Electronic Otterstat

[Bitsyncmaster]

I've started playing with LMT01 temperature sensor to design an electronic otterstat. This sensor can work to 150 deg. C so it should be fine running in our coolant. It is a digital pulse stream so it will be less susceptible to electrical noise. Accuracy is 0.5 deg C so I do not need to do any calibration.

I've prototyped this sensor to a micro and wrote code to read the sensor value. My plan is to have the user set the "trip" temperature via a DIP switch. I also plan to put an audio warning (buzzer) if a problem occurs (coolant temp running to high).

The plan is to just insert the sensor into an existing coolant pipe and the two small wires would get clamped between the existing hose and pipe. I'm interested in testing the "otterstat" in the return coolant line to see if that is a better way to turn the fans on and off.

I've never had a problem with my otterstat in my car so really did not consider the need for this project. But I have been reading where some owner are have otterstat failures.

[dmcnc]

Definitely interested. My otterstat is failing intermittently and Toby's solution has been out of stock for a while.

[djdogbone]

Wow. With the availability issue with this part, it's the right time to intro this Dave!

[Bitsyncmaster]

Pretty much done with my testing of the temperature sender. I set my prototype software to turn an output on at 80 deg. F and off at 75 deg F. So I could just put my finger on the sender to warm it up and see the output turn on. Then let it cool to room temp and see the output turn off.

Have been thinking of the best way to package this unit so I can get a prototype circuit board made to run testing in my car. I need access to a DIP switch and my "buzzer" needs to be exposed to hear it. Right now I'm thinking of making it the size of a relay so it can plug into a standard relay socket. I have two spare relay sockets in my relay compartment (the AC panel light dimmer and the red resistor are blank). I need the 5 pins connected for the unit. So my plan is to have a double PCB board and the top board will remain exposed and the space between the boards will be potted.

I was thinking the buzzer would sound 3 short notes to warn if your coolant is getting to hot. And maybe another three if the temp keeps climbing. I will also sound a warning if I detect a failure like the temperature sender is bad. With a failure I will keep the fans powered along with the warning.

If you have any other ideas, let me know.

[vwdmc16]

How about a tie in to your solid state fan fail relay that flashes the fan fail light along with the buzzer.

[djdogbone]

Go for it Dave!

[Bitsyncmaster]

How about a tie in to your solid state fan fail relay that flashes the fan fail light along with the buzzer.

Both Fan Fail and the Electronic Otterstat use all 5 pins of the relay socket. So a hard wire improvement is not possible. Putting WIFI into units would make the price go to high.

[Horsebox]

I have suffered Otterstat failure and very quickly the engine overheated, to the point of hissing and spitting out of the expansion tank overflow hose, before I could turn it off.

I can't wait to see what you come up with!

In the meantime I have a new Otterstat, which I don't trust so have a manual fan override switch in the cabin in case the Otterstat doesn't do its job. Which is only a matter of time.

Possible do you think to have a free floating thermocouple in one of the accessible coolant pipes without leaking under pressure?

Great work as always...

[Bitsyncmaster]

I have suffered Otterstat failure and very quickly the engine overheated, to the point of hissing and spitting out of the expansion tank overflow hose, before I could turn it off.

I can't wait to see what you come up with!

In the meantime I have a new Otterstat, which I don't trust so have a manual fan override switch in the cabin in case the Otterstat doesn't do its job. Which is only a matter of time.

Possible do you think to have a free floating thermocouple in one of the accessible coolant pipes without leaking under pressure?

Great work as always...

I think Toby's adjustable unit does a free floating sensor and the tubing is clamped under the hose. My sensor only has two wires and I will probably use 20 AWG Teflon insulated wire which will hold the free floating sensor.

[Bitsyncmaster]

I finished the PCB layout and ordered one "barebones" board. That lets me get a working unit into my car so I can verify the hardware and software. My only concern is maybe electrical noise from the sensor. If I get noise I can filter it with software or maybe a hardware circuit change.

[Bitsyncmaster]

I've got my prototype PCB and should be installing it soon in my car. I've made my DIP switch select setting the fan on temps in 5 degree F steps. The fan off temps are set at 5 degree F below that setting. I set the alarm (buzzer) at 10 degree above the fan on temps. These are all just my guess of what should work so testing in my car will determine if those values need to change.

I was also thinking of adding a voltage alarm in this unit looking for a sudden drop below 12.5 volts since that would result if your fan belt broke and the alternator and water pump stopped turning. If the water pump stops, then the coolant flow would stop and therefor the coolant temp would not rise to trigger an over temp alarm.

The "buzzer" seems pretty loud on bench testing. Not sure when mounted in the car with the relay cover plate on if the volume will suffice. Also needs to overcome radio background music.

