Hi,
Capacitors are fairly efficient. They usually have series resistance but that's usually small. Resistance is what dissipates power, not capacitance, so the lower the series resistance the less power and the less heat. Also, for AC operation you have to use a capacitor rated for AC operation.
One thing about using a series capacitor over a transformer though is that although the series capacitor limits current, it only limits current at the normal line frequency, and also it does not provide for a true power conversion which means that any current the load draws also gets drawn from the line.
This is different than a transformer because a step down transformer draws less current from the line than the load draws. So for a 12v transformer operating off of a 120vac line the line current is 10 times less than with the capacitor. So if your 12v load draws 4 amps then with the capacitor 4 amps is also drawn from the line itself, but with the transformer only 0.4 amps is drawn from the line. This can make a world of difference. On a normal 20 amp line using capacitor type circuit you can only get away with 5 such circuits because those five would draw the full 20 amps already, but with transformer circuits you could use 50 such circuits before the line sees the full 20 amps.
Capacitors are fairly efficient. They usually have series resistance but that's usually small. Resistance is what dissipates power, not capacitance, so the lower the series resistance the less power and the less heat. Also, for AC operation you have to use a capacitor rated for AC operation.
One thing about using a series capacitor over a transformer though is that although the series capacitor limits current, it only limits current at the normal line frequency, and also it does not provide for a true power conversion which means that any current the load draws also gets drawn from the line.
This is different than a transformer because a step down transformer draws less current from the line than the load draws. So for a 12v transformer operating off of a 120vac line the line current is 10 times less than with the capacitor. So if your 12v load draws 4 amps then with the capacitor 4 amps is also drawn from the line itself, but with the transformer only 0.4 amps is drawn from the line. This can make a world of difference. On a normal 20 amp line using capacitor type circuit you can only get away with 5 such circuits because those five would draw the full 20 amps already, but with transformer circuits you could use 50 such circuits before the line sees the full 20 amps.
