Kim, don't ask Luke what size wire, or you'll end up with an extra 20 pounds on that cruiser.
The Turnigy 6s-5000 packs use 10-gauge wire and 4mm bullet plugs. I'd use 10-gauge from the LVC boards to the controller, etc. which are fairly close in your setup.
Although I have your LVC boards built, and ready-to-go, I'm holding off sending them to you until I get I the HVC and balancing stuff sorted out. Based on some things I did yesterday, I may add the HVC logic to the pack-resident LVC/4p adapter board, and then put the cutoff circuit with the small adapter board that combines the charge leads with the two balance plugs, into the single 18-pin charge/balance connector. I had planned to include this on the balancer board, but this is changing.
Yesterday I received the four 6s Battery Medic
balancer units I ordered from HC. These are pretty amazing little units. They are tiny, compared to the small 6s 50W balance chargers (about 1/3rd the size...), but they have much larger displays that also include graphics. They also have double the balance current. I took apart one of the Turnigy 6s 50w balance chargers I received a couple days earlier, to measure the shunt resistance used. It just didn't seem like it was using the 300mA of balancing current they advertise. It turns out each channel has six 120 ohm resistors in parallel, which is about 20 ohms, so the max current is only about 200mA, not 300. I then popped the case off of the new 6s balancers I just received, and it has ten 100 ohm shunt resistors in parallel, so 10 ohms. That means 400mA is the max, which is closer to the listed 450mA max, shown on the web site. Here's what these look like, along with a AA cell for size comparisons:
One of the big problems I've had with RC-based balancers, and balance chargers, is that they balance to whatever the lowest cell is at, not to a set voltage. What happens is that you end up with the 6s blocks in the pack having different voltages. This balancer, however, also has a balanced discharge mode as well, which lets you balance to a fixed voltage point that is settable from 2.0V to 4.2V in .1V increments. Problem solved.
What I'm looking at now is simply doing a 6s shunt "booster" unit for each of these that will boost the shunt/balancing current up well over an amp. That will perfect for even the largest capacity ebike packs. I'll be testing this idea this weekend.