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Battery charging

I have one altenator on my engine, how many batteries could I safely charge using just the one altenator

Asked by: DenisAlcock  | 6.33pm, Sunday 17 May

WW says:

Generally, I would suggest that no battery bank is bigger than 5 batteries, or you might find failure happens quicker! You can split battery banks, if you want more than 5 batteries in one system.
Also, bear in mind that if you have a 55A alternator, to charge a very large battery bank will require many house of charging- without external control, the current produced often drops quite quickly, as the alternator senses the battery is "full" when it isn't.
I would suggest voltage sensing relays, rather than a split charge relay, as otherwise the voltage at the battery terminals won't be as high as you might like it.
A sophisicated alternator controller can make a substantial increase in the amount of charge that enters a battery bank.

Mark Langley  | 7.15AM, Wednesday 20 May

Readers say:

As many as you want :-) I used to charge 5: 1 engine, and 2 sets of 2 'house' batteries. You'll need a "split charge relay" (or diode) rated more amperage than your alternator can output, to link your batteries together *only* when the alt. is producing a charge. Try Googling "Split Charge Relay". Hope this helps! Mark

Mark  | 10.43AM, Monday 18 May

There really is no limit to the number of batteries that you can fit. The alternator will not be overloaded as your question seems to imply. In deciding on the design of the system you need to do a power audit (Link to my spreadsheet for this: http://www.smartgauge.co.uk/bits/electrical_audit_published_2.xls ) In most systems the limiting factor is the charge source rather than the battery capacity.

Nicholas Cooke  | 3.53PM, Sunday 24 May

The number of batteries you need will depend on what they have to drive. Do an audit as suggested BUT there is an alternative to the split charger. I use Sterling's Battery to Battery Charger off a standard alternator to charge one starter and three domestics. It cheats to make the alternator think the starter is full then diverts the charge to the domestics. All (110 Ah)batteries survived the last very long cold winter and have given me 2 weeks lights and pumping before I thought about recharging. Very simple to install. 2 years trouble free so far.

Roger Noblett  | 4.46PM, Monday 12 July

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