Charging batteries from shore power

noswellplease

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My post is simple but can it be presumed that there is no problem charging up my domestic battery while tied-up even if the starter battery is in parallel. I'm thinking of my engine alternator and hope that I'm in the clear if the engine isn't running!

Only 50 jobs left now and I'll be in the water!
 
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Anonymous

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You can have the batteries in parallel all the time if you like, there are no technical issues except that it becomes one bigger battery and if you flatten it you won't have a battery to start the engine with. Otherwise it's perfectly safe and fine. That's how mine are arranged all the time.
 

cliff

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[ QUOTE ]
You are better charging the seperatly.......

[/ QUOTE ]Why seperately? I always set the selector to charge all batteries at the same time and so far have not noticed any problem so why is it better to charge seperately?
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sarabande

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Isn't there an issue if the batteries are of different aH capacities ?

e.g. where one battery is smaller than the other, it will charge up first (thus requiring less from the charger) but the other battery will still be needing more power, so the charger keeps pushing out lots of volts which could disadvantage the smaller battery by overheating it.
 
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No, let's look at a water analogy. Different sized beakers all have different capacities (litres = diameter = Ah) but the same voltage (voltage = height of beaker). If you put a number of empty beakers of the same voltage (height) but different capacity into a basin and fill the basin with water by turning on a tap, all the beakers will start to fill at the same time (when the water level reaches the rim) and the water in the basin will be held constant as the beakers are filling. Eventually all the beakers are full and you must turn off the tap or the level will rise and overflow (charger voltage controller).

Don't try to stretch the analogy too far, but it sometimes helps to think of electricity as though it is water, and the analogy is good, and much easier to grasp and remember than electricity.
 

shmoo

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batteries sometimes have a pair of diodes to seperate them while being charged from the alternator. Its best, if using a little domestic charger, to get onto the battery side of this unit. It gives you an extra 1/2 a volt of so at the battery, which with a small charger, makes a difference.

Upshot of this is to clip charger direct to one battery at at time. MAKE SURE THE CHARGER IS SWITCHED OFF WHEN CLIPPING ON AND OFF. The sparks can and will (and in my case, have done) cause the out-gasses to explode.
 

William_H

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I would suggest that for shore power if it is to be connected for long periods that you use a regulated voltage charger. ie it provides a steady 13.75 volts or up to 14 volts constantly. This emulates a generator (alternaor) it will charge a depleted battery but not particularly fast and will provide correct voltage for supplying your services while the charger is on. The batteries simply take what they want at this voltage regardless of capacity. However I am guessing from your question that you want a quick boost sso this tyope is not appropriate.

If you go to a stepped or 3 stage charger you will find it will recharge very quickly and hopefully go to float mode when it is recharged. However this may be confused by extra current drain while you are on board and may not suit several different capacity batteries. (I may be wrong here) and is expensive.

Of course if you just want to recharge the batteries from the mains occasionally over a few hours and do not intend leaving the charger on for long periods then the very crude cheap auto charger with an ampmeter will push some charge in fairly smartly. the bigger the better. The output is in the form of pulses which rise to relatively high voltage and fall again at 50 or 100 times per second. This higher voltage gets more into the battery once its inherent voltage has risen but being pulsed the total current is manageable. the internal resitance of the transformer is usually enough to li9mit the current to the ratring of the charger (or less) It may give trouble with electronics being used at the same time. They do have the potential to overcharge a battery if left on too long.
The ampmeter should indicate actual current going in which if multiplied by time in hours gives amp hours replaced. You can guess the amount you need to replace and add 50% from knowing the total battery capacity.

Yes just paralell the batteries and they will share the current acording to need. olewill
 
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