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Old 04-02-2016, 14:52   #1
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house bank size and charging

Question, given the same amount of power usage, let's call it 150 amp hours a day , Will time to fully recharge be any different if the battery bank size is 300 Amp hrs as opposed to 700 amp hrs?
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Old 04-02-2016, 15:12   #2
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Re: house bank size and charging

700ah should be faster - as when you are getting close to full charge the charging potential drops and will say 700ah will charge the last 150ah about 2x faster then 350ah bank - assuming if you have powerful enough alternator e.g 100a if you have 50a the difference will not be great...
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Old 04-02-2016, 15:29   #3
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Re: house bank size and charging

Not much, if at all. What you take out is what you have to put back plus inefficiencies.

The larger issue is battery life. The larger a bank, given the same daily load, will simply last longer 'cuz you are using less of the overall % of capacity.

Largest House Bank 101 (by Nigel Calder)

http://c34.org/bbs/index.php/topic,5....html#msg45046
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Old 04-02-2016, 15:57   #4
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Re: house bank size and charging

Larger AH capacity battery banks will accept charging current faster than smaller AH capacity banks. No question.

This is true both at early charging stages and in the final stages.

Batteries decide how much charging amperage they will accept, given constant voltage.

If a 100AH capacity battery will accept 25A charging current @ 14.8VDC when 50% depleted, then two 100AH capacity batteries of the same age, make, and condition will accept twice that amount, or 50A charging current.

This is true at any SOC.

Therefore, the larger the battery bank, the more recharging energy it will accept at any given SOC.

How long it will take to reach a full charge, however you choose to define "full charge", will depend on a number of factors. But, the larger bank will always win out.

And, as Stu noted in the referenced Calder response, the larger the battery bank the greater its longevity under any given conditions, because its discharge will be shallower than will the discharge of a smaller bank.

Also, not mentioned earlier, the larger the battery bank the more Mr. Peukert comes into play. Thus the 20-hour rated capacity might well understate the actual AH available from the battery.

Larger is almost always better, if you can stand the hit in your wallet and have the space to put the batteries, and the willingness to maintain them properly.

Bill
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Old 04-02-2016, 20:39   #5
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Re: house bank size and charging

As others have said...

Given your specific example:
- 300 amp-hr would probably be the minimum I would want.
- A little large would be nice (maybe 400-450amp-hr)
- 700 amp-hr is probably overkill

There is a point of diminishing returns and battery banks often die a short death from charge malfunctions and other maintenance issues. Better to accidentally kill an appropriately sized battery bank than an expensive oversized bank.
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Old 05-02-2016, 08:14   #6
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Re: house bank size and charging

Quote:
Originally Posted by btrayfors View Post
Larger AH capacity battery banks will accept charging current faster than smaller AH capacity banks. No question.

This is true both at early charging stages and in the final stages.

Batteries decide how much charging amperage they will accept, given constant voltage.

If a 100AH capacity battery will accept 25A charging current @ 14.8VDC when 50% depleted, then two 100AH capacity batteries of the same age, make, and condition will accept twice that amount, or 50A charging current.

This is true at any SOC.

Therefore, the larger the battery bank, the more recharging energy it will accept at any given SOC.

How long it will take to reach a full charge, however you choose to define "full charge", will depend on a number of factors. But, the larger bank will always win out.

And, as Stu noted in the referenced Calder response, the larger the battery bank the greater its longevity under any given conditions, because its discharge will be shallower than will the discharge of a smaller bank.

Also, not mentioned earlier, the larger the battery bank the more Mr. Peukert comes into play. Thus the 20-hour rated capacity might well understate the actual AH available from the battery.

Larger is almost always better, if you can stand the hit in your wallet and have the space to put the batteries, and the willingness to maintain them properly.

Bill
Mr. Trayfors has nailed it. The bigger bank is better not only due to charge acceptance, but because you cycle it less deeply between charging sessions. If you can stay above 70% SOC, you can add years to the bank's lifespan, assuming you keep things clean and watered and have properly sized cabling, etc.

