Inverter/battery advice for a newbie

I have been advised to yank my generator as it sat for 10 years without running, it in a difficult to service location, and is generally overkill for my needs. The idea pitched to me was to install an inverter for use when shore power is unavailable. The only draw would be the 10 gallon water heater, a 110v norcold freezer, occasional smartphones, or laptops, occasional use of an air compressor.
My reefer is 12/110 and I am beginning to convert all interior lighting to LED.

I use a bank of 2 ea 8D batteries for hotel and 1 ea 8D for starting.

The same individual suggested swapping the 8D's out with six deep cycle marine batteries in three banks of two.

My main questions:
Are there "in line" inverters that install between the DC and AC systems so that you continue to use the existing 110V outlets, or do you have to plug directly into the inverter? (deal breaker)


Thanks in advance for any thoughts or ideas.

Jmitchell said:

I have been advised to yank my generator as it sat for 10 years without running, it in a difficult to service location, and is generally overkill for my needs. The idea pitched to me was to install an inverter for use when shore power is unavailable. The only draw would be the 10 gallon water heater, a 110v norcold freezer, occasional smartphones, or laptops, occasional use of an air compressor.

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My first question is "Why"? Does the generator still run, if so leave it in place, service or repair it!! Going to a 12 volt system without a generator to back it up, has as many drawbacks as advantages. First off, it would significantly decrease the resale value of your boat. An inverter has it's place, but must be used judiciously they can be power hogs. Inverting 12v x 110v is very inefficient, you would need to add a lot more battery capacity than what you have to power your fridge and water heater for more than a day or two on the hook.

There are lots of people who swear by golf cart batteries coupled with inverters and change them out every 4 or 5 years. I personally stick to lead acid 4-D's and 8-D's with an average life span of 8 to 10 years and use the inverter only when the main engines are running. Living off an inverter at anchor with no generator will drastically shorten the battery life.

But pick your poison, either way you will eventually pay for the power you use . Best advice is get the generator running.

Hey Bud, this book was recommended by several members and I picked it up. Would highly suggest you try and locate one also, tons of good info!
Boatowner's Mechanical and Electrical Manual by Nigel Calder.
Good luck and welcome!

Crusty Chief said:

Hey Bud, this book was recommended by several members and I picked it up. Would highly suggest you try and locate one also, tons of good info!
Boatowner's Mechanical and Electrical Manual by Nigel Calder.
Good luck and welcome!

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Yes, start with this book. The first three chapters cover all your issues in comprehensive and easy to read detail. A must-have-on-board tome anyway.

Here are my thoughts, starting with the last question:

Yes, what you want is an inverter with a transfer switch. You rewire your incoming shore power to go to the inverter and then to the main A/C panel. When there is no shore power voltage present (you are not plugged in) the inverter takes over and supplies power to the panel.

I am not a fan of Xantrex, but they have a new model inverter, the XM1000 and XM1800 which would do your job nicely.

You have some big AC loads. How do you operate your water heater without a generator now? Trying to heat water will take a lot of amphours, about 100 or so to heat up one 10 gallon tank full of water.

Your 120V freezer is probably your next biggest load. Small in AC amps, maybe 1 or so, but since it runs all day, at a 50% duty cycle it will take a 100 amphours per day to run.

It would take all of your house battery capacity to run these two appliances for 24 hours from an inverter. And after 24 hours, how would you recharge them? Run the generator, right!!!

Get the picture, big A/C loads or even small loads that run all day need lots of amphours.

But how long do you need to be away from the dock? For one or two nights, the water should stay hot. Look into an Engle 12V freezer. These have good insulation and an efficient cooling unit and should use half of the power of your Norcold unit.

And finally 8D batteries are for starting and except for high end manufacturers like Lifeline, few 8Ds are deep cycle. The best bang for the buck is golf cart batteries as your friend recommended.

David

Here's how we do it (The opposite of what most people on this forum do):

We have a 12v Inverter/Charger rated @2500 watts, which feeds a Inverter service panel which most of our 110v loads are on except for water heater, davit, water maker, etc. Those are on the 240v panel and 110v non- inverter service panel.

Anytime were cruising or at anchor we run the generator which gives us AC and all those other amenities. If our genny brakes down (Hasn't yet, knock on wood) we have a 270A Lecce Neville alternator which would take over charging needs. We also have 8-8D Lifeline batteries rated @255Ah's each which gives us the ability to "Rough it" if the genny breaks down.

So to summarize, run the genny, it's good for it!

OK, I'm going to provide a different minimalist view of inverter operation. My boat is almost identical to yours except I have no built-in generator. I have a 34 ft Californian designed for 12V and propane in the late 70s.

I have a Honda eu2000i gas powered generator. I have a 1000W inverter which delivers power to one countertop of appliances through a dedicated line and completely separate from the boat's 110V system. No transfer switch required, but I plan to install one soon to minimize the switching of power strips to the needed plug outlets.

