whitedd_58

Sizing Battery Bank Capacity

2 posts in this topic

I'm trying to calculate the battery capacity (Amp-Hours) I need on my sailboat after adding a GPS and Radar.  I can calculate the expected load from all the house loads, but I'm unsure as to how to add in the capacity requirements of starting the engine.  To be clear, I understand the requirement for MCA (Marine Cranking Amps) to ensure that the engine starts.  What I don't know how to estimate is how much that takes out of the batteries in terms of Amp-Hours.   My guess is that it's pretty minor.  Something on the order of 200 Amps for 30 seconds, which would be less than 2 Amp-Hours.  Does anyone have any thoughts on this?  I appreciate the help.

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I'd suggest having two separate battery banks, one for house items like lights, GPS, Radar, etc and another dedicated battery just for starting.  Typically you would use a Deep cycle battery for the house bank which is designed to be run down and recharged.  The other get a starting battery that is designed to out put marine cranking amps for a short period then recharge back to full capacity.  These would be run on a battery switch designated A (starting), B (house) and Both.  That way when your engine is not running you would run off the house bank not draining the starting battery.  When the engine is running you could use Both so both batteries are being charged.  If your starting battery is drained or low you could use Both to get the engine started.

 

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