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Old 26-07-2009, 06:11   #1
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Battery Banks / Inverter Strategy

Hi guys:

I should close on my boat deal finally this week.

The Chosen One was a marina queen, so only 800 engine hours in ten years and less than 200 hours on the generator, and very well cared for. Upside: she's like new in many respects. Downside: she is not at all equipped for any serious adventures. Including electrical system. She doesn't even have an inverter.

She's a 24 volt boat, which is great. She has two battery banks each providing 220 amp/hours at 24 volts (each bank has four 110 amp/12 volt Varta leisure batteries). The service bank powers the thruster, four electric winches, windlass. The house bank powers everything else. The batteries are charged by a wimpy 35 amp * 24 volt Newmar charger (with a separate 10 amp * 12 volt Newmar charger on the engine start battery).

I guess the designers figured that it wouldn't be too bad for the generator to be running most of the time when not in port -- the boat's got a 6.5kW slow-running quiet Kohler generator, after all. And any motoring wll rapidly charge both banks with the beefy 110 amp * 24 volt alternator. But that's no good on long passages or quiet anchorages, which is the real point of cruising for me. So I need to make some changes.

I was thinking of adding a Victron Phoenix charger/inverter, which will give a 50 amp charge to one of the service banks and provide 2000 watts continuous true sine wave AC power when needed without starting up the generator. I would leave the 30 amp Newmar on the other bank in this case.

The only problem with this is it seems to me that I would want the inverter not on the house bank, but rather on the service bank. I will not need AC power when I'm using winches, thruster, windlass, and that seems like a good way to spread the loads around, since the 220 amp * 24 volt house bank is not so big for a 55 foot cruising boat.

And I'll want the bigger charger on the house, not the service bank since that's where the continuous DC loads are (refrigeration, lighting, electronics, autopilot).

Or maybe the path of least resistance (and most $$$) is just to toss the existing Newmar charger (or sell it) and put on TWO Victron Phoenix's -- one on each service bank. They can be used in parallel which will give 4000 watts of AC power from the batteries if ever needed, and will charge each service bank at 50 amps. I don't quite imagine needing so much AC power, but I guess you can never have too much.

You guys have any words of wisdom? Cheers, Dockhead
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Old 26-07-2009, 06:50   #2
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And I'll want the bigger charger on the house, not the service bank since that's where the continuous DC loads are (refrigeration, lighting, electronics, autopilot).
A new charger would help being a marina queen but means nothing at all cruising. Adding an Inverter will make AC power easier to drain all your batteries. With the number of batteries you have, the ability to recharge the banks fully and properly is limited. You will need to run the generator a lot longer by adding an inverter. You need to work the problem backward. Compute the amp hours used over a period of time say 2 days. Compute when they are being used to find your peak loads and use patterns, then add them all up to make your energy budget. Toss out as many batteries as possible. Extra batteries you don't need is money down a rat hole. They prevent you from fully charging the entire bank. As batteries near full charge the number of amps that can be added drops. It means you never get the batteries fully charged unless you are plugged into the shore power or run the generator a lot. That has it's problems since running the generator with a very light load isn't very good for it either. Time you peak use periods to match when you are running the generator to take maximum advantage of the output load.

As I see it changing the charger out is of little value and adding an inverter means you use more power. You need a plan that computes how much you need to run the generator to top off the battery banks. That requires a close look at how and when you use power. I would leave the two banks as they are with the service bank set for the way it is so you can always have that power available to operate the powered boat systems. Connecting the inverter to it just makes it really easy to leave yourself with two dead banks.

Your existing chargers when on shore will eventually charge the banks is you park long enough. The bigger charger only can shorten the time while on shore and means nothing when cruising.
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Old 26-07-2009, 07:18   #3
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First, I'd say combine your service and house bank. Others may disagree, but the only seperated battery you'll need is a start battery for your generator, combine all the others into one big bank. You'll almost always have the engine running for the bow thruster and windlass anyway.

Get a battery monitor, something like a link 10 for keeping track of them and don't let them below 50%.

2000W inverter is plenty big. Smaller boat, but my 1250W has never been too small, biggest load is the microwave.