My stove is propane, heat is propane, #1 fridge is 12V/110V that switches automatically, #2 fridge is 110V only (my major power pig), Kurig Coffee is 110V (1500W, gen only), Mr. Coffee is 110V (600W and inverter or gen capable...you can tell I like coffee!) and my microwave is 900W (inverter or gen capable). My water heater is 110V shore power or stbd engine powered. I have a 120A alternator on my stbd engine, so when I heat water, I'm providing a good charge to my house bank.

Like you, I had 3 8D batteries, one for start of both engines and two dedicated to house use. I replaced the 2 house 8Ds with 6 golf cart wet cells as you described. I gained a 50% capacity increase in the identical footprint of the 8Ds.

My #2 apartment size fridge requires approx 90-100 AH +/- per day. My total daily need is 175-185 AH/day. I use my stbd engine to provide hot water since it's not really efficient to run a water heater on an inverter.

To live onboard with BOTH fridges operating, I need about 5 hrs of gen operation with my 55A shore charger to meet my daily needs. This comes in the morning, afternoon and evening when the battery needs are the greatest and the charger provides the most output. If I move the boat, I gain charging through the alternators, reducing the Honda gen operating needs. As the batteries approach 80% charge, their acceptance rate decreases to the point that I can't get more than 10A/Hr into the batts. So the gen time is best utilized providing higher charge rates and I live between 50% and 80% on the charge curve.

If I had a built-in gen, I'd keep it, even if it was pickled for future use. I would not remove capabilities if not needed. If your needs change in the future, you could always recommission it.

My recommendation would be to get a Kill-A-Watt AC meter and a DC ammeter and determine your true electrical needs. Buy the Niger Calder book and study it closely. Then, when you have questions, post them here. Please keep us posted!!

I agree with Eidelweiss, if it will run or is reasonably repairable why spend a bunch of money to take it out? Surely having it working will increase the value of your boat whenever you sell it.
Good luck either way.

I say repair the genset.

Yes, you can buy an inverter with a built in transfer switch or you can buy an inverter without a built in transfer switch and add an external transfer switch.

The main problem with your idea is, you would need a bilge full of batteries to run an electric water heater and a freezer as well as a refrigerator. You would also need a way of keeping these batteries charged and the standard alternator on your engine isn't going to cut it.

Inverters don't provide "free" power from batteries. It takes roughly ten times the current (in amps) from the battery to provide an amount of current at 120 volts AC. That is, if you have an appliance that draws 15 amps at 120 volts AC (think electric water heater), it takes roughly 150 amps DC from the battery to supply the appliance. Figuring not discharging your batteries more than 50%, a 300 amp hour battery bank would only run this appliance for one hour before the batteries would need to be recharged.

I think I have the power problem solved, just plug your battery charger into your inverter. There, wasn't that easy, surprised no one else hasn't thought of it

Jmitchell said:

I use a bank of 2 ea 8D batteries for hotel and 1 ea 8D for starting.

The same individual suggested swapping the 8D's out with six deep cycle marine batteries in three banks of two.

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Just addressing this part...

An 8D for each engine might be overkill. A Group 31 for each with decent cranking amps might be fine. Check engine MCA/CCA requirements, and starter motor cranking amp requirements...

Two 8Ds in parallel on the house side might be giving you approx. 490 Ah (2x245, from memory...). Six 6V golf cart batteries (e.g., T-105s) in series/parallel would give you approx. 675 Ah (2x225), take up approx. the same space (maybe a little less) and each battery would be much easier to shuffle about. And somebody also made the point about 6V GCs being true deep cycle batteries...

If all your batteries are in roughly the same space, you might even be able to reuse more 8D space for 6Vs, maybe a bank of 8 if you like, assuming that G31 thing would work to start your engines...

-Chris

Edelweiss said:

But pick your poison, either way you will eventually pay for the power you use . Best advice is get the generator running.

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Agree. With the generator you have options. It is the best of both worlds kind of thing. A good battery charger, alternator set up, inverter, and batteries will give a lot of flexibility. Wind or solar generation is about all you could add to that. Why not have all the power you need on tap? Just makes sense to me.

I really thought I would have gotten some play by charging your batteries from an inverter..
I only have my tv and cable box on the 1500 watt pure sine wave inverter. All else genset or 12 volt.

Mule said:

I really thought I would have gotten some play by charging your batteries from an inverter..
I only have my tv and cable box on the 1500 watt pure sine wave inverter. All else genset or 12 volt.

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Actually I thought it was funny..

But then I was told to search for a skyhook as a Cub Scout.

Reminds me of snipe hunting. We had fun with that in my Sportsman's Club in high school.

...and a metric Cresent wrench.

Go down to engineering and get me a tub of relative bearing grease was always one of my favorites.

The good prop wash is hard to get due to it's rather aggressive nature, you should expect to have to fill out an "I-D-10-T" form before they will let you have it.

When I was in Air Traffic Control, the newbie would be sent to the Airfield Operations Office for some flight line, the key to the approach gate or radar polish.

I smile just thinking of those poor newbies just after the FAA ATC Strike of 1981.

