What Size Battery?

[On The Rocks]

I currently have two 4D batteries used for starting two Perkins 4-154 engines and serving double duty as the house batteries. I would like to set up a seperate house bank and have two smaller batteries used exclusively for starting the engines. My engines start quickly, they only need one or two revolutions of the starter to get going. The area I'd like to put the starting batteries in is small so I'm wondering if I can go as small as 2 group 24s or if something bigger is needed.

Any suggestions?

 

[Phil Fill]

Before you do anything you need to guestimate the total DC amps required to size the house bank correctly. Two 4 D might be to small. Are the 4-D start of deep cycle? House should be deep cycle. Are you going to run an inverter if so how many DC amps will it take? 1 AC amp = 10 DC amps

And you thought this was going to be simple

 

[On The Rocks]

Yeah I know the 4ds won't be enough for cruising. I've got room for 6 to 10 golf cart batteries for the house bank. Iwas just going to get by with the 4ds until they wear out, right now I really do more day and weekend cruising so they are fine. I would like to have the starting batteries seperated from the house though.

 

[BruceK]

There is a useful article on sizing the battery bank in December "Afloat" magazine <www.afloat.com.au> by marine electrics specialist Kurt Kupper, under the heading "Boat Electrics". Nothing new, just how to calculate loads for how much battery you need, with some other ideas included.

 

[FlyWright]

Boat Electrics - Determining the power requirements of a boat

Good intro article. It points you in the right direction, especially with regard to a power requirements assessment of your boat. I have found that a Kill A Watt meter is very helpful in measuring my 110V consumption through my inverter. I picked mine up at a local electronics store for around $20.

Large house banks can be nice, but they come with larger charging requirements to keep them healthy. A quality smart charger is essential, and generally, bigger is better when it comes to charger power. The same can be said for alternator charging...large amperage and smart charging are key for a happy bank. And to keep an eye on everything once it's installed, a battery monitor makes life much easier for around $200 additional bucks.

 

[Fighterpilot]

I use two standard type batteries from Sams to start my 3208 Cats. I have them wired in parallel to double the cold cranking amps but one at 800 CCA would start the engines in the summer. Don't know about 30 degree temps however, but in parallel plenty of cold cranking amps. If you wanted to go with a 31 series one would be enough for your engines I would think.

 

[Datenight]

Rocks,

I used a group 27 to start the 6-354 in the old boat for years. Worked great.

Rob

 

[DavidM]

This is what I have seen installed in my boats and OP's boats as a starting battery:

2,3 cylinder small Yanmar, Volvo, all gensets-----Group 24
Larger 2 liter Yanmar and your W 4.154----------Group 27
5+ liter Yanmar, Cummins, Perk, Lehman---------Group 31, 4D, 8D

It seems that for the big engines they get crazy and install the 4 and 8 Ds which is way overkill IMO. Probably comes from 18 wheeler experience. But those are now 8+ liters mostly.

David

 

[Datenight]

Rocks,

I should have also mentioned the house was 4 6 volts at 215 amps each for a total of 430 amps at 12 volts. Lights including anchor were all changed to LED. Propane range and Isotherm 12 volt reefer.

The charger was an older smart 40 amp xantrax I bought on line before ebay (!). It still works fine. Had a 140 amp alternator built at the local electrical shop for about for $100. ish. A Balmar smart regulator took care of charging. It also controlled the output of the alternator which I kept around 90 amps as I never went to a dual belt drive.

We used a 600 watt cheapo inverter to charge the laptop. Cell phones used the 12 volt car charger.

Way more info than you wanted but it worked well for us for the 15 years we had that boat.

Rob

 

[Daddyo]

I've used group 24s to start my Lehman 120s for years with no problem at all. We have (10) 6v cart batteries for the house. We have a 160A charger but this notion that a large house bank requires a large charger I think is rediculous. A large charger is only needed if you run your bank down and you need to charge it quickly. The larger your bank then the less likely you are to run it down before external power becomes available ie: shore, alts, genset. The key to all of this is of course to not discharge your batteries anymore then is avoidable. Deep discharge equals short battery life.

 

[Captain K]

Thanks Daddyo for your comments. I've got two 4D's for starting my twin Lehman 120's. I've wanted to expand my 6 x 6volt house bank to 10 x 6 volt but not enough room. Now I can replace by two big 4D's with group 24's and have plenty of room left over for the house bank expansion!

 

[Gulfstar 36]

Rocks,

I have the same boat but with the 4.236 engines. I have 1 4D AGM for starting and 4 4D AGMs for the house, so I have 5 of them all together. Once I figured the previous owner had the A-B switch labeled backwards everything is now fine. This is plenty of juice for us in the Chesapeake.

