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ELECTRICS
Is dual battery use a good idea?
Q I have a large house battery bank made up of 3 x 100Ah deep-cycle lead acid batteries. Is there any reason why I shouldn’t use this to start the 30hp Yanmar diesel engine?
I believe the starter draws around 90A so that’s 30A per battery. Is this well within the operating range for a deep-cycle battery?
The reason for not just using the engine start battery is that I only have a 1/2/both/off rotary switch, so having to remember to use it every time I start/stop the engine is a hassle, and I may forget one day and discharge all the batteries.
Richard Hole
DUNCAN KENT REPLIES:
You can start the engine using a deep-cycle battery but it’s not advisable to do it regularly. A starter battery has lots of thin plates designed to push out a huge current for a short period of time, whereas a deep-cycle battery has fewer, thicker plates to allow for slow discharge over a long period without plate damage.
Sometimes, ‘leisure’ batteries are sold as deepcycle, when they’re not really. However, provided they display a cold cranking amps (CCA) rating on the label they are more suitable for starting than a proper DC battery. With AGM type batteries it’s not quite so bad, although I still wouldn’t do it too often – only in emergencies.
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