Can I make an analog temp guage?

I’m reading these recent posts about temp gauges. I always wanted one, but refuse to pay the price for the trail tech. It’s a $10 piece (by my pricing biases) and I won’t cough up the cash.

I googled the spark plug thermocouple. <$10

I googled an analog auto voltmeter ~$12

If a person was to use the thermocouple as it is, a heat-varied resistor, reverse polarity, and bench test to create a new scale for the gauge faceplate, would it reasonably display temp?

It would need its own clean power source.

Yes it’s more trouble. I’m a rebel damnit.

Re: Can I make an analog temp guage?

Yep, that's about all they are. The thermistor they use is industry standard so someone might already sell a calibrated gauge.

A 3v lithium cell should be plenty, I'm sure an analog gauge will burn slightly more current but those squatty camera batteries would probably last a very long time.

If you come up with something post it up, I'd like to find a cheaper source for the spark plug ring terminal/ sensor.

Re: Can I make an analog temp guage?

I used ultralight airplane gauges for my old rd. All analog

Re: Can I make an analog temp guage?

Airplane? Aren’t all avionics issued two extra zeros on the price just because?

I’ll see what I can do. I’ll be sure to post if it’s a fail or success. Not too worried about power consumption since it would just be for tuning. Once the thing is set, I can easily feel a change. Maybe click it on momentarily during hard pulls for peace of mind.

Re: Can I make an analog temp guage?

Here you go pretty cheap.

Screenshot_20200725-150333_Google.jpg

Re: Can I make an analog temp guage?

Not real fast acting but good for keeping an eye on things.

Re: Can I make an analog temp guage?

That’s still a little pricey... buuuuuut

I would feel cool about airplane parts on my moped.

Could tip the scales in that direction.

For now I’m gonna start with the cheap-ass version just to see if it works and share that with all the other cheap-ass moped people I know are on here.

Re: Can I make an analog temp guage?

Amazon deals. $20 for both with shipping. It’s gonna take months to get to me. Don’t hold your breath.

F9435C9B-0492-408D-B85D-155373B86818.jpeg

Re: Can I make an analog temp guage?

> Papa _ Wrote:

> -------------------------------------------------------

> Amazon deals. $20 for both with shipping. It’s gonna take months to get

> to me. Don’t hold your breath.

Thing is, the meter reads volts and the thermostat couple puts out a variable resistance depending on the temperature it senses.

Just curious what plans you have to hook the two together.

Love to know.

Re: Can I make an analog temp guage?

Easy - just get a type K thermocouple and a dial for millivolts, then check for the chart for the k-type and plot from zero to 50mv for minus 18 to 2500 degrees f for a EGT gauge. 500 degrees is like 10mv so you need to plot that if you are doing CHT.

Re: Can I make an analog temp guage?

Rebel seems to know more about it specifically than I do.

I was just running with the idea that the thermocouple decreased resistance as heat increases. Which would cause a measured increase on the voltmeter.

The meter I bought was for 0-15VDC. So, according to Rebel, I’ll never see it budge if the varied resistance Going to cause <10mV range.

Maybe have to get a mV scaled meter or hack the one I bought. Won’t know until I get ahold of it and try some stuff.

Re: Can I make an analog temp guage?

Terbo Speghetti /

Following this. I had this thought, but I wanted to add a second thermistor on one of the exhaust studs for a more complete look at your temps.

Re: Can I make an analog temp guage?

That was I was referring to. I’m an electrical engineer so I get the physics of the situation. I was referring to the post where you showed the 0-15 VDC dial voltmeter; usually used to check the state of a 12 VDC (nominal) battery.

A posible way would be to use a simple voltage divider circuit with the thermocouple and a scalable resistor in series. Get a volt meter in millivolts and read the voltage drop across the scalable resistor to adjust the meter. The scalable resistor could be a simple potentiometer. Once the meter is calibrated it might be wise to read the resistance of the potentiometer and replace it with a fixed resistor to avoid it shaking out of adjustment from vibration.

Just an idea off the top of the head.

> Papa _ Wrote:

> -------------------------------------------------------

> Rebel seems to know more about it specifically than I do.

>

> I was just running with the idea that the thermocouple decreased

> resistance as heat increases. Which would cause a measured increase on

> the voltmeter.

>

> The meter I bought was for 0-15VDC. So, according to Rebel, I’ll never

> see it budge if the varied resistance Going to cause <10mV range.

>

> Maybe have to get a mV scaled meter or hack the one I bought. Won’t know

> until I get ahold of it and try some stuff.

Re: Can I make an analog temp guage?

Thanks Jai Dot.

I’m an electronics maintainer. So, definitely not qualified to engineer things. But, familiarity with components makes me feel brave.

I am assuming that the electromagnet driving the needle on my gauge is the same as many others. Scaling accomplished by resistors and such inside like a multimeter.

Re: Can I make an analog temp guage?

An issue to consider is that the response of the sensor to heat is not linear. So you need to match the response curve of the sensor to metering device. Also consider that the voltage across the meter’s terminals will vary depending on the pole voltage of the circuit’s voltage source.

If you want to tinker with a meter maybe consider using an auto temperature gauge (analog meter) That you can get cheap from an auto parts store. They are already ready ranged to around 300 degrees at the upper limit of the meter and usually don’t come with number readout. Rather they use a green zone/red zone indication. They also have an analog response to better match the thermistor’s value. Using a standard voltmeter that has a linear response will require you to compensate for the response curve of the thermistor with additional circuit components. .

Re: Can I make an analog temp guage?

I was just going to have a custom, wonky scale if needed. Mark the dial at 200,300,400,500. Wherever the needle may be at those temps. Not perfect, but functional.

If I get the parts and a skeleton of it working, maybe y’all can help me make it nice.

My current MO is to carry my IR temp gun and stop quick to shoot the head after a WOT run. Which is not accurate but for tuning I can see 260* as: “it probably didn’t cool down that much.” and 320* as: “dang that could have been pretty high 20 seconds ago.”

Hell, if the gauge is a flop, maybe just build a circuit that turns an “over temp” light on at a set point. Have that be adjustable.

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