2 battery chargers

[rigpigpaul]

I have just bought a boat with a 110amp domestic battery and a 90amp start battery which is charged from a 25amp Mobitronic charger. I would like to increase the battery bank to 300amps approx. and add a second charger of the same type and size. Does this make sense and does the size of charger have to be matched to the size of battery bank.
The refrigeration is run from the engine.

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[Talbot]

Better off having a single charger driving the two banks. IIRC the 25amp/hr charger should be on nthe top limit for 300 a/h of battery. If the charger will only drive a single bank of batteries, you could wire it so that it works only with the selected battery on the main switch panel (which will reduce the number of a/h of battery it is trying to drive, or upgrade to a larger charger, and sell on your 25 a/h. My 45a/h mobitronic charger will drive 2 banks of batteries.

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[Benbow]

At the risk of appearing too anal, I feel the need to say that battery capacity is measured in amp hours. Presumably we are talking about 110 AH and 90AH batteries, while charger output is measured in amps, presumably again we are talking about a 25A charger.

It is quite important to the mental picture of what is going on.

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[mikewilkes]

Anal is probably the word I would use.
Does it really matter if it is in upper case or lower when it is perfectly obvious what he is talking about!!!

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[mikewilkes]

Anal is probably not the word I would use.
Does it really matter if it is in upper case or lower when it is perfectly obvious what he is talking about!!!

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[rigpigpaul]

now now chaps, all I want is some sound advice

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[roly_voya]

Assuming you are goining to be living on the boat at least for long periods
1. Are you marina based with shorepower, if so the 25a charger will be fine as it will be running as apower supply for the boats consumption and keeping the batteries topped up, I had a 40 amp Sterling doing this and never got anywhere near its limit
2 Are you on a swinging mooring or somewhere where batteries will be cycled. - If so you probably need to look at much more capacity and probably wind/solar as well to stand a chance, given a power drain to the boat services and a battery down to 60% you may be looking at 12-15hours to get the battery back up. In practice you wont do it and your batteries will die.

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[Benbow]

OK, at the risk of vanishing further up my own rear end.

No, I wasn't commenting on a/h for AH by Talbot, but on amps to size a battery in the 1st post. There is potential for confusion because you can describe a batteries ability to deliver current in amps and its 'capacity' in AH and they are entirely different things. I think you are right that it was obvious from the numbers what was being talked about, but it suggested a fundamental confusion which the original poster may benefit from having pointed out.

(although of course a/h is also wrong; that means amps per hour (or better ah^-1) which is the opposite of amp hours)

Its very dark in here...

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[Talbot]

If we really wish to be anal, the engione starter battery really ought to be measured in CCA (Cold Cranking Amps), but that is really being picky. Personnally I reckon a solar panel is a really great item (mine is a whopping 180watt panel) Dont have anymore problems with low batteries!

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