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| Older temp gauge https://slantsix.org/forum/viewtopic.php?t=61882 |
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| Author: | JohnnyDees [ Sun Jan 28, 2018 3:37 pm ] |
| Post subject: | Older temp gauge |
I just bought an older electrical temp gauge from ebay. The needle is all the way to the right when not hooked up. If I apply voltage it pegs to the left. If I bring volts down to 3 volts it goes to the middle. Why would it stay to the right ? Anyone ever repaired one? Thanks |
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| Author: | Pierre [ Sun Jan 28, 2018 4:44 pm ] |
| Post subject: | Re: Older temp gauge |
What did you buy exactly? A stock dash gauge? |
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| Author: | wjajr [ Mon Jan 29, 2018 8:14 am ] |
| Post subject: | Re: Older temp gauge |
Temp gauge operates on about 5 volts supplied from the voltage limiter located under dash as does the fuel gauge. I say about 5 volts, as limiter reduces wire harness nominal 12 volts to an average of 5 volts by opening and closing a set of contact points attached to electrically heated bi metal arm. In other words, as the point set is supplied 12 volts, the point set opens opens at some point cutting off 12 volt to gauge, cools and point closes, over and over, resulting in a pulsating 12 to zero to 12 volts over time that the gauge sees as an average of 5 volts. Gauge also has a bi metal coil that heats from current pulsating current supplied which moves gauge needle by thermal expansion... Kind of like an electric stove burner set on low cycling on, off, on, off maintaining an average btu output over time to whatever is cooking. Gauge is feed average 5 volts which goes to ground via the temperature sender/sensor near thermostat housing in head. Sensor changes resistance as coolant temperature increases or decreases which throttles limiter's average 5 volt output level to gauge's coil which sees between zero volts to average of 5 volts. So when you supply that gauge with 12 volts, it will peg to hot, and if left operating at 12 v for just a short time will melt gauge's coil. Kind of a messy explanation, but hope it helps. |
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| Author: | JohnnyDees [ Mon Jan 29, 2018 4:30 pm ] |
| Post subject: | Re: Older temp gauge |
Thanks for the rep!y. The problem is the needle is pegged to hot with no wires on it. If I apply 5 volts it goes to cold if I gradually reduce voltage the needle moves toward hot. My power supply stops at 2.5v and the needle is in the middle. I used a 1.5v battery and it was near hot. So the gauge seems to work. But why does it start at hot (with no wiring on it)? Any ideas? |
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| Author: | wjajr [ Tue Jan 30, 2018 6:45 am ] |
| Post subject: | Re: Older temp gauge |
That is odd, gauge should be pointing at cold with no voltage. My sending unit reads 0.34 ohms on 2000 ohm scale at 60 degrees. |
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| Author: | Charrlie_S [ Tue Jan 30, 2018 6:59 am ] |
| Post subject: | Re: Older temp gauge |
Quote: I just bought an older electrical temp gauge from ebay.
Again, what is the gauge? Is it the correct gauge for the car? Is it an aftermarket gauge? Is it a stock gauge for a different car?
Thanks |
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| Author: | JohnnyDees [ Tue Jan 30, 2018 2:54 pm ] |
| Post subject: | Re: Older temp gauge |
Sorry, I thought I posted that it is an older, 60s 70s dixco type gauge. It looks like other dixco gauges I have just no markings on it. Maybe one they made for someone else. It's a 2" with three terminals on the back. |
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| Author: | Pierre [ Tue Jan 30, 2018 6:02 pm ] |
| Post subject: | Re: Older temp gauge |
If it has a 3rd terminal then I'd guess it takes a sensor to operate normally. Putting just voltage to it without a sensor may not lead to predictable results. If there's no markings on it, how do you know it wasn't meant to be mounted so the needle points down and the pivot is at the top? |
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| Author: | Charrlie_S [ Wed Jan 31, 2018 4:26 am ] |
| Post subject: | Re: Older temp gauge |
If I recall correctly, one terminal goes to switched 12 v, one to ground, and one to the sensor. See if the terminals have markings. It may need a specific sensor to read correctly. I= switched 12 v S= sensor G= ground |
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| Author: | JohnnyDees [ Wed Jan 31, 2018 5:23 pm ] |
| Post subject: | Re: Older temp gauge |
It has a - sign and a + sign and I'm assuming the third terminal is the sender. I was thinking of rigging a /6 sensor to the third and trying it. |
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