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Can somebody explain voltage drop? And how it affects running some new wires in my boat?
Slight correction: resistance of wiring is constant (at a given temperature). Though it is correct that a higher current through a given resistance yields higher voltage drop (in accordance with Ohm's Law: V = I x R).Basically:
there is resistance in the wires, the more current that flows though the wire the more resistance there is, this results in lower voltage at the end
saab?i thank the members of the sheerly academic answer brigade.
i shall now make a reply on behalf of the non-academics....
by the time a wire has done a long lap around the boat from the battery bank it will have dropped a fair bit of voltage, say half a volt. This is nothing to worry about.
However, if at the end of that long wire run is a difficult bit of equipment, for example, a fridge or freezer, you may be on the cusp of getting a problem.
So if you are running new wires and its going to be a long run: Battery bank to switchboard, to other side of boat then look carefully at the wires already installed and try to buy a thicker one.
If you go stupidly thick they will not fit through the existing conduit and will be very expensive.
If your new wiring is for a shorter run, or for a small drawing unit just buy the same size wire as you already have.
I'm pretty sure he was describing measurement under load. In fact, his methodology doesn't really serve any purpose if the circuit is not under load, since there would be no current flow.Iowa-
It makes a whole lot of difference when you measure the voltage drop under load. Not just the drop in the bare unloaded wires, but the actual drop when the device at the far end is pulling power. Drop under load will usually be much higher than drop on bare wires. Neither one is good.
You are right - my statement that no current would flow in a no load condition is a bit of a simplification, since the meter draws a minuscule amount. However, my point was merely that Iowa's useful suggestion to measure the voltage drop across a component (like a wire) would only be meaningful in a loaded condition (as he mentions) for precisely the reason you state in your solar panel example.Rusty, even with no load but the multimeter, that's still "a" load, and current will indeed still flow. If it didn't, you couldn't measure anything. The problem is that modern electronic multimeters are very high impedance, very low load, which is a mixed blessing.
Put on one on the leads from a solar panel 1/2 hour before sunset and you may measure 12 volts. Now hook up a light bulb...and watch the voltage drop to 7 volts.