Battery Capacity

[S/V Alchemy]

This is a more nuanced discussion than we usually see here. Thanks to all involved.

I think it's important to separate the concepts of bank size and usable amps. The only reason I am going for a bigger house bank (4 x 8D or equivalent) is to obtain a slightly larger "usable" band of available amps between 75% and 100% SOC. This is actually fairly narrow and implies that I get best results in terms of longevity and sulfation if I can continuously charge via solar and wind, and occasionally charge to a higher set point via regulated alternators (when, for instance, motoring).

The fallback position is a pair of Hondas to supply 30 amps for power tools, anchor winch bank charging and general "let's not involve the inverter in this, shall we?" Yes, I have an inverter in the mix, but that's primarily to provide "spot loads" on AC, like four minutes of microwaving or a couple of hours of gadget charging in the milliamp range.

As I want the ability to run a fridge on five cloudy, windless days at anchor, I arrived at 1000 Ah as a main bank size, but with generally modest draws all around in order to remain in the "useable" band. Realistically, there will be few calm nights at anchor when we have the boat fully lit up, but my desire is to avoid running the engine to supply charge unless I absolutely have to. I've seen first-hand that even a modest wind gen, running all night in during a 20 knot passage, can pretty easily "fill" a good-sized bank to the point where the wind gen is audibly cutting out. Same with four solar panels: between 10 am and 2 pm on a cloudless tropical day is a great time to make water or use appliances, because you can calculate based on observation what you are likely to make, and therefore what you can freely consume.

Like ice in your beverage after working through lunch!

[noelex 77]

Originally Posted by S/V Alchemy

This is a more nuanced discussion than we usually see here. Thanks to all involved.

I think it's important to separate the concepts of bank size and usable amps. The only reason I am going for a bigger house bank (4 x 8D or equivalent) is to obtain a slightly larger "usable" band of available amps between 75% and 100% SOC. !

The priorities when deciding battery bank size will vary considerably from one cruiser to another.
Its worth remembering that the goal of low overall battery cost (cost per year) is also worth considering. Many people focus on the longest battery life and fit a very large battery bank. Adding weight and complexity and sometimes considerably increasing their overall battery running costs for little benefit.

[Bill Balme]

Bill (Trayfors),

Once again thanks... my batteries are wired per method 2 - phew!

This morning when I came to the boat, I disconnected the charger and let everything sit for 3 hours then measured SG in all cells. 23 cells topped the scale on my SG tester, one came in at 1250 - indicating fair.

I'm thinking that I should still go ahead and equalize them - is there any harm in it? Will it perchance equalize the one cell?

Seems like the batteries are in good condition right? No need to replace before heading off for Europe next year...

[Bill Balme]

Bill T:

I am NOT getting 14.7V - more like 14.3 occassionally 14.4... Even during equalization I only see 14.6 I think...

All my Prosine 2.0 manuals say that an installer only can change the settings for adsorbtion rates - is there a way around that?

(Clearly want to keep these flooded Rolls 8D's in best shape possible...)

[S/V Alchemy]

Originally Posted by noelex 77

The priorities when deciding battery bank size will vary considerably from one cruiser to another.
Its worth remembering that the goal of low overall battery cost (cost per year) is also worth considering. Many people focus on the longest battery life and fit a very large battery bank. Adding weight and complexity and sometimes considerably increasing their overall battery running costs for little benefit.

True, of course. If you are coastal or a dock queen/daysailer, you can have as little battery capacity as you need to run the lights, and fair enough.

We have a full keeler and intend to linger in unserviced and distant lagoon when not crunching bergy bits. I can put half a tonne of batteries right under my mast, which would actually stiffen the boat up a bit, so the weight and complexity are not the same issue to me as to many others. It's a 30,000 pound boat unloaded with a dozen or more lead ingots forward just for trim. If I put batteries and gear in, and take lead ingots out, I will probably have a net weight loss!

[S/V Alchemy]

Originally Posted by Bill Balme

Bill T:

I am NOT getting 14.7V - more like 14.3 occassionally 14.4... Even during equalization I only see 14.6 I think...

All my Prosine 2.0 manuals say that an installer only can change the settings for adsorbtion rates - is there a way around that?

(Clearly want to keep these flooded Rolls 8D's in best shape possible...)

There are a lot of variables here, like the quality of your volt meter, the temperature, corrosion (perhaps) and the SG of the electrolyte (which you should know, and should take with "rested" batteries).

But I would guess that a) you're OK once you test the electrolyte and b) a good equalization charge might well bring that "fair" cell back to "excellent".

I will wait for the wizards like MaineSail to chime in, however, as I am still only following these practices for more typical banks, not big'uns.

[Surfer Girl]

Originally Posted by mcarling

I know that's not what you wanted to hear.

Obtaining a full charge does not require turning everything off. It's only necessary that the charging current exceed the load current by a sufficient margin and for a sufficient duration.

Thanks for the reply mcarling. I'm happy to hear anything (as long as it's not the usual CF mudslinging), that's why I asked the question...

Originally Posted by noelex 77

There is no need to be obsessive, however. A 100% charge every few weeks will still give a very good battery life.

For best battery life reducing the depth of discharge is the most important factor.

The best way to charge them up to a 100% is with a slow charging method like solar. If you are using less than you can produce your batteries are likely to get to get up to 100% often enough.

