Maker Pro
Maker Pro

How do I keep a flashlight bulb from prematurely burning out when charging batteries?



Jan 1, 1970
I am building a rechargeable flashlight which uses 2 1500 mah NIMH AA
batteries and a .78watt 2.6V 0.3A T1 bi-pin bulb, and on/off switch.
The charging transformer output is 7.35v DC 550 mA, which plugs into
the bootom of the flashlight via a dc jack.
How can I wire the flashlight so that if the user turns it on while
plugged into the charging transformer it will not cause the bulb to
burn out from too much power. Specifically, should I put in a
resister? If yes, How many ohms? and where in the circuit?
My preference would be to have the flashlight bulb not come on at all
if someone tries to turn it on when the batteries are recharging. Is
there a way to do this easily? And if so, How?
Any help greatly appreciated.!

Dick Johnson

Jan 1, 1970
Make the switch a single pole double throw type. Connect the battery to the
bulb in one direction and to the charger in the other direction.

John G

Jan 1, 1970
DC jacks have built in switch just for this purpose generally.