Checking battery charge.

[Québec]

On our first longish trip, and thought I'd check how the batteries are doing as we don't have anything like a Smartgauge.

We have one starter and three leisure batteries. Evenings we're running a couple of 20w halogen bulbs for no more than a couple of hours. Overnight the 12v fridge is on and we usually charge at least one phone. The water pump and gulper are on for washing and showering.

 

This morning, before starting the engine, the Starter battery was showing 11.7v (12.64 with engine running at 10k rpm)

Leisure batteries were showing 11.72 (12.57 with engine running).

 

Is this within the bounds of OK?

 

Edited to add: we're into our fifth day of travelling.Been moored (no engine running until this morning) for 24 hours so far.

Edited July 18, 2012 by Québec

[bottle]

No

 

Are you sure your volt meter is accurate.

 

It is strange that the start and domestics are reading the same voltage.

 

ps. does your engine really run at 10,000 rpm, typo I suspect.

[Chalky]

I usually start a charge when the batteries reach 12.4V (engine not running) and stop when the charge current gets to a couple of amps (usually around 14.3 / 14.4 V).

 

Which gas turbine are you running the alternator off?

[bizzard]

I'd get rid of the fridge or turn it off over night and replace those two halogen lights with LED's. And check the alternators drive belt for tightness.

[dor]

You shouldn't have used much more than 30 AHr overnight, which should not have dropped your batteries from fully charged by more than about 0.2V.

 

What voltage did you have when you stopped (after allowing them to settle -about an hour or more, less if the fridge was running). Make sure you read the voltage when the fridge was not running. Presume you have a danfoss- type 12V fridge, not a 12V coolbox (whcih draw 8 amps or more continuously).

 

The starter battery should have read differently and higher, assuming you have split diode or split charge relay.

 

How old are the batteries?

 

If your readings are accurate and taken with no load on the batteries then it suggests that either your alternator isn't charging properly or your batteries are badly sulphated.

 

ETA: for what it's worth, with 4 x 100AHr batteries, fully charged; with 12V fridge, LED lights, several hours TV & sat receiver plus pumps and laptop charging I still get a reading of 12.6+ V in the morning.

Edited July 18, 2012 by dor

[twinpot]

With the starter battery reading 11.7 volts im surprised it started.could be your volt meter.

[pistnbroke]

just so you know ..

 

14.4v with engine running at cruise speed and a low ( 2 A )charge current means they are fully charged ( does not mean they are any good but they are charged.)

Having stood for 24 hrs unused if below 12.5v suspect.

 

Minimum volts you should run the battery down to is 10.8v ..below this you will start to brak the plates. however this represents 100% discharge and 50% is as low as you should go for long life.

 

 

Buy a hydrometer !!!

[bottle]

just so you know ..

 

14.4v with engine running at cruise speed and a low ( 2 A )charge current means they are fully charged ( does not mean they are any good but they are charged.)

Having stood for 24 hrs unused if below 12.5v suspect.

 

Minimum volts you should run the battery down to is 10.8v ..below this you will start to brak the plates. however this represents 100% discharge and 50% is as low as you should go for long life.

 

 

Buy a hydrometer !!!

 

This bit I agree with, if they are open wet lea acid, with the qualification you will need to know how to read and interpret it correctly.

 

To Quebec

 

As you can see from all the answers, you may or may not have a problem.

 

The simplest answer is you have not been charging your batteries enough but as to why that needs investigating.

When the problem is solved, I would recommend getting the Smartgauge, costly I know but would save you having a problem again.

[blackrose]

You shouldn't really let the batteries go below about 50% a/h capacity which equates to around 12.2v, but that's without any battery charge or discharge (ideally for several hours which is difficult if you're on the boat). As Dor said, next time you take the voltage readings make sure everything is switched off. Perhaps leave the fridge switched off one night and take the readings in the morning.

[nb Innisfree]

OP for your information, 10.8v is a flat battery, 100% DoD (depth of discharge) or 0% SoC (state of charge) is about 11.9v.

 

100% SoC or 0% DoD is 12.65v or more.

 

Both readings after battery has been disconnected for several hours

[Arthur Brown]

12.0v is a good reading for end of useful charge content for a rested lead acid, below that and you could well be trading current drawn against serious loss of battery life.

 

You really need to check the rest state voltage with a known good meter several times. Try before morning engine start and after cruising. Do you have a fitted ammeter? Can you actually prove what current the alternator provides.

[smileypete]

On our first longish trip, and thought I'd check how the batteries are doing as we don't have anything like a Smartgauge.

We have one starter and three leisure batteries. Evenings we're running a couple of 20w halogen bulbs for no more than a couple of hours. Overnight the 12v fridge is on and we usually charge at least one phone. The water pump and gulper are on for washing and showering.

 

This morning, before starting the engine, the Starter battery was showing 11.7v (12.64 with engine running at 10k rpm)

Leisure batteries were showing 11.72 (12.57 with engine running).

 

Is this within the bounds of OK?

Er, probably not! But it depends on the condition of the batts and their connections, and how much they've been charged in the first place.

 

I'd recommend having a digital panel ammeter as well, then reading up on The Battery FAQ and via google, about the bulk and absorption stages of batt charging and what the volts and amps do while it's taking place.

 

Then have a read up on what the volts roughly mean while the batts are discharging too.

 

cheers, Pete.

~smpt~

[Québec]

Thanks all, much appreciated and apologies for the delayed reply...been away from t'internet for a few days,

 

My brain needs charging after all that information!

 

Turns out it WAS a dodgy meter.... once I'd got hold of a fully working and tested meter.

 

Will be investing in some proper kit.

 

Paul

[ditchcrawler]

Thanks all, much appreciated and apologies for the delayed reply...been away from t'internet for a few days,

 

My brain needs charging after all that information!

 

Turns out it WAS a dodgy meter.... once I'd got hold of a fully working and tested meter.

 

Will be investing in some proper kit.

 

Paul

Good result then

[smileypete]

Thanks all, much appreciated and apologies for the delayed reply...been away from t'internet for a few days,

 

My brain needs charging after all that information!

 

Turns out it WAS a dodgy meter.... once I'd got hold of a fully working and tested meter.

 

Will be investing in some proper kit.

Good stuff, what make/sort of meter was it?

 

cheers, Pete.

~smpt~