Battery Bank considerations/advice : 38 ft yacht

[MS_Adventure]

Hello All, I am looking for some guidance/advice please: I am just finalising the purchase of a 38ft yacht (Moody). One of my first tasks (as we prep it for living aboard and extended cruising) will be to review the battery bank. In place today are 3* domestic + 1 * starter battery. I am a novice in terms of battery knowledge, so some questions that have come up so far (and I'm sure there will be many more) are below. In summary, some general advice on how to set up a reliable, efficient and cost effective bank would be very much appreciated!

- how many domestic batteries are needed?
- what Ah should I be looking for?
- what type of battery is optimal (all AGM?)
- do non-marine batteries suit? e.g. golf cart batteries? caravan leisure batteries?
- is it useful to be able to connect them all (+starter) in series? And what benefits does that bring?
- what are the isolation considerations?


Thanks

 

[nortada]

Hello All, I am looking for some guidance/advice please: I am just finalising the purchase of a 38ft yacht (Moody). One of my first tasks (as we prep it for living aboard and extended cruising) will be to review the battery bank. In place today are 3* domestic + 1 * starter battery. I am a novice in terms of battery knowledge, so some questions that have come up so far (and I'm sure there will be many more) are below. In summary, some general advice on how to set up a reliable, efficient and cost effective bank would be very much appreciated!

- how many domestic batteries are needed?
- what Ah should I be looking for?
- what type of battery is optimal (all AGM?)
- do non-marine batteries suit? e.g. golf cart batteries? caravan leisure batteries?
- is it useful to be able to connect them all (+starter) in series? And what benefits does that bring?
- what are the isolation considerations?


Thanks

If you connect them all in series you will have a line voltage of approvimately 48v, which won’t be too good for many of your 12v devices️

 

[sarabande]

The topic is well covered in many websites and forums.

This is a good and comprehensive summary of batteries and boats.

https://www.yachtsurvey.com/boat_battery_basics.htm

and would be good homework.

You need to list all your devices, and the expected daily consumption to reach a "how many" answer, but I would be surprised if Moody had got the answers wrong in their specification.

If the batteries and electrics are in good condition, then buy yourself a good multimeter (one with a clamp ammeter would be useful), and start recording the voltage before, during and 24 hours after, a charging session by engine or shore power. You then have a basis for making any changes if they are needed, but so many variables that it is not poss to comment in detail without having some metrics.


What is the present configuration (size, type, condition etc) of the batteries ? What is the size of the alternator ? Any battery management device ? What shore power charger is installed ? What are you planning to add e.g. freezer ? Do you have solar/wind power ?

Fill in the blanks with as much detail as poss, and targeted help will be forthcoming.

 

[MS_Adventure]

Great - thanks for the info. I will supply some further details re: the current setup when I am next aboard.

 

[macd]

Advice above is good. I'd suggest your demand/supply inventory should be on the basis of what you plan to fit, not on what's already there.

In brief:
- how many domestic batteries are needed? The number is more to do with available space and the weight you'd want to carry...
- what Ah should I be looking for? ...because total Ah is what you're looking for. Bear in mind that a 100Ah lead-acid battery should usually be regarded as offering only around 50Ah of useful output.
- what type of battery is optimal (all AGM?) Much will depend on your budget. AGM are expensive but good (although being an AGM won't make a badly-made battery a good one). But they are not all the same: for domestic use go for deep cycle AGM, or deep cycle open lead acid. The latter are more easily monitored, at some small cost to your spare time...
- do non-marine batteries suit? e.g. golf cart batteries? caravan leisure batteries? Any battery describing itself as "marine" is probably lying. So yes, esp anything designed to be heavily discharged. "Leisure" is so abused a term it means little.
- is it useful to be able to connect them all (+starter) in series? And what benefits does that bring? Not in series, as said. The main desire is to be able to use either bank to start your engine in an emergency. You'll also need to consider whether you want dedicated batteries for any windlass/bow thruster and how they might be integrated.
[/QUOTE]

 

[Pavalijo]

Hi Michael,
We have 345 ah in the house bank which we have found absolutely fine for summer live aboard use (May- September inclusive) when coupled with our 240w solar array via mppt.

