View Full Version : Cables connecting battries

06-12-2005, 12:09 AM
What size cables should I use to connect battries on my E20!

06-18-2005, 11:51 PM
the bigger the better!

06-27-2005, 02:40 PM
What size cables should I use to connect battries on my E20!

This is a good method for computing wire gauge:

STEP 1: Calculate the Following:

VDI = Voltage Drop Index (a reference number based on resistance of wire)
FEET = ONE-WAY wiring distance (1 meter = 3.28 feet)
%VOLT DROP = Your choice of acceptable voltage drop (example: use 3 for 3%)

STEP 2: Determine Appropriate Wire Size from Chart

Compare your calculated VDI with VDI in the chart to determine the closest wire size. Amps must not exceed the AMPACITY indicated for the wire size.

AWG| VDI | Max amps
6 | 12 | 75
4 | 20 | 95
2 | 31 | 130
0 | 49 | 170

The complete chart can be found here:

The worst case condition is when your batteries are towards the 0% SOC and you need to pull lots of amps. Both lower volts and higher amps mean a higher % voltage drop. (i.e. % energy lost.)

Since the formula uses a 'one way' distance value, for an ETrak you should add up the total length of your battery cables and divide by 2.
When you run the numbers for say 150A@30V and 'one way' distance of 6 feet your voltage losses would be:
AWG| % V-drop
6 | 2.5%
4 | 1.5%
2 | 0.96%
0 | 0.61%

In the case of an ETrak, I would use a 1% v-drop or better. If you used 1/0 GA, (aka 0 gauge), instead of the standard 6 GA (used in my E12S), you would get a savings of 2% during those high amp loads. And since batteries are least efficient under high amp loads, (Peukert's formula), you will get an additional payback beyond simple wire losses, as your batteries will benefit from a 2% lower peak amp draw.
Going to a larger GA wire is a one-time cost in extra copper versus
lower wire losses and higher battery efficiency every time you use the ETrak.

Craig R. Paynter in Renton, WA