I have a camera battery charger which is driven from a 12V (measured 12.2) switched mode wall wart rated at 1A. All three items (charger circuit, wall wart and battery) are stock, but all three heat up pretty quickly, which got me worried. The items work – the battery gets charged – but all items, especially the wall wart, are very hot in the end. I measured the current through the wall wart cable to be 1.5A. Now how should I go about limiting it?
I thought about adding a 4 ohm resistor in series with the wall wart supply, as I calculated would be adequate. I also thought about adding a few diodes in series to drop the voltage, but I was worried, it might interfere with the internal circuitry of charger (there's a couple of ICs and inductors and what not in there, too complicated for a beginner like me to reverse engineer).
Or would I need an active current limiting circuit?
Best Answer
Many chargers use a fancy charging method called pulsed or burp charging:
(from http://www.mpoweruk.com/chargers.htm)
A high current is used to charge for a certain pulse length, and after, the battery receives a short discharge pulse. Effectively, this increases the charge speed, however, this method depends on certain calculations for the optimal voltage and current to charge with.
If you change the input current and voltage of the charger, you can't expect this to work properly anymore, which may harm the battery and/or increase the charge time.
Therefore, it would be the best not to use these devices together, but to get a power supply rated for 1.5A.
However, if you bought these items together, there's (almost) nothing to worry about. Many devices get hot during normal use (especially wall warts). And if it booms, you have your warranty.