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Pascal · 06-11-2008, 08:12 PM

An inverter is one of the best accessories you can add to your boat BUT you're not going to run your aircons even under way.

Air cons use a lot of power and once you do the math, you'll see that it will not work.

FIgure you have two AC units on your boat (under 40', right?), so with the pump that's going to be around 25amps altogether. At 12 volts, that's going to be around 300amps which means that even if you have a 150 AMP alternator on each engine, it's only going to feed the ACs, and nothing else.

Engines off, assuming a 50% on/off cycle, you're going to need about 125 Amp Hours... so.. your typical "marine" batteries will be dead in an hour.

These are rough calculations but you get the idea. Running the genny to power Aircons is much better idea!

now, if you want to add an inverter to power other things, like lights, TVs, fans, microwave, etc... while anchored out, then an inverter and extra batteries is a great idea. I added a 3kw inverter on my boat along with 8 golf cart batteries and my annual generator hours went from 1200 to 300. In other words, the whole thing paid for itself in a year of fuel savings.

When adding an inverter, the entire system needs to be matched : Loads - Inverter - Batteries - Charger - Generator. In other words, there is not point in putting a big inverter to power large loads with too few batteries. Or there having a big battery bank will not work with a small charger or a small generator that can't power a large charger.

usually, most marine inverters also include a high capacity charger so that's one fewer things to worry about. A typical 3000W inverter can usually charge batteries at about 150Amps. So if you're going to use 300 amps, it's goign to take 2 to 3 hours to recharge at night. Now, if you buy a cheap inverter only and rely on your 50 amp charger, it will take 6 to 7 hours to recharge... get the picture? :-)

if you're going to add an inverter and batteries, you need to add what you will power. usually in Watts, convert that to AMPS then AMP/HRS and see what you need.

06-11-2008, 08:12 PM	#2
Pascal Senior Member Join Date: Feb 2008 Location: Miami, FL Posts: 208	An inverter is one of the best accessories you can add to your boat BUT you're not going to run your aircons even under way. Air cons use a lot of power and once you do the math, you'll see that it will not work. FIgure you have two AC units on your boat (under 40', right?), so with the pump that's going to be around 25amps altogether. At 12 volts, that's going to be around 300amps which means that even if you have a 150 AMP alternator on each engine, it's only going to feed the ACs, and nothing else. Engines off, assuming a 50% on/off cycle, you're going to need about 125 Amp Hours... so.. your typical "marine" batteries will be dead in an hour. These are rough calculations but you get the idea. Running the genny to power Aircons is much better idea! now, if you want to add an inverter to power other things, like lights, TVs, fans, microwave, etc... while anchored out, then an inverter and extra batteries is a great idea. I added a 3kw inverter on my boat along with 8 golf cart batteries and my annual generator hours went from 1200 to 300. In other words, the whole thing paid for itself in a year of fuel savings. When adding an inverter, the entire system needs to be matched : Loads - Inverter - Batteries - Charger - Generator. In other words, there is not point in putting a big inverter to power large loads with too few batteries. Or there having a big battery bank will not work with a small charger or a small generator that can't power a large charger. usually, most marine inverters also include a high capacity charger so that's one fewer things to worry about. A typical 3000W inverter can usually charge batteries at about 150Amps. So if you're going to use 300 amps, it's goign to take 2 to 3 hours to recharge at night. Now, if you buy a cheap inverter only and rely on your 50 amp charger, it will take 6 to 7 hours to recharge... get the picture? :-) if you're going to add an inverter and batteries, you need to add what you will power. usually in Watts, convert that to AMPS then AMP/HRS and see what you need.