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Help Wall A/C charge vs USB computer charge seems to have a dramatic difference in charging times

cabbie

cabbie

Android Expert
Anyone notice this? My EVO shoots up incredibly when plugged into a wall versus my computer. There was a difference too on my Hero but it wasn't so dramatically different that I would prefer wall to computer. The EVO seems to inch up plugged into the PC, but the wall seems to give it an injection of red bull cocaine.
 
cabbie said:
Anyone notice this? My EVO shoots up incredibly when plugged into a wall versus my computer. There was a difference too on my Hero but it wasn't so dramatically different that I would prefer wall to computer. The EVO seems to inch up plugged into the PC, but the wall seems to give it an injection of red bull cocaine.
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Yep. This is a reality.
 
EVO went up from 50% to full in less than an hour on the wall outlet. It'd probably be at about 60 on the PC.
 
cabbie said:
Anyone notice this? My EVO shoots up incredibly when plugged into a wall versus my computer. There was a difference too on my Hero but it wasn't so dramatically different that I would prefer wall to computer. The EVO seems to inch up plugged into the PC, but the wall seems to give it an injection of red bull cocaine.
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The bundled USB wall charger outputs 1 amp whereas PC USB ports are limited to 500 milliamps (1/2 of an amp). So, if your phone was off it would charge twice as fast when plugged into the wall.

But, the difference is actually more dramatic than that. When your phone is on it will be using power just to run itself and any excess will go towards charging the battery. So, just for discussion sake let's say that the phone uses 300mA to power itself, that would mean that the other 200 are going towards charging. But, when you plug it into the wall it is able to devote 700mA to charging. Way faster than running it off your USB port.
 
USB port on the computer can only provide 500mA @ 5VDC by spec. The wall charger puts out 1000mA or 1A @ 5VDC. The wall will charge faster. Simple voltage math.
 
Yeah, it has to do with the amount of current each source can provide. The max current a USB port can provide is 500mA, but significantly less if you're plugged into a hub or a laptop. A wall outlet can provide a much greater amount. This is why you might see some small external hard drives with 2 plugs on one end of the usb cable so they can draw enough power.
 
You are probably seeing the charge rate difference because the wall charger porvides more amperage than the USB port. A 1500 mah battery can safely be charged at 1.5 amps, but your USB will be luck to put out 1 amp, most are 0.5 amps.
 
Meltz014 said:
Yeah, it has to do with the amount of current each source can provide. The max current a USB port can provide is 500mA, but significantly less if you're plugged into a hub or a laptop. A wall outlet can provide a much greater amount. This is why you might see some small external hard drives with 2 plugs on one end of the usb cable so they can draw enough power.
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dang, you beat me...:D

Crap, Fubie beat me too...I need to learn to type faster....lol
 
Thanks for the replies. So why would there be such a difference between Hero vs EVO? I haven't done benchmarking, just observing what I recall, but there seems to be a definite difference.
 
cabbie said:
Thanks for the replies. So why would there be such a difference between Hero vs EVO? I haven't done benchmarking, just observing what I recall, but there seems to be a definite difference.
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Basically what was said a few posts up. The EVO needs more power to charge when on. I've actually watched the battery drain when making a call with the screen on while charging via USB. I've also heard it stated that if you are running the WIMAX radio and the WIFI hotspot the wall charger won't be able to keep up. I am teathered with PDANet on my EVO while I'm posting now and I am barely charging.

The Hero, being older, slower and with a smaller screen takes less power to run and charge.
 
BUMP UP.

So - I'm reading about trickle charging makes a BIG positive difference in battery life and how people around here are shopping for them.

Turns out I guess I've already got one - my MacBook Pro. Like the statements above, mine is clamped to an available current draw of 500 mA - as opposed to the 1 A available with the Evo's included charger (also noted above).

So - all of us that have laptops (can't speak for desktops on this one, don't know) can try that as our trickle charger and see if it makes any difference in battery life for us.

Important tip: do not leave the screen on while charging or it won't be a trickle charger - with the mobile net PLUS screen on, it's like a near-eternity charger.