We have a low wattage kettle that we use via the inverter when at anchor and rarely see the state of charge at less than 85% each morning. We do have an efficient fridge with beefed up insulation which helps.

We did try using the induction hob through the inverter for a short period but on a grey day state of charge dropped to 60% and with grey days following was slow to get back to 100%. I had assumed that the power settings from 400 rising by 200 increments was a wattage display but it turned out that the hob just cycles on and off at 1800w, more on time at higher settings.

When I was researching our fit out it seemed that many cruisers have an extra 100ah or more than we now do, but we have limited power requirements at anchor with the efficient fridge (no freezer) and all LED lights; we recharge phones and laptops during daylight hours; we carry an extra 107w of solar panels that can be deployed on deck when at anchor on grey days and we’re not trying to run a 40” plasma screen for entertainment or microwave for cooking! That said we did have a 600w microwave on board and used that at anchor occasionally (but not enough to warrant the space it took up and so removed it last year).

We would have put more capacity in the house bank but that would have meant creating a new battery box and so we thought we would see how we go with 345ah - and after 2 years (x 5 months) have no need to revisit that.

We did get a battery paralleling switch installed so that we can start the engine with the house bank in an emergency.

We installed Rolls AGM batteries (and similar style Optima starter and thruster batteries) with Victron mains charger and MPPT. I read that they are not the most expensive (or best) AGMs but seem to have a good reputation. The benefit of AGM for us is that we can charge them up, disconnect them and leave them for our 7 month winter with very limited self-discharge compared to wet lead acid batteries - and the three Rolls batteries fit our battery box perfectly!

Paul

 

[Graham376]

As suggested above, do some reading of past threads and other info on the web, there are quite a few cruising forums out there with advice from people who have lived aboard for years. There are of course different factions, open lead acid v AGM and now lithium are appearing.

Not sure if the 38 is the same but some earlier Moody models including my 376 have very poorly insulated fridge boxes so when you get into hotter climates, that's the main battery killer. In common with many who live aboard for long periods, I have Trojan open lead acid, T105 (225ah) being the most popular, pairs of 6v wired in series and then the pairs connected in parallel. Main problem is the footprint, 2 x 6v won't fit into a standard battery box so they have to be remade. 4 x T105 will give total of 450ah which is about right in our case. Car batteries are fine for engine start.

 

[Mistroma]

All very useful information above. I'd put following in rough order of importance.

1) Reduce consumption (LEDs, good fridge insulation, wind scoops for cooling etc.)
2) Fit a lot of solar, it's a game changer (Only consider wind-gen when you can't fit another 50W panel)
3) Get the correct battery capacity for your lifestyle and charging system. Monitor the batteries
4) Have a decent charging system for times you do get to 50% SOC.
Item 1 is pretty obvious.
Wind-gen can be useful but it is expensive.

The sweet spot for battery capacity will vary with usage, charging system and battery type. I'm guessing it would be somewhere around 450Ah at 12V but that really is just a guess.

e.g. Take a couple of silly examples with flooded lead acid batteries.
2000Ah bank using 100Ah per day means you will usually be sitting around 95% for much of the time. This is the area where charging is inefficient and you would need a pretty high capacity charging system running for several hours to get back to 100%. A lot of energy would be going to waste every day.

200A bank using 100Ah per day obviously puts you into 40%-50% state of charge most days and battery life will be reduced.

Obviously these are very rough and silly examples which don't take any notice of usage patterns. You could have a eutectic plate to reduce overnight consumption etc. But I hope you get the general idea.

Most boats will have a reasonable alternator and mains charger. Probably not fully up to the job of charging as quickly as possible at low SOC. Sometimes OK when combined with solar but you do need to look at charging output as well as battery capacity. Do adjust settings to improve charging, my solar and mains charging is set to reach at least 14.8V as I have T105s.

I bought a clamp meter many years ago and it was tricky to weed out the ones only able to measure AC current. Many adverts didn't make it easy to spot that they could not measure DC current via the clamp. I don't know if that is still correct but do make certain you are buying a clamp meter which is able to measure DC current.

Don't believe meters showing battery state of charge without further proof. Many, probably most, are horribly inaccurate. They are a useful indication but I've been told by many people that their batteries are back at 100% every day when a brief check confirms that is not correct.

