In the last chapter I explained Ohm's Law, that wonderfully elegant and simple relationship between three variables that allows us to clearly understand just about any problem we have with our boat's electrical system.
Now let's look at some practical applications: how batteries charge and voltage regulators work—two of the most misunderstood pieces of gear on a voyaging boat.
To make this easy, we are going to use lead-acid batteries in all or our examples. Yes, I know, you want lithium. That's fine, we will get to those in a later chapter and the stuff we learn in this chapter will make understanding lithium systems way easier.
First we need to do one of those algebra trickery things (that we all slept through in school) so Ohm's Law will get us the answer for any one variable as long as we know two others:
That is:
- Amps equal volts divided by ohms.
- Ohms equal volts divided by amps.
- Volts equal amps multiplied by ohms.
Real World
Now let's say:
- Our system is 12 volt.
- Our lead-acid battery bank has 400 amp hours capacity and is half discharged.
- We are sailing along using 20 amps for various loads.
- We have 200 watts of solar panels and it's sunny so they are putting out 100% of their capacity—unlikely, but it doesn't matter for our purposes.
- We have a 100 amp alternator on the engine.
- Both the solar panels and the alternator have regulators.
