[phpzon]Volvo Penta, 1, All[/phpzon]
My boat has 2 batteries (Volvo Penta 230b 120HP engine) and they keep running dry - why?
I run the boat with the battery switch on BOTH - is the alternator good enough to charge both batteries when the engine is running? I just put 2 new batteries on (good cranking amps) but they started the boat once and now they're flat. I always turn battery swith to OFF when not in use. Can anyone help?
You need to prove the regulator/rectifier is functioning correctly. Use a multimeter to check voltage with engine running - this should be around 13.8 to 14.5 V. Above this voltage is a fault and must be serviced as there as there no ability to limit the charge rate and the batteries will be rapidly destroyed. Three phase AC signal will be present in the DC signal, and will not do anything good to anything in the circuit. Below this and the alternator may have failed, or the brushes, or even just a loose connection or broken wire.
If the batteries are going flat - then you are looking at a circuit somewhere, perhaps a voltage leak to water, a faulty bilge pump or switch. If the batteries go flat with the terminals taken off then they are actually faulty themselves. Perhaps your switch is faulty. They are cheap - buy a new one and try. Selector switches must not be operated while the engine is running - should the charge circuit be interrupted for any reason the reg/rectifier can blow diodes instantly.
The alternator will not be 'strained' unless the batteries or electrical load are ridiculously oversized. Brushes and commutator rings will need more servicing, but the alternator will simply produce it's rated output and no more - this just means the alternator sees one battery of twice the capacity anyway so is unlikely to have relevance in this issue. There is no issue with batteries of even much different capacities being combined in parallel as long as the internal structure is the same - in other words only use like with like. If that is flooded cell, Gel, AGM etc. doesn't matter much at all just don't use two different types in the same circuit - ever - and you can't go wrong
Without special circuitry there is little chance of the alternator producing high outputs for very long anyway in a standard system, so the safe policy is to use a good multi-stage charger and keep your batteries fully pressed up as it were and maintenance charge them to keep them cycling at 95 - 100% capacity at all times.
The cheapest option may be to get a good qualified service person or workshop to check the system for you, unless the fault is found quickly you will cost yourself some batteries and that is not good for the hip pocket.
A better circuit involves Voltage Sensitive Relays and an automatic seamless charging of the house battery and starting battery depending on charge state and load.
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