More or less batteries

[ROBDEN]

Morning all.

 

Looking at another thread about batteries, I am wondering if it's better to have more or less batteries.

 

Less means they'll run down quicker but should be easier to keep nearer to fully charged.

 

More batteries and they'll last longer between charges, but may be harder to keep, near to fully charged.

 

Thanks for any help/advice/opinions.

 

Rob....

[Neil Smith]

What is your expected power use age, do you have landline, solar or wind power, alternator size?

 

Neil.

[Phil Ambrose]

As Neil says the decision as to what size of battery bank to have should be based on all the factors as stated by Neil. If you do a power audit and can tell us about all your power management regime then some meaningful answers will be supplied.

Phil

[nicknorman]

I'm going to make what will hopefully be a useful contribution, but only if I'm allowed to say this first: it's "less" for an amorphous quantity. Eg " less sugar in my tea please" but it is "fewer" for an integer quantity eg "fewer batteries". There, I feel much better now thank you.

 

So the answer is, the right number is best. To many is bad, too few is bad. The main criteria are of course the amount of power consumed on average, and the time between recharges.

 

It's pretty easy to see why too few is bad. The batteries get into a low state of charge between charges. This means that some services won't work well, especially inverters and fridges. The batteries' voltage will dip under load to the point where these things won't work properly. The lifespan of batteries depends on the depth of discharge and whilst I think the "50% rule" is overplayed, it is certainly true that repeatedly taking batteries to a low state of charge shortens their lives, and significantly so if they are "leisure" batteries that are in reality re-badged starter batteries.

 

As for too many well firstly there is the cost, space required, weight, and increased time taken to service them.

 

But more subtley with a large excess of storage capacity the owner will not know that things are going wrong (things mainly being inadequate charging) until the actual capacity has fallen massively such that it impinges on the owners normal routine. Thus the owner doesn't have an opportunity to fix the problem until the entire large bank is caput.

 

But then again, if money is no object then the reverse of the above is that an excess of capacity allows carefree use and substantial degradation before there is a problem. But most of us do find money is an object so it's best to have the right capacity.

 

To work out the right capacity as I mentioned at the beginning, you need to consider the normal power demand and the interval between recharging. If you have solar this also has to be taken into account. The frequency of recharging depends on whether you cruise daily, or whether you are mostly static and running an engine only for electrical generation (and this whole thing presumes you are not on shore power).

 

I would say that you want to aim for daily discharge of 25% in winter as a ballpark figure. This gives you scope to either not recharge for a couple of days if you are static, and/ or allow the batteries to become pretty knacker before they need replacing. There is of course no absolute "right answer" but that is a ballpark figure.

[Paul C]

I was going to type something out, but Nick's pretty much said it, and better than I could have explained!

[Tony Brooks]

Morning all.

 

Looking at another thread about batteries, I am wondering if it's better to have more or less batteries.

 

Less means they'll run down quicker but should be easier to keep nearer to fully charged.

 

More batteries and they'll last longer between charges, but may be harder to keep, near to fully charged.

 

Thanks for any help/advice/opinions.

 

Rob....

 

I do not understand the logic in this. The time it takes to recharge a bank or battery from a given source is dependant upon how many Ahs were taken out so given the same charging regime the bank size should make little difference to how easy they are to keep fully charged. That is unless you decide to go longer between charges but then it is your use that has caused the problem, not the bank size.

 

Nick's figure of having a bank size of about four times the discharge between charging periods is a good guide but if you are talking about 440 Ah or 550 Ah (say) then remember the lower the discharge as a fraction of capacity the greater the banks effective capacity courtesy of Mr P. In that situation I would always go for a slightly larger bank.

[ROBDEN]

As Neil says the decision as to what size of battery bank to have should be based on all the factors as stated by Neil. If you do a power audit and can tell us about all your power management regime then some meaningful answers will be supplied.

Phil

Hi Phil.

 

Not a problem, was just wondering is all.

 

Rob....

[ROBDEN]

I'm going to make what will hopefully be a useful contribution, but only if I'm allowed to say this first: it's "less" for an amorphous quantity. Eg " less sugar in my tea please" but it is "fewer" for an integer quantity eg "fewer batteries". There, I feel much better now thank you.

 

So the answer is, the right number is best. To many is bad, too few is bad. The main criteria are of course the amount of power consumed on average, and the time between recharges.

 

It's pretty easy to see why too few is bad. The batteries get into a low state of charge between charges. This means that some services won't work well, especially inverters and fridges. The batteries' voltage will dip under load to the point where these things won't work properly. The lifespan of batteries depends on the depth of discharge and whilst I think the "50% rule" is overplayed, it is certainly true that repeatedly taking batteries to a low state of charge shortens their lives, and significantly so if they are "leisure" batteries that are in reality re-badged starter batteries.

 

As for too many well firstly there is the cost, space required, weight, and increased time taken to service them.