Jmitchell said:

The only draw would be the 10 gallon water heater, a 110v norcold freezer, occasional smartphones, or laptops, occasional use of an air compressor.
.

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Those are some potentially hefty power loads, particularly the hot water heater. I don't think a house battery bank of a pair of 8Ds will cut it. Even if they could handle that load through an inverter they will run down pretty quick. So unless you're going to be running your main engine(s) every day for several hours going someplace, your house bank will never get a sufficient recharge unless you're on ground power long enough to do it.

We have a generator and soon after we bought the boat in 1998 we had an inverter/smart charger installed to replace the boat's failing original dumb charger. The inverter/charger is a Heart Freedom 25 with a 2500 watt inverter. We almost never use the inverter other than charge electronics batteries and maybe use the microwave to heat a cup of coffee underway. We use the generator to heat water and throw a charge into the house bank on the days we don't run the engines going someplace. The 10-gallon Atlantic Marine hot water heater is 120vac or heated by the coolant from the starboard engine.

So an hour on the generator heats water that will last about 24 hours (unless we use it up) and tops off the house bank charge. On the days we go somewhere we don't need to run the generator at all.

The boat we used to charter had no generator, only an inverter. Having had a generator now for a bunch of years, we would not want to be without one for a number of reasons, most of them covered by previous posters.

If the diesel unit that came with your boat is non-functional and you don't want to spend the bucks to fix or replace it, then the route suggested by Al is a smart one. Get a portable generator rated for your maximum AC load, carry it and its fuel in a safe place, and you're all set. You can run your AC stuff and charge your batteries, too. The newer generations of Hondas (and perhaps other makes) are very quiet to boot.

High Wire said:

...and a metric Cresent wrench.

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Good one, took me a second to catch it.

ranger42c said:

Six 6V golf cart batteries (e.g., T-105s) in series/parallel would give you approx. 675 Ah (2x225), ...

-Chris

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Edit/typo correction: Six 6V golf cart batteries (e.g., T-105s) in series/parallel would give you approx. 675 Ah (3x225), ...

-Chris

You guys forgot being sent (on a Navy ship) to the Bosun locker for 200feet of shoreline, or the electrician/electronics tech striker sent out to look for 115v Fallopian tubes...

I know that you guys are having fun. But has anyone noticed that the OP has not responded after 21 replies, some asking questions about how he uses his boat?

I think we drove him away.

David

I sorry OP...please come back...

ranger42c said:

Edit/typo correction: Six 6V golf cart batteries (e.g., T-105s) in series/parallel would give you approx. 675 Ah (3x225), ...

-Chris

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And you can use only half of that before recharging.

Yep, and I try to leave a 65% charge instead of half.

The original poster is at the very beginning stages of putting this all together. He is talking about specific batteries (an 8d) not its capacity in amp hours. He talks about configurations of banks, but again not capacity. Configuration is how we figure out how to make it fit into a particular space, not whether it can supply a particular capacity. It's okay, we all start somewhere, but we have to give the original,poster an idea as to whether it is even feasible.

In short, it's possible, but not easily feasible without a very significant investment in charging, battery capacity, wiring and load planning. The red flags in this scenario center primarily around large energy consumers. Large energy consumers are first any load that generates heat. Specifically in this case the water heater. A water heater can consume roughly 75 amp hours from cold and another 50 to reheat from warm. For three or four showers in the morning plus morning dishes it's possible we're talking over 150 amp hours alone. A coffee maker is a surprisingly large load and can consume 20 amp hours. A fridge/freezer easily takes 150 amp hours each day. So right there with some very rough math we get a daily load of 320 amp hours. How much battery capacity do we have? Two 8d batteries are in the neighbor hood of 450 amp hours, but we can only use about 50% of that when really needed or about 225 amp hours. For lead acid batteries that we want to last, we actually should not even go to 50%, so let's call a normal daily load closer to 200. Already, we have seen we have 120 amp hours in load more than we have capacity to supply, but we have not even considered everything:
-what other loads do we need to supply? Will anyone try running a hair dryer? Curling iron?
-What kind of compressor?
-what about cooking, do you use propane?
-what is our charging capacity? We need to put back over 300 amp hours this day and that could be over 6-12 hours with a standard 60 amp alternator or battery charger.

The point is that each of us will have to do some very specific math. Those of us using battery power for large loads, tend to track and husband each load and amp hour expected to be used. You will need a worksheet and a plan for both consuming and charging. Nigel calders book is a great place to start.

This can work. I have a 1200 amp hour bank, sometimes cook with electric and top up the temp of the water heater once in the morning, and can often get by with either running the boat or a generator for two hours each day to get most of the load replaced. By the third night, I either need about six hours of engine running or generator to charge back to full capacity.

It can be done, but it's not cheap or simple. Having a generator for most people is the best option and using the inverter at night when you don't want to make noise.

Thanks ghost, that was so well explained even I got what you where saying. Not everyone comes to the table with the requisite lingo and it's refreshing when someone understands the subject well enough to be able to break it down.

Agreed!! Great explanation of the underlying fundamentals, Ghost.