# Electricity Question Amps & volts confusion

1. Oct 20, 2014

### Barclay

1. The problem statement, all variables and given/known data

A) If a laptop computer charger is designed for use in a country where mains voltage is 230V. Will the user still be able to charge the laptop computer in a country where the mains supply is 110V?
B) Also what happens if a 110V charger is used in a country where the mains electricity is 230V?

2. Relevant equations

I don't think there are any particular equations to consider but the equations for other questions in this topic have been : P=VI (Power of an appliance in watts = voltage x amps) and also E = VIt (Energy transferred = volts x amps x time)

3. The attempt at a solution

In A) the charger may not work at all or charge very poorly because the transformer will reduce the CURRENT (or MAINS voltage??) by the same factor for either the 230V supply or the 110V supply. So because the person is in the 110V country there may not be enough current (amps) to charge the charger.

In B) there may be too much current (or voltage??) entering the device via the transformer so may damage the device (though the device may work at first). Later the device may overheat. The fuse may blow at the socket anyway, even before the current reaches the charger.

I'm quite confused about VOLTS and AMPS. I think AMPS and VOLTS belong in this answer and I think I've talked about the terms correctly but am not sure.

Thank you

Last edited: Oct 20, 2014
2. Oct 20, 2014

### phinds

Transformers do not change current directly but only as a result of their basic function which is to change the voltage.

You are basically right in your statements except that you ascribe to the transformer current properties which it does not have.

Take a step-down transformer (which charger transformers are). The output voltage is a fixed ratio of the input voltage. Say 12V out for 120V in. That means that an input voltage of 220V will produce an output voltage of 24V. What that does to the current depends on the load. A passive load such as a pure resistor will simple take on the amount of current given by Ohm's Law. An ACTIVE load such as a power supply circuit of some kind (usually with diodes and transistors) will act differently but you need to know the specific circuit to tell just what it will do.

You should look up and study "step-up" and "step-down" transformers to get a feel for this.

3. Oct 21, 2014

### Barclay

In A) the charger may not work at all or charge very poorly / slowly because the transformer will reduce the MAINS VOLTAGE by the same factor for either the 230V supply or the 110V supply. So because the person is in the 110V country there may not be enough VOLTAGE to charge the charger.

In B) there may be too much VOLTAGE entering the device via the transformer so may damage the device. The device may work at first but later the device may overheat. The fuse may blow at the socket anyway, even before the current reaches the charger.

Is that last sentence about the fusing blowing correct?

Also is the current charging the charger or the voltage?

I didn't understand this:

"What that does to the current depends on the load. A passive load such as a pure resistor will simple take on the amount of current given by Ohm's Law. An ACTIVE load such as a power supply circuit of some kind (usually with diodes and transistors) will act differently but you need to know the specific circuit to tell just what it will do".

Last edited: Oct 21, 2014
4. Oct 21, 2014

### phinds

yes

The current is doing the charging, but the current is a function of the voltage.

Study circuits. I'm not up for writing a course on basic circuits.