adding second domestic battery - wire in parrallel or series

PaulR

PaulR

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staggeringly cold this morning (wished I had proper camera to have photographed decks and rig in 0850 blizzard)and crept out of bed turned on new eberspacher and back but an hour later it shut down due to low voltage as domestic battery finding weekend on board (first of the season) with very little engine running more than it could manage - thinking of adding second domestic battery - do I connnect it to existing domestic battery in parrallel or in series ??

thanks
 
If you add two batteries in series, you are in effect adding the voltages together, so parallel is the way to go.
 
Connect in parallel, positive to posoitive and negative to negative. That gives you twelve volts with an increased current capacity. Connecting in series would give you 24 volts (and probably blow all your electrics) but would not increase the capacity at all.
 
Does antone know if you have to mod the charging circuit as effectively you are halving the resistance to charge

Batteries in parallel 1/Rtotal = 1/R1+1/R2
 
[ QUOTE ]
Does antone know if you have to mod the charging circuit as effectively you are halving the resistance to charge

[/ QUOTE ] No you do not have to alter the charging arrangements.

Forget resistance calcultions its got nothing to do with it.

If both batteries are used and charged together as though they are one you could use a higher output charger or a higher output alternator to shorten the recharging time.
 
Still on the subject I have one small starter battery and a larger leisure battery for domestics/navlights.

I have a 12 AMP output from the outboard can I link the two in parrallel and charge simultaneously or due to the different size and type of batteries do I need to fit a changeover switch and charge them individually?

Sorry if this is thread drift but its basically the same question.
 
Snow in Pwllheli this morning, moi am a smartarse, put 3 times 85 amp hr batteries in parrallel 2 years ago, have a 56 watt solar panel, when we got there friday night, bats were fully charged, switched eber on along with fridge etc, bats lasted all weekend with eber running continuously along with fridge. was nice and cosy!! but snow was a shock!
Stu
 
Hi Graham the batteries should be charged in paralell. ie both at once.
While you have a quoted 12 amp charger on the o/b that is usually a max rating which is more likely a max supply current for running lights and other loads. You need 14 volts to charge a battery but the charger is probably only good for about 13 volts max on or near max. load so don't count on 12 amps for charging.

Batteries take a charge current depending on their charge state and the voltage of the charger. So one battery will take eg 10 amps diminishing to 3 amps after a few minutes of charging. Another battery will take the same current at the same time. If the charger cant give the total current then the voltage will drop a little until the total current is in its capacity. But as soon as the batteries take a little charge the charger will be able to provide the 3 amps to each battery.
So more/bigger batteries means more total charge current so more total Amp Hours replaced for a limited engine run time.
More generator capacity does not mean more charge current. Or perhaps only slightly more at initial charging. Unless the generator charging capacity is the limiting factor. ( a 3 stage smart charger can utilise more of the charger capacity for longer so sometimes justifies a larger generator) olewill
 
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