[Bitsyncmaster]

I wrote the software to see a sensor failure and turn the fans on and beep 5 times. That works good but then I put the sensor into a glass of water and the sensor pulse level changes due to the water conducting some current away from the sensor. It still works but I don't like the levels changing. The sensor puts out current pulses (very small currents) related to the temp. So my software counts the pulses to know the temp.

So I either have to water proof the sensor or mount it on the outside of the coolant pipe. I'm thinking mounting outside the pipe should read the same temp as the coolant inside as long as not much air is blowing over that sensor. Just wrapping it with Teflon tape should prevent any air cooling or heating.

[Bitsyncmaster]

Now this is an interesting test. I taped (wire wrap tape, no sticky) a thermocouple on the metal pipe passenger side feeding the water pump. Air temp is 60 deg. F so fans never came on and dash temp gauge peaked at just below the 1/4 mark.

I was not expecting the temp to rise until the thermostat opened so I missed the first few minuets.

2:39 = 101 deg F
2:40 = 114 deg F
2:41 = 126 deg F
2:42 = 137 deg F
2:43 = 147 deg F
2:44 = 155 deg F
2:45 = 163 def F

Then I saw a peak around 166 deg F and it quickly dropped to 141 deg F and it kept doing that cycle. So the passenger side is following the engine temp. I assume the pump keeps water flowing in the heater core. Then when the thermostat opens the flow through the radiator cools the engine down below the thermostat temp and closes the thermostat.

[Horsebox]

I thought the thermostat was designed to open at 188F...

And that the water pump sends the coolant in a clockwise direction to and from the radiator.

I wonder what results you would get if you did the same test on the drivers side metal coolant pipe.

[Bitsyncmaster]

Here is the same run with a thermocouple taped to the outside of the otterstat pipe.

Engine start
3:05 = 58.2 deg F
3:06 = 59.1 deg F
3:07 = 60.0 deg F
3:08 = 61.5 deg F
3:09 = 62.7 deg F
3:10 = 64.5 deg F
3:11 = 66.0 deg F
3:12 = 67.2 deg F
3:13 = 68.1 deg F
3:14 = 69.6 deg F
3:15 = 71.4 deg F
3:16 = 72.0 deg F

Then right at 3:16:01 the temp rapidly climbed to 167 deg F in about 55 seconds, then slowly dropped to 165, then climbed to 174, dropped to 171, climbed to 176 deg F.

So my thermostat is cutting all the flow off until it opens. Yes probably the coolant temp is a little higher than reading the outside of the pipe. It also is another cool day with air temp at 58 deg F. I assume my thermostat is stock. Normal dash gauge stays right around the 1/4 mark. Fans did not kick on today and temp gauge stayed a little below the 1/4 mark.

[Bitsyncmaster]

It was probably good I had to break away from this project to build up some inventory of my other products. I am always thinking about improvements.

I started this design because people were finding the otterstat has not been reliable. So I thought about replacing the otterstat with an electronic temperature sensor. I added an audio "buzzer" to give a quicker warning of engine overheating. So some people may just want this unit for the "buzzer" function. I also thought you can keep the OEM otterstat and use my unit as a redundant unit which will also turn the fans on even if the OEM otterstat fails.

I got some high temp epoxy which I plan to try to coat a sensor to install inside the coolant pipe.

I also am thinking of just using the the temp gauge signal so we won't need another sensor.

I do like the idea of removing the OEM otterstat and using a straight pipe so no chance of the otterstat leak or blow out.

[Drive Stainless]

As i was just saying in another thread, I could never get the otterstat to seal 100%. I let Megasquirt run the fans now, but otherwise I think your product would be a great upgrade, using the existing gauge sender.

[FABombjoy]

I let Megasquirt run the fans now
Do you have a second coolant sensor for this, or are your fan on/off temps based on a single sensor? If single, have you found some on/off temps that work best?

[Drive Stainless]

Do you have a second coolant sensor for this, or are your fan on/off temps based on a single sensor? If single, have you found some on/off temps that work best?


My fan on/off temps are based on the single coolant temp sensor that MS uses. I use the FIDLE output to turn them on and off. The settings are:

51466

[Citizen]

[snip]...have a manual fan override switch in the cabin in case the Otterstat doesn't do its job.

Hey, would you mind sharing a schematic diagram of this? Or at least some instructions? I'd like to do the same thing, and would like to use one of the dummy switches in the center console.

Thanks,
Thomas

...

[Farrar]

I do like the idea of removing the OEM otterstat and using a straight pipe so no chance of the otterstat leak or blow out.

