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Old 12-04-2013, 04:57 AM   #1
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Start Battery setups

Hello trying to find out how big of a battery i should have to start my mains. So far i dont see a requirement in the engine manual, but will look a 3rd time....

The current set up is one that i don't like as it would seem to be "bigger is best because we did no know better" mind set that was used in the old days

Current setup. Twin engine with two 8Ds hooked together to make a large start battery ( i always forget which is parallel /series). Both batteries start either engine and has a 12v starter.

Looking for thought of what others are using. The boat is set up with the ability to start using the house battery if needed so in my mind one battery to start both mains is more than enough power.

So the questions that comes to mind.
1.Why not use a single 8D to start both mains?
2. Do you think a single type 31 is big enough to start the mains.
3. How about two type 29 or 31 to start either engine if the MCA is needed (lets face it, the 8D is very heavy and i dont think i can lift it nearly 5 feet up to get it out of the engine room)

I am leaning towards #2 as the first choice then #3.
Engine are cummins V555 that start fast.

Thank You.
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Old 12-04-2013, 06:53 AM   #2
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Most folks find that 2 ser 31 make a great replacement for an 8D .

The CCA is higher , and they are much easier to get aboard.

For a house most will use (2) 6V golf cart batts , wired in SERIES to create 12V for the most common voltage.

2-4-6-8 however big your house bank needs to be.

A single battery bank used to start both mains is fine IF you can find a rotary switch with enough ampacity to do the job.

Some twin engine folks will use the 31 pair (parallel wired) to start one engine and the house set to start the other. Less complex wiring , and the ability to do a cross feed start can remain.

.KISS!
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Old 12-04-2013, 08:31 AM   #3
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I had the same setup you have except the 8Ds are split and can be tied. I busted my jewels moving the 8D so I went to 4Ds. The have close to the 8D CCA and capacity and they can be move by one person.
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Old 12-04-2013, 12:21 PM   #4
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I would noty have a single staty battery (bank) for both your main engines.

If for whatever reason you loose that bank, you are dead in the water.

We have Cummins 330 engines and have a 8D for each engine.

We also have a combine switch to parallel the batteries in case one goes bad.
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Old 12-04-2013, 12:57 PM   #5
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On our 42' Island Pilots (IP395 & IP435) with a pair of 6 cylinder Volvo Pentas (350 HP & 435 HP), we use a single AGM 8D for starting both motors. We chose to do this because we have a house bank of 4 each AGM 8Ds for close to 1,000 AH. We also have a battery combiner that automatically combines, in parallel, the starting battery with the house bank. We felt that using the exact same, deep cycle AGM for the start and house batteries benefited once combined for charging and discharging.

The 5 AGMs are combined when ever there is a charging voltage, either from the engine alternators or the shore power charger. This allows for the house bank to be charged from the engines while underway. The house and starting batteries are disconnected when no charging voltage is present. There is an override switch to combine the batteries should the start battery be too low to start the motors (the equivalent of jumper cables).

Our 7kW genertor is totally isolated and has its own start battery. It is, however, charged from the shorepower charger though an isolated circuit.

This system has worked well over the years. It would also work, regardless of the size and type batteries you use, whether flooded lead and/or 6 volt (in series AND in parallel) or gel or AGM.
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Old 12-04-2013, 01:51 PM   #6
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Do you really need that much battery to start those motors? I mean, I only have a Group 27... or maybe a 31 to start my Perkins 6-banger. Just askin'.
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Old 12-04-2013, 01:59 PM   #7
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No. We don't need that much to start the diesels. As I wrote, we marched the starting battery to those that make up the house bank. Same chemistry. Same size. That way, same charging when combined (which is most of the time ).

GRP 31s would suffice for starting only.
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Old 12-04-2013, 02:22 PM   #8
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I was more asking the OP if they needed big ol' 8D's to start them. I don't know if the cummings need that much battery to start them. My old Perky doesn't take much. (at least in warm weather it doesn't)
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Old 12-04-2013, 05:11 PM   #9
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The IG 36 has 2 8Ds, one associated with each engine, it auto combines them for starting. They are probably bigger than needed for starting. A 6D I just got for the genset has more CCAs than the 8Ds. Battery output for size has increased since the 8Ds were specified. However, too much battery is better than not enough.
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Old 12-04-2013, 06:58 PM   #10
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My setup was like yours. 2 8D's one for each engine. Then I wired the alternators different and have a single starting battery. I now use a 31 which works great. The starboard engine charges that battery and only that one. The port engine charges the house bank. I can join them for starting or charging if I wish with a Blue Seas switch made for this setup.

