Electronics > Beginners

6V EDC cable not powering theodolite

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rinconpaul:
[/img]I have a question in regard charging cable. I bought an old theodolite (20+ yrs old) The charger is stuffed. The theodolite has a 3 pin 6volt socket for external power input. The charger cable with the male plug to suit the 6V power input socket has a black, red and blue wire. I soldered two cables to the black and red and attached via alligator clips to a 6V lead acid battery. Unfortunately it won’t power the theodolite. There was one battery that came with the theodolite that carried a charge, so I know the theodolite works. What is the 3rd wire for and how do I get it the theodolite to accept an external power source? Cheers

Yansi:
What does an old theodolite need power for?

amyk:
1. Make sure you get the polarity correct --- never trust the colours.
2. A "6V" lead acid battery is closer to 7V fully charged.

Check how that third connection is wired on the original battery; it could be a lower-voltage tap to supply some other circuitry, or a "presence" signal, or a thermistor, or something else entirely like a custom DRM chip/1-wire EEPROM (although I'm not sure if that was so common 20 years ago.)

Jwillis:
First guess would be a temperature sensor.Second guess is a communication wire for charge balancing .Third guess is a battery gas gauge.Without knowing the product it difficult to tell. 

Jwillis:

--- Quote from: Yansi on September 02, 2019, 09:09:13 pm ---What does an old theodolite need power for?

--- End quote ---

Some have self levelling ,inclination sensors and digital readouts.

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