Gauges for a 6 volt system

[Wayne S. Johnson]

I'm installing gauges in my '66 Beetle. I found a Voltage gauge with a range of 6 to 16 V, for $22.50 at PILOTSHOP.COM. The 120 A gauge will be replaced with the voltage gauge seen below.

I tested the tach at 6 V, which worked with the display a little dimmer.
The Amp meter and CHT gauges do not require power except for illumination. 6 V bulbs are available, it's easy to make LED replacements.

I have a three gauge panel for oil pressure, oil temp and 12 V battery. All the gauges will be wired with connectors, so I can remove them if I want go to a show with the stock look.

I'm designing a 6 to 12 V DC TO DC converter with a 6 A output. The converter will be connected to a 12 V gel cell to power any additional items requiring 12 V.

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[Bug-nut]

What tach are you using? I'd love to find a 6 volt tach or a 12v one that would work that doesn't cost both my arms and a leg
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1959 Fjord Blue Volkswagen Beetle
http://www.thesamba.com/vw/forum/viewtopic.php?t=6...highlight=

1962 Austin-Healey Sprite

[Wayne S. Johnson]

The digital tach circuit uses an internal 5 V regulator, which requires 6-7 V to operate. Get a tach you like and test it in your 6 V system. If it needs more voltage to operate you can get a 6 to 12 V DC to DC converter for a few dollars on eBay. Depending on the converter output current, you can power several gauges.
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[Wayne S. Johnson]

This is my DC TO DC CONVERTER, 6V TO 12V @ 1A OUTPUT. It's designed stay on all the time to power a 12V CD Player memory or USB charger. The output has a relay to also provide a switched 12V output for gauge power, which is wired to the ignition switch. The input range is 5V to 8V. I measured the current of a digital tach at 0.6 A.

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[herbie1200]

Dear Wayne

For my '63 my choice was like yours but with those three analogic gauges:

Oil pressure
Oil temperature
Water temperature

http://www.ebay.it/itm/52-mm-Triple-kit-Oil-Temp-G...210fc629eb
http://i.ebayimg.com/00/s/NjQwWDY0MA==/z/V7kAAOSwQjZXPhOO/$_12.JPG

Then I used the water temperature connected to the oil temperature sensor, wich range is appropriated.

So I've put the Oil temperature bulb into the waste hot air from cylinder heads, so I have a measurement of air t° from heads, ~head temperature.

I read, under load, 130-140°C.

All gauges feeded with a simple dc-dc converter; LED illumination directly by 6V after stock dimmer.

For Voltage I preferred a digital unit (4$), more appropriate to a 6V because a 16V gauge like your has no efficiency in the 6Volt range.

Choose a voltage meter with separate input for feed and for measurement so you can feed it with the 12V DC (more stable) and check the voltage directly on the 6V battery. It gives precious informations on how dynamo regulator is working.

http://www.ebay.it/itm/Voltometro-Pannello-DC-0-10...FYs25WyC-g

Finally, put a simple LED with a resistor between +ign and the FIELD terminal of the generator, so you can check how generator is controlled.

I will post a photo of my arrangement.

[Wayne S. Johnson]

Hi Herbie1200,

That is a great setup. Have you seen this CHT gauge for $22.50? It requires a $10 sensor that goes under the sparkplug.

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[Wayne S. Johnson]

I found an old stile 2" voltmeter with a 0-10 range. The reading was a bit off at 7V. I adjusted the zero adjust to get a more accurate reading at 6V and 7V.

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[herbie1200]

Dear Wayne,

No, I did not find a so cheap gauge, do you have a link to this? I'm interested, but I found only digital CHTs.

[Wayne S. Johnson]

[Wayne S. Johnson]

I’m installing this trip computer my ’66 Beetle. It’s great to see the MPG in real time at different speeds. The cruise control works well, which improves gas mileage at freeway speeds.

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[herbie1200]

[Wayne S. Johnson]

CHT gauge.
http://www.pilotshop.com/catalog/inpages/cr-001.php?clickkey=3029428

More gauges.
http://www.pilotshop.com
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[herbie1200]

Many thanks! I will add it!

[herbie1200]

Added my CHT gauge. Problem: readings are too low!

Tried it out from car with boiling water and all seems OK.

BUT when in the car I read very low temperatures.

Value starts from 20°C - 68°F and in 5 - 8 minutes raises up to 85°C - 185°F and almost stays there.

Temperature increases only when I'm stuck into traffic, or when engine is shutdown.

So my hypotesis: is my sensor too much exposed to fresh air and, instead of spark plug temperature, measures air temperature?

Thank you.

[Wayne S. Johnson]

A thermocouple senses the temperature where the two wires touch. The output voltage is the difference between the two ends of the thermocouple wire.

Some CHT gauges consider the ambient temperature error to be small enough to not need cold junction compensation. Without compensation the measurement will be the CHT minus the ambient temperature. I tested my Westech CHT gauge using a soldering iron and a Fluke 80TK Thermocouple Module, which has cold junction compensation.

http://www.aircraftspruce.com/catalog/inpages/westcombos-6.php

Ref.
https://en.wikipedia.org/wiki/Thermocouple
https://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

http://www.aircraftspruce.com/catalog/inpages/westcombos-6.php
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[herbie1200]

Thank you, I'm confident about my thermocouple accuracy.

My doubt is that the great mass of fresh air blown in the spark plug zone affects the suspended part of the thermocouple.

The wire couple is soldered not directly on the circle but on a sort of its protrusion, so is exposed to fresh air.

The very fast measurement increase at the moment that rpm drops (~5°C degrees into 10 seconds) take me to consider that the real head temperature is only a far image of what I read on the gauge.

I don't think that a cylinder head really has a so speed temperature increase (thermal gradient?). Instead a little sensor does.

[Wayne S. Johnson]

I would recommend testing the thermocouple and gauge on the bench, I have tested several that read low.

To reduce the cooling effect, bend the lug at the plug edge so the crimped part is against the plug body, use some bear 22 AWG wire to hold the it against the plug. Keep in mind the measurement point is where the two thermocouple wires first touch each other. Leave room for the plug socket to fit.

Probe installation:
http://thesensorconnection.com/sites/default/files...0Guide.pdf

The lugs in this pic are very thick to reduce the cooling effect.

http://thesensorconnection.com/sites/default/files...0Guide.pdf

Testing on the bench:
http://rst-engr.com/rst/articles/egtcht.pdf
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[EVfun]

When I saw that gauge at the top of this thread the first thing that came to mind was Westach. It turns out that isn't one of their gauges, but they do have a small number of 6 volt gauges they build. There is a 0-10 volt meter and a 0-5000 tach for 4 cylinder engines.
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[Wayne S. Johnson]

The EGT gauge I have requires about 1mA, which can be applied using a 1.5V bat and a 10-50K pot. connect the bat and pot with the pot in the hi position, slowly turn the pot until you see the pointer at the operating position. Then measure the voltage at the meter. Look up the Temp. vs. voltage of your thermocouple.

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