Optimising batteries

[oldbilbo]

I'm puzzling over how best to utilise the battery facilities I have. Experienced comment would be most welcome....

It's a Manky Auld Boat I'm refurb'ing. There are/were two x 110Ah conventional batteries, one each side, supporting the 'engine start' and 'domestic services' tasks. One has seemingly died, showing 10.8V. The other, showing 12.5V after extended charge, seems serviceable. The engine is a modest Kubota 12HP lump with a so-far unidentified and unmeasured-output alternator.

There's a basic 'One-Two-Both-Off' rotary control switch, and I have 4 battery isolation switches available.

All - yes, all - the 'lecky lighting is being changed to LED. Apart from engine start, the main electrical loads would seem to be VHF, GPS, sounder, and nav lights ( LED ) and - if I so choose - electrical bilge pumps. There are some nav/performance ST60 instruments, but it is not yet known whether they function. There will be occasional requirement to run a small inverter, but that will be supported by either shore power connection or a small suitcase genset.

I have acquired 3 AGM batteries - 1X 80AH ( Avon/Varta Ultra ), and 2 x 66Ah ( Optima BlueTop 5.0 )

The question is how best to utilise the resources.

I recognise I'll need to buy some form of charge controller, so should I use:

A: 1 x 80 Ah AGM for engine start and 2 x 66Ah AGM for domestic services

or

B: 1 x 80 Ah AGM and 2 x 66Ah AGM for domestic services, with engine start being supported by 1 x 110Ah conventional battery

Should Option A seem best, how do I utilise the conventional 110Ah battery? Could this be used to power the auto-bilge pump, which starts up every few minutes, checks for resistance, then shuts down....? Manually selected , only when I'm away from the boat.....? I expect to get to the boat at least every couple of weeks.

I intend to provide some solar power resource to keep charge in one or more of the battery banks.... up to 60-80W....but could provide a rather smaller unit for the bilge-pump task.

So, what's best....or close?

 

[Gwylan]

Charge splitter for separate banks, diode or one of those new fangled things people keep talking about.

Have an Adverc to optimise charging from the alternator.
Take a view on whether you want the 1, 2, 3 switch.

Separate bank for the starter circuit.
Run the domestic off the other two. Look for how to wire them correctly.

Make sure you can fuse each bit of kit separately.
Use reasonable sized cables for everything.

 

[superheat6k]

I would pair the 66AH onto say term 1 with the 80AH onto term 2 of the selector switch. Then the domestic batteries are matched so won't tend to fight each other. Then whenever you start the engine select both, as soon as you stop the engine go back to '1' only.

Apply the solar panel to the domestics before the selector, which will presumably run the automatic bilge pump.

Getting into the habit of switching to '1' only whenever the key is turned off doesn't take too long.

I would suggest the Sterling Universal controller. Details of how to install here ...

http://turbo36.files.wordpress.com/2013/01/sterling-universal-advanced-regulator.pdf

 

[DaveS]

If you're OK with the weight and space, I would recommend your option B. The 3 AGMs together would give a bigger domestic bank and the conventional battery will normally get only lightly used in cranking. I would agree with suggestions for an advanced charge controller - there are at least 4 makes available, all with slightly different operational characteristics: each claims to be best, so worth a detailed read of the specs. before choosing - set for AGM (slightly lower max. voltage than ideal for the conventional battery but, as I said, it will normally always be nearly fully charged so not an issue). An AVR to automatically separate the banks when off charge is more efficient than a splitter diode. Some means of powering the starter from the domestic bank is useful: either an emergency paralleling switch or, maybe better and certainly more flexible, a jump lead. I personally do not like 1,2,B,off switches and would just put an isolator on each bank.

 

[JimC]

I personally do not like 1,2,B,off switches and would just put an isolator on each bank.

I would also take precautions to avoid opening the engine isolator whilst the engine is running as this can blow the alternator diodes. Personally, for an engine battery isolator I like the ones that fit direct to the battery terminals. These are only a few quid on ebay and, as they are likely to be comparatively inaccessible, they are not likely to be operated inadvertently.

 

[oldbilbo]

The above is most helpful, and I'll implement most of it. The wall space freed up by dispensing with the '1-2-Both-Off' switch will prove useful when recycled into a mounting/home for a needed second fuel filter....

Thanks, guys.