# 6 Volt power supply not working

#### Rinconpaul

Joined Sep 2, 2019
6
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

#### be80be

Joined Jul 5, 2008
1,944

Model would be nice

#### dl324

Joined Mar 30, 2015
9,155
Welcome to AAC!

Have you measured the voltage between the wires to make sure you're providing 6V to the input?

It would be helpful if you provided a model number.

#### Rinconpaul

Joined Sep 2, 2019
6
Thankyou for your interest. It's a Sokkisha SET4

#### Rinconpaul

Joined Sep 2, 2019
6
AAC Fanatic, yes 6 volts across wires

#### Rinconpaul

Joined Sep 2, 2019
6
Pics of plug and wider view

#### be80be

Joined Jul 5, 2008
1,944
Your missing something that has a cord made for hooking to a car battery the third pin is for the charger to start or stop and i bet the car battery
Cause There a box that hooks up before any thing else did.

And the 6 volt external hooked to a battery pack with the pin cord
you need find out what the third pin did

Last edited:

#### Rinconpaul

Joined Sep 2, 2019
6
be80be You've been very thorough, and I appreciate highly your assistance. Just above that diagram is the one which shows Cable (6V) EDC3 connected to External Battery. Now I''m using a 6V lead acid battery and the lead is the one between the CDC11D charger and EDC11 battery charging adapter. The EDC11 is the adapter for the small portable batteries which I only have one left. Because the inlet socket at the base of the theodolite is for an external power source which can be a cigar lighter, car battery with a voltage reducer inbetween (12 to 6V) or and another 6v battery or an AC power adapter. Why does it need the 3rd wire. if it's to tell the theodolite something about the charge level or suchlike, how can I modify that to carry out it's duty?

#### be80be

Joined Jul 5, 2008
1,944
It's hard to tell I looked for a pinout on this couldn't find one but I'm betting the third pin switches the internal battery off
So you have maybe 2 pins that need 6 volts and one is ground.

Take the cover off and trace the wire from the plug to see where there going.

#### LesJones

Joined Jan 8, 2017
2,363
If you have the faulty charger then trace the schematic around the area where the charging cable was connected to confirm the black is negative, red is positive and what the blue wire was connected to. Also are you sure that the charger is faulty and it is not the charging circuit in the theodolite that is causing the problem ?

Les.

#### Rinconpaul

Joined Sep 2, 2019
6
OK an update. I did trace that 3rd wire back to the source? It was cutoff inside the plug, so not used! Then why won't it work? A bit more googling to find this, "Your SET Instrument power connector is marked as 6 volts. However the external power needs to be 7.2 - 7.4 volts for the internal battery display to indicate the correct charge state. This is the same voltage range the original SET external battery pack (BDC12) delivered."
So now I need a 12v battery with a dc-dc step down to 7.2 v. You can buy a surveyor brand for $400+. That's US$, for me in Australia that'll cost double that with exchange rate and postage. Anything survey equipment branded is a rip off! I bought the theodolite for the equivalent of US\$75. On to the next phase. Thanks for the replies, much appreciated.

#### dl324

Joined Mar 30, 2015
9,155
So now I need a 12v battery with a dc-dc step down to 7.2 v.
Or you could use a boost converter. How much current does the device require?