How much domestic battery capacity?

[neil1967]

I am shortly going to replace the domestic batteries on our recently acquired Oyster 406 - there are 2 knackered Trojan 130AH domestic batteries on board. I know about calculating load etc, but I am interested in how much battery capacity liveaboards have found is necessary in reality. We will hopefully heading off in a few years to lifeaboard full time in the med, caribbean and beyond, with a fridge, and I think around 400AH - probably 3 x 130AH Trojans - would be sufficient (I'll replace/relocate the engine start battery). I am keen not to discharge the batteries too deeply in order to prolong their life. Grateful for any thoughts.

Regards

Neil

 

[Mistroma]

400Ah sounds like a lot except that you'll probably run between 50%-80% depth of discharge most of the time. So actually only 120Ah available most of the time (assuming usual flooded batteries).

If you have a gen-set or big wind-gen and lots of solar panels then 400 Ah would be about OK. You need to know how much power you will use each day and compare with amount you will generate.

Capacity not much of an issue if doing a lot of motoring or with a gen-set. However, it rapidly becomes an issue if you hang around an anchorage for a day or two.

What power generation sources will you have and how much kit will you be running?

 

[neil1967]

We have a fischer-panda generator, although I would prefer to use it as little as possible (it is only there because the previous owner fitted it) - preferred power source will be solar (I am considering 4 x 80 watt panels, perhaps with a wind gen as well. Otherwise, opportunistic use of the diesel engine. Plan is to spend many happy days on anchor when not sailing!

Neil

 

[multihullsailor6]

Neil,

Step 1 is to do your power requirements spreadsheet, it will give you your daily consumption. IMHO add 50% to that for items / life style you have underestimated like 2hrs daily of DVD-reader running, 1 hr of laptop for wireless internet .. when at anchor.
Step 2 is to work out the charging power of solar panels and wind generator, you NEED both, factor in only about 50% of what the manufacturers say. You might even want to look into water driven generation. And just in case, have a look at doubling your engine alternator charging power either by adding a 2nd one, an uprated one or one of the smart electronic engine battery charging systems.
Step 3 will take you to the size of your battery capacity at 50% if you want some kind of life out of them.

I have 440AH house batteries with approx. 150W solar panels and a wind generator and will be adding another 200W of solar panels. In my current configuration I can last about 4-5 days, unless there is a lot of wind day and night! Remember the wind generator can charge at night, not so the solar panels.

 

[Mistroma]

Sounds as if you are going to be OK assuming decent charge setup from main engine with gen-set as backup.

I'd imagine that properly positioned 320W of solar would meet your daily power needs in places you mentioned. I have no actual data to prove it but try here to get an idea of output from your panels. Just point to location in med.,put panels at 0 deg. and enter 320kW for size. You'll get a warning about size but just ignore it.

Read 1st column avg. kWh each day as Wh and divide by around 12.5V to get avg. Ah per day.

http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

I don't know how accurate the predictions are. However, they seem sensible when compared with general guesses I've made in the past. I intend to check this year as I can now log Amps generated over time (regulator keeps track for me).

 

[Gerry]

We have 4x125amp lead accid house batteries. These are charged by a Kiss wind generator and the engine when there is no wind!
Our refrigerator is mechanical, we use parrafin lights and are generally low power useage as a boat.
Our batteries last, on average, seven years.

We anchor a great deal of the time and have spent the last 8 years in the Caribbean. Your fridge will be, by far, the largest consumer of power.

We have a seperate 125amp starting battery which is now 14 years old and still going strong!

Hope this helps a bit!

 

[whipper_snapper]

Just to add, one of the 'nicest' ways to increase your battery capacity is to reduce your power needs. Switching all lights to LED and using a very efficient (water cooled), well insulated fridge with a smart controller* can make a big difference.

We use a fridge mate, it is not expensive and I would not be without it

 

[charles_reed]

I'd suggest you start with doing an ACCURATE power-needs analysis, per 24 hours, work out the maximum solar-panel capacity you can fit, subtract from your 24-hr usage 20% of nominal PV panel and windgen input and then multiply by 10 any shortfall.
In my case daily usage is 80ah, I've 318 w of PV panel.
In practice, using 215ah of fully-charged battery, I get 5-8 days at anchor before having to start the engine to recharge.
I really need 400 ah of battery, but have no place to fit them (I've actually got a total of 320ah but one of 2 batteries is on standby for engine starting).

 

[Koeketiene]

We use a fridge mate, it is not expensive and I would not be without it

Thanks for that - may very well be just what I'm looking for

 

[RAI]

400 Ah is ok but more is better IMHO. Look at an Odessey TPPL AGM battery for a starter battery, you can get away with a tiny one tucked in close to the engine.

 

[sailinglegend420]

If you have a battery monitor use that to get an average of what you actually use every day.

With a usage of 100 Ah/day and at 50% discharge, you need at least 200 Ah of battery capacity, and that would mean charging the batteries every day. For a better liveaboard experience only charging every three days then triple this value to 600 Ah.

But if you think that figure is already too large then consider what happens most of the time to the actual battery capacity of most cruising liveaboards. Batteries can charge quickly to 80% of their maximum, but take many many hours to get to 100%. This can’t be done by running the engine or a generator for just a few hours. So if the batteries only get 80% charged most of the time what is the actually capacity available? It’s a simple calculation – a 100 Ah battery only charges up to 80% = 80 Ah. It must be charged when it goes down to 50Ah, so in this situation there are only 30 Ah available for use from our 100 Ah battery. That’s 20 Ah less than the 50Ah you thought you had, lower by 40%.

So whatever your original estimations was you need to add an extra 40%, so a service bank calculation of 600Ah would take the capacity really needed up to a massive 840Ah! This is about twice the capacity of many cruising boats.

Solar panels can make a huge difference, but they must be large enough replace the 100 Ah used each day, and have spare Ah to try and get the batteries back up to 100%.

 

[temptress]

..... I am interested in how much battery capacity liveaboards have found is necessary in reality. .....
Regards

Neil

Fit as much as you have space for! I spent years calculating my daily load, working out what used power and what did not. messed about with different battery technologies, charging systems and the like.

Having lived on 2 boats(36ft and 47ft) over the last 20 years I just keep it simple. Get a battery monitor and then fit as much domestic capacity that you can and have a dedicated engine battery. Keep an eye on the charge and start charging (a whole different topic) when you get to say 60 percent.

Living aboard you will soon learn how long your charge lasts and how difficult it is for you to put that charge back. then go from there. What works form one may not suit another.

Battery usage is a variable thing, it depends on so much that life to too short to worry too much about it.

 

[jordanbasset]

We have 4 x 140 Ah batteries (560 Ah´s), a dedicated starter battery and 2 x 100w solar panels, We also have LED´s and a keel cooled frdge, plus have 2 computers and t.v. with built in DVD Player. Since fitting the 2 panels (previously had 1 x 60w) we have had no need to run the engine except when we move the boat and need to due to lack of wind. This is for the period April to the middle of October, winter months if not on shore power may require more engine running.