Very Simple Automatic 12 volts battery charger[Designed but need modification]

Alec_t

Joined Sep 17, 2013
14,312
but my first circuit in this Thread seems to be not automatic charger , so if i leave it permanently with battery , is it possible to be dangerous or reduce my battery life ?
Yes. Simulation of that circuit shows the final output voltage (battery fully charged) would be 14.35V, which is higher than the recommended 13.8V for an SLA battery. Also, the current-limiting limits the current at ~840mA, which is too high for the 200mA transformer you have. Something is likely to cook.
Here's the sim result (ignore the horizontal time scale):
ChargerAsIs.PNG
I suggest you make R1=3.3Ω to reduce the charging current limit to ~200mA, and replace R3 with a 1.8k resistor in series with a 500Ω trimmer configured as a rheostat, to enable critical adjustment of the final full-charge voltage.
i'm really confused
:confused:You're not the only one! Posts 13 and 19 are inconsistent regarding the battery Ah rating and the transformer current rating.
 
Last edited:

Thread Starter

ShayanFiroozi

Joined Nov 18, 2015
41
Yes. Simulation of that circuit shows the final output voltage (battery fully charged) would be 14.35V, which is higher than the recommended 13.8V for an SLA battery. Also, the current-limiting limits the current at ~840mA, which is too high for the 200mA transformer you have. Something is likely to cook.
Here's the sim result (ignore the horizontal time scale):
View attachment 104885
I suggest you make R1=3.3Ω to reduce the charging current limit to ~200mA, and replace R3 with a 1.8k resistor in series with a 500Ω trimmer configured as a rheostat, to enable critical adjustment of the final full-charge voltage.

:confused:You're not the only one! Posts 13 and 19 are inconsistent regarding the battery Ah rating and the transformer current rating.
Dear Alec_t
thank you very much
but i never seen my battery voltage goes higher than 13.5

also with your suggestions you think is it safe to leave batt permanently with these ?
because i wanna use it a battery backup , so maybe 1 or 2 years the battery could be plugged to this charger !!! if not any circuit suggestion please ,because i'm gonna make about 500s of it , i don't wanna fail

thank you again
 

Alec_t

Joined Sep 17, 2013
14,312
That looks like an improvement over the original circuit. You might also consider using a dedicated charge controller IC, for example something from here .
 
Top