Hello everyone,
So I need a three stage SLA battery charger, but rather than go out to buy one, I thought I'd challenge myself and build one. It will be an A.C based charger, with a transformer stepping the mains voltage down. After rectification, I want to limit the charge current to 2 amps, which is the maximum the transformer can safely handle.
The biggest challenge I'm facing is how to limit the bulk charge current easily and efficiently. I initially thought of linearly limiting the current (using an LM317 or similar), but that would be wasteful. Buck converters are the other option but I don't want to get into switching current regulators just yet.
I can regulate the battery voltage during the float charge using PWM like it's normally done with solar charge controllers, why can't I do the same with current? I'll be using an Arduino to run the show, and I could scale the PWM like 0 < my_control_signal < 255 to correspond with current 0 < charge_current_of_2_amps < 5 amps (assuming the maximum current to be 5 amps without current limiting). A current sense resistor plus a differential amp with a filtered output (to even out the PWMed current) will provide information on how much current I've got charging the battery. I haven't built or tested it out yet, but the logic here is that the Arduino will read the current and use PWM to raise or lower the battery voltage to the point where 2 amps (average) are flowing into the battery. If this could work, I'd only lose power in the shunt resistor and switching of the power transistor, which would be far more efficient than linear current limiting. Also the battery would have to be fine with switched current.
I appreciate your thoughts.
Isaac.
So I need a three stage SLA battery charger, but rather than go out to buy one, I thought I'd challenge myself and build one. It will be an A.C based charger, with a transformer stepping the mains voltage down. After rectification, I want to limit the charge current to 2 amps, which is the maximum the transformer can safely handle.
The biggest challenge I'm facing is how to limit the bulk charge current easily and efficiently. I initially thought of linearly limiting the current (using an LM317 or similar), but that would be wasteful. Buck converters are the other option but I don't want to get into switching current regulators just yet.
I can regulate the battery voltage during the float charge using PWM like it's normally done with solar charge controllers, why can't I do the same with current? I'll be using an Arduino to run the show, and I could scale the PWM like 0 < my_control_signal < 255 to correspond with current 0 < charge_current_of_2_amps < 5 amps (assuming the maximum current to be 5 amps without current limiting). A current sense resistor plus a differential amp with a filtered output (to even out the PWMed current) will provide information on how much current I've got charging the battery. I haven't built or tested it out yet, but the logic here is that the Arduino will read the current and use PWM to raise or lower the battery voltage to the point where 2 amps (average) are flowing into the battery. If this could work, I'd only lose power in the shunt resistor and switching of the power transistor, which would be far more efficient than linear current limiting. Also the battery would have to be fine with switched current.
I appreciate your thoughts.
Isaac.
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