Converting on-board battery to external power
There's nothing worse than a battery running dead in the middle of a great night of imaging (or other endeavours). Many pieces of equipment come with a 'wall-wart but for those that don't you can convert them to use one... or use the same 12v that powers your telescope.

Not every piece of equipment can be modified, but most can. What you have to do is look at the schematic diagram for the gear (if you can get it) or study the printed circuit board. What you are looking for is either a largish, square, three-legged chip with a metal flange (possibly attached to a heat sink) that is labeled something like 7805, 7806, 7808 etc. The smaller version of this chip is a small, black, cylindrical part with a flat on one side labeled 78L05, 78L06 etc. These tell you that the voltage from the battery is being 'stepped down' to operate the equipment.

If you've found a voltage regulator as described above you can modify the equipment. First obtain a DC plug, I get mine from old broken pieces of gear that I cannibalize; but they're available. These have three leads on them. One on the back end which is positive, and two somewhere on the body; one of which will be 'switched' and the other which won't. To find the switched lead plug in a matching DC jack. You'll be able to see a lot of the barrel of the jack. Now use a multimeter and check to see which of the plug's leads has continuity with the barrell and which doesn't. The one that does is fixed and the other one is switched.

What you want to do now is to find out where the battery power runs onto the circuit board. When you've found it un-solder the negative wire from the board and solder it to the switched lead on the DC plug. Now add a new wire from the positive on the plug and connect it to the same place as the positive from the battery. Another new wire will now run from the fixed lead on the plug to where the negative lead was soldered to the board.

What you have now is a 12v source that breaks the circuit to the battery when it is plugged in. Why? Well, not many 9v batteries will enjoy being 'charged' by a 12v source; so you want it disconnected when you plug in your externl power.

That's about it. Now you can power your unit for hours with no worry about the battery dying mid-exposure.

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