I think the point Paul missed about the battery chargers is that you'll need them when charging off of your generator. You'll want plenty of shore power chargers to minimize that run time. But there's a better solution:

Get a few solar panels and an mppt so you don't become a slave to your generator run time. Generators are a nice backup, but don't base your charging plan around the generator. I've seen the look hundreds of times in people's eyes, "Hey, want to go diving?" - "No, I need to run my generator"
"Hey, we're having a cookout on the beach, come on over" - "No, I need to run my generator for a couple hours first"
"hey, we're renting a car and exploring the island.......

Generators are great for running the air conditioner and washing machine, but seriously, you'll thank me in the long run if you don't plan your charging around the gennie, and just use it for an occassional top up.
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Old 26-07-2009, 08:03   #4
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My take is a bit different.

First, your house battery bank (220AH @ 24V) is woefully undersized for a 55' cruising boat away from the dock. I have the equivalent of 337AH on a 42' boat, and it's none too much.

Second, your "service" battery bank may be appropriatly sized, but it's likely to be way underutilized. How much of the time are you using your windlass, winches, and thruster?

Third, your 6.5KW generator is none too large to attempt to power a big inverter charger, much less two of them. The Victron's have a 1.0 power factor, so use available genset power better than, e.g., some Xantrex chargers which have a 0.7 PF. Xantrex recommends a MINIMUM 6.5KW generator to power 100A of charging @ 12VDC!

I like the idea of combining these batteries into a single large house/service bank. That would give you 440AH @ 24V....much closer to the needs of a boat this size. Also, it would simplify the charging. When rearranging the batteries, I'd think ahead for the time you want to replace them with something better and simpler, resulting in fewer interconnections and greater longevity.

I'd go with one Victron MultiPlus inverter/charger. And, a Balmar DuoCharge (or similar device, like an EchoCharge) to automatically keep the separate start battery charged.

One advantage of the Victron is it's Power Assist function when in the inverter mode: it can provide additional needed AC power to start motors (A/C, frig, etc.) beyond that provided by the genset, by drawing on the batteries momentarily as needed.

Toss the existing chargers or keep them for spares.

Finally, congratulations on your new boat. What design is she?

Bill
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Old 26-07-2009, 08:11   #5
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Originally Posted by Fishspearit View Post
Generators are great for running the air conditioner and washing machine, but seriously, you'll thank me in the long run if you don't plan your charging around the gennie, and just use it for an occassional top up.
I can't underscore this strong enough. Gensets are wonderful things, but only when you don't have to count on them! They are cantankerous beasts and Dr. Murphy seems to have a special affinity for them.

One of the things I've learned after two seasons is "more solar!"

As Paul suggested, "work the problem backwards". This is a great time to re-think the boat's entire electrical system. I was amazed how many electrons we burned through. Like money, there's only two possible solutions, get more or use less. If you have Calder's manual, it has a really good chapter for how to plan it out.

Before combining the banks, you're going to want to test each of the batteries and make sure that they're equivalent -- one bad cell in one will pull the rest of them down. The Victron Phoenix is a good unit and will do fine at charging the combined bank.

Have fun!

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Old 26-07-2009, 08:24   #6
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Another plug for combining the battery banks--there is probably a crossover switch which does that, and most live-aboard boats just leave it closed. The number of battery cycles versus percentage pulldown is non-linear, so your batteries will last longer as one big bank. If you connect the inverter to one bank and the charger to the other, you can always open the crossover if something goes wrong.
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Old 26-07-2009, 08:54   #7
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Thanks for all the great, knowledgeable input! I hadn't thought about combining the battery banks -- now it seems to me a great idea. I think they were separated to keep the windlass and/or thruster from disrupting the electronics, but it seems like an inefficient way to do that, doesn't it? As someone said, the main engine will be always be running when these power-hogs are running, and with a 110-amp (by 24 volts) jumbo alternator, there really shouldn't be much drain on the batteries.

To Paul: Yes, as someone said, the idea of more charging capacity is to reduce the genset runtime when charging the batteries. So that I can run all day or at least half a day on batteries, and then charge for an hour or so, and then shut the genset back down again. With the little Newmar charger I would have to run the genset all day, and it will be under loaded, which gensets don't like, and I don't like to hear the d*mn thing all day at anchor. I thought I would want maximum charging capacity compared to the size of the banks in order to optimally load the genset and reduce the run time of the genset.

