Charger USB AA-AAA





This is a very cheap unbranded usb powered charger for AA and AAA batteries, can it be used?
I found this charger at fasttech sku:1298100



No box just a plastic bag inside the shipping envelope.



The charger is powered from usb.



There is a led for each battery, they will be red when there is a batteries in the charger and off otherwise. There is no indication when the battery is full.



The front battery connection can be flipped to select between AA and AAA length slots.







Measurements

• When not connected to power it will draw below 1uA from a battery.
• Charging start at 0 volt with 230mA and is down to 144mA at 1.5 volt.
• Charger never stops charging.

The charger do not terminate the charging, but continous to charge. The battery will get completely filled, even if it is an old worn down battery, but it will damage LSD cells.
Due to the low current the temperature raise is very moderate.



Second channel is the same.



About 1000 minutes or about 16 hours to charge a 2500mAh cell.



The current is the same for AAA.



The total current is the sum of the two channels, there is no switching regulator in this charger.



M1: 30,8°C, M2: 30,8°C, M3: 55,7°C, HS1: 84,2°C
With the low charge current the batteries stays cool, only the charger gets warm.



M1: 37,7°C, M2: 37,4°C, M3: 53,4°C, HS1: 79,8°C
When the batteries are full they cannot accept the current anymore and converts it to heat, i.e. they are warmer. Due to the slightly higher battery voltage, the charger has less power to get rid of and is slightly cooler.



When power is turned on the charger starts charging immediatly, there is no microprocessor that needs to do some checking first.



Because the charger is supplied from usb power there will not be any safety issues with it, but be careful with the usb power adapter.



A look inside

I decided to do a fast tear down of this charger.



It was very easy do do, only 3 screws to remove.



No real electronic (i.e. transistors or chips) in the charger, only a couple of resistors and diodes.



Conclusion

This charger is as simple as it gets, due to the low charger current it can be used for old style NiMH and NiCd batteries, but it is not good for modern LSD (Low Self Discharge) batteries. Letting batteries stay in the charger for days will wear them down.

I will not recommend this charger for normal batteries, but for people that like to get the last life out of batteries, it might be useful to charge batteries other chargers refuses.



Notes

Here is an explanation on how I did the above charge curves: How do I test a charger