bobequus Use the heaviest gauge wire you can find. 12 is great and 14 is good. 20 is too small.
If you are going to use anything heavier than 18 AWG, make darn sure that you have an inline fuse. I have a fuse even with the 18 AWG that I use.
18 AWG is adequate if it is truly 18 AWG and copper, and is short. Most of the cheap spools at Amazon that claim 18 AWG are at best 20 AWG and many don't have much of a copper core.
In my case, I use a 25 ft 14 AWG cable run (SLA battery with a 15V buck/boost converter) in series with a 4 ft 18 AWG cable run just to power my RST-135 (worst case 2A when slewing -- the RST-135 uses a real servo motor, rather than the stepper motor that is used in the AM5, and my mount has a power supply tolerance of 11V to 16V). The 4 ft section is one that has silicone insulation, so that it stays soft even in sub-freezing temperatures. At 14 AWG, the usual vinyl insulation will stiffen too much in cold weather -- even regular 18 AWG will already stiffen too much.
The key is to use a short cable. 18 AWG is 6.4 ohms per 1000 feet. Since the cable also has a ground return, that would make a 18 AWG cable pair come in at 12.8 mΩ per foot. At 5 Amp draw, that would be a voltage drop of 65 mV per foot. A 5-foot cable would represent a voltage drop of 325 mV, which should be within the specifications of even your mount.
FWIW, a 14 AWG wire pair has a resistance of 5 mΩ per foot (compared to 12.8 mΩ per foot for 18 AWG), so you can use a cable length that is 2.5 times longer for the same voltage drop.
Chen
