Batteries (again)

[mick]

Thanks to all who replied to the first question in my recent post - much food for thought. Here's the second one again: If I replace one of my two 75AH batteries with one rated, say, 90 or even110AH to give more starting grunt would there be any disadvantages apart from size and price? I have a standard alternator and a heavy duty 1-Both-2-Off switch, but no sophisticated electronic devices. Basically, I am wondering about charging problems. Thanks in advance.

Mick

 

[pvb]

Why do batteries give this grief??

Batteries are simple things. The Ah rating indicates the overall capacity of the battery - but is based on discharging it slowly. Buying a bigger Ah battery won't give you "more starting grunt". There's another measure used for batteries called CCA (Cold Cranking Amps). This tells you how much current the battery will supply to your starter, and is a better indicator for you if you're really concerned about starting. However, a 10hp boat engine doesn't need much to start it. The tiniest automotive battery would be sufficient. Anything bigger is overkill, assuming your charging system works properly. One final point; starting a boat engine typically consumes much less than 1Ah. If you're worried that the alternator won't replace that while the engine's running, you need to review your system very carefully.

 

[Guest]

No such thing as a standard alternator, what rating is it? Also depends on how much you use your engine, have you considered a solar panel? It doesn't take a great pull on the battery to start a small diesel engine provided it's in good nick. I had a single 110ah semi traction battery on my last boat with a 10 watt solar panel. The battery was always fully charged. You can get away with one semi traction battery if a) you have the space for a bigger single battery, b) it gets plenty of charge, c) you carry something like the small power packs that you can take off the boat and carry enough charge to start you engine in an emergency.

Regards,

Peter
http://www.mistressofmourne.com

 

[Paulka]

Re: Why do batteries give this grief??

Very good answer.
I would not replace the starting battery by a "bigger" (in term of Ah) one, rather by a smaller one, just because I am a tightarse. ;-)
But, I would (as I do it on my own boat) keep both batteries (starting and Utilities or domestic) strictly separated on the consumer side. Thus, place the "1 - 2 - both" switch on 1, and leave it there, unless the staring battery gets accidentally flat. ... And then, switch to "both" just the time of starting the engine, and come immediately back to 1.

Of course, you then have to charge both batteries through splitting diodes, or splitting device.

Have a look at:

http://www.adverc.co.uk/technical/technical-boat.htm

The diagramm 1 is exactly how I wired my batteries, and have no problem at all since years.

Please, Mick, feel free to ask more questions via PM. I'll be glad to help you find the most adequate system for your nneds.

Paul