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nac

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I am fitting an autopilot and raymarine radar on my 36i odyssey and would like advice on whether I need an extra battery.At the moment there are 2 batteries.1for engine and one for electrics.I got prices to supply and fit same and there was no mention of extra battery.If you could advise I would be grateful.
 
Yes, you certainly need more battery capacity. Ideally, look to have at least 400Ah for domestics, plus the engine start battery.
 
You need to calculate your typical daily Ah requirement, then decided on what % of drain on the batteriers you want to do, some discharge the batteries to 50% some 60 or 70 I am sure you get the idea.

You then need to know how many Ah you can put back into the batteries depending up on type i.e. wet, gel etc. This will dictate how you recharge them its all a balancing act, if you get it wrong you will have the engine on the whole time or spend a load of money you don't need to. What plotter you getting?
 
Any charging capacity - wind or solar, if so how much? How big is the domestic battery? How long between engine runs when the battery is being charged? Do you sail for a couple of hours then back into the marina or sail away for 3 days without wanting to run the engine? There's lots of info needed in order to help.
 
More battery capacity means more charge current when engine is running(which is good) and more capacity when it is not. But also means more cost initially and ongoing replacement. It also means more natural discharge when not in use.
A lot depends on your sailing style. I think you should give it a go with the existing capacity and see how you go. olewill
 
[ QUOTE ]
I think you should give it a go with the existing capacity and see how you go.

[/ QUOTE ]I don't think he'll get far! The radar system will take at least 3A, plus say 2A for the autopilot, and I guess there's a fridge too taking say 2.5A, plus VHF, instruments, etc. Maybe at least 8A in daytime use. In only 4 or 5 hours the single battery will give up.
 
Some of these loads will be used mainly when the engine is running and hence the alternator would take care of them!

Still, without further load info I would probably add a second battery of the same type/size parallel to the existing domestic. It can't do any harm to increase capacity!
 
yes it all has to be worked out.

But we stick the fridge on minimum setting when sailing. Works a bit more like a cold box, but is acceptable for the time we are at sea between cruising ports/harbours.

Our bette noir is the chart plotter. It is a combined plotter/radar, and uses 3+amps per hour even whe the radar is not on. It is continually heating the radar...

I have to switch the unit off at anchor, and just use the GPS alone. No real problem, when you are aware of consumption etc.

Also if at anchor, fridge is set on minimum, and is not a huge drain on power reserves...

Still rely on an hour's charge at anchor, or if in port everything is turned up to best requirements (keeping the tonic very cold)
 
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