Batteries

[LandLubber No More]

Could someone explain to me the real difference between a group 27 and a group 30 battery and where 4D and 8D come into the mix. How big of a battery do I need on a 29' 36 year old cruiser(pacemaker).

[John E Hardiman]

The Group 27,30,31, etc is a BCI (Battery Council International) standard for case size. Every Group 27,30,31, etc case is the same size. The Group size has nothing to to with the real measures of battery power such as amp-hours (AH, total power stored in the battery), cold cranking amps (CCA, the maximum current a given battery can deliver for 30 seconds at zero degrees F without dropping below 10.5V), and reserve capacity (RC, the length of time the battery will support a 25A load).

The Group 4D,8D, is the BCI (Battery Council International) standard for case size for heavy-duty commerical batteries, and also has no requirement for minimum AH, CCA, or RC.

Get the biggest heavy duty deep cycle battery you can fit in the hole with the most AH, CCA, and reserve capacity.

"There is no substitue for sheer power" :D

[Bruce Hooke]

Will this battery be for starting the motor or for running accessories (or both -- not generally the best idea)? The size of the former should be tied to the requirements of the motor. The size of the latter is based on how long you need to run how much stuff between charges. A good book on marine electronics will help you design a suitable system -- or you can just get the biggest batteries you can afford and see how it works out...

[John E Hardiman]

Bruce is right of course; that normaly there is a "hotel" battery and an engine or "captian's" battery (i.e. "no one uses the captian's battery without his approval"). Normal hotel loads are off the hotel battery with the engine battery isolated while not charging. Most circuts allow either to be cut in to feed the other, but they are usually kept isolated to prevent a single cell failure from flating them both. There are various (at least two that I know of) ways to wire this and each has it's own pluses and minuses (bad pun!) which I suppose you will be exposed to if you ask around enough. I perfer two completely independent circuts that you have to cut in the hotel battery in order to charge it. I recommend heavy duty deep cycle because the cell fabrication methods are more robust vibration wise, but gel-cells are another option. Gel-cells tend to have lower CCAs and RCs for the same size/voltage/AH due to the reduced mobility of the electrolyte.

[GB-32]

IMHO, for a boat of your size with some electronics you should have a “house battery” for all your cabin lights etc. and a seperate starting battery.

What the house battery bank capacity should be will depend on what you want it to do with the electrical equipment you have onboard.

If you have an electric fridge that consumes 100 to 150 AH per day plus some lighting and pumps using a little more, and you want to stay on the hook for at least 2 days, you will want a battery bank capable of delivering 250 or more AH between charges.

Based upon 80% charging efficiency while cruising and 50% discharge down to 12.2 volts before recharging, your battery bank should have at least 650 to 700 AH capacity.

You can adjust the numbers above to fit your scenario to determine what you need.

The starting battery can be either a 4D or 8D, your choice as either will do the job based on your engine requirements.

Ya' know in some cases bigger is better, so fudge a little on your numbers and go for the next larger size on batteries if your budget can afford it..

[Gary E]

Your boat has for all intents and purposes a auto / truck engine found in real rear wheel drive cars and normal size pickup trucks.. Get a PRACTICAL battery..meaning if you have either of the above get 2 of the biggest batteries you can fit in the car / truck, get them from Sears or your local auto supply store of choise, that way the garanteee is for the car or truck, but you probably never need it... Then also get a Dual Battery switch that allows you to use Bat #1 or Bat #2 or Both.. get the kind of switch that allows switching while the engine is running so you dont blow the altenator..

G

[LandLubber No More]

Thanks for the advice guys. I am off to price out some options. Cheers!

[Peter Malcolm Jardine]

Surrette, if you can afford them. Canadian made.

[mmd]

Geez, Peter! Not only are they good and Canadian, they are Nova Scotian! Made in Anne Murray's hometown of Springhill. ;) :D

http://www.surrette.com

[ 01-14-2004, 09:55 AM: Message edited by: mmd ]

[LandLubber No More]

Haven't found the Surrettes yet but it has been recommended to me that 2 Trojan T-105 batteries (6 volt) crossed together would give me more amp hours for the money. Are there any disadvantages to using 2 six volt vice one 12 volt?

[ion barnes]

If two 6v battries (golf cart size) have 215ahr and you want 12v, you can only get 215ahr. If you want 6v, you can get 430ahr. In a perfect world! Do not tie more than four battries together in series or parallel, because the banks begin to fight each other and you have a sorts of battry failures. If you want and have space for a little bigger battry with the same footprint of the golf cart size, there is a 'L' class that puts out 370ahr and is about 6" taller.

There is a lot more to setting up a system, but if you do your homework, starting with the indiviual loads and work back through sub panels to main panel and the to the battries and charging unit, you will be fine. I recogmend Blue Seas gear as its real good quality at a fair price.