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3 batteries

Old 03-23-2007, 09:26 PM
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Default 3 batteries

can anyone tell me how to add a 3rd battery to my twin outborads
Old 03-24-2007, 06:23 AM
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Default Re: 3 batteries

Welcome to THT.


Some info would be helpful (type of boat, type of motors, existing batt setup) Adding your location to your profile is often helpful in answering questions


Start here

http://www.thehulltruth.com/forums/t...139593&start=1



Old 03-25-2007, 11:21 AM
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Default Re: 3 batteries

Why do you want a third battery? If you need a battery to run instruments or other loads and want to avoid running down a starting battery you should use a Combiner. A Combiner will divert excess alternator charging current to the third battery as it becomes available after first charging the starting battery.

There are a number of ways to do it. These methods make sure the load on the third battery will never discharge a starting battery. Although you could use a manual switch, the extra uncontrolled load the switch would put on the alternator(s) may overload them.

1. A combiner between just one of the starting batteries and the third battery. Whenever that engine is running the third battery will get a charge. Charge is only delivered in increasing amounts as capacity becomes available from the alternator after satisfying the starting battery first. But if the running time is too short to get enough charge to it you could consider #2.

2. Uses two combiners - one between each starting battery and the third battery. Now either engine or both if both are running will provide alternator capacity to the third battery as power becomes available.

3. But my preference is to dedicate one of your existing batteries for starting and the other for the auxiliary functions. Just put both starter cables from the OB to one battery, and then just one combiner between it and the second battery which is now dedicated to house loads. There is little justification for having separate starting batteries when one will be adequate so this saves the cost and weight of the third battery, plus it allows operation with just one combiner. If you are concerned that both engines are now dependent on one battery for starting, install a $15 emergency parallel switch that would allow the second battery to be put in parallel with the first one so both batteries in parallel are now available to provide starting power.

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