 

But more subtley with a large excess of storage capacity the owner will not know that things are going wrong (things mainly being inadequate charging) until the actual capacity has fallen massively such that it impinges on the owners normal routine. Thus the owner doesn't have an opportunity to fix the problem until the entire large bank is caput.

 

But then again, if money is no object then the reverse of the above is that an excess of capacity allows carefree use and substantial degradation before there is a problem. But most of us do find money is an object so it's best to have the right capacity.

 

To work out the right capacity as I mentioned at the beginning, you need to consider the normal power demand and the interval between recharging. If you have solar this also has to be taken into account. The frequency of recharging depends on whether you cruise daily, or whether you are mostly static and running an engine only for electrical generation (and this whole thing presumes you are not on shore power).

 

I would say that you want to aim for daily discharge of 25% in winter as a ballpark figure. This gives you scope to either not recharge for a couple of days if you are static, and/ or allow the batteries to become pretty knacker before they need replacing. There is of course no absolute "right answer" but that is a ballpark figure.

 

Thanks for that Nick, very informative.

 

Oh yeah.....and thanks for the grammer lesson.

 

Rob....

[nicknorman]

Oh yeah.....and thanks for the grammer lesson.

.

And thank you for ignoring my missed apostrophe!

[ROBDEN]

And thank you for ignoring my missed apostrophe!

 

But yeah but as I didn't say what size, shape or type of battery, couldn't they be classed as amorphous?

If so then that will make me correct and you (teach') wrong.

 

Back of the net!!!!

 

Rob...

[nicknorman]

But yeah but as I didn't say what size, shape or type of battery, couldn't they be classed as amorphous?

If so then that will make me correct and you (teach') wrong.

 

Back of the net!!!!

 

Rob...

Yes you're right, amorphous was the wrong word (it means undefined shape of course ) when I meant .... can't think of a better word ... uncountable. There must be a better word...

 

 

Anyway, so the outcome is unfortunately 2-1 to you!

[Alan de Enfield]

 

I do not understand the logic in this. The time it takes to recharge a bank or battery from a given source is dependant upon how many Ahs were taken out so given the same charging regime the bank size should make little difference to how easy they are to keep fully charged. That is unless you decide to go longer between charges but then it is your use that has caused the problem, not the bank size.

 

Nick's figure of having a bank size of about four times the discharge between charging periods is a good guide but if you are talking about 440 Ah or 550 Ah (say) then remember the lower the discharge as a fraction of capacity the greater the banks effective capacity courtesy of Mr P. In that situation I would always go for a slightly larger bank.

 

Just the thoughts of a simpleton.

 

If you use 100 amps from a 200 amp bank, the SOC is at about 50%

If you use 100 amps from a 400 amp bank, the SOC is about 75%

 

You still need to replace 100 amps

 

A bank at 50% SOC will accept a higher charge rate than a bank at 75%, so, assuming using the same charging method a smaller bank will in fact charge quicker than a larger bank.

 

Right or wrong ?

[nicknorman]

A bank at 50% SOC will accept a higher charge rate than a bank at 75%, so, assuming using the same charging method a smaller bank will in fact charge quicker than a larger bank.

 

Right or wrong ?

However if we presume that these banks are at different SoCs because they are different sizes, the question becomes:

Does a bank at 50% SoC accept a higher charge rate than a bank twice the capacity, at 75% SoC? And the answer is less clear-cut.

[Paul C]

Yes you're right, amorphous was the wrong word (it means undefined shape of course ) when I meant .... can't think of a better word ... uncountable. There must be a better word...

 

 

Anyway, so the outcome is unfortunately 2-1 to you!

 

indiscrete? (Not to be confused with indescreet).

Edited March 5, 2015 by Paul C

[Keeping Up]

I agree with Nick's suggestion that 4 times your daily usage is good because it would typically mean you only need charge on alternate days.

 

It's worth remembering where the "50% rule" came from. It was never intended to be a recommendation on how far to allow the batteries to discharge before recharging, it was instead specifically formulated (by Gibbo) to answer precisely the question that the OP is asking - namely "how big a battery bank should I buy?", to which it it answered that you should "buy a bank just big enough that you will usually discharge it by 50% before you recharge it". This figure (50%) was derived from purely financial considerations, based on the cost of new batteries (obviously a bigger bank costs more to buy) versus how soon they'll need replacing (they have a shorter life the further they are discharged).

 

It's still a good rule but I wonder if the calculations should be revisited given that battery prices have increased a lot since the rule was formulated, that many suppliers have pricing strategies have pricing structures that give bigger discounts for quantities, and battery performance characteristics may have changed as elements such as calcium are added to battery plates. And my brain keeps going around in circles when I try to work out whether the price of diesel comes into the equation or not.

[ROBDEN]

Yes you're right, amorphous was the wrong word (it means undefined shape of course ) when I meant .... can't think of a better word ... uncountable. There must be a better word...

