JohnMuchow
Joined: 25 Aug 2004
Posts: 21
Location: New York City, USA
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quote:
Originally posted by Team Hell Bent!:
How many amps contin can 12g wire handle?
You can pull 40A without melting the standard plastic insulations (PVC, etc.) but you can pull a lot more current if you use silicone-insulated wiring. It has a temperature rating of 150-degrees C (occasionally 200-degrees C.) vs. a max. of 105-degrees C. for the plastic insulations.
In addition, silicone insulation may be thicker than THHN and the other very thin insulations, but it takes a lot of abuse.
But, the voltage drop in 12AWG wiring might be a problem, even if the insulation isn't melting. Be sure to check the resistance of the wiring you're considering using and calculate the voltage drop (current times resistance). Whatever this value is, it's not getting to your motors. It's just being dissipated as heat. If you have a lot of connectors, you may need to factor in any voltage drop across them too. Typically, this is only a concern at really high current levels though.
An example:
12AWG = 1.71 ohms/1000ft. (depending on the stranding)
8AWG = 0.752 ohms/1000ft. (depending on the stranding)
If you have 3ft. of 12AWG wiring (18 inches out to your motors and 18" back to the batteries), then the total resistance is .00171 x 3 = .00513 ohms. With a current level of 40A, the voltage drop thru the wiring is 40 x .00513 = 0.21V. Not too bad. But at higher current levels, lets say 80A, the voltage drop is 0.42V and this doesn't even take into account the voltage drop of any connectors, the battery's internal resistance voltage drop, and any drops caused by the battery bars or inter-battery braid. It adds up quick and can easily cause enough of a voltage drop to really affect the max. speed of your motors.
Using the above example, at 40A, 8AWG wiring only has a voltage drop of .09V, almost nothing.
If you have room for the larger cable and can afford the extra weight (and cost), I always recommend going to 10AWG or 8AWG for a typical LW. The cable runs cooler, last longer (more durable), and the voltage drop is lower. _________________ John Muchow, CamLight Systems
http://www.camlight.com
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