View Full Version : Inverters

11-08-2012, 01:29 PM
I didn't want to hijack the thread that just started on batteries ( I am really excited to see the posts on that subject) so I will start this one on inverters. I know I need to carefully size my system, but my question revolves around simplicity and reliability. For those of you that run an inverter on your boat, what system do you use, how easy was it to install, how trouble-free has it been, and what would you buy today for your boat if you were going to do it again? I know some of this has been discussed in the old forum, but for me being new, I would like to hear current thinking. Price is always a consideration, so if you are the type that always buys the very best, humor me and pretend you are like me, a blue collar guy that wants to be able to afford a few beers on the weekend and has to save some pennies to get that done :p


11-09-2012, 04:54 AM
Installation can be as easy or as hard as you want to make it. A basic inverter on an independent circuit is easy. Tying it in to existing 120v circuits gets more complicated. An automatic inverter-charger is probably more complicated yet but would be the easiest to use once installed.

Size: Your inverter needs to be big enough to start what you want to run (fridge), plus smaller loads that may be on at the same time (TV). Your BATTERIES need to be big enough to carry the average load for a given time (your call). Forget about Air Conditioning or Hot Water, while you can find an inverter big enough to run them, the batteries you'd have to carry to make it practical would be VERY expensive (and heavy). I use a 1750 watt inverter and it will run my fridge and everything else I might have on with no problem. It won't run the AC or the water heater.

Get a good handle on your loads; a "Kill-a-Watt" meter (Home Depot) is handy for this. Narrow your selection down to 2-3 inverters and then go online and download the installation manual and read it CAREFULLY. Then go down to your boat and do some head scratching. Most common inverters are NOT safe in the engine compartment, yet at the same time want SHORT battery cables. Accomplishing both "easily" depends on your boat. You'll also want a battery monitor (Trimetric, Link) which will keep track of your usage over time and help you size your new (expensive) battery bank. It'll also help you manage your consumption and charging in the future, so install it in a convenient location. Your batteries will thank you...

In other words, do your homework. It will take more time than the actual installation.

What would I do if I were to do it again?
Currently I have a 12v inverter on 6 golf batteries, which also double as my 12v supply and emergency starting battery. The system is simple, easy to maintain and pretty much trouble free. It's connected to my 120v panel through a manual transfer switch. For most folks I think the only difference needed would be an inverter-charger to automatically charge the batteries when you plug in and which (I think) would eliminate need for the transfer switch. But since I charge from solar the inverter-charger is unnecessary.

Some folks recommend a separate 120v distribution panel for the loads that are on the inverter. It would be nice but I don't have one, my inverter (through the switch) powers the entire existing panel. However I do have to remember to turn the water heater and AC off before switching to inverter, or the inverter will choke.

11-09-2012, 05:30 AM
I have a 2500 watt inverter/charger that was installed from the factory. It is connected to 12 6v lead acid golf cart batteries. That battery bank also serves as my house bank. Mine is wired through a series of relays that control which 120v circuits are powered by the inverter - this takes the place of the separate distribution panel.

You should listen to Mr. Willie. Do your research and do this one time the right way.

11-09-2012, 09:21 AM
I built my system up over time. If I were to do it again from SCRATCH I'd go with a 48v inverter/charger and a big 48v battery bank, with a much smaller 12v bank for 12v loads. I'd have a 12v solar controller between the two so if the 12v became depleted it would recharge from the 48v system. Then I'd install at least 2kw of PV panels (at 48v) to keep it all charged up.

Why 48v? Working with 12v involves currents in the hundreds of amps, and some humongous wiring with it's associated cost and heat losses. That would be less with 48v, and I think more efficient. I'd also like a couple 48v electric motors for propulsion, to replace the heavy, noisy, smelly, messy diesel I now have. Can't do that with 12v.

We can all dream, can't we???

11-09-2012, 10:27 AM
I started to talk about 24v inverters, but thought that would confuse the issue as well as the wiring.

11-09-2012, 10:29 AM

I am still fond of the way that I wired up my boat. I am still working on the final fitting for the inverter, but I will do that in the off season. I imagine that your boat is currently wired like mine was when I purchased it. You probably have a 2+off switch for your power. I replaced my panel and switch with a 3+off. That way I can switch between the Gen, Shore, and Inverter.

11-09-2012, 01:53 PM
I have a small inverter (1200 w maximum) with a dedicated circuit that I use for the TV and sound system. It seems like a good compromise over a full blown install since pretty much everything else either runs directly off the battery or requires a large amount of power (i.e. generator required)

11-11-2012, 06:08 PM
I appreciate all of the comments/advice, the thing that stood out the most to me is the sizing of the inverter. I know I will have to do a study to truly determine the size I will need, but it seems apparent to me it will be smaller than I had imagined. The point that Willie made about not running A/C or hot water spoke volumes to me. I think I may have tried to incorporate hot water into my system. Determining things like this early on helps in the overall design of the physical plant. I am a bit up in the air about 12v - 24v - 48v, as we don't have a system yet the door is wide open but some very good points have been made for different voltage choices. Reading in this thread and the one on batteries really opened my eyes to the costco 6v golf cart batteries. I don't think I would have considered these but now they are seriously on my radar.

I am sadly under-educated on PV panels, that will be an area I have to get up to speed on. Can you just add these to an existing system or do I need to consider this into my inverter purchase?

If you are following this thread and have a system aboard would you list the particulars and let us know how you like the performance of your system.

Thanks again for the comments.

11-12-2012, 11:01 AM
While I think a 24 or 48v inverter bank would be more efficient you STILL need a 12v system to run such things that you can't get in the higher voltages, so in essence you're going to need two battery banks (plus the engine starting battery). A straight 12v system would be a lot simpler, easier, and probably less expensive to put together. The inverter bank doubles as the 12v bank and the emergency starting bank. It'll also be a lot easier to figure out if something goes awry. With 12v you can simply upsize your existing "house" bank and add the inverter. That's pretty much all there is to it. Inverters aren't really that hard to install IF YOU FOLLOW THE DIRECTIONS. An automatic inverter/charger (I think) will eliminate the need for another selector switch.

Solar: Solar is really just a fancy (expensive) battery charger that runs off the sun. You can install it any time or not at all. Solar arrays can be set up to run at any voltage from 12v to about 500v by simply connecting the panels in series. As long as the controller output matches your battery voltage you're fine.

However let's do this one step at a time. Get you inverter and batteries installed, and you can install your solar in a year or so IF you think you need it. As you already have a generator, you probably don't need solar at all. You'll be running the generator for air conditioning and possibly water heating and possibly cooking. At the same time your generator will be charging your batteries through your new inverter/charger.

My boat is a lot smaller and I don't even HAVE a generator, so solar makes a lot more sense. I'm also a bit of a nut about it; my home is solar powered too.

Sizing: The folks with boats your size can give you better recommendations as to the size of inverter or inverter/charger you need and an idea on the battery size. Refrigeration and lights are probably the kicker, modern electronics really don't draw that much. How many refrigerators do you have (and icemakers). Is your lighting LED, fluorescent, or mostly incandescent? Let us know and someone will give you a recommendation.

11-12-2012, 03:22 PM
Read Endurance's post on batteries on the other thread. He explains it better than I can.