Felling stupod about USb ports...

M

MAXXMODDER

Limp Gawd
Joined
Jan 3, 2003
Messages
158
hey everyone,
I just got an Ipod shuffle and I'm trying to rig up a AC adpator for charging since I don't run my computer all night. I know a USB port puts out 5V, I have a 5V transformer, but it outputs 5V @ 3000ma will that work? I was reading and the maximum a USB device shoulduse is 500ma (I think) so can someone tell me what I need to do to change my existing transformer or if possible will he one I have work as is? thanks!
 
nope, you can directly connet your transformer to any USB device.

if voltage is the same and current is at least 500ma then it will work perfectly

a 3000ma transformer can power as many as 6 usb devices pulling max current, or more if they are small. you can never have too many milliamps (alright, but not in this case, lets not get all [h] on my ass)
 
The 3000ma rating is what it can output. What it actually outputs depends on the resistance of the circuit and the output voltage (in this case 5v).

Since the ipod is designed for a 5v power supply, as long as your power supply is capable of supplying enough current, then it will work fine.
 
You're gonna want to make sure that 5v is regulated so you don't fry your shuffle.
 
rm.o said:
You're gonna want to make sure that 5v is regulated so you don't fry your shuffle.
Click to expand...

that was my next question, how can I tell if it is a regulated transformer, I love my shuffle to much for it to fry :(
 
Plug in a meter while there's no load and measure the voltage. That'll at least tell you if the voltage is too high, though not if it's completely stable.
 
mattg2k4 said:
Plug in a meter while there's no load and measure the voltage. That'll at least tell you if the voltage is too high, though not if it's completely stable.
Click to expand...

under no load it read 5.13v
 
that will be fine, many ATX PSUs have read worse then that... and the regulation inside anything made by apple is very sturdy... as long as theres DC commin out of it, ittl be alright :)
 
So cheapo transformers that go from 5v-7v are the unregulated transformers?
 
They can be. Walwarts come in regulated and unregulated forms. I have an unregulated 9v wall wart that puts out 13v with no load. It's pretty easy to regulate them, to get 5v off that very transformer I added a 7805 and it worked great. I dunno if you're gonna be able to add a 5v regulator on your current 5v line and still get 5v. I'm pretty sure regulators need a volt or two more than they regulate. You may want to search out a 7-9v wall wart to use if you're not comfortable with your current transformer.
 
Most regulators need I think about 2-3v higher on the input than you want on the output.

They make low drop out regulators which would be better suited, but even those usually need at least 0.5v of headroom.
 
so you thik 5.13 will be alright? also and corect me if I'm wrong because my electronics skills are limited, I think I could use a diode to drop the voltage .2v right? if thats truewould you guys recomend that and what type of diode would be best suited for it. thanks again for the help!
 
5.13 will be fine.
is it a wall transformer or one thats like a brick (laptop supply like) if its the latter then its almost certainly regulated. If it says input voltage 100-240V then its a switchmode, which is regulated by definition.
 
yes it will be fine the way it is

dont add a diode... the minimum drop is .7v, but that varies based on current draw, its not as simple as a set in stone voltage drop. just hook it up w/o modifcation, and it will be fine (as long as you get the + and - wires right :p )
 
theshadow27 said:
yes it will be fine the way it is

dont add a diode... the minimum drop is .7v, but that varies based on current draw, its not as simple as a set in stone voltage drop. just hook it up w/o modifcation, and it will be fine (as long as you get the + and - wires right :p )
Click to expand...
No, not always. Depends on diode type. Some are lower.
 
NleahciM said:
No, not always. Depends on diode type. Some are lower.
Click to expand...
thanks for the [H] answer, but i was trying to get across the point that diodes are not the aprorpreate soulution here... thanks for the clarifcation anyway.

btw i have not seen a .2v fv diode
 
ahh! after all that I hooked it up and the led blinks like theres an error I don't know if it's charging or not I guess it needs to comunicate with the computer to charge also :( project failure

edit: but apple makes an AC charger... I wonder what i'm doing wrong!
 
well... you can do it the old fasion way and leave it playing with headphones in and the volume all the way up till the battery dies, then hook your thing up for an hour and see if it came back to life....

i know that the apple AC charger for the regualr ipod is dumb, i.e. nothing more then a 12v source.
 
theshadow27 said:
thanks for the [H] answer, but i was trying to get across the point that diodes are not the aprorpreate soulution here... thanks for the clarifcation anyway.

btw i have not seen a .2v fv diode
Click to expand...
Nor have I. I think the smallest I've seen was like .3V or .45V or something like that.
 
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