Jerboy you have no idea what you are talking about. A 6V voltage drop on a 12V line?
Excuse me? you're the one who has no freaking clue. First look at the resistance for 12AWG copper wire.
http://www.epanorama.net/documents/wiring/wire_resistance.html
I was not quite right on this particular calculation, but you didn't even make a calculation to before making a judgement against me. It all depends on the current draw, because I guessed on wire resistance.
A 12AWG copper wire has 1.87x10^-3 ohms per foot. Say he runs 50ft of cord from his battery to UPS and his UPS draws 20A(which is what fully loaded 350VA should draw more or less)
1.87x10^-3ohms per foot x 50foot =0.0935ohms x 2(wire goes two ways, therefore 50 x 2)=0.187ohms. Ohm's law states that V=I x R. We know R is 0.187ohms and I is 20A. So voltage drop is 3.74V, which is 31% of 12V and this is totally unacceptable. When you push 20A of current through this set of cords, it will always take away 3.74V. It doesn't matter if the power source is 12V, 120V, 277V, 480V or etc. Low voltage wiring is a hell because small drop in voltage means great percentage of total voltage.
What if he use a pair of 12AWG 2.5ft wires to connect the battery outside and used a 50ft of 18AWG extension cord to pull the 120V into his house?
battery side:
0.00187ohms per foot x 2.5 x 2 x 20=187mV, 1.6% voltage drop between the battery and the UPS. Acceptable
output side:
since 350VA is about 3A at 120V, let's say output current is 120V 3A.
18AWG cord has a constant of 7.51ohms/ft
0.00751ohms per foot per one direction x 50ft x round trip=0.751ohms. 0.751 ohms x 3A=2.25V lost on 120V side. 1.8% voltage loss. No problem at all.
wth are you running extremely thin wires to another state? lol!
12AWG is considered a relatively thick cable by most people. Do you have any idea how much 50ft of jumper cable size wires would cost?
oh and also stop calling the UPS (uninteruptible power supply) a PSU (power supply unit).
Oops my bad.
Touser, you don't have to put the UPS outside, just the battery. You can safely run normal cable outside your window to the UPS.
You nor I are in the position to make a conclusion yet. He did not specify length of run or cable gauge. You have to use the copper wire resistance factor, ohm's law, length and current draw to figure out the voltage drop.
Also i wouldn't use a marine battery if i were you, I would use an automotive battery, they love to be constantly charged. not sure if the same is true for marine batteries, are they lead acid? if so then it is ok. I have a UPS that came with its own lead acid battery, same technology as an automotive battery essentially.
Automotive batteries are not designed to be drained beyond 20% depth of discharge. Discharging them further will significantly shorten their lives. They're designed for high current short duration load such as starting an engine.
Its true tho that a 350VA UPS is pretty weak. Get yourself a bigger UPS, then when its internal battery dies and can no longer be charged (5 years more or less) you can replace with an automotive battery or 2 depending on if it is 12V or 24 V
Yes you can physically, but it is not proper for the reason I described above.