Rechargeable Batteries

[dilawar987]

Hi,

power consumption.
I just wanted to know how much electricity is consumed when charging rechargeable batteies.
my adapter/plug says 240v and 0.3a.
but back of my battery charger say Input DC 12v - 700ma.
which one do i use to calculate enery consumption.

thanks.

 

[Squirrel61]

What counts is the total power in Watts. In an ideal world, the drawn on the primary (240v) side of an adapter is equal to the power delivered on the secondary (12v) side. Since this is not an ideal world, there's some energy lost in the process of bringing the voltage down, but as a rule-of-thumb, you can ignore it since the loss is very small.

That means if your charger is maxed out, the power drawn will be 12*0.7=8.4 VA (which is almost the same as W). That means, at that moment the power drawn from AC is also 8.4 VA, or 8.4/240=0.035 A, or 35mA.

It looks like your adapter could power over 8 chargers...

 

[Squidge]

energy consumption of AC device = Volts*Amps*PowerFactor
energy consumption of DC device = Volts*Amps

Is the adaptor a linear transformer unit or a SMPS device? Does it have a power factor control circuit? What is the power factor of the adaptor?

Assuming 0.8 for PF, maximum power consumption from the AC mains will be 240*0.3*0.8 = 57.6W.
However, maximum power consumption from the charger itself is 8.4W.
Adaptor seems a little over specced for the charger if thats the case (but does no harm of course, better to be over specced, than under, or on the limits)

I know my own charger uses 25mA at 240V with a PF of 0.2 to charge two AA batteries, so we would have 0.025*240 (=6VA) * PF0.2 = 1.2W drawn from mains.

 

[dilawar987]

hi

thanks for the help.
just to get to the point the final out put is 8.4w of electricity is used. this is what i used to get the find price of the electricity i have used. not to get too technical.

Thanks.

 

[Squidge]

just to get to the point the final out put is 8.4w of electricity is used. this is what i used to get the find price of the electricity i have used. not to get too technical.

Where did you find that? Just an empty set of batteries typically has a different PF to a 50% charged set of batteries, so the wattage will be different depending on how charged the batteries are (unless of course there is PFC somewhere in the electronics to that charger. Doubtful).

I think you over estimating by using 8.4W, unless of course your charger is for a 12V Lead acid battery, but then again, the specs you list do not match such a charger.

If it's 2xAA's you are charging and you don't need an exact value, use 2W from the mains.

Or, better still, buy yourself a Killawatt, charge your batteries, and it'll tell you exactly how much the charger has used from the mains in Kwh.