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Shaggy

Leisure Battery Voltage

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Hi

Just got a new boat and at handover they said that I shouldn't let the leisure battery voltage drop below 12v. At first this was easy as the voltage seemed way above 12v. However a few weeks in and now the batteries drop below 12v at only 85% charged. Is this normal? or is there somekind of problem?

Many thanks

Shaggy
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That's not normal. If terminal voltage is less than 12V then they are not 85% charged.
Pick up the batt phone and call for.... GIBBOMAN!
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[quote name='Shaggy' post='170591' date='Oct 30 2007, 08:57 AM']Hi

Just got a new boat and at handover they said that I shouldn't let the leisure battery voltage drop below 12v. At first this was easy as the voltage seemed way above 12v. However a few weeks in and now the batteries drop below 12v at only 85% charged. Is this normal? or is there somekind of problem?[/quote]

What's telling you they're 85% charged?

If it's an 'amp-hour' meter then it's probably telling fibs.

It does sound like the batteries aren't getting charged nearly enough.

cheers,
Pete.
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[quote name='snibble' post='170598' date='Oct 30 2007, 08:09 AM']That's not normal. If terminal voltage is less than 12V then they are not 85% charged.Pick up the batt phone and call for.... GIBBOMAN![/quote]Here is a set of Voltage v. % charged data that I inferred from one of Chris W's posts a few months ago.
Off load voltage/ %Charge

12.65 / 100

12.55 / 90

12.45 / 80

12.35 / 70

12.25 / 60

12.15 / 50

12.05 / 40

11.95 / 30

11.85 / 20

11.75 / 10

11.65 / 0

I am told that you should not allow any lead acid battery to fall below 50% charge which means, but this data that the [u]open circuit[/u] voltage should not be allowed to fall below 12.15V You do need an accurate voltmeter with good resolution for this measurement, though, and you need to allow a long time (30 minutes?) on no load for the voltage to settle down.Be patient and Gibbo and Chris W will give, or direct you to lots of interesting and enlightening information.Nick[quote name='Theo' post='170659' date='Oct 30 2007, 10:49 AM']Here is a set of Voltage v. % charged data that I inferred from one of Chris W's posts a few months ago.Off load voltage %Charge12.65 10012.55 9012.45 8012.35 7012.25 6012.15 5012.05 4011.95 3011.85 2011.75 1011.65 0I am told that you should not allow any lead acid battery to fall below 50% charge which means, but this data that the [u]open circuit[/u] voltage should not be allowed to fall below 12.15V You do need an accurate voltmeter with good resolution for this measurement, though, and you need to allow a long time (30 minutes?) on no load for the voltage to settle down.Be patient and Gibbo and Chris W will give, or direct you to lots of interesting and enlightening information.Nick[/quote]Forgot to add that a search for "battery voltages" in this forum may well bring up something useful.N Edited by Theo
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[quote name='smileypete' post='170657' date='Oct 30 2007, 10:42 AM']It does sound like the batteries aren't getting charged nearly enough.

cheers,
Pete.[/quote]


It does sound like the batteries aren't getting charged at all.. Can you measure the voltage when the engine is running.
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[quote name='Theo' post='170659' date='Oct 30 2007, 10:51 AM']Here is a set of Voltage v. % charged data that I inferred from one of Chris W's posts a few months ago.
Off load voltage/ %Charge

12.65 / 100

12.55 / 90

12.45 / 80

12.35 / 70

12.25 / 60

12.15 / 50

12.05 / 40

11.95 / 30

11.85 / 20

11.75 / 10

11.65 / 0[/quote]
A quick at a glance chart!

[img]http://img57.imageshack.us/img57/2784/leadacidcu1.jpg[/img]
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[quote name='Shaggy' post='170591' date='Oct 30 2007, 07:57 AM']Hi

Just got a new boat and at handover they said that I shouldn't let the leisure battery voltage drop below 12v. At first this was easy as the voltage seemed way above 12v. However a few weeks in and now the batteries drop below 12v at only 85% charged. Is this normal? or is there somekind of problem?

