iPhone Supply Current?

[theEdge]

Hello,

I'm wanting to build a super-powerful FM transmitter for the iPhone and was wondering if anyone knew how much current I can draw from the dock connector without causing any problems. I know that the voltage source is 5V, but I am more interested in how much current I can actually pull from it. Any info would be appreciated.

Thanks!

[suzuran]

Nowhere near enough to operate a transmitter of any appreciable power output.
For a "super-powerful" transmitter (I am assuming you mean 5 watts or more of output) you will need some sort of outboard power supply. Even if you took the battery out of the iphone and used it directly it won't operate a transmitter at that level for more than a few minutes. You would have to use D cells or lantern batteries. (Two lantern batteries in series for 12V works pretty well for this sort of application, but it's not very portable.)
Avoid using a car as a power supply unless you want to build DC filtering for the input, since the electrical noise in the car will couple into your output.

[theEdge]

Thanks suzuran,

I should have went into a little more detail about the super. I'm not talking major (watts) power, but I'm hoping to get more range than say an iTrip. It has to run off of the iPhone battery though. That is a requirement. So any idea on what kind of mA I can get from the iPhone with out hurting it? Or any idea what the iTrip or similar device draws from an iPod?

Thanks

[suzuran]

Oh, sorry - No clue. I don't own an iPhone. I'm just a radio dork. ^_^

[gamempire]

Edge, I get back to school in a few days, I'll run some tests on some of our equipment in the lab and get back to you with an answer. I'd probably guess its somewhere in the 30mA to 50mA range though, but it could be significantly higher. Remember, a standard desktop USB port normally outputs 5v @ 100mA (500mA maximum depending on the device), so its going to be something significantly less than that.

[freeproductions]

theEdge:
If you have an iTrip that you can tinker with, maybe pop it open and put a voltmeter across the 5v in and see how much current it's drawing.
My guess would be that of gamempire's though, at about 50mA max.
The internal voltage regulator supplying that 5v is pretty damn small with probably little or no heatsink. Do be careful!

-

[gamempire]

theEdge:
If you have an iTrip that you can tinker with, maybe pop it open and put a voltmeter across the 5v in and see how much current it's drawing.
My guess would be that of gamempire's though, at about 50mA max.
The internal voltage regulator supplying that 5v is pretty damn small with probably little or no heatsink. Do be careful!

-

Now that I'm thinking about that after looking at the iTrip, there is no way the iPhone puts out more then 30mA when discharging for a peripheral.

I'm guessing you want a "super powerful" transmitter so you don't have any distortion between your iphone and your car radio. That logic is flawed though, because if this is the case, don't bother, you'll always have less than CD quality audio over an FM transmitter. Just build a nice little dock in your car like a BMW has and output the sound from the dock connector, so its digital all the way through.

If however you're trying to build a mobile radio station via your iphone....your battery might last about 2 or 3 minutes for that kind of use :D but as free said, with no heatsink on the voltage regulator....good luck with it lasting more then a few seconds.

[theEdge]

The original idea was an FM transmitter, but now I'm just curious as to what kind of current I can get from the iPhone.

I tested my old old iTrip and it pulls around 20 mA, with a max around 30 mA. I am interested in others results also!

Thanks!

[theEdge]

Hrm, I attempted to power an LED today, just as a first attempt at drawing power from the iPhone. The circuit works just fine with external power, and draws 20mA. When I use the iPhone pinouts for power, it never lets me draw any current, but I do get a message talking about airplane mode.

I used pin 1 for ground and pin 11 for V+. Anybody have any idea what I did wrong?

Thanks