Whats the difference between regular power transformers and a battery charger?

I have a 'trickle' battery charger with an output of 1.5A, and I have a few other transformers from various older electronics. A low battery can very well pull more than 1.5A from the charger, but that is all it supplies, but a normal transformer may put out amperage over it's own rating and burn up. What makes a transformer capable of limiting its amperage output regardless of the circuit's ability to draw more?|||The limiting circuit built into it, and the isolation transformer it uses.





Google isolation transformer and current limit circuit for additional information.|||You didn't tell us enough about your chargers, but it is not usual for battery chargers to need no current protection. 1.5 amp is a lot of current for a "trickle", so I assume that this is for a gel cell or automotive type wet cell battery. In this case, the current limiting is based on 2 factors. 1, when the battery has been discharged, it has a high effective internal resistance. This internal resistance begins to diminish as it gains a full charge. The resistance of the battery itself limits current. 2. the voltage out from the charger transformer is sized so that it is just about the same as the battery standing potential. as the battery reaches full charge, the current delivered by the charger tapers off appreciably. So these 2 factors mean that for battery charging service, the transformer can be sized to provide a rated current that is at a defined maximum at mid-charge level without special circuitry. If the charger is used for something besides charging batteries, then the amperage delivered is at the mercy of the load.





The other type of "trickle" charger is for nicad type batteries. These employ a constant current design, so they are ok even with the output shorted because the load as seen by the tranformer is constant.|||A transformer on its own can't regulate the output current. It needs a regulator circuit to limit the current which can be as simple as an incandescent bulb but is more likely to be some semiconductor electronics such as a three pin regulator chip.