperature. If someone else were driving my truck I worry that they would needlessly pull over thinking that the truck was about to explode.

I've done some calculations and my favorites so far are:

R1 = 110 and Rd (diode replacement) = 110
or
R1 = 100 and Rd = 75

R1 = 110 and Rd = 110 gives the following:

just above the bottom of the red line
(.749 volts across L1) = 228 (R2=31.0375)

just below the bottom of the red line
(.6 volts across L1) = 219 (R2=36.0389)

center
(0 volts across L1) = 189 (guess from observation)(R2=62.0456)

208 F (R2=44.0578) .38729 volts across L1 which is about 236F on the unmodded gauge​

R1 = 100 and Rd = 75 gives the following:

just above the bottom of the red line
(.749 volts across L1) = 227 (R2=31.4474)

just below the bottom of the red line
(.6 volts across L1) = 221 (best guess)(R2=35.5765)

center
(0 volts across L1) = 193-194 (guess from observation)(R2=56.405)

208 F (R2=44.0578) .328817 volts across L1 which is 231F on the unmodded gauge

218 F (R2=36.8199) .557464 about 1/2 to 1/4 a needle width below the bottom of the red zone​

So far that's all I've calculated. I think the R1 = 100 and Rd = 75 is the more appealing to me.

 

[Rookie2]

The nice thing about Raven's deal is that it's tested and you pretty much know for sure what temperature equates to bottom of red, top of red etc.. Maths a great thing and all, but unfortunately with this extrapolation, you won't be for sure you don't have a turd floating in the punch bowl somewhere, once the different resistors are in.

So far I like the mod. There's still a dead spot in the middle once the rig gets to operating temp, and I haven't really had more than a needles width movement above center. We'll see if summer time affects that much.


Rookie2

 

[Beowulf]

So far I like the mod. There's still a dead spot in the middle once the rig gets to operating temp, and I haven't really had more than a needles width movement above center. We'll see if summer time affects that much.

I see the same thing with the Greddy so this probably is NOT a dead spot in the modified guage; your engine has reached operating temp and it stabilizes.

-B-

 

[Darwood]

I see the same thing with the Greddy so this probably is NOT a dead spot in the modified guage; your engine has reached operating temp and it stabilizes.

-B-

What B said. If you see a "dead spot" in the gauge it's because the temperature has stabilized at that temperature.

The math I've done is based on Raven's tests and should be pretty sound. I think I'm going to test it out this weekend by modifying my gauge again with the new values and then read the temps from the ECU. The correlation between the ECU temps and Ravens tests is close enough that it will give me some good readings.

The reason I didn't post this in the official mod thread is based on the fact that it hasn't been tested yet. This is still in development.

Also I posted my results to give back what I've found out. It's the least I can do.

 

[RavenTai]

Darwood hold off on modding your gauge, several have asked about less sensetive gauges, maybe after the 93 is done (soon) we can work on testign one of the solutions youhave coem up with.

I have been reading just have not had the time to give a propper reply yet.

 

[Darwood]

No promises but the odds of me getting to the mod this weekend are pretty low considering I'm also planning a dual battery install, all before the Death Valley trip starting Tuesday. I'm anxious to try out my calculations.

As far as the 93 gauge goes I'm 90% sure that it will behave the same as the 95-97 gauge. Considering the sender and the R1 resistor are the same the behavior for the gauge would be probabaly be very different than is observed if there was a difference in the inductors. I'll be astonished if there is a diffrence. What time frame are you thinking of for the 93 gauge and other experiments after that?

 

[Rookie2]

I see the same thing with the Greddy so this probably is NOT a dead spot in the modified guage; your engine has reached operating temp and it stabilizes.

-B-

No, I didn't mean dead spot in the since that due to the circuitry of the guage, the needle still stops in the middle. I meant it in the since that the guage stops moving once the vehicle warms up. Bad phrasing on my part.

My point was to clarify for those that may be reading along, that the modified guage doesn't hover around the red line under normal conditions. If it starts to move up that high, then you NEED to be watching it. If your needles around that area so much that you think it could desensitize you to the gauge, then it seems to me you've got a problem somewhere.

