maximum length of wire?

I have some video equipment i need to power off directly from my
car's
battery. I need a wire that is not too big, because i need to solder
on a special quick-release connector that will be used to easily
disconnect the cable from my video equipment. The cable requires 2
wires inside, one for positive and one for negative on the battery.
The biggest cable i found with 2 conductors, has 2x 22AWG wires
inside. Some tell me that it is too small and some say it will work
no
problem. I don't want the wires to start melting and cause a fire!
The
video gear will draw no more than 1 amp total, directly off the car's
12V battery. My question is, what is the maximum length of cable i
can
use to remain safe? Thnks for your advice.

 

[Lostgallifreyan]

rose250@hotmail.com wrote in news:0c242155-f18b-44b2-8f6d-
c5d8d00682fb@l33g2000pri.googlegroups.com:

I have some video equipment i need to power off directly from my
car's
battery. I need a wire that is not too big, because i need to solder
on a special quick-release connector that will be used to easily
disconnect the cable from my video equipment. The cable requires 2
wires inside, one for positive and one for negative on the battery.
The biggest cable i found with 2 conductors, has 2x 22AWG wires
inside. Some tell me that it is too small and some say it will work
no
problem. I don't want the wires to start melting and cause a fire!
The
video gear will draw no more than 1 amp total, directly off the car's
12V battery. My question is, what is the maximum length of cable i
can
use to remain safe? Thnks for your advice.

Increased length will have more resistance, so the current will fall, it
won't get hotter with increased length, but cooler. Even so, avoid running it
in a tight loop on a reel at full current, if it's loose on the ground it
should be safe, even if slightly over 1 amp. The biggest problem you'll have
is the voltage at the video gear end of the line, it might be low because of
cable resistance. Worse, you might have power converters in the video gear
that convert to other voltages and if the input voltage falls, the power
converter will try to draw more current to maintain the power (which is a
multiple of voltage and current, so as one falls, the other has to rise).

So length isn't the issue for avoiding overheating, but thickness is. Try to
get 20 SWG at least, it should make enough difference. Also, it might be
worth putting a 47,000 ľF capacitor across the video gear end of the cable
with in it, to allow surges of demand in the equipment to be satisfied from a
local reservoir that prevents sharp voltage drops.

Maybe the simplest way is to do the main cable with a run of something
bigger, like heavy speaker cable (fused at the battery end), ending with a
short piece of 22AWG cable to fit the connector. That's not a neat answer but
it's simple, and the short bit won't get hot enough to cause bother if you
have an average current of 1 amp.