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Go Back   SailNet Community > On Board > Gear & Maintenance > Switching battery banks with engine running
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Thread: Switching battery banks with engine running Reply to Thread
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Topic Review (Newest First)
10-01-2008 10:15 PM
Maine Sail
Dual purpose no..

Quote:
Originally Posted by harryrezz View Post
I'd suggest that the optimal setup where space is limited would be two "Dual Purpose" type batteries. That way there would be plenty of CCAs in either batery to start the engine, and nearly as many amp hours in reserve as one would have with a pair of "deep cycles" .... and I believe you'd get more longevity than with a pair of deep cycles which had been subjected to starting use. At least that's what the tech advisors told me at Decca Battery which is located near where I used to live.
Did the tech bother to ask you how many cranking amps you engine actually required? Sure, if you have a 3208 Caterpiller you might need 700 cranking amps but with a small aux diesel you don't!

For example my 44HP 4 cylinder Westerbeke has a max rated cranking amp draw of 160 amps. In the real world, as measured by my Xantrex XBM, she's never pulled more than 100 amps to actually start my engine. Even the smallest personal water craft battery has more than 100 CCA!

People often over estimate the amount of load or amp use caused by engine starting. I can start my engine and not even measure 1 tenth of an amp hour used.

Standard deep cycle batteries will last longer and also will start any sailboat aux engine in the 30-50 foot range. Using start batteries or dual purpose batteries is 100% unnecessary with small aux engines unless you need to save money. I have not owned a start type battery in over 10+ years...

Here are two photos I took the first is prior to starting, after a night on the hook, the second is immediately following engine start. As you can see the amp hours required to start my 44hp diesel were not even measurable...
Before Start:

Immediately after start:
10-01-2008 09:22 PM
captbillc
battery & charging setup

small diesels like the yanmar 2GM20F in my 30 nimble express do not need the CC amps that larger diesels require. i have 4 golf cart 6v batteries in 2 banks with a rotary switch & a battery combiner. i have plenty of ampere hours for my needs with this system and do not have to worry about accidently turning the rotary switch off because the 2 combiner outputs are hooked to the 2 battery connections on the rotary switch.
10-01-2008 11:10 AM
camaraderie Harry...a typical 100amp group31 deep cycle battery has 1/2 the CCA's as a starting battery. Thus TWO group 31 deep cycles can provide exactly the same CCA's as a group 31 start battery AND provide 200amp hours (100amp hours to 50%) of house bank needs. This is a MUCH better solution than a dual use battery which has thin plates and a short life in deep cycle applications.
************
BTW...I am assuming you have the same Perkins as I do..and I have the same Balmar setup...but my 8kw gen does my charging typically with a 135amp charger to 1000amphours of 8D AGM's. A very different situation than is being discussed here.
10-01-2008 11:03 AM
JohnRPollard
Quote:
Originally Posted by harryrezz View Post
Camaraderie - I agree to a point .... that would certainly be better than two "starting" batteries ... but I'd suggest that the optimal setup where space is limited would be two "Dual Purpose" type batteries....
Harryrezz,

I'm going to respectfully disagree with you on that point. On a sailboat lacking space for a dedicated starting battery, the better arrangement would be two deep cycles. They have no problem handling the starting loads, and are much better suited to handle domestic loads for long periods between charging.

If we were talking about a motorboat, like an express cruiser or sport fish, where abundant charging takes place any time the boat is underway, I'd agree with your suggestion.
10-01-2008 10:37 AM
harryrezz Camaraderie - I agree to a point .... that would certainly be better than two "starting" batteries ... but I'd suggest that the optimal setup where space is limited would be two "Dual Purpose" type batteries. That way there would be plenty of CCAs in either batery to start the engine, and nearly as many amp hours in reserve as one would have with a pair of "deep cycles" .... and I believe you'd get more longevity than with a pair of deep cycles which had been subjected to starting use. At least that's what the tech advisors told me at Decca Battery which is located near where I used to live.
I should have mentioned in my post that there is also confusion among many people about what constitutes "different types of battery" when it comes to combining them in one electrical system. This was mentioned briefly in this thread, but it bears underscoring.
It is fine to combine "starting", Dual purpose" and "deep cycle" batteries in one system as long as they are all of the same construction type. By this I mean they should all be "wet cell" types (the typical battery with lead plates suspended in an acid solution and which usually must be topped up with water) OR "AGM" batteries in which the acid is absorbed in glass mats between the plates OR "gel cell" batteries in which the electrolyte is in the form of a gel. The latter two are considerably more expensive to buy, but generally offer more usable power size-for-size, will not spill acid out if overturned (such as in a knockdown or capsize) and last longer with minimal maintenance. Wet cell, AGM and gel batteries should NOT be used in the same system because they have different charging parameters. Because they accept charges at different rates when they are in the same system the probability exists that one type will be under charged while the other will be over charged and ruined.
FWIW, I probably should also have mentioned that I personally am using a Balmar 100 amp alternator fed through a Balmar three-stage "smart regulator" and a battery combiner such as mentioned earlier.
10-01-2008 10:28 AM
bubb2 John on my bennie, the batteries (2) are on separate on/off switches and the 3th switch is the master on/off. The battery switch and the master must be on in order for the battery to charge.
10-01-2008 10:21 AM
JohnRPollard
Quote:
Originally Posted by bubb2 View Post
No John, that black one is the electrical disconnect, the one you don't want to touch when the engine is running!!!!!
Uh oh!

Just kidding. I don't think they ever fiddle with them, but I'll be sure to remind them.

On their boat, they only have two batteries, and they are connected. In other words, either one can be selected and used as the starting battery, and they can be used singly or in combination as a house bank. That might be different from Tim's set-up?

Thanks Mike.
10-01-2008 10:11 AM
bubb2
Quote:
Originally Posted by JohnRPollard View Post
That's the typical French set-up. My sister's Bene 285 has it as well. She has two reds, and one black T-handle. I always thought the black was the combiner?

No John, that black one is the electrical disconnect, the one you don't want to touch when the engine is running!!!!!
10-01-2008 10:06 AM
JohnRPollard
Quote:
Originally Posted by sailortjk1 View Post
Thanks Mike.
I knew I couldn't be the only one out there.
When are you leaving for St. Pete's?
That's the typical French set-up. My sister's Bene 285 has it as well. She has two reds, and one black T-handle. I always thought the black was the combiner?
10-01-2008 08:58 AM
sailortjk1
Quote:
Originally Posted by bubb2 View Post
My boat has the same set up, I like it also. It is easy to cut a battery in or out for charging or starting.
Thanks Mike.
I knew I couldn't be the only one out there.
When are you leaving for St. Pete's?
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