“Hey Krabby - can I buy you a hot rum?”
“Of course you can, it’s about that time of the year. Let me guess you, you have a question...”
“We are decorating our boat for the parade of lights and my husband says we need to rent a noisy smelly portable generator. I was hoping the 2500- watt inverter and 100-amp alternator already installed on the boat would do the job, but he has his doubts. I don’t really understand what that all means but it sounds like it should run a few Christmas lights.”
OK. This will require more than one hot rum and some math too. The math is easy; like what I helped my third grade son with the other day. Lets start with basic review of electricity as it relates to the question. Forgive me if I am telling you something you already know, but electricity can be dangerous if you assume a wire is positive when it is really negative.
Your 2500-watt inverter takes the stored electrical energy from your boat’s batteries in the form of direct current (DC) and converts that energy to alternating current (AC), which will run your lights. Modern inverters are somewhat remarkable thanks to their smart circuitry. They manage the use of energy and shut down before your batteries are depleted or you overload the system by plugging in too much stuff.
So far we have talked about stored energy. If you want to use the inverter to power the lights you will have to replenish the stored energy you will use or you will be limited to the capacity of your battery bank. You have a 100- amp alternator that runs off your engine. 100 amps X 12volts DC = 1,200 watts that your inverter can convert to AC power. This scenario is in a perfect world, not a boat world. You should be safe if you deduct about 25% that will give you 900 watts for a couple hours on the bay. Keep in mind that this includes all the electrical energy you can use in total. You will need to account for additional things like navigation lights and other essential electrical devices you might need while underway.
Now that you know how many watts you have to use, a good idea would be to use LED lights for your decorations. A typical string of 100 lights only uses 8 watts. 8 watts X 20 strings of lights = 160 watts - not bad for 2000 lights.
One last thing, this would be a good time to check out you boats electrical system. Make sure your batteries, alternator and drive belt, and inverter are in good working order and all the electrical connections are clean and tight. If you are not confident enough to do this yourself, hire a marine electrician to help you give your electrical system a once over.
I think I have earned my second hot rum now. Merry Christmas!