Also thank you noelex 77. So from what you & mcarling said above, our large capacity solar bank should do the job nicely......

[DeepFrz]

How does it look on your power spread sheet? How much are you using, what is the expected solar input for your area?

[noelex 77]

Originally Posted by S/V Alchemy

True, of course. If you are coastal or a dock queen/daysailer, you can have as little battery capacity as you need to run the lights, and fair enough.

We have a full keeler and intend to linger in unserviced and distant lagoon when not crunching bergy bits. I can put half a tonne of batteries right under my mast, which would actually stiffen the boat up a bit, so the weight and complexity are not the same issue to me as to many others. It's a 30,000 pound boat unloaded with a dozen or more lead ingots forward just for trim. If I put batteries and gear in, and take lead ingots out, I will probably have a net weight loss!

Actually those boats that use marinas often and can access shore power generally benefit from a bigger battery capacity.
A reasonably cheap and easy power supply involves charging your batteries at a marina every few days, or once a week. This needs a big battery bank, but if you do without a generator and multiple solar panels it can be a good solution.

Unfortunatly I usually only get shore power every couple of years, so even a boat load of batteries cannot store much of this power.

On some yachts, like the lifting keel models, the battery balast can be placed close to the normal balast so the weight penalty is minimal, but this is exception rather than the rule. Even then they have to carried off and on. Getting 70kg batteries from the dingy to the boat is no fun.

The optimal battery bank size depends on lot a factors, but there is a tendency to fit very large battery banks. This is a trend from the days when most power was supplied by the main engine, or generator.
The cheap cost of solar panels and wind generators has altered the goal posts, and many yachts utilising these power sources would benefit, at least in running costs,from fitting a smaller bank.

[goboatingnow]

Surfer girl, there isn't an easy answer to your question, its depends on charging sources, Diesel tankage and engine running hours. On short passages where you have sufficient diesel you can charge by running the diesel as often as necessary to recharge the banks , usually as you say up to about 85%. Then if you have alternative charge inputs these can be used to supplement that energy. This is typical in the 3-5 day trip. When your trip is over you should try and bring the bank to 100% as soon as possible. Whether you discharge to 40-50-60 or 80% on the trip will be dictated by circumstance.

On longer trips , you typically may not have or want to use the diesel. Hence you need to balance consumption against WORSE case recharging ability. The last thing you need is flat batteries. Hence running no interior lights at night ( use head lamps) limiting fridge and freezer and prioritising power for the key electronics like autopilot etc. I've run a few trips with head lights !

A good battery monitor displaying Ah , that you know is reasonably reliable, is worth its weight in gold

Dave

[sailorboy1]

I think it should be noted that if using a generator or your engine alternator to get a mid size or large size battery bank from 85% charge to 100% charge it probably will take the same amount of time. By that time the batteries are already accepting less that what the charge source can provide and it is just a time issue. So whether the bank is 400AH or 800AH probaly doesn't matter. It is minor to the charge source if it is providing 8 amps or 16 amps charge current.

[Surfer Girl]

Originally Posted by goboatingnow

Surfer girl, there isn't an easy answer to your question, its depends on charging sources, Diesel tankage and engine running hours. On short passages where you have sufficient diesel you can charge by running the diesel as often as necessary to recharge the banks , usually as you say up to about 85%. Then if you have alternative charge inputs these can be used to supplement that energy. This is typical in the 3-5 day trip. When your trip is over you should try and bring the bank to 100% as soon as possible. Whether you discharge to 40-50-60 or 80% on the trip will be dictated by circumstance.

On longer trips , you typically may not have or want to use the diesel. Hence you need to balance consumption against WORSE case recharging ability. The last thing you need is flat batteries. Hence running no interior lights at night ( use head lamps) limiting fridge and freezer and prioritising power for the key electronics like autopilot etc. I've run a few trips with head lights !

A good battery monitor displaying Ah , that you know is reasonably reliable, is worth its weight in gold

Dave

Thanks Dave, this is exactly what happened last time when we made passage from the Saints (Guadeloupe) to Panama! We didn't have
sufficient solar charging capacity and I ran the engines too late - we depleted the batteries and I had to become an electricity Nazi....

This time, I want ample generated input from the solar panels and no depletion of the batteries.

BTW, it's 1.30am on the 1st January 2013 here on the east coast of Oz - Happy New New everyone..... I've had a champagne or 10........

[Bill Balme]

My Battery Tester (Hrydrometer) has a scale from about 1.1 to 1.3. My batteries are testing out at 1.3+ though Rolls says that 100% charged should read 1.26 or thereabouts. Can someone explain to me why I'm seeing such high numbers.
Additionally, the scale is labelled with "Needs Charge" to "Fair" to "Good" - but the 1.26 lies right a the bottom of the "Good" portion...

Thanks.

[nigel1]

Hi Bill

I reckon its pretty cold in MA, (if thats where you are). Colder the battery, the greater the density
see
Trojan Battery Company

You can get a hydrometer with a built in thermometer which helps with this

[Bill Balme]

Hi Nigel - have thought of that - but with a variation of +/- .003 for every 5C change, even if it were freezing - which it wasn't - at 100% charge that would equate to 1.29. I'm getting about 1.31...