adding LED indicator to charger

[snoggert]

If a charger was using a simple full wave bridge rectifier design (such as: **broken link removed**). How could you modify it to have an LED indicator about the charge status of the battery? My original thinking was to run an LED in series with the load (rechargeable battery), but that was based on thinking that the battery would eventually stop taking a charge and no current would flow through that node anymore...so the LED would shut off. I've decided that probably wouldn't work though. Can someone help me with this?

 

[audioguru]

You forgot to say what is the chemistry of the battery you are trying to blow up without having current-limiting. Lead-acid, Ni-cad, Ni-MH or Lithium?

The circuit doesn't have voltage regulation so the battery could easily be overcharging at a very high current if the mains voltage is a little high.

 

[snoggert]

The battery would be a Li-ion used in an iPod. I think we're supposed to assume that the battery wouldn't fry because of no voltage regulator and just show how an LED indicator could be implemented. If you just assumed things were regulated, how could you modify that circuit to include an LED indicator?

 

[audioguru]

A lithium battery will catch on fire (a very hot fire, look in Google at videos) if it is incorrectly charged or discharged.

1) A circuit must sense the battery voltage to be more than 3.0V for ordinary charging. If the voltage is less than 3.0V then a low charging current is used.
2) The charging current must be regulated to the amount recommended by the battery manufacturer.
3) The voltage must be regulated within 1% of 4.2V. A current-sensing circuit must detect when the current has dropped to 3% of the regulated amount.
4) The current-sensing circuit must turn off the charger to prevent overcharging.

Use a battery charger IC made to charge a lithium battery.

 

[Hero999]

You could probably trickle charge a Lion battery at 1/10C continuously providing you restrict the voltage.

An LM317 with a series resistor on the output will probably do.

 

[audioguru]

You could probably trickle charge a Lion battery at 1/10C continuously providing you restrict the voltage.

No.
Lithium catches on fire because it becomes unstable when it is incorrectly charged.
The Battery University says: