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battery banks

I read so many ideas about battery banks and also told 5 110amp leisure is the maximum what is this the reason for this

Asked by: mick turner  | 4.36pm, Thursday 18 February

WW says:

There is a suggestion that the resistance incurred with more than 5 batteries in parallel can cause problems with charging.
However, the science is not exact behind this, but in practice, it does seem that 5 batteries per bank is the limit- though the capacity could be above 110Ah (the reason that 110Ah batteries are used is that they tend to be the most cost-effective).
Also, if you have a failure of one battery in a bank, a larger bank may hide that defect, to the detriment of the other cells, which is one reason proposed for limiting the number of batteries in a bank. If you wish to have large capacity, think also about the recharge rate of the system- not just alternator capacity, but also the charging profile (i.e. a standard alternator with in-built regulator is unlikely to give efficient charging), as well as suitable cable thicknesses, to avoid voltage-drop (and potential overheating).
For example, a 110A alternator, running just above tickover will produce around 50A- so recharging fully a havily discharge bank of 5, 110Ah batteries would take around 6 hours to charge, assuming the batteries were cycling between around 50 and 90% capacity. in practice, without external regulation, that is more likely to be over 10 hours...!
So, in general, banks of 5 batteries or less are easy to handle, fit and can make life easier for wiring (thinner cables needed) and maintenance.

Mark Langley  | 10.47AM, Friday 19 February

Lee, it is probably that, assuming you do not have an external voltage regulator, then the current output will soon decrease from the alternator, to around 5amp. This happens as the internal resistance of the battery increases, so the voltage applied needs to increase- at which point, the charging is reduced. most alternators fitted to marine engines are not designed to recharge deeply discharged batteries.
This means that, if you are letting the batteries reach 11.7V, then you are cycling between about 55% and 70% of the battery capacity... An external voltage regulator (Adverc, Sterling, etc all make them), you will probably get twice as much (at least) useable output, while charging the batteries much quicker- at the expense of having to top the batteries up a bit more often, with distilled water.

Mark Langley  | 1.51PM, Thursday 4 March

Readers say:

I have 4x 135ah domestics (total 540ah)charged by a 135a alternator and 1x 95ah starter battery charged by a 75a alternator. And to be honest it does take around 4-5 hours to get them up, i never let them drop lower than 11.7 volts. but they don't seem to last me long, maybe i'm watching to much tv.

Lee Farrell  | 4.45PM, Monday 1 March

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