Believe me, KISS keep it simple stupid works. I have never needed a jump and the single battery works great starting in sequence. Starboard first which charges the battery back after starting, then the port.
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Old 12-04-2013, 09:31 PM   #11
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Harbor,

I don't know how big a Cummins V555 is. I replaced an 8D we used to start a Perkins 6-354 with a group 31 because the 8D was too big to move alone. The Perkins always started instantly with the 31.

YMMV

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Old 12-05-2013, 03:07 AM   #12
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Thanks for your answers.

I think that two type 31s for the engines with the abilty to parallel them might be the best. The house bank has 4 trojan 105s which can also start the mains if need be

Wish i could find the MCA for the mains. They are 555ci, 8.1 liter mains
(Does anyone have the MCA for a cat 3208? That might be about the same size
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Old 12-05-2013, 07:02 PM   #13
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Your starter motors may have labels with info about cranking amp requirements...

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Old 12-05-2013, 07:24 PM   #14
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ya who's curl idea is it to put an 8d in a boat? unless you are the body builder type it is a 2 man job lifting them off the truck, down the dock, up into the boat, down in the ER adn up into the battery compartment. i am not a light weight by any means but lifting 160# that far is more than i can do alone.
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Old 12-05-2013, 07:36 PM   #15
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Quote:
Originally Posted by eseyoung View Post
ya who's curl idea is it to put an 8d in a boat? unless you are the body builder type it is a 2 man job lifting them off the truck, down the dock, up into the boat, down in the ER adn up into the battery compartment. i am not a light weight by any means but lifting 160# that far is more than i can do alone.
I just did it last month by myself and wont do it that way again. Ouch!
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Old 12-05-2013, 07:57 PM   #16
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while no proponent of large batts anyway...there are other methods of moving heavy weights around boats other than with backs if you do choose big batts.
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Old 12-05-2013, 11:18 PM   #17
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That was the original reason I switched from 8-D's to 4-D's, 60 lbs less per battery without giving up too much battery capacity. As it turned out, I then had room for an extra 4-D and gained it all back anyway!! Funny how things work out sometimes.
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Old 12-06-2013, 06:14 AM   #18
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The weight of lead is the size of the battery bank , although there is more lead and less case material in big batts than a heap of small ones , its still just the lead that does the work.

More tiny batts mean more corroding connections to maintain.

IF your back is OK crawling to water and polish the multiple connections is a fine way to vacation.
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Old 12-15-2013, 01:22 AM   #19
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Your weather conditions are similar to mine. Vancouver/Gibsons, B.C.

I do not believe one group 31 will start the engine if the engine and weather is cold. You will get stranded. I'm going to suggest at least 2 PER engine of that size with the ability to parallel if needed.

That engine has no starting aids and it must be spun fast. In cold weather those batteries, any battery, will lose a lot of power and may not be enough. If I'm proven wrong then fine but i sure would hate to see you out in cold weather and the engine cold soaked and you stranded.

For reference that engine is no comparison to any of the engines mentioned so far. It is 9 litres, 555 cu. inches, 17:1 compression so is larger by alot than those mentioned.

I have one, the V555M. I measure over 1,000 amps to get it rolling and then once actually moving the draw drops to about 800A. Mine does fire up fast also. If the engine is too cold and the least bit balky you will not start with one # 31.

Remember too that although battery tech. has moved forward a bit your engine hasn't. It still requires brute power to start reliably in all conditions. You have a Delco 42MT or similar direct drive starter and they are strong but they need a solid belt of power with minimal voltage drop..

I understand your interest in cutting handling of large heavy batteries but don't jeapardize your safety. Maybe one 4D PER engine would do also.

Just for interest i use 2 x 8D. I darn near got stranded one year in very cold weather where we had been out for several days of not running. Never again, at least for that reason.
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Old 12-15-2013, 01:56 AM   #20
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I had the V504M Cummins installed new when I built a boat.
The specs called for (2) 8D batteries in parallel.
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