USB Charging

  laurie53 09:22 06 Jun 09

Can there possibly be any difference between charging through the usb connection of a computer and using a usb adapter through the mains?

I have a couple of devices which are charged through a usb connection and while I have no problem using a computer connection the mains adapter does seem to give problems (I've tried three different ones).

One of them takes a long time to charge up, 16 hours against the normal 2 - 3 hours, and the other one needs a complete reset every time it is charged using the mains.

Given that the dc voltage from a cheap mains adapter may have a bit of a ripple on it, is this going to have much of an effect?

The output must still surely be to a certain standard, and should not affect the device, or should it?

  Fruit Bat /\0/\ 12:16 06 Jun 09

You are possibly right about the DC ripple.
I would suspect there is little smoothing in a mains charger compared with a PSU in a PC / Laptop.

My MP3 player takes ages to recharge off the mains (overnight) but seems to recharge quickly from the 12v adaptor plugged into the car cigarette lighter.

  Peter 14:37 06 Jun 09


Perhaps the problem here with some of the charging devices is current limitation. The voltage of the charger only has to be slightly above that of the battery being charged for quite a high current to flow. Taking account of the variability of the battery voltage between its uncharged and charged states then the chargers may involve current limitation as a protection mechanism.


  Arnie 18:32 06 Jun 09

"Perhaps the problem here with some of the charging devices is current limitation."

You're correct Peter.
If the charger is thoughtfully designed, the charger should supply a decent charging current and then at the charging end point the current should fold back.

If the user forgets to switch off the charger, the cell/battery will not be overcharged.


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