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Know Your Coaxial Connectors
By Michael Covington - 12/28/2005
"The trouble with standards," someone said, "is that there are so many of them to choose from."
That's certainly true of the coaxial connectors that telescopes use for DC power. Make a mistake, and you can fry your telescope's circuitry.
Both the inside and the outside diameter of the connector can be any of several sizes. Celestron 12-volt plugs, for instance, are 5.5 mm outside and 2.1 mm inside, with the center positive.
Meade plugs are like Celestron but with a 2.5-mm inside diameter. This means that if you connect a Meade power supply to a Celestron telescope, it will work, but the connection will be slightly loose. This can cause very erratic performance with computerized equipment.
There are also plugs with outside diameter 5.0 instead of 5.5 mm. They will fit in the sockets, but, again, they're a bit loose and give an unreliable connection.
SBIG CCD cameras have the same connector as Meade - 5.5 mm o.d., 2.5 mm i.d. - but the polarity is reversed; the center is negative. That means an SBIG power supply can seriously damage a Meade telescope, or vice versa. I'm told that SBIG equipment has fuses to protect against reversed polarity, but older Meade equipment does not. So be careful!