# Reverse Current and battery

1. Aug 8, 2008

### spidey

i am connecting a wire to a battery and i pass current in wire and so battery will be charged.suppose if i change the direction of current then will the battery charge? i.e if i change the direction of current alternatively after some time?

why i am confused is because of this? suppose if i move magnet through a coil connected to battery then an emf will be generated and is stored in battery.then if i move the magnet away i.e in opposite direction then the direction of current is reversed so now will the battery charge?

2. Aug 9, 2008

### Averagesupernova

When you hook up a circuit to a battery to power a light for instance, current will flow until the battery is drained. Reversing the direction of the current through the battery using an external power source will charge the battery. This direction is the ONLY direction that charges the battery.

3. Aug 10, 2008

### hxtasy

I would say it depends on the battery type. A capacitor, electrolytic for example, can be charged in either direction. A car battery or chemical battery structure may be different.

This is a good question, if you think about one of those cheap, shake up flash lights - they have a coil and then a metal slug in them, so the slug goes through the coil and this produces energy that gets stored in the battery. If it goes the other way though, you just drained that battery. My guess is that they have a diode built into them and that you only get power in one direction.

4. Aug 11, 2008

### Staff: Mentor

Guys, you use a diode rectifier to couple the AC from a coil into a battery to form the charging circuit. The diode also keeps the charging circuit from being a load to the battery.

5. Sep 6, 2009

### forumpankaj

how can we aviod reverse current charging

6. Sep 6, 2009

### vk6kro

You have to be careful to avoid this.

If you connected a battery charger the wrong way around to a car battery that was already flat, you could attempt to charge the battery the wrong way around and it would possibly harm the battery by causing unwanted chemical reactions in the battery.

Although the battery charger contains diodes, they would be conducting normally in this case, but still doing damage to the battery.

This is why dedicated battery chargers, like those used on laptop computers for example, always have a plug that can only be connected the right way around.