I know when the voltage for a 12v battery reaches 14.1v then you must stop the bulk charge and start the constant voltage charge. My problem is that I do not know when to measure the battery voltage, that is, should I measure it while the charger power is on? Or must I disconnect the charger and then measure?
Because if I measure while the charger is on then I get a high voltage but as soon as I take the charger off the battery the voltage drops until it reaches a level where it levels out. So what must be 14.1volts then? The volts with the charger still connected or the volts with the charger off?
Unless you are charging at very high rates the voltage under charge and quiescent
won't differ much due to the very low internal resistance of SLA batteries.
I've seen 13.8V, not 14.1V, as the usual CV value.
MarkT:
Unless you are charging at very high rates the voltage under charge and quiescent
won't differ much due to the very low internal resistance of SLA batteries.I've seen 13.8V, not 14.1V, as the usual CV value.
I do however get a large difference, almost half a volt difference. Does this mean my battery is old or not functioning properly?
Carefully study that web page. It is the same one I gave you in another thread. It will tell you all that you need to know.
polymorph:
Carefully study that web page. It is the same one I gave you in another thread. It will tell you all that you need to know.
No it doesn't, not from a beginners point of view. How should I know how I must measure the voltage of the battery? With the charger on it or without the charger on it? If I didn't ask I would not have known my battery is broken.
polymorph:
Carefully study that web page. It is the same one I gave you in another thread. It will tell you all that you need to know.
No it doesn't, not from a beginners point of view. How should I know how I must measure the voltage of the battery? With the charger on it or without the charger on it? If I didn't ask I would not have known my battery is broken.
As far as it need concern you and has already been explained, for a SLA battery there is rarely a need for a "smart" charger.
All you do is to provide a constant voltage source - I favour 13.8V as I said before, whilst others think 14.1 is OK if the battery will be used (discharged) frequently and need prompt recharge - with a current limit integral to the single regulator device. Since you are not yet even close to comprehending the design principles involved, you have little choice but to copy - exactly - a tried-and-true design.
If you wish to provide a "charged" indication, then this should indicate when the charge current has dropped to a very low value.
The voltages and currents on that graph are during charging.
I agree with Paul__B.