Voltage measurement/display of a battery WHILST being charged.

[antong]

Hi

I am new to the forum and a newbie regarding Electronics.   I have a question regarding devices that display
the current voltage of a battery whilst being charged.  How is that done exactly?

If you connect a voltmeter across the terminals of battery (e.g. a car battery) it would measure approx 12V
depending on the state of charge.   That is fine.   However, when the battery is connected to a charger (conventional or
solar charger), it charges at a high potential difference e.g. +14V.  But how does the charge controller reflect the true
voltage (12-13V) and not the higher voltage whilst being charged? 

Does it stop charging for a split second, measure the voltage, display it, and then resume charging or what?

Any info/reference would be appreciated.

I have also heard of the term Battery Driver.  Is this similar to a charger except that you could leave it connected or is that
another device?

Regards
Anton   

[amspire]

You certainly can stop charging, let the voltage settle and measure the voltage, but the old-style chargers with analog meters just had a green region that was the normal discharge range, and say an orange region above the green that was the charging voltage range. They didn't try to show the actual zero current battery voltage while charging at all or even estimate the percent charge. They often had a line in the orange region for "Float Charge". When you see the normal charge cycle is complete and the battery is sitting on the float charge line, you know the battery is fully charged.

You also have to take into account the fact that the battery voltage changes with temperature - the charger should change its voltage with temperature too.

[danadak]

Some basics on charging Lead Acid batteries -


https://www.powerstream.com/SLA.htm


Regards, Dana.

[David Hess]

One trick that may be used is to modulate the charging current slightly and read back the modulated voltage.  Between these two things, it is possible to calculate the battery's resistance and from there, the "open circuit" battery voltage can be estimated.  Offhand I do not know of any commercially available chargers which bother doing this though.

Usually just the charging current and voltage at the battery terminals are good enough.