Battery Bank Size?

[Fuss]

Another thing about balancing the charging against the battery size on a boat around the size of the Ops.

I work on the concept that I want to stick in as much as I can into the battery in 15 minutes as I want to run the motor as little as possible and 15 mins is maybe what it takes to get out of the harbour.

Its often the case that you do other charging jobs at the same time as you start your motor.
Fridge kicks in, Watermaker,boiler maybe, some water boiling, charge some other batteries as well etc etc are a few of the possibilities.

So get yourself a wopping great alternator thats 25% of your battery size plus another 10% for the things that will be running when charging.

Don't get a car one, It will not handle the heat. Leece Neville, fire truck, bus alternator etc.

Make sure the regulator is setup to the right volts for absorbtion so the 15 minutes is optimised.

Its such a shame to see the charging when motoring reduced by all the additional power hungary things going on at the same time resulting in maybe 10% of the alternators output going into the batteries. Or the absorbtion volts set too low for the battery specs.

Its such a golden opportunity on a sailing boat to ram a whole lot of amps in. Especially when the battery has not been charged for a while and its acceptance is high.

[JK n Smitty]

Originally Posted by Don L

It is pretty amazing what solar can do when you would think it wouldn't do anything. I was getting 5 amps the other day during the rain!

It is cloudy today and my boat is out on the mooring with the refrigerator on. Even if the sun doesn't come out the panel will still replace most of the power from the refrigerator running overnight. The system wouldn't go into absorption and truly fully charge but my 460 AH banks can do this this for a long time.

How large is your solar system?

[Dockhead]

Originally Posted by Fuss

Another thing about balancing the charging against the battery size on a boat around the size of the Ops.

I work on the concept that I want to stick in as much as I can into the battery in 15 minutes as I want to run the motor as little as possible and 15 mins is maybe what it takes to get out of the harbour.

Its often the case that you do other charging jobs at the same time as you start your motor.
Fridge kicks in, Watermaker,boiler maybe, some water boiling, charge some other batteries as well etc etc are a few of the possibilities.

So get yourself a wopping great alternator thats 25% of your battery size plus another 10% for the things that will be running when charging.

Don't get a car one, It will not handle the heat. Leece Neville, fire truck, bus alternator etc.

Make sure the regulator is setup to the right volts for absorbtion so the 15 minutes is optimised.

Its such a shame to see the charging when motoring reduced by all the additional power hungary things going on at the same time resulting in maybe 10% of the alternators output going into the batteries. Or the absorbtion volts set too low for the battery specs.

Its such a golden opportunity on a sailing boat to ram a whole lot of amps in. Especially when the battery has not been charged for a while and its acceptance is high.

This is good advice.

My second alternator is a 110 amp * 24 volt Leece Neville. It produces something like 2800 watts at full chat. It puts a huge amount of charge into the batts in a short period of motoring and will run anything on board. I have even run the washer/dryer from it and done complete loads of clothes during longer motoring passages in dead calms. It is regulated by an unconventional external regulator -- an Adverc -- which shoots the batteries with a lot of current at higher voltage than is sustainable, then lets off just before they start to boil, lets them rest, then does it again, etc. It seems to work very well.

I think it's very important to have a powerful alternator, properly regulated. It's great to arrive wherever you're going with full batts and a tank of hot water.

[sailorboy1]

Originally Posted by JK n Smitty

How large is your solar system?

290W with a MPPT controller, 460AH 6V wet cells

[noelex 77]

Originally Posted by Maine Sail

100Ah bank, Peukert 1.25, load 8A = 88Ah - "P" Corrected Load = 9A
200Ah bank, Peukert 1.25, load 8A = 211Ah - "P" Corrected Load = 7.6A
300Ah bank, Peukert 1.25, load 8A = 351 Ah - "P" Corrected Load = 6.8A
400Ah bank, Peukert 1.25, load 8A = 502 Ah - "P" Corrected Load = 6.4A
600Ah bank, Peukert 1.25, load 8A = 834Ah - "P" Corrected Load = 5.75A
800Ah bank, Peukert 1.25, load 8A = 1200 Ah - "P" Corrected Load = 5.4A

Maine Sail your point about the Peukert effect is well made.
However with a average load of 8A, or 192 AHrs a day the smaller battery sizes you quote are not an option which evens out the numbers and makes the practical effect of Peukets reasonably minor unless you are intermittently running high powered loads.

I am also puzzled exactly how you got those numbers.
Using C25 8A and 1.2 as the measurement of battery capacity or example I get
100AHr bank equivalent load is 8.8A
800AHr bank equivalent load is 5.8A
C20
100AHr bank equivalent load is 9.2A
800AHr bank equivalent load is 6.1A

The discrepancy is not too critical to the message, just curious why I cannot match you figures.

[sailinglegend]

Originally Posted by Stu Jackson

It doesn't matter how big your house bank is (excepting an unusually tiny one) because the amount of time required to recharge is exactly the same based on how much you take out!....

Nobody has picked up on this incorrect statement yet!!!!!! One of the reasons for having a larger bank is that you CAN recharge your bank faster - it will be more efficient and accept more Ah more quickly from all charging sources during the boost phase up to 80%.

