Battery voltage related to charge percentage

[RichardS]

The problem with the chart posted is there is no reference to the Ah capacity of the battery in question.

Are you sure about that? Obviously in a chart which has any reference to "time elapsed" then the Ah rating is essential. However, I've always believed that Voltage vs % Capacity is a feature of the chemistry involved and, like SG, is independent of battery size.

Richard

 

[VicS]

It would be nice if there was a chart that allowed for different Ah battery capacity and I have over 12 thind the capacity that this chart refers too and I was/am looking for a chart the SWMBO could use as she gets paranoid over battery voltage, which to a point is good think.

Are you sure about that? Obviously in a chart which has any reference to "time elapsed" then the Ah rating is essential. However, I've always believed that Voltage vs % Capacity is a feature of the chemistry involved and, like SG, is independent of battery size.

Richard

I nearly queried that but then realised what Roger meant.

Its the volts vs amps figures ( at any particular SOC) that are only valid if the size of the battery is given. A 5 amp or 10 amp discharge will have a much smaller effect on the terminal volts of a large battery than they will on a small battery

 

[rogerthebodger]

I nearly queried that but then realised what Roger meant.

Its the volts vs amps figures ( at any particular SOC) that are only valid if the size of the battery is given. A 5 amp or 10 amp discharge will have a much smaller effect on the terminal volts of a large battery than they will on a small battery

Glad to know at least one person on here thinks I make sense Vic.

Have a read og the doc's referred to by Hydrozoan in post #17. They both make to capacity / by a discharge time factor to get amps for a particular voltage / capacity graph

What I was thinking about is that I have 12 x 105 Ah domestic batteries and I not do see anything like the volt drop when I am discharging at say 5 amps.

5 amps over 12 100 Ah batteries will be less the 1/2 amp per battery (assuming equal discharge which there will not be in real life) and this would have a much small effect than 5 amps on a 100 Ah battery as the internal resistance would e much less than a single battery of the same size.

Glad to be proved wrong.

Of cause with the sealed batteries we cannot measure the SG which is the real measure so we have to either go the calculating the capacity by adding the in's and out's then applying a factor/formula or estimate it by voltage.

 

[Hydrozoan]

Glad to know at least one person on here thinks I make sense Vic.

What I was thinking about is that I have 12 x 105 Ah domestic batteries and I do see anything like the volt drop when I am discharging at say 5 amps. ...

I guess you mean 'do not see'!

 

[rogerthebodger]

I guess you mean 'do not see'!

Yes fingers too slow.

 

[nemodreams]

Said a while back - 'check each cell ' ?

Given open vents - how can you check for a duff cell ? - ie electrically, not specific gravity. Can it be done with a multimeter on the plates ?

At nine years old my Numax are most certainly stuffed - but will still register 13.8 at full charge. However - the slightest current draw and they are 12.4- 12.5.

 

[RichardS]

I nearly queried that but then realised what Roger meant.

Its the volts vs amps figures ( at any particular SOC) that are only valid if the size of the battery is given. A 5 amp or 10 amp discharge will have a much smaller effect on the terminal volts of a large battery than they will on a small battery

Ah yes, I see what you mean.

Thanks

Richard

 

[rogerthebodger]

Said a while back - 'check each cell ' ?

Given open vents - how can you check for a duff cell ? - ie electrically, not specific gravity. Can it be done with a multimeter on the plates ?

At nine years old my Numax are most certainly stuffed - but will still register 13.8 at full charge. However - the slightest current draw and they are 12.4- 12.5.

If you have access to the cell interconnection links yes but these days the intercell connections cannot be accessed.

A fulley charges cell should be above 2 volts if duff mast likely below 1.5 to very little is shorted internally. This would also cause the other cells to be cooked as you now have 13 + volts across 5 cells and not 6

 

[temptress]

What is the difference between zero amps current draw and "rested"? And why the drop in value if there is no current draw??

0A is when the use stops - rested needs to be sitting say 5 to 10 minutes without any draw on the battery

 

[coopec]

I think the above comments adequately answer William_H's query but I came across the following article people may find interesting and informative.

https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

 

[VicS]

0A is when the use stops - rested needs to be sitting say 5 to 10 minutes without any draw on the battery

I think to get a rested figure you need to allow several hours before taking the reading. Earlier in the thread I suggested 24 hours but in practice I usually allow 12 hours.