I have a Smartgauge fitted and find it useful and simple to install. However, I don't blindly believe it when it reads 100%. I don't believe my other system either showing amps. in and out. I have checked state of charge based on temp. corrected SG. I think I have a pretty good idea these days based on readings shown and historical data.

 

[RAI]

Remember, batteries only store electricity, they don't generate it. So you need to consider how you plan to generate it to match your needs. Extremes might range from being on shore power nearly all the time in a marina, to being at anchor or on an ocean passage. Your power consumption must be a bit less than your power generation capability.

 

[Graham376]

Don't believe meters showing battery state of charge without further proof. Many, probably most, are horribly inaccurate. They are a useful indication but I've been told by many people that their batteries are back at 100% every day when a brief check confirms that is not correct.

Agree that with most, the capacity remaining is a rough indication rather than fact, as with our NASA BM1s. However, the voltmeter and ammeter displays are invaluable to see what's happening at a glance and the effect on battery draw by switching items on/off.

A decent solar regulator such as the Victron Smartsolar which can have charging parameters altered to suit battery type is worth installing and will tell you what the panels are actually putting out and historic info for a month or so, via bluetooth connection to android or data lead to pc.

PCs by the way can be a battery killer, I binned our large HP laptop and got an Asus netbook which does what I need and draws about one third the power so I normally just leave it on all day.

 

[Mistroma]

Agree that with most, the capacity remaining is a rough indication rather than fact, as with our NASA BM1s. However, the voltmeter and ammeter displays are invaluable to see what's happening at a glance and the effect on battery draw by switching items on/off.

A decent solar regulator such as the Victron Smartsolar which can have charging parameters altered to suit battery type is worth installing and will tell you what the panels are actually putting out and historic info for a month or so, via bluetooth connection to android or data lead to pc.

PCs by the way can be a battery killer, I binned our large HP laptop and got an Asus netbook which does what I need and draws about one third the power so I normally just leave it on all day.

Completely agree, I was trying to say not to simply believe one instrument. Much better to have it properly configured and even then use other information to back up what it is telling you.

I also said "Do adjust settings to improve charging, my solar and mains charging is set to reach at least 14.8V as I have T105s". I've often been told batteries are fully charged because the regulator has gone from amber to green. I much prefer something I can configure to match daily needs. Default settings for flooded batteries on one of my systems would pretty much stop charging at 80-85%. It would get to 100% if I ever had a week of sunshine 24 hours everyday.

Good point about laptops, we use tablets quite a lot. I try to run laptops on internal batteries when needed in the evening and charge during the day with any excess solar. I also have a PiZero set up to play video if we ever want to watch a program on TV. Much lower power than HDMi from a laptop. Not that we watch much TV in summer.

 

[MS_Adventure]

Thanks all for the valuable info!

 

[Pasarell]

Hi, and welcome to the forum.
If you haven't already done so it may be worth joining the Moody Owners Association as there is a wealth of information available about your new boat. Electrics and everything else.
I've lived aboard in the Med for 2 years now and the simple answer to how many batteries is as many as you sensibly can, or rather as much capacity as you sensibly can. If you're going to be in hot climates your fridge will use a lot of power. I have a domestic bank of 420Ah and 200W of solar which is just about enough for my requirements but I intend to increase both to give spare capacity. All my lights are led and I have a keel cooler for the fridge. Phones, laptop TV etc all run / charge from 12v so I'm completely self sufficient when cruising

I had to replace all the AGM batteries when I got the boat as it had been standing for 2 years with no charging. First thought was to go for led but they weren't available at short notice in Greece so I got ordinary sealed lead acid. I would do the same again when necessary as they're simple, relatively cheap and can be replaced anywhere. My only AGM battery is an Odyssey engine start battery that survived the neglect before I got the boat. It's tiny but starts the engine easily. When a previous owner installed it, it freed up space for a 4th domestic battery.

Your boat probably already has a paralleling switch - most Moody's do - and it enables you to start the engine from domestic bank if the start battery is flat. Unless the start battery fails you probably won't need it and anyway, a pair of jump leads would do the same job

 

[Pavalijo]

I've lived aboard in the Med for 2 years now and the simple answer to how many batteries is as many as you sensibly can, or rather as much capacity as you sensibly can. If you're going to be in hot climates your fridge will use a lot of power. I have a domestic bank of 420Ah and 200W of solar which is just about enough for my requirements but I intend to increase both to give spare capacity.