Many thanks

Shaggy[/quote]

Shaggy

Can you confirm that you are measuring the battery voltage with everything turned [b][u]OFF[/u][/b]. The voltage will vary up and down depending on what's switched on and can drop to below 12v with a load on it but that doesn't mean it's not charged. Voltage is dropped across the battery's internal resistance due to the current supplied.

If it's reading 12v with [u]everything switched OFF[/u] it is at about 40% charge so whatever or whoever is telling you it's 85% charge under those circumstances, is wrong!

Chris
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[quote name='Neil.A' post='170808' date='Oct 30 2007, 06:32 PM']A quick at a glance chart!

[img]http://img57.imageshack.us/img57/2784/leadacidcu1.jpg[/img][/quote]


Your graph doesn't agree with my figures so you must be wrong. Nyaaa. :blink: :smiley_offtopic:

Nick
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[quote name='Theo' post='170882' date='Oct 30 2007, 11:01 PM']Your graph doesn't agree with my figures so you must be wrong. Nyaaa. :blink: :smiley_offtopic:

Nick[/quote]
Well it came from NASA's website....
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[quote name='Neil.A' post='170889' date='Oct 30 2007, 11:19 PM']Well it came from NASA's website....[/quote]

There the ones with exploding batteries!

( I know)!
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[quote name='Neil.A' post='170889' date='Oct 30 2007, 11:19 PM']Well it came from NASA's website....[/quote]

Not for wet-lead acid batteries though!!

Chris
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Dont discount the voltmeter not reading right, ie bad connection etc. Are your lights very dim? TV not working etc, if everything else is working this could be the case.
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[quote name='GRPCruiserman' post='171184' date='Nov 1 2007, 08:11 AM']Dont discount the voltmeter not reading right, ie bad connection etc. Are your lights very dim? TV not working etc, if everything else is working this could be the case.[/quote]
Seconded. My mates Sterling inverter charger has a digital voltmeter, and according to both my multimeters it is reading 0.3 Volts low! A country mile out!
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[quote name='catweasel' post='171351' date='Nov 1 2007, 09:25 PM']Seconded. My mates Sterling inverter charger has a digital voltmeter, and according to both my multimeters it is reading 0.3 Volts low! A country mile out![/quote]
obviously both your meters are wrong, Mr CatW :) :lol:

PS still in the bath, I see. How can we persuade you to show us your nicer face? :)
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My suggestion is to spend a few quid on a multi meter from Maplins,Screwfix or where ever and see what the charging voltage is i.e.with the engine running.If your alternator is working O.K.you should get a reading of at least 14.00 volts any less and you may have a charging problem.
Multimeters are wonderful things,they can save you hours of guess work and its not black magic,any body can use one!
Should I hold seminars in the local hostelry on basic boat electrics,I wonder?????
Cheers Ian F B. :lol:
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[quote name='chris polley' post='171406' date='Nov 2 2007, 05:51 AM']obviously both your meters are wrong, Mr CatW :) :lol:

PS still in the bath, I see. How can we persuade you to show us your nicer face? :)[/quote]
Specially for you Chris:

[img]http://i24.photobucket.com/albums/c1/stan-hesketh/catweazl.jpg[/img]
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[quote name='catweasel' post='171735' date='Nov 2 2007, 10:04 PM']Specially for you Chris:

[img]http://i24.photobucket.com/albums/c1/stan-hesketh/catweazl.jpg[/img][/quote]
much better, thx :) :) :lol:
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I preferred the distant view :lol: :)[quote name='Ian F B' post='171707' date='Nov 2 2007, 08:39 PM']My suggestion is to spend a few quid on a multi meter from Maplins,Screwfix or where ever and see what the charging voltage is i.e.with the engine running.If your alternator is working O.K.you should get a reading of at least 14.00 volts any less and you may have a charging problem.Multimeters are wonderful things,they can save you hours of guess work and its not black magic,any body can use one!Should I hold seminars in the local hostelry on basic boat electrics,I wonder?????Cheers Ian F B. :)[/quote]But make sure its accuracy is AT LEAST +/-0.5% or better otherwise it's is no good at all for measuring boat batteries where 0.1v difference in terminal voltage is approximately a 10% state of charge difference.Chris
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[quote name='catweasel' post='171351' date='Nov 1 2007, 09:25 PM']Seconded. My mates Sterling inverter charger has a digital voltmeter, and according to both my multimeters it is reading 0.3 Volts low! A country mile out![/quote]
My boat has a Mastervolt system and digi readout in the galley informing me of all sorts of lies so all i do is every few days do a reset on the panel and we start off at 100% but really its an expensive unit that is not right!
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[quote name='redfastlad' post='172062' date='Nov 4 2007, 04:38 PM']My boat has a Mastervolt system and digi readout in the galley informing me of all sorts of lies so all i do is every few days do a reset on the panel and we start off at 100% but really its an expensive unit that is not right![/quote]
Not really ideal when you have spent money. I just have an old analogue meter in the cabin for voltage, but of course it is just a rough idea of the voltage.
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Hi

Thanks for the advice, the engineer visited the other day and he thinks its just the battery monitor has got 'out of flunter'. So he advised connecting to shore power for a couple of days and see if it helps. haven't got shore power at moment so am just "over-charging" and then resetting the battery monitor. Will see what comes of it.

Cheers

Shaggy
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If it's giving use percentage charge based on ampere-hours used, it will always read innacurately. If you use 100AH and then charge at say a continuous 20A for 5 hours the meter will read 100AH back in and so will indicate 100% charged. However, due to the battery chemistry during charging you will only have put back in about 70AH and so the batteries will NOT be fully charged despite the AH meter.

Gibbo has a good article on this issue on his Smartgauge pages.

Chris
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On the GRP cruisers I had, I had two 85Ah batteries which the outboard put a bit in here and there. With frugal use, you could manage a fortnight on these with the blacka and white TV, and this dropped to 10 days with the colour one later. That's with water pumping, summer use of lights, CB Radio, Amateur Radio, Marine VHF etc.

I would start the fortnight holiday with them both fully charged at home with the mains charger. When the lights went dim and the TV stopped working it was time to swap to the other battery, and on extended cruises, it was necessary to stop at the odd boat yard and pay them the £1 or so they usually charge to recharge the first, flat battery.

If it got to the point where both batteries went flat, it was an early night with slow pumped water, and using the recoil start in the morning to start the engine instead of the electric start.

Dead simple, £23 a battery every three years when they wore out, and nothing really to worry about except missing 'The Bill' if I timed it wrong.

You know when it's flat when things stop working!!
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Just as an aside to the above post, note that one will get more hours use out of two batteries in parallel than 2 single batteries used one after the other.

eg: Suppose you have 2 fully charged 110AH batteries and you ran 40A out of one of them till it was 50% discharged (you shouldn't go below 50% charge or the battery life will be decreased) and then swapped to the other one and ran that at 40A till 50% discharged.

The maths reveals that the expected run time of each battery will be 45 minutes giving a total run time for the two batteries of 1.5 hours.

However, if you paralled the two batteries and ran the combination down to 50% discharge the run time calculates out to be 2 hours. That's a 33% increase in apparent capacity and the reason why it's much better to run one large bank for domestic batteries rather than a couple of smaller banks.

Chris

PS: Note also that the correct maths reveals that the run time is far shorter than a simple AH calculation would indicate. For a 110AH battery, 50% charge is 55AH and at 40A, one would suppose that the run time would be 55/40 = 1.4 hours per battery giving around 3 hours total whether they were used singly or in parallel. Calculating AH usage this way is incorrect. Edited by chris w
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