<off-topic>
I'd have been happy with a threaded hole instead of the silly clamp thingy. I think that would reduce leak & blow-out. Screw-in switches have been used for years on other cars... But that would require a different pipe, I suppose. Surprised no vendor has offered this and a cross-referenced switch as an "upgrade."
</off-topic>

That said -- I'm a big fan (pun intended) of your work, Dave, and will follow this project with interest! :)

[BABIS]

<off-topic>
I'd have been happy with a threaded hole instead of the silly clamp thingy. I think that would reduce leak & blow-out. Screw-in switches have been used for years on other cars... But that would require a different pipe, I suppose. Surprised no vendor has offered this and a cross-referenced switch as an "upgrade."
</off-topic>

That said -- I'm a big fan (pun intended) of your work, Dave, and will follow this project with interest! :)

this may be the one you need: https://www.deloreango.com/it/new-style-water-pipe-with-screw-in-otterstat.html

[Farrar]

this may be the one you need: https://www.deloreango.com/it/new-style-water-pipe-with-screw-in-otterstat.html

Ooh, shiny! Thanks -- I didn't know that was even a thing. :)

[mr_maxime]

Lol that's exactly what I was asking about and got Dave to start working on this.

I can't tell on mobile but the one I found was in the UK and I wanted to make sure it used NPT threads so that it would work with universal cooling fan switches in the us.

[Bitsyncmaster]

I finally got caught up on low inventory building. So I did a little checking of the stock temperature gauge sensor circuit. Car gauges compensate for voltage variations so I'm working a way to do the same when I use that circuit for my electronic otterstat. Anyway, I tested the sensor (I assume mine is original).

Engine off sitting at 74 deg. F the sensor reads 2.69 Kohms.
Temp gauge at 1/8 scale (needle between the first and second marks) the sensor reads 283 ohms.
Temp gauge a little below the 1/4 mark is where my thermostat opens, the sensor reads about 230 ohms.
Waited a long time for the fans to kick on gauge about one needle width above the 1/4 mark, sensor reads 160 ohms.

Also measured the current in that circuit when the fans kicked on at about 70 ma.

Voltage on that circuit measured to ground is 14.1 volts cold, 11.7 volts at 1/8 mark, 10.6 volts at 1/4 mark.

Voltage on that circuit measured to cars "12 volts" was 3.02 volts engine off but heated to the 1/4 mark. With engine on it was 3.77 volts. So using car voltage referenced to the gauge circuit is not perfect. I will probably be measuring the car voltage along with the sensor voltage and have software tables do the correction.

[Bitsyncmaster]

I wired my red relay socket for the electronic otterstat. I'm going to make up a new circuit board and order one protype board for testing and debugging. Using the dash gauge temp circuit I only need four pins in the socket.

Pin 85 ground.
Pin 86 voltage from fuse #5 which is the same power used for the dash gauges and the otterstat.
Pin 30 is tapped onto the temp gauge sensor. (Green/blue wire in relay harness).
pin 87 will be the output. Plan to just tap onto the existing otterstat wire. Not sure if I need a diode yet but don't think so.

There are many green wires in the relay bank harness. I had to lift my fuse block to find the correct green wire going to fuse #5. I also found a cut green wire but not sure if I did that or it's just for the auto transmission circuits.

I don't think any radios have a mute signal input. If they did, I could use the extra pin for that to mute the radio if I signal an over temp condition. By the way, that gauge sender seems to respond very quickly to engine warming up.

[Bitsyncmaster]

Was just thinking about my software for checking for a sudden voltage drop to warn the driver since that often means the alternator belt has failed (stops your water pump). So to prevent the warning when the engine shuts off, I'm changing the power source for my "electronic otterstat" to the RPM relay output (second output that drives lambda).

I was thinking it's best to use the same power source as the temp gauge but that is powered even with the engine stopped.

So my electronic otterstat can be used for:

1) Just an audible warning device. Engine overtemp and or alternator failure.
2) A backup for the standard otterstat failure. Redundant otterstats powering the fan relay.
3) Eliminating the standard otterstat.

[Bitsyncmaster]

I got my "bare bones" circuit board. I assembled it and started writing software. I ordered a decade adjustable resistor so I can simulate the function of the temperature gauge circuit on the bench. I did a quick check of the sensor before and I posted those results but I really need precise readings.

The gauge drives the sensor through a coil of wire in the gauge. That coil has a cold resistance of 54.13 ohms.

When I get my decade resistor box I will replace the sensor with that box so I can get precise resistance values which the gauge shows 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8, and full scale. Not that I need to know all those values but it will be good info.

[Horsebox]

How can I help? I'm sorry, I don't understand what info you are looking for.

Need to remove temp sensor and test output resistance against temperature? I'm not going to do that to my car, but if I have misunderstood and can test something else then please let met know.

Mark

[Bitsyncmaster]

How can I help? I'm sorry, I don't understand what info you are looking for.

Need to remove temp sensor and test output resistance against temperature? I'm not going to do that to my car, but if I have misunderstood and can test something else then please let met know.

