Why do you need a large house battery bank?

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Polly1

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Maybe this is a stupid question but....
Either you are generating sufficient for your demands or you arent. If not you reduce power by turning off the fridge etc or switch to another source if possible. I appreciate supply and demand fluctuate but a battery can only delay any deficit, a larger capacity delays it for longer.
A larger bank will be able to supply energy for longer before significant voltage drop occurs but it is still a question of time.
A bank of double the charge capacity gives you double the time. Is there more to it than that?
I ask as my 500 Ah bank is due for a replacement
 
Polly1 said:
A larger bank will be able to supply energy for longer before significant voltage drop occurs but it is still a question of time.
A bank of double the charge capacity gives you double the time. Is there more to it than that?
I ask as my 500 Ah bank is due for a replacement
Click to expand...

Whatever suits you best. It really depends upon your pattern of usage and how frequently you can expect to re-charge the bank. If you're running a 500Ah bank into the ground and don't think a larger bank would make things better I don't think the bank size is your problem.
 
Well, considering that to improve lifespan of the battery one should not discharge more than 60 percent. So that reduces your large
bank already to 300 Ah. In this day and age this is not considered large anymore.
If you really wnat to know what you need get one og those cheap battery monitors from China. Let it run over a typical weekend sail and see the consumption. Divide the number by .6 add a bit of safety margin and you get the required capacity needed :-)
 
I've always taken the view that it's best to turn off things that I'm not using. For instance, many sailors leave their instruments, including fishfinders and radar, on when on their moorings which seems dumb to me. Also, many leave all internal lights on when they're nowhere near them. I turn them off as I move around. Admittedly I've never had high usage equipment like fridge or TV and no battery monitor.
 
The obvious reason for a large house battery bank is that, no matter how much electricity you can generate during the day from solar or engine/generator running, you cannot put any more power into the batteries once they are full so, from that point onwards, the leccy is just being wasted. If you are able to re-charge the batteries up to full every day then the wastage doesn't matter, but if you anchor for a couple of days and the sun doesn't come out and you don't want to disturb the peace by running the engine/genny, you will regret throwing away that surplus power. :(

Richard
 
You have to decide what your requirements are.
If you insist on being able to run fridge, PC, TV, heating etc etc for days on end you will need a lot of capacity.

In the old days, we just wanted to run navlights, instruments, gps for a channel crossing.
The fridge was the first game changer, followed by the eberbasto. Time for a second house battery!
When we got out first plotter it seemed shockingly current hungry compared to the old GPS120.

On the on hand I hanker for the simple life of basic yachting, OTOH, I'm trying to work out where 10kWh goes every day at home.
 
Sandy said:
I sail quite happily with a total of 220 Ah.
Click to expand...

Similar, I replaced all lamps with LED equivalents, reducing amperage by a factor of 6. I still switch them off if not required. I never run wired-in electronics unless under way. The fridge is only powered when on mains or engine running. The only big consumers are pumps for water , occasional Webasto heater? No TV?
I guess people have all sorts of different priorities.
 
It all depends on your style of sailing.

If you mainly day sail (engine on for an hour or two each day, sail to a marina and plug-in), then a single battery will do you fine.

If however, you want to sit somewhere at anchor for days on end of you are sailing longer distances, then having a big bank is necessary.
 
There is no universal answer, it depends on what power use use during your typical sailing pattern. If you are a day sailing trailer sailor you just need enough battery capacity for the day and plug into the mains when you get home. If you go away for a week or two at a time, with a power hungry boat, it'll be a whole different ball game.

Once you have worked out how much power you need to store for the day/week/whatever you then have to arrange for enough power generation to fully charge the batteries as often as possible, aiming for daily.
 
I think another thing that's changed over the years is fewer mid-size yachts have generators built in these days, as solar and big battery banks have become the norm?
 
Polly1 said:
Either you are generating sufficient for your demands or you arent. If not you reduce power by turning off the fridge etc or switch to another source if possible.
Click to expand...

If you're a day sailing marina dweller with no frozen food to go bad, that's fine but, if you live aboard on mooring or anchor, enough power is needed to manage for 2 or 3 days without sun. On passage, enough power also needed for autohelm, lights, radar etc. without having to start engine just to recharge batteries.

Few people say they have too much capacity but plenty suffer from not enough. What's "needed" depends on your own usage.
 
We produced power when sailing as we had a towed generator and then used the Amps when anchored or moored. We needed enough capacity to run all the electrics for a few days fridge, laptop, lights etc, it was supplemented by a wind generator but that was all. We rarely used the engine. It's nice to have spare capacity and not have to start the engine every day.
 
Polly1 said:
Maybe this is a stupid question but....
Either you are generating sufficient for your demands or you arent. If not you reduce power by turning off the fridge etc or switch to another source if possible. I appreciate supply and demand fluctuate but a battery can only delay any deficit, a larger capacity delays it for longer.
A larger bank will be able to supply energy for longer before significant voltage drop occurs but it is still a question of time.
A bank of double the charge capacity gives you double the time. Is there more to it than that?
I ask as my 500 Ah bank is due for a replacement
Click to expand...

Correct me if I am wrong, but from your other posts seems you have quite a large boat in the tropics and perhaps have cruising in mind. In that case, 500aH capacity (effectively 250 between charges) is quite modest. As others have said you need to determine your typical daily usage and typical daily generation to get your net usage. Divide that into your usable bank capacity and that gives you the number of days you can be independent of either shorepower or running the engine/generator. clearly the larger your bank the longer the period.

There are two ways of extending this "range". one is to reduce consumption and the other increase generation capacity. The problem with the former is that the heavy consumption items such as fridge and autopilot on passage are the ones that you would probably not want to lose; the latter has its limits and can be unpredictable.

So the larger the battery bank, the more you can smooth out these competing variables. Another benefit of a larger bank in relation to net usage is that working thee batteries less hard tends to extend their life.

So, once you have done these sums in relation to your expected usage pattern, you will probably find that your current capacity is adequate but not excessive.
 
Tranona said:
So the larger the battery bank, the more you can smooth out these competing variables. Another benefit of a larger bank in relation to net usage is that working thee batteries less hard tends to extend their life.
Click to expand...

Plus there's the added benefit that a larger bank will absorb the available charge more readily.
 
I came to the conclusion that the only sensible way of charging batteries is sun or wind. My Genset while great for charging batteries is very inefficient at doing so. The engine is fine but the idea is not to use it, if sailing is possible. I therefore added nearly a 1,000W of solar. The key was then to make sure that all the solar produced during the day could be banked to drive everything at night, including a nights sail on autopilot, hence the need for a large bank. If the bank is to small the energy goes to waste and you have less power to take you through the dark hours. Of course if you wind generate as well then it becomes less of a problem, but I am not keen on wind generators.

I have 1,000AH and that works pretty well without ever having to really worry about power consumption other than in the winter. Inevitably a little motoring usually does the trick.

Of course there is no substitute for a Genset when it comes to those things that use significant amounts of power (water heating, washing machine, water maker, compressor etc). but I do manage to run the small A/C from the inverter.
 
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