I currently have two 4D batteries used for starting two Perkins 4-154 engines and serving double duty as the house batteries. I would like to set up a seperate house bank and have two smaller batteries used exclusively for starting the engines. My engines start quickly, they only need one or two revolutions of the starter to get going. The area I'd like to put the starting batteries in is small so I'm wondering if I can go as small as 2 group 24s or if something bigger is needed.

Any suggestions?

 

[Daddyo]

Thanks Daddyo for your comments. I've got two 4D's for starting my twin Lehman 120's. I've wanted to expand my 6 x 6volt house bank to 10 x 6 volt but not enough room. Now I can replace by two big 4D's with group 24's and have plenty of room left over for the house bank expansion!

Go for it, it works perfectly and no 4Ds to lug around anymore. My other experience is the 6Vs need much less water maintenance then the 4D and the group 24 could/should be a throw away "no" maintenance auto battery (cheap and works).

 

[FlyWright]

To reduce battery maintenance, I added Water Miser battery caps to my 6x6V house bank and have been very happy with the improvement. I still check my batteries every 3 months (any month divisible by 3) but find that I only need to add an ounce or two of water after 6 months. There is no evidence of water or acid venting on top of the batteries.

 

[Marin]

Our boat was built with two 8Ds for house and start and a single 4D to start the generator. The two 8Ds could be independently designated to be house, start, or combined. Very flexible system.

Three years ago we took the advice of the owner of the marine electric shop we use and replaced the two 8Ds with six 6vdc golf cart batteries. This entailed no change ot the boat's battery boxes or wiring. An 8D battery box will hold three golf cart batteries. Two pairs of the batteries were wired together and connected to the leads hat had connected to the port 8D. This group became our house bank. The other two golf cart batteries were wired together and connected to the leads that had gone to the starboard 8D. This became our start bank, although the flexibility to designate either bank for either purpose or connect them all together is still there.

An 8D is about 100 amp hours. Two pairs of 6vdc golf cart batteries is about 200 amp hours. So we have doubled our house capacity and retained the original start capacity with no physical or electrical change to the boat at all.

 

[dwhatty]

Got rid of two 4Ds and replaced them with Six 6v Trojan 105s this spring. These handle the house and start. Also have a 4D bow thruster battery that can be paralleled with the house to start if needed (absolutely no need to date) and a completely seperated AGM Group 27 (?) for the generator. We more than doubled our house capacity in the same space. But this did add weight that I compensated for by adding some lead to the opposite side.

 

[FF]

When cruising IF you can recharge the bank there is seldom a problem with a huge battery bank. Since normal use will draw it down the least , it should last the longest.

As most cruisers charge from about 50% up to 85% due to time constraints , the lonh term undercharge will shrink the batt capacity over time.

All pluses for the large set and using 6V golf carts is a cheap way to go.

BUT , if the boat is not cruised , the batteries are dieing slowly (6-7 Years) at your expense.

I would go with 2 Group 31's for engine starting that can be paralleled if needed , and as many pairs of 6V deep cycles as you need.

Figure out the total 12V house batt capacity at the 20 hour rate., then cut that in half for 50% SOC.

Then be sure your alt system can pump about 25% of the number you just got to be able to recharge the house set.

 

[BruceK]

As most cruisers charge from about 50% up to 85% due to time constraints , the lonh term undercharge will shrink the batt capacity over time.
BUT , if the boat is not cruised , the batteries are dieing slowly (6-7 Years) at your expense.
.

Solution is, add some solar. It will gently charge your batteries to full, whether you cruise regularly or not, and maintain them. If you fit enough watts,it will power(or help power) things like 12v fridges during daytime. It`s not hard to do, and the cost will be repaid in battery life and available amps.

 

[FF]

"and the cost will be repaid in battery life and available amps."

Esp with the forced overproduction bringing the Buck a Watt panel to the market

 

[rwidman]

I currently have two 4D batteries used for starting two Perkins 4-154 engines and serving double duty as the house batteries. I would like to set up a seperate house bank and have two smaller batteries used exclusively for starting the engines. My engines start quickly, they only need one or two revolutions of the starter to get going. The area I'd like to put the starting batteries in is small so I'm wondering if I can go as small as 2 group 24s or if something bigger is needed.

Any suggestions?

If you can find the required CCS for the engines, that's all you need, no matter what size or group.

That said, bigger is better so if you can put two group 31 batteries in the space, that's what I would do.