Question about cellphone charger

[Yoko Sabi]

Hi, I measured the amperage on my cellphone charger. I measured 2 different cellphones with 2 different batteries.

The output of the charger is 5v 1 amp.

The first battery has 3.7v 1 amp. I measured .420 amp while charging.

The second battery has 3.7v 1.4 amp. I measure .980 amp while charging.

My question is, I am getting 2 different results, what factors affects the values?

Thank you so much.

 

[reidintransit]

1. There's a couple things that could be happening, see this post for battery changes. https://electronics.stackexchange.com/questions/19107/do-batteries-lose-voltage-as-theyre-used-up
2. Separate from the battery itself the charging circuits may have different resistance values that will impact the maximum current. Charging/discharging some types of batteries to fast can cause them to overheat.

 

[Yoko Sabi]

Thank you. These are Li batteries. On the first battery, do you know why .420 amp not 1 amp? Thanks.

 

[kam1787]

different cellphones = different charging circuits = different behaviour and different efficiency = different current

different batteries = different states = different charge rates = different current

 

[reidintransit]

The current on the charger is a max current rating not a guarantee that that current will flow. V = IR, the voltage is fixed from the charger and the resistance will be determined by the charging circuit which will pull the current to make the statement equal.

 

[Yoko Sabi]

If I know the ratings of the charger and the battery, is there are formula to get the current?

 

[kam1787]

The current on the charger is a max current rating not a guarantee that that current will flow. V = IR, the voltage is fixed from the charger

The current rating is the MAXIMUM current the charger can supply at that voltage.

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If I know the ratings of the charger and the battery, is there are formula to get the current?

You seemed to have missed the point. A proper charger charges at a current set by the state of the battery. There is no magic formula. It depends on the battery and charger.