 

 

Anyway, so the outcome is unfortunately 2-1 to you!

 

Wow...I was right?

Wow...I was correct?

Whatever call it a draw.

 

I agree with Nick's suggestion that 4 times your daily usage is good because it would typically mean you only need charge on alternate days.

 

It's worth remembering where the "50% rule" came from. It was never intended to be a recommendation on how far to allow the batteries to discharge before recharging, it was instead specifically formulated (by Gibbo) to answer precisely the question that the OP is asking - namely "how big a battery bank should I buy?", to which it it answered that you should "buy a bank just big enough that you will usually discharge it by 50% before you recharge it". This figure (50%) was derived from purely financial considerations, based on the cost of new batteries (obviously a bigger bank costs more to buy) versus how soon they'll need replacing (they have a shorter life the further they are discharged).

 

It's still a good rule but I wonder if the calculations should be revisited given that battery prices have increased a lot since the rule was formulated, that many suppliers have pricing strategies have pricing structures that give bigger discounts for quantities, and battery performance characteristics may have changed as elements such as calcium are added to battery plates. And my brain keeps going around in circles when I try to work out whether the price of diesel comes into the equation or not.

 

Not sure about the price of batteries going up.

When I bought my current set of (cheapo) batteries they cost me £320.

To replace them like for like now, they'll cost £262.

 

Surely the price of diesel has to come into it.

If you need to run, say an extra 8 hours a week to get a full charge, multiplied by 52, that could be about the cost of another set of batteries.

 

Rob....

Edited March 5, 2015 by ROBDEN

[nicknorman]

indiscrete? (Not to be confused with indescreet).

Or even "indiscreet"?

 

Yes but I think it should be non-discrete. But a lot of folk don't understand the word "discrete", never mind it's antonym. "Uncountable" is perhaps more user-friendly.

[RLWP]

Or even "indiscreet"?

 

Yes but I think it should be non-discrete. But a lot of folk don't understand the word "discrete", never mind it's antonym. "Uncountable" is perhaps more user-friendly.

 

I can feel the word 'integer' floating around somewhere in this.

 

Richard

[nicknorman]

I can feel the word 'integer' floating around somewhere in this.

 

Richard

Hmm, floating (point) integer, definitely an oxymoron.

[Keeping Up]

 

Surely the price of diesel has to come into it.

If you need to run, say an extra 8 hours a week to get a full charge, multiplied by 52, that could be about the cost of another set of batteries.

 

Rob....

 

Yes but the total energy supplied to the batteries is the same (or is it?) so if you have to run it for longer but less often, is it cheaper or dearer? And if the load on the engine changes with battery state of charge, how much does that affect it? No, my brain is still doing circles!

[RLWP]

Hmm, floating (point) integer, definitely an oxymoron.

 

I'm not sure of your point about floating - both floating and float seem appropriate to this subject

 

So, let us say that you have done your sums on consumption, and the answer is four and a half batteries. Would you install four or five? My inclination is four based on highly unscientific principles

 

Richard

 

I'm leaving puns about oxen and mental faculties for others

[Keeping Up]

I can feel the word 'integer' floating around somewhere in this.

 

Richard

As the subject is complex, does that mean there are imaginary numbers of batteries too? Or real numbers of imaginary batteries?

[RLWP]

As the subject is complex, does that mean there are imaginary numbers of batteries too? Or real numbers of imaginary batteries?

 

 

i don't know

 

Richard

[nicknorman]

Surely the price of diesel has to come into it.

If you need to run, say an extra 8 hours a week to get a full charge, multiplied by 52, that could be about the cost of another set of batteries.

 

Rob....

 

A few presumptions:

 

Generators/boat engines running as generators are very inefficient at low power demand, efficiency is better when they are working harder.

 

You could conceptually split the charging phase into two, the bulk phase where most of the charging is done at the limit of the charging device, and the final phase where, pretty much regardless of the size of the battery bank, it takes ages to put those last 10% or so of AH back in, with the generator / engine having a very low power demand and thus being very inefficient.

 

The amount of diesel/energy required for the bulk phase is going to be the same whether you have a big bank that you recharge every second day, or a smaller one that you recharge daily.

 

But by charging daily, you are maximising the long running period to get to 100%. But if the bank is twice as big and you only have to charge every other day, you halve the amount of time spent on the final phase reaching 100%.

 

On the other hand, you might have a charging strategy whereby you only charge to say 85% on some days, whilst taking up to 100% on some other days so the answer is not clear cut.

As the subject is complex, does that mean there are imaginary numbers of batteries too? Or real numbers of imaginary batteries?

Well certainly when your batteries are flat, you have the square root of nothing in the way of power to your boat. Edited March 5, 2015 by nicknorman

[RLWP]

Well certainly when your batteries are flat, you have the square root of nothing in the way of power to your boat.

 

I thought it was some vulgar fraction like four fifths of five eighths of f all

 

Richard