(Actually, it occurs to me that turning various radios on/off will therefore control the power left available for charging - so - your laptop can be a configurable trickle charger.)
 
EarlyMon: that is not trickle charging, and the phone itself does any sort of "trickle" anyway.

In fact, the phone does what is called "float charging", which is safer and better. It trickle charges until it finishes, then shuts off. Normal trickle charge does not shut off, meaning it can accidentally overcharge a battery. Once a float charging device reaches 100%, it keeps the charger off until the battery reaches ~95%, then charges back up to 100%. You can actually see this in action on your Macbook Pro's battery. Charge it up to 100%, unplug it, let it drain ~2%, then plug it back in. You will notice it does not start charging again.

Also, an extra note to this thread. USB2 spec is indeed 500ma, but a device CAN ask for more. Thus, SOME PCs, especially their rear ports, may actually provide up to the 1amp current, but not all.
 
Vincent Law said:
EarlyMon: that is not trickle charging, and the phone itself does any sort of "trickle" anyway.

In fact, the phone does what is called "float charging", which is safer and better. It trickle charges until it finishes, then shuts off. Normal trickle charge does not shut off, meaning it can accidentally overcharge a battery. Once a float charging device reaches 100%, it keeps the charger off until the battery reaches ~95%, then charges back up to 100%. You can actually see this in action on your Macbook Pro's battery. Charge it up to 100%, unplug it, let it drain ~2%, then plug it back in. You will notice it does not start charging again.

Also, an extra note to this thread. USB2 spec is indeed 500ma, but a device CAN ask for more. Thus, SOME PCs, especially their rear ports, may actually provide up to the 1amp current, but not all.
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Yep, I've seen that on my MacBook Pro's battery.

OK - so - MANY thanks for squaring me away on this.

My next question is simple: I'm seeing my phone charging much more slowly now.

Any reason to believe this will be beneficial?

I guess I'm not asking a particularly new question, and I must have gotten the idea reading this sort of thing:

http://androidforums.com/htc-evo-4g/103485-end-all-all-way-making-your-battery-last-all-day-without-shutting-everything-down.html

Not arguing - sincerely asking, with thanks in advance.

Full explanation here - this doesn't matter, as Vincent tried to explain to me:

http://androidforums.com/htc-evo-4g/102869-why-your-battery-drops-10-15-first-20-minutes.html
 
95% of the "battery saving" ideas on this forum are fud. Generally people don't realize the true cause (rebooting the phone closes the apps that was devouring their battery).
 
So something like this for EVO might charge quicker or allow "hotspot" usage?
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I posted about this around june 7th or so, but no one brought up the .5 amp usb point, some intel boards provide a full 1 amp on usb, most asus I've been told. Go check out some iPad forums for more info on how to charge faster, they pull even more from a wall plug, and cannot charge at all on most usb ports without powering the unit off.

I've noticed a significant slow down in charging since this last update. I can plug into the wall all day at work and the battery never hits 100%, starting at 8am with 25% charge, unplugging at 4:55 pm, with 6.5-ish hours of screen on (mostly web browsing and playing robodefense).


I posted about this around june 7th or so, but no one brought up the .5 amp usb point, some intel boards provide a full 1 amp on usb, most asus I've been told. Go check out some iPad forums for more info on how to charge faster, they pull even more from a wall plug, and cannot charge at all on most usb ports without powering the unit off.

I've noticed a significant slow down in charging since this last update. I can plug into the wall all day at work and the battery never hits 100%, starting at 8am with 25% charge, unplugging at 4:55 pm at 70%-85% charge, with 6.5-ish hours of screen on (mostly web browsing and playing robodefense).

If I try to do the same on usb, the charge will either decrease! Or only go up 1% after 3 or 4 hours of charging. I have a 2-1 usb cable for an external hdd, but no adapter to use it on my evo, if I can find one (probably on amazon) I'll get it and test it.

Right, off to see if this is discussed on another topic post...
 
Wow this is quite interesting, I've just started using HTC desire, and my difference between AC and USB (on a hub) is quite dramatic as well.

It takes about 2 hours on AC and 9 hours on USB!
 
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