Mark

Thanks. I have not thought of anything I can not test myself yet. I just pull the pin on the bulkhead connector to open the circuit for the temperature gauge. What I'm going to do is get resistance values for temperature gauge readings that are above what my car gets. My car never shows much above the 1/4 mark on the temperature gauge. I'm hoping this data can help some owners check why their gauge shows higher normal temps then other owners. So is the difference the gauge, sensor or something else.

My otterstat unit will have user adjustable trip points anyway. I have eight switches (a DIP switch) so if all 8 are used to set the "trip" value that gives 256 adjustments. I will probably use some switches for other adjustments. I know I need to have a test mode so the owner can hear the alarm (buzzer) just to know what is sounds like and how loud it is.

[Bitsyncmaster]

I'm still waiting on some parts to setup calibration of my electronic otterstat. So I wrote software that checks the 12 volts. It will warn the user if the 12 volt (car power) drops below 12.5 volts for one second by sounding 5 beeps from the "buzzer". I do that just in case your alternator belt breaks which would quickly over heat the engine. I only do that warning once just in case your alternator goes bad you would not want that constant beeping. But it looks like the temperature gauge sender responds very quickly anyway but if you get a warning a few seconds earlier all the better to let you pull off the road sooner.

I will also warn the user if the unit detects higher temps than normal. The user will set the fan on switch point and I will use that setting plus some yet to be determined increase to warn the user. I'm guessing about an 1/8 of a gauge increase to set that warning. Will probably keep that warning sounding.

[Bitsyncmaster]

I got my high power variable resistor today and recorded the resistance that the sensor must have to show each value on the dash temperature reading. I did this with the engine running but the gauge compensates for the car voltage. You can verify the compensation by stopping the engine (alternator stops) and see the gauge still reads the same. My alternator puts out about 14.5 volts running. I also recorded the voltage over the resistor just so I could compute the current in the circuit. You can not use the voltage for calibration since that varies with the car voltage. I "eyeballed" the gauge as close as I could.

For the gauge reading at 1/8 scale the resistance on the sensor is 244 ohms at 11.60 volts.
For the gauge reading at 1/4 scale the resistance on the sensor is 154 ohms at 10.49 volts.
For the gauge reading at 3/8 scale the resistance on the sensor is 117 ohms at 9.56 volts.
For the gauge reading at 220 the resistance on the sensor is 94 ohms at 8.91 volts.
For the gauge reading at 5/8 scale the resistance on the sensor is 83 ohms at 8.38 volts.
For the gauge reading at 3/4 scale the resistance on the sensor is 73 ohms at 7.83 volts.
For the gauge reading at 7/8 scale the resistance on the sensor is 64 ohms at 7.30 volts.
For the gauge reading at 260 the resistance on the sensor is 55 ohms at 6.66 volts.

[Bitsyncmaster]

So with my test data, it looks like not much change in sensor resistance results in pretty large changes in your reading on the temperature gauge. Most of us see the temperature read around the 1/4 mark for normal running temps. Some people see running around the 220 mark for normal running temps.

I don't know if the gauge calibration or the sensor calibration is different causing those differences. It seems pretty sensitive calibration for both the gauge and sensor.

You could adjust the sensor calibration by adding a resistor in series with the sensor. But it's not a linear change so your calibration would only work in a limited range.

[DMC5180]

So with my test data, it looks like not much change in sensor resistance results in pretty large changes in your reading on the temperature gauge. Most of us see the temperature read around the 1/4 mark for normal running temps. Some people see running around the 220 mark for normal running temps.

I don't know if the gauge calibration or the sensor calibration is different causing those differences. It seems pretty sensitive calibration for both the gauge and sensor.

You could adjust the sensor calibration by adding a resistor in series with the sensor. But it's not a linear change so your calibration would only work in a limited range.

it wouldn't have anything to do with this blue device, would it?

https://uploads.tapatalk-cdn.com/20170625/0b8005029bb7d97ed0f4532b7fff4a5c.jpg


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[Bitsyncmaster]

it wouldn't have anything to do with this blue device, would it?

https://uploads.tapatalk-cdn.com/20170625/0b8005029bb7d97ed0f4532b7fff4a5c.jpg


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That would probably be the gauge calibration resistor. How most old automotive gauges work is there are two coils inside the gauge. One coil provides magnetism using the cars 12 volts. The other coil is powered through the sensor circuit. That is how they make the gauge accurate no matter what the voltage is.

With newer cars they use a regulated voltage (5 volts) so the gauges don't require so much power to operate.

It may be coincidence but the temperature gauge full scale resistance (54 ohms) is equal to the power coil resistance and hence would have the same current in each coil.

