Tony-B...
Posted: Fri Sep 05, 2008 2:24pm
Post Subject:
Battery banks
Dear Sheila, the Smartbank system and what it does is described on http://www.smartgauge.co.uk/smartbank.html.
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The designer is very knowledgeable about boat electrics. The using splits the charge from one alternator so that two battery banks receive optimum charge from a single alternator. This is not what you appear to have because you say the domestic bank has a dedicated alternator. Smartguage (the company) also market devices for combining the output from twin alternators so the "engine" alternator's potential output is not wasted once the engine battery is well charged - probably about half an hour after starting. If the Smartbank is combined with that then you will get more available charge whilst you are running. If not then I can not think what its use would be UNLESS there is also a separate bowthruster battery. I need more information to be more specific, but if you contact Smartguage I am sure they will talk you through what is available. The boatyard should be able to give more info on what they propose to fit. Something called Peukert's effect means that you will get more capacity from a larger battery bank than the numbers would suggest so 4 x 150 Ah batteries will effectively provide more than 160 Ah extra capacity than 4 x 110 Ah batteries. Its the AGM part that concerns me. Most batteries on boats are destroyed by lack of charging and some degree of neglect and although AGMs allow higher charging currents and lower discharges I can not in all honesty say that they are more cost effective than an ordinary wet cell battery. They may well have longer POTENTIAL life, but the life in the real world may be rather different UNLESS you have regular access to a shoreline and use the charger to keep the batteries fully charged. IT is also important to establish the maximum charging voltage for the particular AGM batteries being fitted (getting a definitive source for this info can be very hard) because some types will be damaged by "normal" charging voltages - especially those from the battery charger. Without knowing your electrical consumption and engine running time per day plus the alternator's output I can not answer your question about the need for the upgrades. I would be especially concerned over what you intend to do with a 3KW inverter. At full output that would be drawing 300 amps from your batteries and the very high current would reduce their effective capacity so from typically charged batteries (rather than fully charged) you may only have an hours use with the AGMs - then you have the problem of recharging them. If you are not going to have regular access to a shoreline please take great care. I fear for the reliability of any battery type and you may be better spending the extra money on solar or wind generation to help charge the batteries. You may well find that you have to modify your use of electrical appliances or run the engine for very long periods without a shoreline. Tony Brooks
