Our team needs to lengthen our 6 AWG wires because our PDP is now further away from our battery than we normally place it each year. We know that on the battery side, the 6 AWG wires have to be ~12" or less.
Is there any documentation as to the recommended or required length that the rest of the 6 AWG wire needs to be between the robot’s Anderson connector and the breaker-to-PDP loop? In our case, we may need a run that is 2 to 3 feet long to connect to our battery’s connector (plus the 12" of the battery’s wires).
Also, would this be a scenario where bumping up to 4 AWG might be beneficial? Looking to follow best practices given where our electrical components have now found themselves after some mechanical adjustments
R103-B dictates no more than 12" of cable per leg on the battery.
While there is no requirement in the rules, as a best practice you generally want the total run from battery to PDP to be as short as is reasonably possible. Going to 4 AWG will help to some degree, especially for longer runs, but I don’t have any hard numbers as to how much difference it will make.
6 AWG wire is about 0.4 milliOhm per foot at room temperature. Goes up to 0.44 when hot to the touch. So if your system is drawing 200 Amp and the 6 AWG wires are about two feet each for red and black, voltage at the power panel will be about 200 x 4 x 0.44 = 352 milliVolt less than at the battery terminals. That’s gonna cost you about 200 x 0.35 = 70 Watts that go to heat your 6 AWG leads instead of accelerating your robot.
There is almost no reason to stretch out your 6 wiring. If you look closely, you will find a way to place your battery and PDP/PDH close together. As Rich has pointed out above, there is loss in everything, there is no free lunch. I prefer to think in terms of the “Wire Foot” something that I introduced many years ago. The reference is 10 wire which is .001 ohms/ft. 6 is roughly half of that. So in terms of real loss, 2 ft. of #6=1ft. of 10. At 100 amps, there is a 0.1 volt loss for every wire foot. What you propose is adding three feet (6 feet total, both red and black) of 6 wiring to your robot. Added to the battery cable, that is 8 feet or 0.4 volts per 100 amps. If you stall four drive motors @100 amps each then your total loss will be in the range of 1.6 volts before that voltage is even distributed in your robot. Now, if your robot was already running near brownout and you add 1.6 volts of additional loss, you are just that much closer to brownout protect or worse, reboot. Changing to 4 wire for those runs is about 33% reduction so the change in wire would be only 0.6 volts less loss. You can gain more if you changed the 6 feet of 6 to 2 feet with a small redesign.
The critical factor here is protecting the brownout from occurring. In most cases I would rather trade placement of components for the additional weight of 6-8 ft. of 4 wire.
