Feasibility of Large Battery Banks

[kmacdonald]

Don't 12V battery banks over 500 Ah become less attractive than a generator? The weight and complexity of charging large banks and the ability of a generator to run AC seems to favor generators instead of large battery banks.

[StuM]

I'd much rather have my 800W of solar and 1000Ah of batteries than a generator

[Evenstar]

Originally Posted by kmacdonald

Don't 12V battery banks over 500 Ah become less attractive than a generator? The weight and complexity of charging large banks and the ability of a generator to run AC seems to favor generators instead of large battery banks.

I'm not sure that makes any sense. Nobody wants to listen to a generator runnning all the time. The loads a boat uses are quite light compared to what even the tiniest generator puts out. It's really inefficient to run even a dinky 1Kw Honda noisemaker to service even 15A (180W) worth of house lights and refrigeration. Better to run the goddamnednoisybox to charge up your batteries in a couple of hours then enjoy the quiet.

We've got 720Ah @24V of LiFePO4 batteries. Works just fine with a 7Kw generator running every three days or so for about 5 hours. We can invert for all the AC we need.

[Evenstar]

Originally Posted by StuM

I'd much rather have my 800W of solar and 1000Ah of batteries than a generator

Me too, but I don't have decent deck space for it without reworking a lot of stuff.

[kmacdonald]

Originally Posted by Evenstar

Me too, but I don't have decent deck space for it without reworking a lot of stuff.

Cats seem to have the space for solar but monos don't without making it look hideous.

[motion30]

I have over 1100 watts of solar, and over 1200 amp hours of battery
I mainly run my generator to make hot water for the shower. Even in the winter I am 90% sufficient in the summer there is no question

[SailsWithFists]

Originally Posted by kmacdonald

Don't 12V battery banks over 500 Ah become less attractive than a generator? The weight and complexity of charging large banks and the ability of a generator to run AC seems to favor generators instead of large battery banks.

"run AC"?

Do you mean run A/C (air conditioning) or run AC power? Big difference.

There is no complexity in charging large battery banks unless you have many small batteries comprising the bank. If you need to generate AC power for short periods of time, a quality inverter will do the job.

If you need to generate significant AC power over long periods of time, then a generator is usually the best option. But if you are wanting a generator in order to run A/C (air conditioning), just remember that A/C is called "generator eaters" for a reason. If you cannot keep your generator loaded up when it is running, it will have a short lifespan.

[valhalla360]

500amp-hr of lead-acid batteries is only about 3kwh of usable power if you start out fully topped up. Less if you only got back up to 80% full the day before.

Generators are really best to handle big loads like air/con. They are pretty limited for battery charging as once you hit 80-90% charge, the charge acceptance by the batteries drops off quickly.

If you aren't running the air/con or similar, solar can keep up nicely with that battery bank and reasonable loads.

[Pizzazz]

Power generation is the key, not battery capacity. It is either solar, portable gas gen, diesel gen or engine. I am still amazed at people who size their batteries to handle 4-5 cloudy days when you can easily run the engine Midway and be done with it.

The problem with batteries over 5-600 AHrs is that they are heavy and serve no need on a typical sailboat.

An inverter helps with short loads but if you use aircon, electric pressure cooker or electric heat, it is a non-starter. I agree with you that a small portable genny is much more useful than solar charging, discharging, heat, inverter fan noise and the other issues with high current applications. For a larger boat, a diesel genny.

[ranger58sb]

Originally Posted by kmacdonald

Don't 12V battery banks over 500 Ah become less attractive than a generator? The weight and complexity of charging large banks and the ability of a generator to run AC seems to favor generators instead of large battery banks.

I don't look at generator and battery bank as an either/or proposition.

Our genset will run our aircons and electric cooktop, heat water, charge batteries... and when we power lighter loads, the batteries do fine, quietly... for a while.

IOW, we use both, as appropriate for our purposes.

Certainly boat size and usage would guide, though...

-Chris

[rom]

Originally Posted by Pizzazz

Power generation is the key, not battery capacity.

Could be for you. For me they are two keys of a complex mix which doesn't work the same from january to december, where the boat is, how many people are onboard.

Originally Posted by Pizzazz

The problem with batteries over 5-600 AHrs is that they are heavy and serve no need on a typical sailboat.

If a typical sailboat is a 31' monohull that is being used as you use it, then maybe you right.

[sailorboy1]

Originally Posted by StuM

I'd much rather have my 800W of solar and 1000Ah of batteries than a generator

So would I and I have a generator. But a generator is still worth having.

[Malabarista]

Can’t someone tell the scientists to hurry up with the solar sails?
We need ‘em cheap and we need ‘em now

[LoudMusic]

Originally Posted by Pizzazz

The problem with batteries over 5-600 AHrs is that they are heavy and serve no need on a typical sailboat.

You say that as if generators and the fuel they consume don't also have significant weight and take up significant space.

They're also significantly more complex, require routine maintenance, and increase trips to the fuel dock.

Personally I'd rather fill a generator locker with batteries.

[S/V Alchemy]

Mine are quite feasible. 1,575 Ah over six L-16s deep cycle FLA batteries in series-parallel. Right under the mast with a set of companionway stairs over 'em. Charging is via wind (300w) and solar (135w x 4 on an arch) and, soon, a 250 A alternator for "equalization underway". Oh, and a couple of Honda 2000s should I experience a failure (or need to operate power tools ashore).

The point was to stay as much as possible in the high end of SOC (75% or over). That meant sizing for anticipated use (daily drawdown) and working within that "band". I do not want a typical below-decks genset, but portables ganged are fine, because I use those for other things. I do not wish to run the auxiliary diesel just to make power, but when I do run it, I want to get as high an acceptance rate as I can when doing runs like "motoring out to the three-mile limit for pump-outs".

A lot of my ideas come from homesteaders, who've basically solved these issues already. I realize that most production boats don't want to haul 320 kilos of batteries, but I have a custom pilothouse in steel (see picture to left). Putting the batteries in has actually stiffened the boat up. The only thing I would recommend is taking a full-systems approach, starting with an honest appraisal of how much power you need and the importance of shore-independence to you. Other decisions, like solar/wind capacity, charger/inverter selection, and even wiring and fuse sizing, proceed from that initial appraisal of what you'll be safe with in terms of minimums (keep the nav lights and radio working) and what you'll be happy with in terms of amenities (hot water, "movie night" and ice cubes after three days of cloudy and calm weather). https://alchemy2009.blogspot.ca/2016...wering-up.html