To Fishspearit: well, you've got no practical choice for charging for a boat this size, than the genset, if you're at anchor and don't want to run the main engine. I hear you about solar and wind, but I don't think I can make much of a dent in the daily consumption without acres of solar panels or an industrial-size wind turbine.
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Old 26-07-2009, 08:57   #8
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Originally Posted by donradcliffe View Post
Another plug for combining the battery banks--there is probably a crossover switch which does that, and most live-aboard boats just leave it closed. The number of battery cycles versus percentage pulldown is non-linear, so your batteries will last longer as one big bank. If you connect the inverter to one bank and the charger to the other, you can always open the crossover if something goes wrong.
"Crossover"? What is that exactly?

Maybe a battery combiner which would open automatically when the thruster or windlass is being used? Hmm.
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Old 26-07-2009, 09:02   #9
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Combine the battery banks. This may sound peculiar but the run time of a generator or engine is less to fully charge a large battery bank than one half its size ( in terms of engine hours to Amphrs). You will be charging at twice the rate after the amperage starts to drop.
For example for a 200 amphr bank you will spend a long period of time at 20-50 amps.
This is equivalent to 40-100 amps for a 400 amphr bank.
This results in less wear and tear and fuel. Also when you use that inverter the Peukert Effect is roughly half so you have a “bigger” battery bank.
I like solar and some wind, I have a 900 amphr battery bank. If the sun is weak I can go a week or more without charging. Then I can charge at an extremely high rate due to the size of the bank thereby loading the engine, preventing cylinder glazing, reducing run time and fuel use.
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Old 27-07-2009, 00:20   #10
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My take is a bit different.

First, your house battery bank (220AH @ 24V) is woefully undersized for a 55' cruising boat away from the dock. I have the equivalent of 337AH on a 42' boat, and it's none too much.

Second, your "service" battery bank may be appropriatly sized, but it's likely to be way underutilized. How much of the time are you using your windlass, winches, and thruster?

Third, your 6.5KW generator is none too large to attempt to power a big inverter charger, much less two of them. The Victron's have a 1.0 power factor, so use available genset power better than, e.g., some Xantrex chargers which have a 0.7 PF. Xantrex recommends a MINIMUM 6.5KW generator to power 100A of charging @ 12VDC!

I like the idea of combining these batteries into a single large house/service bank. That would give you 440AH @ 24V....much closer to the needs of a boat this size. Also, it would simplify the charging. When rearranging the batteries, I'd think ahead for the time you want to replace them with something better and simpler, resulting in fewer interconnections and greater longevity.

I'd go with one Victron MultiPlus inverter/charger. And, a Balmar DuoCharge (or similar device, like an EchoCharge) to automatically keep the separate start battery charged.

One advantage of the Victron is it's Power Assist function when in the inverter mode: it can provide additional needed AC power to start motors (A/C, frig, etc.) beyond that provided by the genset, by drawing on the batteries momentarily as needed.

Toss the existing chargers or keep them for spares.

Finally, congratulations on your new boat. What design is she?

Bill
Thanks -- good advice. Another idea I had -- building on yours -- is to combine the two existing battery banks to use for house, and then just add a whole new bank for the thruster and windlass. This is the exact setup I have seen on some Oysters -- 110amp/h * 24 should be enough for the thruster and windlass, and the new batteries could go forward somewhere reducing the cable runs. Having them on a separate battery bank, as orginally designed, would keep the loads and voltage shocks away from the electronics -- seems desirable to me.

Then I'll have 440 * 24 volts for house (equivalent of 880 amp/hours at 12 volts) which could be charged by the new Victron (maybe 70 amps); I could use the old 30 amp charger for the new service bank.

With both chargers going full blast I guess that would take maybe 4 kW, which is a pretty good load for the generator, close to its practical maximum output. But I doubt if I'll need to charge the service batteries much given the fact, as someone mentioned, that

The boat's a Moody 54. I think I wil use her for a couple of weeks and observe the battery use before making my final decision.
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Old 27-07-2009, 03:50   #11
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Continuing the thought, it looks like bow thrusters like to work with starting batteries, not deep-cycle batteries, which I guess is logical, since you use them for bursts. The Sleipner site specifies that the 11.8 horsepower 24 volt thruster needs minimum 300 cold cranking amps of battery power. So I guess if I made up a new battery bank with two truck batteries, say like the Varta Promotive Silver, even the smallest ones will provide 145 a/h each at 12v and 800 cold cranking amps, so two of them in series will make 145 a/h and 800 CCA at 24v, which should be plenty.

