Adding coolant temp gauge? (1 Viewer)

[RavenTai]

. maybe a power line to the gauge run right from the battery with a relay switched by the current power source would limit the effect?

Well the gauge is not a high current user so that is not really the problem, from what I gather this is systemic system voltage variation so there is no place to pipe in a good voltage from.

Rick I would be interested to see if when you get the needle centered wile at normal operating temperature if you still have this problem. (Assuming the 110 resistor will do so) you would still get some variation at the extremes of hot and cold but assuming you driving voltage is only varying half a volt or less the needle movement should be negligible.

 

[semlin]

landtank

sorry just thinking out loud. I'll take a look tonight on the way home to see how much variance I get.

raventai

I had not realized idle voltage dropped so much. forgive my ignorance again, but is it possible to use a diode or something to limit the voltage getting to the gauge? If so, why don't we calibrate the gauge based on a 12 volt DC signal and then it would be steady?

 

[RavenTai]

landtank

sorry just thinking out loud. I'll take a look tonight on the way home to see how much variance I get.

raventai

I had not realized idle voltage dropped so much. forgive my ignorance again, but is it possible to use a diode or something to limit the voltage getting to the gauge? If so, why don't we calibrate the gauge based on a 12 volt DC signal and then it would be steady?

well at room temprature a fully charged battery at rest is arround 12.7v, an alternator outputs about 14.5 volts, at low RPM's the alternaor cannot output as many amps, if the total load is higher than the alternator can output at its current RPM then its ouput voltage drops, as you put on more load you eventually reach battery voltage and the volt drop stops as the battery fills in the diffrence until its reaches it limits. so at idle voltage can be as low as 12.x volts if the load is high enough, I was calibrating on 14.5 as this was suppose to be a common and stable voltage and you spend a lot more tiem at 14.x than you do at 12.x


There may be something that can be done about this but not going to get to the bottom of that today,

 

[e9999]

I would think this voltage fluctuation thing would be greatly dependent on the condition/age of the battery, no?

 

[RavenTai]

I would think this voltage fluctuation thing would be greatly dependent on the condition/age of the battery, no?

More the alternator and what loads are on. Battery is basically out of the picture above 13v and just becomes a variable load that decreases as it charges.

Ok got the 110 ohm resistor and diode bypass jumper/shunt installed and cooked,

Ok figured out Thevenin Equivalents as it applies to this circuit (I think) and did one calculation (takes a wile) on paper replacing the 75Ω resistor with a 110Ω resistor gets a 198°F "center" as above and at 226°F gets .3678 volt drop across L1, That is equivalent to the current 235°F position, or about the 3/4 mark.

Not even close, 226 wound up almost pegged, so apparently I need to do some work on trying to predict needle position besides center. This is good as that math went against everything else, now diode replacement resistors can be used to further get it where we want it. If 226 had come up low on the gauge we would be stuck with it with no adjustments

on paper these following resistors should center the gauge at....



110Ω....198°

Nope, center wound up around 188 (center found by eyeball not volt meter) Rick unless you are operating @ 188F your gauge may read above center with the 110 ohm resistor.

The rest
Pegged hot 230
Top of red 216
Bottom of red 209
Center 188
Cold line 165
Pegged cold no data

 

[semlin]

weird...

so did the gauge register the same position when at the same voltage as on the earlier cook?

or did the voltages at a certain temp correspond to your calculations?

or neither

 

[Riley]

snip...

I had not realized idle voltage dropped so much. forgive my ignorance again, but is it possible to use a diode or something to limit the voltage getting to the gauge? If so, why don't we calibrate the gauge based on a 12 volt DC signal and then it would be steady?

Perhaps this is would be overkill but one might be able to feed the gauge with from a well regulated supply by wiring in a low drop out regulator at say 11.0 volts and only power the temp gauge with it.

This is probably the easiest way to get steady voltage at the gauge.

 

[landtank]

We had a voltage issue on one of our machines when a new part needed to be subbed in. They designed something with a zener diode as a regulator. I did a search on it and there was a site out there that had a formula and schematic of how to do this. Basically from what I understood it was a resistor and ZD combination.

These aftermarket guages have to have something in them to compensate for the varrying voltage.

 

[Rookie2]

Hey Raven,

Are you going to be installing a dummy light too? What do you think about putting one on the instrument panel right next to the temp gauge?


Rookie2

 

[landtank]

what would be the benefit of an idiot light if the truck had a reliable temp guage?

 

[e9999]

what would be the benefit of an idiot light if the truck had a reliable temp guage?

that you can have a look at the road every so often instead of watching the gauge all the time?

 

[cruiserdan]

what would be the benefit of an idiot light if the truck had a reliable temp guage?

More like a red message that lights up and says "TIME FOR A NEW HEAD GASKET"

 

[RavenTai]

weird...

So did the gauge register the same position when at the same voltage as on the earlier cook?

Or did the voltages at a certain temp correspond to your calculations?

Or neither

Well I don’t know, the Fluke Meter wound up watching source voltage for this cook, needle position per volt drop across L1 should be somewhat constant. (There is that S word again)

Hey Raven,

Are you going to be installing a dummy light too? What do you think about putting one on the instrument panel right next to the temp gauge?


Rookie2

Maybe after the base mod is complete I can play with some add ons. A dim yellow LED at 210 and a very bright red LED at 220? The face card could be drilled and the LED’s super glued into the holes.

We had a voltage issue on one of our machines when a new part needed to be subbed in. They designed something with a zener diode as a regulator. I did a search on it and there was a site out there that had a formula and schematic of how to do this. Basically from what I understood it was a resistor and ZD combination.

These aftermarket guages have to have something in them to compensate for the varrying voltage.

When I get some time I’ll look into it, but that is going to add complication how much of a variance are you getting? On the test bed source voltage changes of 3+ volts the needle is moving but not by that much, your steady state driving voltage (besides idle) should not be moving but a few tenths of a volt.

I think a more pure Wheatstone bridge using separate resistors instead of the inductors of the air core motor for half the circuit would have been more voltage stable.

 

[Rookie2]

what would be the benefit of an idiot light if the truck had a reliable temp guage?

I imagine I scan my instruments more than the regular Joe, but I can not say that I am so anal with it, that "if" an overheating situation were to occur, that I would catch it 100% of the time just because the needle moves in the middle temperature range now.

A light or a buzzer is what I need in order to make this mod. worth while.

Just my $0.02.
Rookie2

 

[RavenTai]

some pics from the last cook. volt memter is showing source voltage, the 1 is hidden.

 

[RavenTai]

more

 

[e9999]

but you don't want to have it in the red at 210 already, right? or do you?

 

[semlin]

Raventai and Landtank,

According to my local electronics store a regulator limiting voltage to 12 volts for up to 1 amp/watt of current costs $1.00. This can be spliced in line to the power lead to the gauge. How much current does this gauge draw?

Not having had to remove a cluster from a live dash I don't know if the temp gauge has a separate power supply wire that would be easy to splice into?

Assuming you did this and looking back at Raventai's earlier tests, a 110 ohm resister with a 12v signal would potentially be much closer to 226 at hot.

E9999

yes, you are correct that the cook result is way off expectation on gauge response. We are shooting for 226 at the start of red.

 

[RavenTai]

Semlin did you ask what the minimum input voltage was?

 

[landtank]

regulator limiting voltage to 12 volts for up to 1 amp/watt of current costs $1.00.

How big is this thing or is it another type of chicklet with a wire at each end that could be soldered onto the back of the guage?