[Bitsyncmaster]

I had bought a gauge sender from Hervey a long time ago. But I never installed it. I will test that sender but the thread size is M14 1.25 so not sure if that is the correct sender for our D. I was looking at NAPA sender specifications for resistance and they are all over the place. The important resistance you want is at 220 deg. F which I measured on the gauge to be a sender resistance of 94.4 ohms.

[Bitsyncmaster]

I tested that Hervey sensor. Glad I never installed it. It would read very low on my dash gauge.

100 F = 1,530 ohms
120 F = 1050 ohms
140 F = 666 ohms
160 F = 447 ohms
180 F = 310 ohms
200 F = 227 ohms
212 F = 168 ohms

I would need to use another fluid other than water to test higher than 212 F.

[Horsebox]

100 F = 1,530 ohms
120 F = 1050 ohms
140 F = 666 ohms
160 F = 447 ohms
180 F = 310 ohms
200 F = 227 ohms
212 F = 168 ohms


I used Excel to plot those values on a graph and it looked like a logarithmic drop in resistance as a function of increasing temperature. It would be interesting to put both Hervey's and DMC's sensors in the same water bath and compare the difference in rate of resistance decrease.

I know the dash gauge isn't linear...when I overheated my car last year the temp gauge moved upwards very quickly as soon as the coolant temp was out of 'normal'. It only took a couple of minutes in stop-start traffic, with the otterstat failed and not turning on the fans, for it to overheat.

[Bitsyncmaster]

I used Excel to plot those values on a graph and it looked like a logarithmic drop in resistance as a function of increasing temperature. It would be interesting to put both Hervey's and DMC's sensors in the same water bath and compare the difference in rate of resistance decrease.

I know the dash gauge isn't linear...when I overheated my car last year the temp gauge moved upwards very quickly as soon as the coolant temp was out of 'normal'. It only took a couple of minutes in stop-start traffic, with the otterstat failed and not turning on the fans, for it to overheat.

I would order a new DMC sensor if it wasn't for the $20 shipping charge. I would like to test it the same way (I made a fixture that stands it in the water that keeps the connection side dry). My meter sensor for reading the temp is held right near the sensor I'm testing.

Yes the sensor responds very fast to changes.

[Farrar]

My gauge reads pretty accurately below 220°F, and then shoots up dramatically as the engine warms up. A temperature gun pointed right next to the sensor showed only 219°F when the gauge was nearly pegged. I wonder if the problem would be the sensor or the calibration resistor. I've never known about the calibration resistor until now.

[Bitsyncmaster]

I'm guessing the accuracy problem is the senders. Although another possibility is oxidation on those nuts where the calibration resistor is mounted. If anyone has there gauge out of the car, can they please remove the resistor and measure it. My guess would be it's in the order of 500 to 1000 ohms.

If anyone has an old OEM sender, I will pay you $20 for it so I can run it through my testing setup.

Here is my test setup. I cover the aluminum plate with water so it should represent what the sensor sees in the car.

[Bitsyncmaster]

I think I thought of the math needed to have my otterstat compensate for car voltage changes. The sensor voltage will be a set percentage of the car voltage at one temperature. At 260 degree it will be 50% of the car voltage.

So I now I have to devise a way to write that code in assembler language using my simple 8 bit micro.

[Bitsyncmaster]

I thought of an easy way to read percentage of the sensor voltage. I will feed my AD (analog to digital) reference voltage with the cars voltage (divided by 3). So I don't need any software to convert the sensor reading (adjusting for car voltage changes).

I also thought of another user warning check. Give the user a "beep" if the car voltage is to great (above 15 volts). I did have a friends car have the alternator go bad and over voltage (above 16 volts).

[Bitsyncmaster]

I've got the bench calibration done for my software. I plan to check the 1/8 gauge reading and the 1/4 calibration values in my car. I won't check the higher values in the car since I don't want to purposely over heat my engine.

I'm leaving for the beach for a week so won't be doing any DeLorean work till I get back.

[Bitsyncmaster]

I got a used gauge sensor from an owner here. It looked exactly like the Hervey sensor I tested before. It even has the same marking of "AC 12V".

So I ran the same test but this time I started at 212 degree F and turned off the burner so the cool down was much slower and would give me more accurate values. The 212 reading was exactly the same and the other readings very close. So I may need to change my testing to drive the same current into the sensor that the car uses. Remember I measured 54 ohms drives the sensor via the cars 12 volts. I'm guessing that self heating will change the values to what I expect. I did not think that heating would change the resistance since the sensor is running in moving fluid. But I will have to retest the sensor with that same drive current. The multimeter uses almost no current to read resistance.

Anyway use this table to test your sensor with a multimeter.