Of course, we are discussing distance cruisers, not club racers, who just need to keep lights and radio running in the fall events.
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Old 05-02-2016, 08:41   #7
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Re: house bank size and charging

btw: in my case I have 400ah battery bank and my daily usage is 180ah to max 200ah - but I have also 240W solars + wind turbine + run the engine usually about 1h a day - this way my batteries do not go under 80-90% but still I can use about 200ah a day and have a good reserve in case..
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Old 05-02-2016, 14:38   #8
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Re: house bank size and charging

I agree, larger bank is better with one proviso, that you ensure you have a charging set up capable of fully charging the batteries often. You can do as much damage to a battery by not fully charging it regularly as letting it get run down too much. The recommendation is your charging capacity should be equal to 25%~33% of you battery capacity. (source: Nigel Calders 'Boatowners Mechanical and electrical manual') so in your case with 700Ahr battery bank = 175Amp~230Amps although if you have solar as well I'm guessing you may be able to drop that down a bit.
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Old 05-02-2016, 15:07   #9
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Re: house bank size and charging

My understanding is that a alternator 50amps can support max 500ah and 100amps can support up to 1000ah ..

I'm with 50amps alternator and all is well with 400ah bank
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Old 05-02-2016, 20:06   #10
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Re: house bank size and charging

Given a balanced system charging time is not dependent on bank size at all, it take exactly the same time to charge 700a/hr as 300 because the charge acceptance rate on the bigger bank is double the smaller one. What does make a difference is depth of discharge. Because bulk charge is at much higher rate if you discharge to 50% then your first 25-40% (C3-C10 charge rates) of charge will go in at a higher rate. At 75% D of C you only get to put in 0-15% at bulk so most of the charge is at a lower rate. In both cases it still takes the same time to get from wherever bulk charging stops to full charge but overall the deeper the cycle the less total time you spent on recharging. This is why people will use the 50-80% capacity range underway then do an equalization charge when back on shore power. Done for too long it significantly reduces batt life.
As 'rule of thumb' I would say the bank should be 3-4x the typical daily load. that gives you a typical 25% cycle for good batt life and the option to run two full days without going below 50% or longer in 'power economy mode'. It is always worth considering that if the engine won't start or charge it will be when the batt is already due for a charge - how much capacity do you then have left?
Therefore for 150a/hr day you should look at 450-600a/hr for the bank. 300 would only be OK for coastal or W/E sailing less than a full day from port.
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Old 07-02-2016, 11:25   #11
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Re: house bank size and charging

Quote:
Originally Posted by roland stockham View Post
you should look at 450-600a/hr for the bank.
450-600a/hr No, it's 450-600 amp hours.

I'm "The Other" Stu

Good discussion otherwise.
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Old 07-02-2016, 12:32   #12
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Re: house bank size and charging

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450-600a/hr No, it's 450-600 amp hours.

I'm "The Other" Stu

Good discussion otherwise.
That's what he said. Abbreviations are allowed.
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Old 07-02-2016, 12:39   #13
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Re: house bank size and charging

"/" means divided by, I'm an engineer. But since we've already had this discussion, ad nauseum, I shoulda just canned it.

Sorry folks.
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Old 07-02-2016, 15:42   #14
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Re: house bank size and charging

Quote:
Originally Posted by mitiempo View Post
That's what he said. Abbreviations are allowed.
I won't can it

Abbreviations are allowed if they are correct ones. Incorrect ones are highly frowned upon

Please take a careful look at
Amps v Amp hours v Amps/Hr
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Old 07-02-2016, 15:48   #15
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Re: house bank size and charging

Well actually my battery bank is much larger than that ,just over 1300 Amp hrs (happy stu ?) I am on the hook and charging with 825 watts of solar, I also have a 40 amp Mastervolt charger and 100 amp Magnum inverter charger. I rarely see battery voltage below 12.5 . and on a nice sunny day this time of year, the solar will produce well over 200 amp hours of power. down the road I do plan to install a battery monitor. but for now I am just trying to make the best educated guess that I can
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