Maybe I'll see things differently once summer temperatures roll around.


Rookie2

 

[RavenTai]

What time frame are you thinking of for the 93 gauge and other experiments after that?

not exactly sure, I will have a very large amount of free time starting April 1, and quite a bit leading up to then as I burn up my remaining vacation but have a lot going on, was hoping to get to it yesterday or today but wound up taking my tool box home last night (heavy SOB) , and doing 12oz curls with a coworker in the same boat I am tonight.

 

[semlin]

RT that sucks. PM sent.

 

[RavenTai]

Darwood, 214 pictures of the 93-97 stock response are on thier way to you, I compromised, watched voltage across L1 on the way up, pictures roughly every 5 degrees and source on the way down. pictures mostly every degree.

 

[RavenTai]

                       93   97  

Pegged hot            269  269  
Top of red            253  259
Bottom of red         242  248
Top of dead band      220  220
Bottom of dead band   168  169
Cold line             129  135

Close

one interesting thing is that the pegged and dead band numbers are alomost identical. these are all based on movement, but readings in relation to the to the face card are off quite a bit, the 97 stock numbers was the first cook I did and looking at the pictures I think the gauge may be tilted, possibly accounting some diffrence in readings when asociated with the face card.

another posibility is the needle is on the sahft slightly diffrent between the two gagues, movement based events are the same but needle position is diffrent.

well eiether way this says that the two are electrically identical. possibly some needle positioning diffrences or maybe just my error.

 

[semlin]

woohoo, we got 93 data

 

[RavenTai]

Ok performed the mod to the 93 gauge and did a cook tonight.

                     93   97
Pegged hot          242  243
Top of red          226  227
Bottom of red       213  216
Center (guestimate) 189  190
Cold line           156  160

Seams the 93 gauge reads a bit cooler, especially at the extremes. But I think this is close enough to call the 95-97 mod also good for a 93 or 94.

Derek these are also on their way to you.

 

[RavenTai]

err edit never mind, FTP is not working right now

Connecting to (ftp.*******.org) -> IP: **.***.**.*** PORT: 21
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Cannot login waiting to retry (30s)...
Continue to login attempt 7...

 

[loquito]

thanks for doing this for us with 93/94 trucks.

 

[Darwood]

err edit never mind, FTP is not working right now

Connecting to (ftp.*******.org) -> IP: **.***.**.*** PORT: 21
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Cannot login waiting to retry (30s)...
Continue to login attempt 7...

FTP should be up now. I shut it down while I was at Death Valley.

 

[Darwood]

Well about a month ago I changed out my resistors for 100 ohms and 100 ohms and this now suits me better. I got to try it out this past weekend pulling a double axle U-Haul trailer. With the old mod I would have been well into the red with I think a high temp of around 215-218. Unfortunately I forgot my OBDII cable so I wasn't able to get any temperature readings, but these are my estimates from some earlier runs I did with some steep hills. As it stands now the guage got up to one and a half needles below the red line with the estimated temperature of 215-218. (I really wish I had that OBDII to confirm)

The calculations I did and the real life performance are very comperable with an error of around 1-2 degrees. The center is now around 194.

I think next I want to do some calculations on what a 110 ohm resistor for R1 will do. I think the resolution is still too fine considering that onthe stock guage the needle wouldn't even be moving when on the modified guage the needle is in the red. According to my calculations the tempurature will be 223 when the top of the needle is just touching the bottom of the red. Based on my observations with the OBDII this seems about right.

 

[RavenTai]

you are now wanting to calcualte what a 110 R1 will do with a 100 ohm diode replacemnt resistor? the R1 110 center point is well documented and should nto change, R1 110 and 100 replacemnt shoul just move the whole scale down proportionally from where you are now.

I am not familair with Martinez, CA, is it a very hot climate? are you sure you are happy with a 215-218 operating temp?

what does it do on more level ground agian? so far mine has not gone that high but all I have seen are upper 80's and lower 90's with the mod,