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Leisure Battery Voltage


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#1 Shaggy

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Posted 30 October 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
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#2 Sir Nibble

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Posted 30 October 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!
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#3 smileypete

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Posted 30 October 2007 - 10:42 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?


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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#4 Theo

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Posted 30 October 2007 - 10:51 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!

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 open circuit 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

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 open circuit 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

Forgot to add that a search for "battery voltages" in this forum may well bring up something useful.N

Edited by Theo, 30 October 2007 - 10:54 AM.

NB TheodoraColecraft 1983. Since saying that I have discovered that she is a Brum Tug with Colecraft bow

#5 John Orentas

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Posted 30 October 2007 - 10:54 AM

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

cheers,
Pete.



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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#6 Neil.A

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Posted 30 October 2007 - 06:32 PM

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

A quick at a glance chart!

Posted Image
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#7 chris w

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Posted 30 October 2007 - 07:48 PM

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


Shaggy

Can you confirm that you are measuring the battery voltage with everything turned OFF. 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 everything switched OFF 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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#8 Theo

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Posted 30 October 2007 - 11:01 PM

A quick at a glance chart!

Posted Image



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

Nick
NB TheodoraColecraft 1983. Since saying that I have discovered that she is a Brum Tug with Colecraft bow

#9 Neil.A

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Posted 30 October 2007 - 11:19 PM

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

Nick

Well it came from NASA's website....
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#10 Yoda

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Posted 30 October 2007 - 11:31 PM

Well it came from NASA's website....


There the ones with exploding batteries!

( I know)!
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#11 chris w

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Posted 31 October 2007 - 11:34 AM

Well it came from NASA's website....


Not for wet-lead acid batteries though!!

Chris
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#12 GRPCruiserman

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Posted 01 November 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.
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#13 catweasel

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Posted 01 November 2007 - 09:25 PM

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.

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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#14 ChrisPy

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Posted 02 November 2007 - 05:51 AM

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!

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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#15 Ian F B

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Posted 02 November 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. :lol:
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#16 catweasel

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Posted 02 November 2007 - 10:04 PM

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? :)

Specially for you Chris:

Posted Image
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#17 ChrisPy

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Posted 03 November 2007 - 06:47 AM

Specially for you Chris:

Posted Image

much better, thx :) :) :lol:
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#18 chris w

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Posted 03 November 2007 - 11:03 AM

I preferred the distant view :lol: :)

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. :)

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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#19 redfastlad

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Posted 04 November 2007 - 04:38 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!

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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#20 catweasel

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Posted 04 November 2007 - 09:11 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!

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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