212 deg. F = 168 ohms
200 deg. F = 210 ohms
180 deg. F = 297 ohms
160 deg. F = 428 ohms
140 deg. F = 633 ohms
120 deg. F = 965 ohms
100 deg. F = 1489 ohms

[Bitsyncmaster]

I ran a test driving the sensor through a 54.3 ohm resistor powered to 14.00 volts. My calculated ohm values now appear to be what I expect from my measurements in my car. So it looks like these two sensors I have are the correct calibration. I was not able to finish the test because the door bell rang and someone driving by my house wanted to buy my DeLorean and I missed recording the values as it was cooling down.

213.2 deg. F = 99.9 ohms. Note in my car the 220 mark needed 94 ohms.
200 deg. F = 119.3 ohms.
180 deg. F = 175.4 ohms.
160 deg. F = 288.1 ohms.
140 deg. F = 452.5 ohms.

No I am not selling my DeLorean. The garage door was open and he saw it from the road.

[Bitsyncmaster]

I plugged my "electronic otterstat" into my car. My DIP switch only has 8 selected values right now. Starts at 1/8 scale on the dash temp gauge and each 1/8 increase after that. I wanted to check the accuracy of those selected values. The first one at 1/8 came out perfect (I set my software to beep above the setting). The 1/4 scale came on a little before the engine got to that gauge mark. By the way that is when my thermostat opens since it started beeping and then the beeping stopped which means the engine cooled down when the thermostat opened.

Now I want to check the rest of the calibration but my engine only heats a little past that 1/4 mark. So I plan to plug one of my spare sensors (that I verified are correct calibration) replacing the sensor in the engine. So I can put that sensor into a pan of hot liquid and finish the testing. That will even give me temperature values for the marks on the temp gauge.

So I need to find a liquid that can be heated past 260 deg. F at atmospheric pressure. Regular antifreeze only increases the boiling temp a little bit past water. The spec of 265 deg. F is at 15 PSI.

I want to calibrate those 1/8 marks so I can use those values to add the finer user selection. I think I will need 32 selected trip points. I need the large range to compensate for each cars tolerance of gauge and sensor accuracy.

[DMC5180]

Do you have a small deep fryer? Cooking oil boils at about 300 C.


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[Bitsyncmaster]

Do you have a small deep fryer? Cooking oil boils at about 300 C.


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Thanks. Good idea.

[Bitsyncmaster]

I did some more in the car testing. I wanted to calibrate the unit to coincide with the OEM otterstat. To my surprise the OEM otterstat turns the fans on a little below the 3/8 gauge mark and does not turn them off until just a little above the 1/4 mark. I never see this because most of the time my AC is on and the fans are running all the time. Or the car is moving and that provides air flow. So that OEM otterstat has a lot of hysteresis (large gap between turn on and turn off). I don't think I will put that much hysteresis in my solid state otterstat.

I bought a hot plate and some canola cooking oil which says it can heat to 500 deg. F. I'm going to put the gauge sensor into a pan of that oil so I can check calibration values for gauge readings up to 260 deg. (full scale).

[Bitsyncmaster]

Sensor in cooking oil test. These reading were taken as the temp dropped. The gauge seems to have some damping of needle moment. This was done with engine running to have the same voltage and ground drops over the circuit.

260 deg. on gauge = 249 deg. F on sensor
7/8 deg. on gauge = 232 deg. F on sensor
3/4 deg. on gauge = 220 deg. F on sensor
5/8 deg. on gauge = 211 deg. F on sensor
220 deg. on gauge = 200 deg. F on sensor
3/8 deg. on gauge = 188 deg. F on sensor
1/4 deg. on gauge = 175 deg. F on sensor

So assuming my thermostat opens around 190 that tells me the sensor I used for testing is different or something is faulty with my testing. Of course it could be my thermostat is faulty or someone stuck in the wrong thermostat. Also my fans kick on with the otterstat a little below the 3/8 gauge mark so that says the otterstat kicks on about 185 deg.

I'm assuming the gauge is a calibrated instrument since there is a calibration resistor on the gauge terminals. Maybe they did a crappy job calibrating or did the calibration for full scale. I would have done calibration at the 220 mark (half scale).

[DMC5180]

Which reading represents the middle White line?


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[Bitsyncmaster]

Which reading represents the middle White line?


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The 1/4 "deg." is the middle white line. That is where my gauge normally shows when driving.

[Bitsyncmaster]

I going to run another absolute temp test (real sensor temp to gauge reading). But I'm going to high temp epoxy my meter thermocouple directly onto the sensor. I'm thinking the oil temp is a little different than what the sensor reads. My meter sensor is about 1 inch away from the gauge sensor.

I'm not using that absolute value for any calibration in my unit, just want to know the accuracy of the OEM system.

I'm basing my calibration from the gauge readings. This is where my first idea of a new temp sensor installed in the coolant line would have been better but make installation harder.

