Battery Banks question

[shemandr]

I have a Freedom 20 charger with the remote and 2 200 ah 4d AGM batteries. Last summer I purchased another 200 sh 4d while on a cruise because of a mis-diagnosis of a problem. Now I have three 4d's which the boat yard mechanic has tested and tells me "..they all test the same." Putting aside for a minute what that actually means, I am trying to decide how to best use them. One notion is to combine the older 2 batteries into one 400ah bank and use the third as an engine battery. Or I could combine all three into one 600ah bank and buy a starting battery. Which I think is a better idea but I haven't run that on Bill Roosa's spreadsheet yet. In any event, should I put the house bank on either the A or B switch of the battery selector or use the echo charge feature of the Freedom 20?
Of course, savy battery-philes on this forum will know that if I use the A/B selector, I should manually adjust the remote control for the size of the battery bank when using either the A or B. That does not appear to be necessary with the echo charger - for what reason evades me.
If I use a 600ah bank I could probaby charge it only at the dock with the Freedom and direct the alternator output (35 amps at best) to the starting battery.
Although the batteries test "..the same.." I am leary of putting the old with the new. I never did that last season but, of course, I found the boat with the selector on "both" after the test.
Advice? Comments?

 

[Ed Schenck]

I have added a battery to a not too old bank without penalty. It would be a shame to lose a 200ah battery to an occasional start of the engine. But 600ah seems like an awful lot of weight on a 36' boat. Nice to have the hours though.

I would trade a 200ah AGM for a small 900cca AGM for a starter battery. Isolate that battery for start only. It sounds like you have two battery switchs, each with 1/2/Both. So I won't get into the wiring of yours.

I have one starter AGM and four house AGMs. The Freedom 20 is connected to the house batteries. The alternator is connected to the battery switch. If on #1 it charges the start bat, if #2(almost always as I start the engine with the house) the alternator charges the house. There is a Combiner wired between the two banks. Once a bank reaches float status the Combiner opens and charges the other bank at the same time. Simple and fail proof so long as the Combiner works. I have had the boat twelve years and never had a problem.

 

[Don S/V ILLusion]

On the issue of combining old and new batteries, I think the fundamental issue is whether or not you NEED 600 amps house capacity? If you do, you can try it and monitor the effect, if any, of the old batteries on the new one. If you really don't need 600 amps, why take the chance?

 

[sailingdog]

IF you can, you really should combine the three into a single large house bank and get a reasonably sized starting battery. However, if the three batteries are very different in age, then combining the newer one with it, unless it is really "testing the same" is a bad idea. A 4D is way too large to be a good starting battery. It is a waste of a 4D.


I would use the Freedom 20's charger to charge the house bank and use a DuoCharge, EchoCharger or ACR to charge the starting bank, rather than the echo charge feature of the Freedom 20. You really should have all the charging sources connected to the HOUSE BANK, as the loads on the starting battery are rather negligible.

 

[Prime Time]

Alternator

If your main charging source is your alternator, you will be severely undercharging your batteries with such a small alternator, Calder recommends an alternator equal to 25% of the amps or your battery bank.

 

[Snotter]

If your main charging source is your alternator, you will be severely undercharging your batteries with such a small alternator, Calder recommends an alternator equal to 25% of the amps or your battery bank.

How so? A smaller alternator just means it will take longer to charge the batteries, provided, of course, demand doesn't exceed supply.

 

[Stu Jackson]

The issue is your system design and how it is wired. Mix all the batteries you want, it sounds like it's working. The bigger a house bank with a small reserve bank the better.

You will be interested in this discussion, the meat starts at the bottom of page 1, then continues on pages 2 & 3: http://forums.catalina.sailboatowners.com/showthread.php?t=104505

 

[Newbie]

If your worried about the alternator charging inefficiently you could put a larger pulley on it to get a little more out of her. that would save you the cost of a new one. Any alternator shop should have one that will fit it.

 

[Chuckbear]

If your worried about the alternator charging inefficiently you could put a larger pulley on it to get a little more out of her. that would save you the cost of a new one. Any alternator shop should have one that will fit it.

An alternator is designed to put out so much current at so many revolutions and is sized to allow output when the engine is at idle. So changing to a larger pulley is not going to make it more efficient. Look at the alternator working properly and look at the regulating system to make improvements. Chuck

 

[woodster]

An alternator is designed to put out so much current at so many revolutions and is sized to allow output when the engine is at idle. So changing to a larger pulley is not going to make it more efficient. Look at the alternator working properly and look at the regulating system to make improvements. Chuck

not to hijack this thread ....is there much horspower diff in say a 35 amp alt to a 80 amp atl in relation to the engines hp......i know on autos the ac compressor takes a big toll on the hp at idle speed when it kicks in and was wondering if this holds true for alts as well....

regards

woody

 

[Ed Schenck]

Yes, nothing is free as you know. An old rule of thumb is "1 hp per 25 amps". So the theoretical requirement for a 100 amp alternator would be four horsepower. But we know that a 100 amp alternator never approaches 100 due to many inefficiencies that I expect MaineSaile will elaborate on. I do know that my 80 amp Balmar creates a lot more rubber belt dust than my old 50 amper did. And it is why anything at 100 amp or more likely comes with a double pulley for two belts. Of course if your batteries are always near or at float stage then the output amps are low and the horses needed are reduced.

 

[shemandr]

update on original

Thanks for your replies:
Newbie - my main source for charging is the Freedom 20 charger/inverter. I plan to address the alternator inadequacy after I've set up the battery banks.
Don - I would like to be able to spend three days on moorings or at anchor without recharging (Via the Freedom). So, yes, I can use the extra capacity. I use about 100 ah's a day.
Ed - the three batteries are on the boat and have been since last season. I would have to pay someone to remove them. I am not going to risk a back injury to do it. I think my boat is wired as you describe minus the combiner. I am interested in adding it but I really don't understand it. Physically, where is it? It must be wired downsteam from the 1/2/both (I have only one - sorry to give impression otherwise) switch and directly to both battery banks. Is that in addition to the battery cables or instead of.
SailingDog - What are DuoCharge, EchoCharge and ACR? Why not the echo charge of the Freedom?
TIA for any further responses!

 

[Ed Schenck]

Andrew, here is an excellent PDF from West Marine: battery combiner . They are small and simple to install. Mine is in the locker with the batteries. It can be mounted almost anywhere within three feet so long as you can route the wiring from the combiner to one house battery and another wire over to the start battery.