Electrical – Using a battery charger instead of a battery


I have built a simple circuit with two diodes that light up intermittently. It requires 9V DC voltage to run.

I don't have a DC source at home, and would like to avoid buying 9V batteries repeatedly to power my future projects, as portability is not necessary.

I however have a battery charger (wall adapter with battery slots), which can also recharge 9V batteries. I thought that battery powered devices are often able to run plugged in without the battery, so this should be the case here, too.

So I tried to connect the wires where the 9V battery to-be-recharged would normally fit, but it's not working as expected: D2 stays on indefinitely, while D1 flashes for a brief moment about once a second.

Note: The charger has a led indicating whether the battery in the respective compartment is charging. It does NOT light up when the circuit is connected.

Normally, they are supposed to flash intermittently, about one second each.

(The circuit works correctly, tested with a 9V alkaline battery).

I don't understand why this happens, and would greatly appreciate some help!

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Best Answer

Your circuit will work at 5V too. It may flash a little faster and the LEDs may not be quite as bright but both those issues can be adjusted by tweaking the values of the 75K and 820 ohm resistors accordingly.

I mention this because of the plentiful supply of cheap 5V USB device chargers around these days. One of these may be a good alternative to powering your circuit.