[Bitsyncmaster]

Well I pulled the sensor from my pan of oil and found the ground wire lug was very loose. I had four nylon stand offs and the ground wire was attached to the screw holding the standoff. I guess the high heat or the oil did something to the stand off to make the nut get loose. So that may have affected my test.

Anyway, I glued the meter sensor (K type thermal couple) to the gauge sensor with high temp epoxy. I will add a dedicated screw to hold the ground lug on my aluminum plate.

[Bitsyncmaster]

I did a new absolute temperature check. Not any big change.

260 deg. on gauge = 243 deg. F on sensor
7/8 deg. on gauge = 234 deg. F on sensor
3/4 deg. on gauge = 224 deg. F on sensor
5/8 deg. on gauge = 213 deg. F on sensor
220 deg. on gauge = 204 deg. F on sensor
3/8 deg. on gauge = 192 deg. F on sensor
1/4 deg. on gauge = 177 deg. F on sensor

This test was also done heating the oil to 270 deg. F and letting it cool down until the gauge hit each mark. I do that because the oil temperature change rate is pretty slow. The gauge drives the sensor though one coil of wire in the gauge. I tested that coil resistance cold at 54 ohms. But at high sensor temps, the current flow is about 100 ma. so that may be heating the gauge and maybe affecting accuracy. I'm going to see if the values change starting cold and increasing the oil temp.

[Bitsyncmaster]

Ran the new absolute temperature test starting cold and slowly heating the sensor by turning the hot plate on and off for very short times. Hence the change in temps was much slower. I still think there is a little heating of the gauge causing a little calibration change when testing hot to cold. Also air temp was cooler this morning at 77 deg. F.

These values look more accurate for gauge calibration.

260 deg. on gauge = 254 deg. F on sensor
7/8 deg. on gauge = 244 deg. F on sensor
3/4 deg. on gauge = 233 deg. F on sensor
5/8 deg. on gauge = 223 deg. F on sensor
220 deg. on gauge = 213 deg. F on sensor
3/8 deg. on gauge = 200 deg. F on sensor
1/4 deg. on gauge = 185 deg. F on sensor
1/8 deg. on gauge = 167 deg. F on sensor

What I really need for perfect results is an electronic heater for my oil bath that holds temps real stable.

[DMC5180]

You need one of those portable Inductive "hot plate" cookers "as seen on tv" product. you can set and hold the temp just like an oven.

Unfortunately the units are about $100 at Walmart.


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[Bitsyncmaster]

You need one of those portable Inductive "hot plate" cookers "as seen on tv" product. you can set and hold the temp just like an oven.

Unfortunately the units are about $100 at Walmart.


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I have a real accurate warming plate I use for my epoxy potting but I don't think if goes much above 200 deg. F. It only has a 75 watt heater.

[Bitsyncmaster]

I finished with the hot oil testing (calibration). I wrote the software to give me 29 steps of the gauge reading between the 1/8 position to the 260 deg. position. I would not need all of that range but it lets users run the unit with a sensor that is not really calibrated for our gauge.

I've got my electronic otterstat now controlling the fan (OEM otterstat disconnected) but what I'm thinking of doing is install one of the higher temp otterstats and that will be my backup. Not that I expect any failures but my unit depends on the gauge and sensor remain working. The OEM otterstat does not need any of that gauge circuit to work. I see DAP has three ottersats to choose the switch temp from.

The user can hear the buzzer by setting the lowest setting and warming up the engine until the "over temp" warning comes on.

I will make the few circuit board changes and place an order for 100 boards soon.

[SS Spoiler]

I think Dave has found a new career....

[Bitsyncmaster]

Photos of first production unit. This is for testing in my car so I should not have potted it but I wanted to play with paint. Sill not sure how I will finish the units.

Switch #1 has to be on. This uses a micro pin that had some dedicated operations so I needed to switch it open if I need to reprogram the software. If you use it with the switch open, the unit will beep at you.

Switch #2 and #3 are not used yet. I think I will make the user fan on temp finer so will probably use #3 along with the next operation.

Switch 4, 5, 6, 7 and 8 are used to set the fan on temp.

[Chris 16409]

Dave, where will this plug into? A new relay socket?

[Bitsyncmaster]

Dave, where will this plug into? A new relay socket?

Yes a new or already unused socket. I started writing up the document today. Boy I hate writing like all engineers.

If you have your AC panel lights jumpered so they only come on with the car lights, then you can use the "Light Relay" socket or the red resistor socket. I used the red resistor socket. Hence why I painted it red.

I changed the software to give the user finer steps for setting the fan on. I added one switch if the user wants less hysteresis (the fan off setting). I'm running this software in my car now just to see if any bugs show up.

[NckT]

The Instruction Manual is just as important as the final product Dave, as typically if it doesn't work, the average user will RTFM last... !