That way I could take the thruster and windlass off the house batteries, and charge the new battery bank with the old 30 amp Newmar charger.

Then I could combine the former house and service banks as you guys have suggested, and voila, I've got 440 a/h of deep cycle batteries at 24v (equivalent to 880 a/h at 12v) for house purposes including the winches. I could charge this with a new Victron Phoenix 70 amp charger/inverter (or is this a little small?).
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Old 27-07-2009, 08:26   #12
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To Fishspearit: well, you've got no practical choice for charging for a boat this size, than the genset, if you're at anchor and don't want to run the main engine. I hear you about solar and wind, but I don't think I can make much of a dent in the daily consumption without acres of solar panels or an industrial-size wind turbine.
Because you have a generator, the point isn't that solar will take care of ALL your charging. The point is that you will be much happier with your life at anchor if you add solar and only have to run the generator occassionally. Figure out what your daily amp-hour usage will be. I have an adler-barbour fridge/freezer, a seperate Waeco fridge, inverter powering a laptop, ssb, windlass, stereo, chartplotter that stays on all the time,lights, electric water pump, etc. and I use about 120 amp hours a day. My 2 solar panels and mppt put in between 50-120 amp hours a day depending on cloud cover. I have no generator, but if I did I would only have to run it once a week or every other week.
Say you use 200 amp hours a day. You can run your generator for 4 hours every single day, or you can add the same modest amount of solar I have and run your generator every few days. Like Intentional drifter mentioned, what's your charging plan for when the generator breaks down? I harp on this because there are lot of people "out there" who leave with the intention of running the generator every day, and the only ones who are happy with it are the ones who have crew to stay behind and maintain the ship while they're off having fun.

And where did you get that stuff about bow thrusters wanting to run off of start batteries instead of deep cycle? An amp is an amp, the bow thruster doesn't care where it came from.
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Old 27-07-2009, 08:59   #13
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(forum wouldn't let me edit the last post)The only reason some people use start batteries for the bowthruster and windlass is because of location, they can put a start battery up there and keep a float charge on it because they rarely get used and always with the engine on. It keeps you from having to run large cable from the house bank up to the bow.
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Old 27-07-2009, 09:06   #14
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(forum wouldn't let me edit the last post)The only reason some people use start batteries for the bowthruster and windlass is because of location, they can put a start battery up there and keep a float charge on it because they rarely get used and always with the engine on. It keeps you from having to run large cable from the house bank up to the bow.
OK, got you on the solar. I'll try to think whether I have a place for it.

Concerning start batteries: these are optimized for this profile of consumption, which is short high amp bursts. Also they are cheaper than deep cycle batteries. I don't know about the windlass, however.
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Old 27-07-2009, 11:50   #15
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That's a pretty big bow thruster, and 300A in bursts is not going to be great with the deep cycle batteries. You're right that they're made for delivery of relatively low amperage over a very long time, compared to start batteries with much more plate area designed to give up a LOT of amperage over a very short time.

So, IMHO, the bow thruster would be fine on start batteries. So would the windlass, while you've got a source so closeby. And, yes, the old charger would maintain this bank just fine.

BTW, I don't subscribe to the thought that "you'll always be running your engine when using the windlass". I like to anchor under sail, and often break out my anchor and leave an anchorage under sail, especially in early morning when others in the anchorage will appreciate your quiet departure. IMHO, the windlass should be able to work with or without a charging source (engine, generator, or battery charger/inverter).

Yes, 70A is probably too small for your newly born house battery bank.

The solar panels are a very good idea, if you have room. So, too, is the power inventory/budget. Look for ways to reduce your electrical consumption. Producing power to recharge the batteries using internal combustion engines is VERY expensive, once you take into account all the relevant costs: POL, periodic maintenance costs, heat losses, amortized equipment costs, etc.

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