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Qi charger power (Watts) rating

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eengr

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Hi

I am bit confused about the Wattage rating of Qi (wireless chargers)

e.g., they come in different flavours as 1W / 5W/ 7.5W / 10W etc

I know P = V x I

But, I am struggling to understand how the above Wattage translates into Voltage & current

e.g., I were to charge a Li-ION battery 4.2V, what is the maximum current that I could get out of the above?

& what happens if battery voltage is different e.g., 4.22V or something like 3.7V (during charging)

& if my receiver demands more current than what Charger is able to supply then would it damage anything?
 

Hi,

you correctly say: P = V x I ....
and you know P = 1W, 5W...
And you know V = 4.2V, 4.22V ....

Thus it shouldn´t be a problem to rearrange the formula to: I = P / V

Now you can calculate I.

But the given "P" is just the nominal power that the wireless charger is able to transmit. It will be internally limited, thus the reciever can only use as much power as provided.

I´d expect less than the nominal power at the revceiver side.
Then the receiver has some circuit inside to generate the charging current for the batteries. Thus there will be additional power loss... and the charging circuit may reduce charging current depending on battery state.

The
 
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