This might be more of a conceptual physics question, but is it possible to use a battery charger directly as the power source if you are controlling a ROV from land? Mainly: is the charger just a simple AC to DC converter? If so, the question I then had is how can the charger define both the voltage and the current without knowing what resistance it is being attached to and still be consistent with Ohm's law? I've heard somewhere that the amperage listed is just the maximum possible current...not sure.
Also, when I was doing testing using a battery charger I wanted to see how the voltage drop was across my tether, so I measured the voltage across the charger and got 12.6V, but when measuring the voltage across the tether I got 14V...is there some reason for this or is my $10 multimeter just giving me bad readings
Using a battery charger directly as a power source
Re: Using a battery charger directly as a power source
Using a battery charger won't give you good results. A typical battery charger consists of a transformer (to step the voltage down) and a diode(s) to "rectify" the current. But AC (at least here in the united states) is cycling at 60 times per second, then the diode only allows current to flow in one direction (think one-way valve) to charge the battery. This means the output is not actually Direct Current; it's pulsed current at 60 pulses per second.
As for the 12.6 volts to 14 volt rise, it's because of the 60 Hz pulsed output of that charger. Those pulses are rounded on top (a throw-back from the original AC source current) When your meter sees that it recognizes it, and gives you the average voltage (called RMS), but at the other end of the cable you see 14 volts because the cable has inductance (kind of a flywheel effect) and smooths out the current just enough to where your meter doesn't recognize the pulses, so it measures the peak of the pulses instead.
As for the 12.6 volts to 14 volt rise, it's because of the 60 Hz pulsed output of that charger. Those pulses are rounded on top (a throw-back from the original AC source current) When your meter sees that it recognizes it, and gives you the average voltage (called RMS), but at the other end of the cable you see 14 volts because the cable has inductance (kind of a flywheel effect) and smooths out the current just enough to where your meter doesn't recognize the pulses, so it measures the peak of the pulses instead.