I am a part of a project making an adapter that will cut power when the current begins to drop. The adapter is a bridge between a standard wall outlet and any ac/dc adapter that charges a battery powered device. The purpose of the adapter is to cut power to a plugged in ac/dc adapter when it is done charging. We are looking to detect when the device is done charging and then cut power to it. The current drawn through the adapter should begin dropping when the device is fully charged.
Does anyone have any experience with a project like this or any suggestions?
We are thinking of hooking a current sensor to an arduino through our adapter and then having it cut power when current begins to drop after reaching a peak.
It would be much safer to monitor the charger from the battery side (assuming it is for charging batteries at low voltages).
If you are charging low voltage batteries using a mains powered charger the drop in current in the mains supply cable might be very small and need a sensitive sensor to detect it. The later stages of battery charging are usually at a low battery current which means an even lower mains current.
A battery charger that has an indicator light that changes when the charge is complete would be best - then you could use a light-dependent-resistor (LDR) to monitor the light.
We are looking to detect when the device is done charging and then cut power to it.
To do that you add another device that needs power to do it's job. So another inefficient power supply to power that device just to cut the power of another device that probably won't use more power if not still charging.
I seriously hope you don't try to prevent overcharging with your adapter because that will fail, you will never be able to detect the correct point where you have to stop charging by measuring the current on the AC side.