Mattblack wrote:Just for future reference, what would be the max wattage before the wiring and socket starts warming up...100W?
Depends entirely on what is in there already. It's pretty common to find 120W sockets (12 volts 10 amps), but some of the cheaper ones are not really up to the job. It also depends on the wiring.
At the risk of getting slightly technical, the wire heats up because it dissipates power. The power it dissipates is equal to I*I*R, where I is the current and R is the resistance of the wire. So at 10 amps, it's 10 x 10 x R = 100 x R. Thinner wire has a higher resistance per meter, so it dissipates more power and hence gets hotter. On the other hand, thicker wire has less resistance per meter, so it dissipates less power, and stays cooler.
This little equation (power = Ix I x R) tells us something else, too. Since it goes up with current squared, every time you double the current you get 4 times the power dissipation.
The other problem is voltage drop. Any time current flows in a resistance, there is voltage drop.
Let's say you are drawing 10 amps, and using 2.5mm^2 cable. It has a resistance of say 10 ohms per km. You have 5m of red wire and 5m of black wire to your socket, so 10m all up. The total resistance of your wire is 10 (ohms per km) * 0.001 (km per m) *10 (meters) = 0.1 ohms.
By Ohm's law, V = IR, so the voltage drop is V = 10 x 0.1 = 1 volt. That means that from your 12V battery, your socket is only providing 11V.
If you pull 20 amps, it becomes V = 20 * 0.1 = 2 volts, so now you only have 10V!
And then it gets worse. The crimp terminals, the wire connection to the socket, the fuse, the fuse holder, the socket itself, the plug on the equipment- these all add MORE resistance, and even more voltage drop!
Different equipment has different sensitivity to voltage drop, but eventually, stuff stops working. And because we're dissipating the power in the wire and the socket and plug instead of in the equipment, it all heats up.
All of this is related, and you can avoid all the problems by
- Running good quality, thick cable.
- Using the right crimps, etc
- Picking the appropriate socket. If you want to run 10A, don't buy a 10A socket, buy a 15A socket. That head room helps it run cool. There is less resistance, so less voltage drop and lost power.
Good fishing