Why do you need a large house battery bank?

[pvb]

Readily, but less efficiently....

If a large bank can, for example, absorb the full output from an alternator, when a smaller bank can't, would that be more efficient?

 

[[70521]]

Quite. If you can't keep your beers cold, what's the point of going sailing in the first place.

Thankfully real ale does not need chilling (or more likely frozen in pubs today).

 

[Heckler]

WHAT!!!! :disgust:

Indeed! What!
Stu

 

[lw395]

If a large bank can, for example, absorb the full output from an alternator, when a smaller bank can't, would that be more efficient?

It takes more Ah to replace 10Ah of discharge in a big bank than a small one.

 

[pvb]

It takes more Ah to replace 10Ah of discharge in a big bank than a small one.

I'm not sure why you think that. Almost every commentary on charge efficiency will say that the charge efficiency of a lead-acid battery is higher at low rates of recharge. With a large bank, each battery will experience a lower rate of recharge than a small bank, so the charge efficiency will be higher.

 

[dslittle]

I sail quite happily with a total of 220 Ah.

And how long does that keep your freezer working in 25+C? We stocked up in April for the summer and the freezer worked hard during the summer - more so than it did when we were on the West Coast when we just kept things in the water!!!

 

[solent clown]

Thankfully real ale does not need chilling (or more likely frozen in pubs today).

.:encouragement:

 

[solent clown]

interesting thread that could be very informative if people with their sailing patterns, and energy requirements put it all down in a post.
What a great resource that could be, from day sailors to liveaboards in sunnier climes, and working boats, all giving their real world experience to help others form a judgement on how to proceed base upon real world experience.
That would be a great read, so bring it on :encouragement:

 

[lw395]

I'm not sure why you think that. Almost every commentary on charge efficiency will say that the charge efficiency of a lead-acid battery is higher at low rates of recharge. With a large bank, each battery will experience a lower rate of recharge than a small bank, so the charge efficiency will be higher.

Nonsense. As a battery reaches 90%... 95%... 98% etc state of charge, the efficiency of' Ah in' to 'Ah stored' drops. And keeps dropping. Yes slower is better, but that's no help when time is limited by twylight.

 

[pvb]

Nonsense. As a battery reaches 90%... 95%... 98% etc state of charge, the efficiency of' Ah in' to 'Ah stored' drops. And keeps dropping. Yes slower is better, but that's no help when time is limited by twylight.

I think you need to read my post again. If you sincerely believe that small battery banks are more charge efficient than larger banks, you need to do some research before you post here.

 

[RichardS]

It takes more Ah to replace 10Ah of discharge in a big bank than a small one.

So if I have an 20Ah battery which is 50% discharged, it will be quicker to put 10Ah into it than if I try to put 10Ah into a 200Ah battery which is 50% discharged?

Richard

 

[William_H]

If you are running a standard alternator with set voltage regulator then surely you get a larger current into a battery initially then the current decreases as apparent voltage of the battery increases. Now if you have 2 batteries in parallel you will get that same current into each battery which means twice the AH stashed away for every hour of engine run. Likewise for another battery in parallel up until the alternator becomes current limited by RPM or its size limitation.
If you fit a smart charge controller this diminishing of charge can be alleviated to a large extent but you still get the same effect.
Now mostly if we are relying on solar charging then the solar power (size and sun) are the limiting factors so more batteries in parallel just means less into each. Probably likewise a wind gen.
All these are factors in the live aboard away from mains power. With mains power of course the battery charger capacity may be a factor.
If however you depart from a marina with fully charged batteries then that capacity will directly influence how long you can go without recharge either by engine run or generator. Possibly extended by solar assistance.
For solar of course you are essentially limited by space for panels, orientation limitations and sunshine.
So as said so much depends on your sailing habits and style. Only your experience can answer that question. But i would be reluctant to go for large battery bank if you were not sure you need it. After all you can add batteries in parallel later. olewill

 

[Polly1]

Interesting replies, thanks.
I have a 40 ft yacht in Singapore. There is not much wind but solar is good and I have just put in 400W. It seems that a lot of the choice is down to personal preference and useage habits.

 

[lw395]

So if I have an 20Ah battery which is 50% discharged, it will be quicker to put 10Ah into it than if I try to put 10Ah into a 200Ah battery which is 50% discharged?

Richard

No, the idea is that you start with the bank fully charged.
Quicker? That would depend on the charge current available.
Charging the 20Ah battery will be something roughly like 90% efficient up to 80% then progressively less efficient.
Charging the 200Ah bank the last 10Ah will be at best 50% efficient.
So if current is limited, it could take half as long again, or if we are talking about solar charging in England this month, not happen before it gets dark again.

 

[RichardS]

No, the idea is that you start with the bank fully charged.

OK. I get it now.

Richard

 

[Amulet]

Obviously, if you are using 100 amp hours per day you have to charge, on average, 100 amp hours per day. You can put it back into a 500 amp hour battery bank in an hour if you are working in, say, the 60% to 70% charged state. If you only have a 200 amp hour bank you have to stuff it full every day - charge from 50% to 100% - which is slow and inefficient. (My numbers might be wrong, but not enough to change the message.)

This means that if your pattern of use creates relatively brief charging opportunities but offers very high charge rates, a big bank can diminish the chances of you running out of power - by spending a lot of time at less than 100% full.

If in a marina, I'm normally in overnight, which is enough time to completely recharge from 50% on my boat. Problem is that here in the western isles marinas are few and far between - and I set up the current configuration when I was in East Anglia where I was in normally marinas every couple of days.

 

[lw395]

Obviously, if you are using 100 amp hours per day you have to charge, on average, 100 amp hours per day. ......

Nope.
You have to put back somewhere between 110 and perhaps 170Ah.
For sure a big bank can take a higher charge rate, e.g. if like us you typically leave harbour under power, so the engine might run for an hour each morning.
Provided that the wiring etc actually gets the full voltage to the batteries. At these currents, it's quite easy to lose a few tens of mV here and there, which can stack up and influence the charge rate disproportionally.

 

[RichardS]

For sure a big bank can take a higher charge rate .....

Which nicely brings us back to post #20.

Richard

 

[MountainGoat]

I came to the conclusion that the only sensible way of charging batteries is sun or wind.

Or aim to marina hop and just plug in to the mains.

 

[lw395]

Quote Originally Posted by ip485 View Post
I came to the conclusion that the only sensible way of charging batteries is sun or wind.

Or aim to marina hop and just plug in to the mains.

Strangely we used to get by, sailing from buoy to buoy to anchorage with just a bit of motoring at each end of the day, before solar was affordable and without wind generators or anything else, other than the standard alternator.
And that was before LED bulbs.