[Bitsyncmaster]

The Instruction Manual is just as important as the final product Dave, as typically if it doesn't work, the average user will RTFM last... !

I must admit I READ THE FXXXING MANUAL only as a last resort.:hihi:

For this unit most users will need it. Setting the fan on switch is a simple binary number (no problem for the software guy). So I have a table showing how to set one of the 57 selected values.

It also shows the wire list for the "new" socket.

[NckT]

I've heard that there are 10 people who know about Binary. Those that do, and those that don't. ..

Good luck with the product testing

[Bitsyncmaster]

I just found a company that sells striped wire for a good price but in 500 and 1000 foot spools.

http://www.pacergroup.net/

Since I will include the new relay pins crimped to a length of wire for this product, the new wires will match the harness wires.

Still working on the document but here is the first draft if you have questions or comment they are welcome.

[BABIS]

I just found a company that sells striped wire for a good price but in 500 and 1000 foot spools.

http://www.pacergroup.net/

Since I will include the new relay pins crimped to a length of wire for this product, the new wires will match the harness wires.

Still working on the document but here is the first draft if you have questions or comment they are welcome.

Thanks Dave, I am assuming that the stock otterstat operation would be achieved with settings #19/20 ?
I would find helpful to see the temperature specified for every settings in the table..

[Bitsyncmaster]

Thanks Dave, I am assuming that the stock otterstat operation would be achieved with settings #19/20 ?
I would find helpful to see the temperature specified for every settings in the table..

The only marked gauge is the 220 and 260 deg. I'm guessing the gauge itself is a calibrated instrument provided the sender matches what the standard normal was.

I'm running #12 which is just above the 1/4 mark and a little below where my otterstat would turn on. I've been running the car with just my electronic otterstat controlling the fans. When I get my new wire, I'm going to hook both up.

[Bitsyncmaster]

I just got my striped wire order. The stripeing is not as good as the stock D wires but at the prices $80 for a 1000 foot of tinned copper 16 AWG, 600 volt I can't complain to much.

[bigmac]

Hi Dave. How much is one of these units please? Thanks. Fred


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[Bitsyncmaster]

Hi Dave. How much is one of these units please? Thanks. Fred


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I have not priced it yet. I was planning on just releasing it at the end of the year. Just not looking to show any more income this year. If you really need one now I can probably sell a few.

[Bitsyncmaster]

Sorry for delays. I'm time limited baby sitting my granddaughter 5 days a week.

I've come up with wires with one relay connector crimped on one end.
1) Black/orange is 46" so you can connect to the fan relay wire. This wire is long so it can wrap with harness so you can lift either relay bank.
2) Green/blue is 28". You find the green/blue wire in the harness on the right side of the relay compartment and spice.
3) Black is 24". Longer than you need but spice into any relay ground wire. Shortest is the light relay ground.
4) Yellow/red is 15" to be splice into the lambda relay.

The kit will also include 4 butt non-insulated connectors and heat shrink to cover those butt connectors.

[Bitsyncmaster]

I have 6 otterstat units ready to ship. These have the same software I was using in my car until my clutch died. I had about a month of running that software with no changes needed. So I need new users that are still driving their cars to get more testing done. I will keep building these units so no need to rush to buy if your car is in storage until the spring.

I have updated my web site so you can download the instructions.

I have priced the unit at $70.

[Bitsyncmaster]

I have shipped a few of these electronic otterstats and finally one user got back to me with a problem. Not sure if the problem would affect other users but his engine the gauge temp reading would increase quite a bit even after his fans turned on. Hence my otterstat would keep beeping most of the time warning him of overheat.

Do other owners see much gauge increase when the fans are running? I know I don't but have not had a chance to run my otterstat in heavy summer traffic and or pushing the engine like going up mountains in high gear.

My otterstat I just chose about a needle width above the fan on setting to turn on the beep overheat warning. I did a software change to let the user set the beep warning value if required. Units shipped still are set to original auto beep warning values.

I attached my new install document which explains how to program a new beep value. Please look over that document and comment if something is not clear.

[Farrar]

Do other owners see much gauge increase when the fans are running?

Is this question for anyone running any type of switch, or specifically for owners running your switch? For what it's worth, I am running a normal switch, and I see a significant delay between when the fans come on and when the temperature starts to go down. However, it is also worth noting that my shroud is partially missing on the passenger side, and the lower radiator duct is absent, thus I consider the cooling system to be slightly overburdened.

[Bitsyncmaster]

Is this question for anyone running any type of switch, or specifically for owners running your switch? For what it's worth, I am running a normal switch, and I see a significant delay between when the fans come on and when the temperature starts to go down. However, it is also worth noting that my shroud is partially missing on the passenger side, and the lower radiator duct is absent, thus I consider the cooling system to be slightly overburdened.

Yes my question is for all D owners no mater what combination of cooling they run.