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jareemon
01-07-2011, 02:48 PM
I want a usb wall charger for my devices. The one I'm looking at says '400-1000mA'. Is this ok for my htc phone and my girlfriend's ipod etc? Is 1amp 'full power' for usb? Will each device just draw however many mA it needs? Does it matter that my phone battery is well over 1000mAh?

:pf1mobmini:

dugimodo
01-07-2011, 03:01 PM
It'll work.

Normal USB2 supplies a max of 500mA, some motherboard manufacturers boost this for charging etc. I believe without looking it up that USB 3 has been increased, I think to 1amp.

Some specialised chargers might pump out dangerous currents for some devices, but it's unlikely. The charging circuit is actually built into your phone and the wall "charger" is just supplying the power.

The way Power normally works is simple, for any given voltage (USB is 5V) the load will draw a certain amount of current, if that exceeds what the power supply is capable of it will draw the max instead (and blow up the power supply if it isn't limited somehow but don't worry it will be).

The rating on your phone battery is in mAh - the h=hours meaning it can supply 1 amp for 1 hour or .1 amp for 10 hours etc (kinda). The same is true in reverse when charging you pump in for eg 100mA for 10 hours or 1000mAh for 1 hour, or somewhere in between. (actually due to inefficiencies etc you would charge @ 100mA for about 15 hours but you get the point). Less available current just means a longer charge time.

jareemon
01-07-2011, 03:12 PM
thanks dugi, btw, should the plug have overcharging prevention or is that the device's job?

:pf1mobmini:

jareemon
02-07-2011, 06:14 PM
*bump

:pf1mobmini:

The Error Guy
02-07-2011, 06:29 PM
That is the devices job. Charging circuits are built into the phone

jareemon
02-07-2011, 06:33 PM
thanks guys!

:pf1mobmini:

Billy T
04-07-2011, 11:14 AM
Some specialised chargers might pump out dangerous currents for some devices, but it's unlikely.

A correctly used charger cannot "pump out" dangerous currents unless its voltage regulation fails or the device being charged develops a fault.

The only chargers capable of causing damage like that are specialised units dedicated to charging, rejuvenating and recharging removable batteries.

I recently built a charger (JayCar Kit that sat unopened in my workshop for about 10 years until my conscience finally got to me) that handles NiCad, NiMH, SLA and Lead Acid batteries, and it certainly fires out voltage and current pulses that would damage most electronic devices if left connected during charging, but it is strictly intended for use only on batteries outside of the device they normally power.

"Intelligent" chargers could possible cause problems but the typical range of USB and wallwart chargers are harmless. The worst that can happen is that you might stuff them by trying to charge batteries of significantly greater capacity or with a lower voltage rating than the charger is designed to handle.

Cheers

Billy 8-{)

inphinity
04-07-2011, 01:47 PM
USB2.0 spec has a unit load @ 100mA and a maximum draw of 5 unit loads (so 500mA). USB 3.0 spec raises a unit load to 150mA, and caps at 6 unit loads (so 900mA).

dugimodo
04-07-2011, 03:50 PM
A correctly used charger cannot "pump out" dangerous currents unless its voltage regulation fails or the device being charged develops a fault.

The only chargers capable of causing damage like that are specialised units dedicated to charging, rejuvenating and recharging removable batteries.

I recently built a charger (JayCar Kit that sat unopened in my workshop for about 10 years until my conscience finally got to me) that handles NiCad, NiMH, SLA and Lead Acid batteries, and it certainly fires out voltage and current pulses that would damage most electronic devices if left connected during charging, but it is strictly intended for use only on batteries outside of the device they normally power.

"Intelligent" chargers could possible cause problems but the typical range of USB and wallwart chargers are harmless. The worst that can happen is that you might stuff them by trying to charge batteries of significantly greater capacity or with a lower voltage rating than the charger is designed to handle.

Cheers

Billy 8-{)

well yeah all true, I was just trying to keep it simple. What I was getting at is there are Chargers that use non standard voltages etc that do have a USB port but are designed to be used with a specific piece of hardware only, generally to fast charge a device.

Some mains or 12V powered USB power supplies are also capable of supplying more current that a standard USB port and could theoretically damage a device that didn't have any regulation on it's charging circuit.

The device in the OP is not really a charger at all but really just a USB power supply and as such will be a 5V supply with a 1A current limit, no electrical difference to plugging into an actual USB 2 port.