chrishelen
N/A
Is this a really silly question? the Alternator on my boat according to the book is rated at 35ah,my engine starter battery is rated at 50ahs. does this mean that it will take just over an hour to charge a flattish battery?
Alternator
- Thread starter chrishelen
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sarabande
Well-known member
depends on how flat the battery is to start with, and how 'good' it is at accepting a relatively big charge.
In any case, batteries tend to charge quickly up to about 80% capacity, and then unless you have some form of smart charging, it takes much longer to squeeze the last 20% in.
Very very roughly, and in the absence of any other data, I'd suggest from a half-charged (i.e. pretty flat) state, you would need a good two hours to make the battery nearly full again. An hour's charging will bring it up to the 80% state. If the battery is not in good condition (plates sulphated etc) then (a lot of) that charge might well dissipate in a couple of days....
Take some voltmeter / ammeter readings before, during and after, and post them here.
In any case, batteries tend to charge quickly up to about 80% capacity, and then unless you have some form of smart charging, it takes much longer to squeeze the last 20% in.
Very very roughly, and in the absence of any other data, I'd suggest from a half-charged (i.e. pretty flat) state, you would need a good two hours to make the battery nearly full again. An hour's charging will bring it up to the 80% state. If the battery is not in good condition (plates sulphated etc) then (a lot of) that charge might well dissipate in a couple of days....
Take some voltmeter / ammeter readings before, during and after, and post them here.
chrishelen
N/A
Thanks, put a voltmeter on it yesterday and it was reading 8 volts, so i guess there is a cell kaput on it?
sarabande
Well-known member
how long has it been at that level?
What type of battery is it pls ?
If one cell dies, then usually the volts are much lower as the continuity between + and - is disrupted.
I'd give it a good charge for an hour or two, watch the meter, and see if the battery heats up. Then take a reading and leave it for 24 hours and take another volts reading. If the battery is dead, you will be down to 8v again. If so, chuck it.
Sorry !
What type of battery is it pls ?
If one cell dies, then usually the volts are much lower as the continuity between + and - is disrupted.
I'd give it a good charge for an hour or two, watch the meter, and see if the battery heats up. Then take a reading and leave it for 24 hours and take another volts reading. If the battery is dead, you will be down to 8v again. If so, chuck it.
Sorry !
Plevier
Active member
It's not unknown for cells to fail short circuit especially if left discharged. It used to be quite common but improved alloys and separators have reduced the occurrence a lot. So you could have 1 or even 2 shorted.
If it's been at 8v for any length of time there is little chance but no harm trying.
If it's been at 8v for any length of time there is little chance but no harm trying.
Tintin
Well-known member
Rarely does an alternator charge at is max rated amount - it could be as low as a third at lower revs.
chrishelen
N/A
No probs, it was living off borrowed time anyway,it has been flat for about 2 weeks, the battery is off a Yaris,it is a 35ah that i replaced on my car when it died about 2 years ago.
I have another 110ah for the electrics that i can use in an emergency to start the engine, it can also easily be started by hand if need be (Sabb 10hp)
It started the engine even in the cold weather last winter, but i think i need to chuck it now.
fisherman
Well-known member
My alternator only achieves full output at 3000 revs, (ie 1000 on the engine)