It takes a bit of very over-simplified maths to prove the point, but a 100 Ah battery that is discharged to 50% may accept 20Ah in the first hour during the boosts stage, maybe 10Ah in the second hour during the start of the less efficient absorption phase, and the remaining 20Ah in another 5 hour. Doubling the battery size to 200Ah, with the same charging source of 20 amps, will accept 10Ah into each battery in 1 hour, that’s 20Ah into the bank. In the second hours it will store another 20Ah. That’s 40Ah replaced in two hours, as compared to 30Ah with a single bank. In the 3rd hour it may still accept 20 amps into the bank because a single battery in the start of the absorption phase could accept 10 amps. That’s 60Ah in three hours.

The key point is that for two hours it is still in the more efficient boost stage where the battery is taking all the current the charge source can give it. Note that the initial boost charging stage has captured 40Ah in two hours, and 60 Ah in three hours. With the smaller bank it could only capture 20Ah in the first hour during boost and 30Ah after the second hour during the start of absorption. The third hour may add another 5 amps. That’s 35Ah with one batteries and 60Ah with two batteries. So a bigger bank will be more efficient and accept more Ah more quickly from all charging sources.

Since a lot of the time we are only charging up to the absorption stage which is about 80-85% then this increase of stored Ah is significant.

[Maine Sail]

Originally Posted by noelex 77

Maine Sail your point about the Peukert effect is well made.
However with a average load of 8A, or 192 AHrs a day the smaller battery sizes you quote are not an option which evens out the numbers and makes the practical effect of Peukets reasonably minor unless you are intermittently running high powered loads.

I am also puzzled exactly how you got those numbers.
Using C25 8A and 1.2 as the measurement of battery capacity or example I get
100AHr bank equivalent load is 8.8A
800AHr bank equivalent load is 5.8A
C20
100AHr bank equivalent load is 9.2A
800AHr bank equivalent load is 6.1A

The discrepancy is not too critical to the message, just curious why I cannot match you figures.

Perhaps the problem is you were using a Peukert value of 1.20? I used a Peukert of 1.25 which is very common for 6V GC2's... I am using a Peukert calculator given to me during ABYC training..

[noelex 77]

Originally Posted by Maine Sail

Perhaps the problem is you are using a Peukert value of 1.20 and I used a Peukerk of 1.25 which is very common for 6V GC2's... I use a Peukert calculator given to me during ABYC training..

Ah that explains it. Yes I was using 1.20. Thanks I hate it when the maths does not work.

[Maine Sail]

Originally Posted by noelex 77

Ah that explains it. Yes I was using 1.20. Thanks I hate it when the maths does not work.

I only added the other capacities to show the relation ship of bank size to load... By going down to 100Ah it shows that the battery is less than 100Ah at an 8A load.... You would need a 5A load to get 100Ah's at the 20 hour rate......

[Stu Jackson]

Originally Posted by sailinglegend

Nobody has picked up on this incorrect statement yet!!!!!! One of the reasons for having a larger bank is that you CAN recharge your bank faster - it will be more efficient and accept more Ah more quickly from all charging sources during the boost phase up to 80%.

Hi,

The real downside of using the "quote" function is that sometimes an important part gets edited out. Please go back and read the rest of my statement, which included a mention of battery acceptance.

Of course, you're right, but that was NOT the point I was making.

Battery acceptance and the affects of Puekert's Law have a very large impact on overall SYSTEM design and operation, but it still comes down to what comes out has to go back in, whether you're working "on the edge" (not too good) or with "room to spare" in the 50% to 80-85% storage capacity area of the house bank.

Thanks.

[chrisjs]

WE have a 50ft trawler with 2 house banks of 540 amps (2x8D) each. In addition we have 2 x4Ds for thrusters, an 8D starter battery and a 4D generator starter. Our expereince is that we modest, careful use of power, we consume 40-50% of the combined house bank within 3 days. We run a small frig. and have 2 small 12V freezers. While anchored in the Bahamas for an extended period, we ran the generator pretty much every other day partly for battery charging and partly for water production.
I think you battery bank need to be significantly larger than it is presently. It is much more efficient to recharge more battery capacity at a single time, rather than need to keep recharging a smaller battery bank more frequently.

[Falshator]

Thanks for all the interesting input on the subject from all parties. Im planning on doubling the Battery Bank size to 660 ah, (a balance of more efficiency vrs weight and storage room taken), getting a bigger alternator, another 145 watt Solar panel (3 in total) that should give me just under 25 amps per peak solar charging hr with a good charge controller
Cheers

[noelex 77]

Sounds like a good plan 435w solar will be a big help. A larger alternator will also help given that your watermaker and other loads will be using a lot of the available power of your 115A unit.
One caution is your current alternator is on the limit for a single belt. If it only has a single belt you will have to modify things to accept a dual belt.
An alternative is second alternator. This requires similar engineering but it helps reduce the sideways load on the crankshaft and gives you some redundancy.

It may be worth starting a new thread on the alternator subject, if you indicate your engine model some members are likely to have done a similar conversion that will help you avoid the pitfalls.

[Dockhead]

Originally Posted by Falshator

Thanks for all the interesting input on the subject from all parties. Im planning on doubling the Battery Bank size to 660 ah, (a balance of more efficiency vrs weight and storage room taken), getting a bigger alternator, another 145 watt Solar panel (3 in total) that should give me just under 25 amps per peak solar charging hr with a good charge controller
Cheers

Sounds like a really good plan A plan to minimize faffing around with power and maximizing cruising enjoyment

Don't forget good external regulation of the alternator.

[Falshator]

To clear up the Water maker issue, It is being run off the engine-belt driven so no power off the Batteries, Thanks