I am no expert, and have not traveled farther South than the Spanish Rias, but wonder whether increasing your solar capacity is more important than increasing battery capacity - so that during the day you are generating sufficient power to both run the fridge AND get the batteries nearer to full capacity to run the fridge through the hours of darkness without over discharging? Perhaps you could try that first before adding a battery of a different age to the others in the bank?

200w would struggle to keep our 345ah batteries topped up on greyer days, when we deploy our extra 107w roving panels which can be pointed at the sun to supplement our 240w (fixed) panels

 

[Mistroma]

I am no expert, and have not traveled farther South than the Spanish Rias, but wonder whether increasing your solar capacity is more important than increasing battery capacity - so that during the day you are generating sufficient power to both run the fridge AND get the batteries nearer to full capacity to run the fridge through the hours of darkness without over discharging? Perhaps you could try that first before adding a battery of a different age to the others in the bank?

200w would struggle to keep our 345ah batteries topped up on greyer days, when we deploy our extra 107w roving panels which can be pointed at the sun to supplement our 240w (fixed) panels

Completely agree, we have 345W and struggle at beginning and end of the season (200W fixed, 145W moveable). A lot depends on power use but 200W sounds rather low for sailing outside peak sunshine months.

I find that the batteries only need capacity to run the fridge overnight, plus odds and ends. They only drop to 85% or more most mornings. That's with 450Ah capacity. I'd rather add solar than extra batteries which would just take more charging. Bigger lead acid batteries means you don't discharge as deeply and the higher your starting point the less efficient charging becomes. If you do run large banks down to 50% over a few days, then the problem becomes one of getting enough power to charge them back. Around 450Ah is a reasonable compromise for me and extra solar panels would be better. I could probably even get away with smaller batteries.

 

[macd]

I am no expert, and have not traveled farther South than the Spanish Rias, but wonder whether increasing your solar capacity is more important than increasing battery capacity...

Trouble is, the variability of solar is considerable. Clearly in the Med most days during the sailing season are sunny. But it's not uncommon to get two or three days of overcast, particularly at either end of the season. (Autumn being worst because daylight hours are so much more reduced). Ideally, battery capacity should be able to cope with that, at whatever rate of demand applies to the boat in question.

 

[Graham376]

We've managed with 200w solar until now but having to be careful, particularly Spring and Autumn. In the process of uprating to 345w - when the welder gets around to making the frame, always next week! Undercharging batteries isn't good for them as is over discharging so, whatever size of battery bank is installed, charging regime has to match.

We have Honda generator & 240v charger for when too many overcast days or power tool use.

 

[Mistroma]

We've managed with 200w solar until now but having to be careful, particularly Spring and Autumn. In the process of uprating to 345w - when the welder gets around to making the frame, always next week! Undercharging batteries isn't good for them as is over discharging so, whatever size of battery bank is installed, charging regime has to match.

We have Honda generator & 240v charger for when too many overcast days or power tool use.

Sorry to disappoint you but 345W won't be enough.

It made a huge difference to us and we had excess power every day until getting towards the end of the season. Really annoying to need the generator again, it hadn't been used for months. Around 350W is getting quite close to being OK most of the summer.

Of course 500W would still be too little right at the end of the season. You'd get used to plenty of power and then output drops off a cliff (relatively speaking) from end of Sept. onwards. I think I'd manage with 500W right into November.

 

[macd]

Sorry to disappoint you but 345W won't be enough.

That rather depends (for the OP's benefit) on the electrical demands. As suggested by others, all LED lighting, efficient, well insulated fridges (esp keel-cooled) and no greedy laptops make a huge difference. We generally cope fine into November with 340W and 450Ah of T105s.

 

[Mistroma]

That rather depends (for the OP's benefit) on the electrical demands. As suggested by others, all LED lighting, efficient, well insulated fridges (esp keel-cooled) and no greedy laptops make a huge difference. We generally cope fine into November with 340W and 450Ah of T105s.

I was joking, mostly. But if I had 500W, laptops on, no need for generator right into November. Bet I'd suddenly find things I really needed to run and couldn't live without (Foot spa!! The sea just doesn't cut it any more.