Modifying my ipod dock to charge my new ipod

awe215 · #1 01-06-2009, 09:54 PM

This is an electricity question so I figure someone here could help.

The new ipod, santa brought, no longer works with my old ipod dock. Apple has changed the pins and charging voltage of the new ipod so, while the old docks will play music, they won't charge your ipod while doing so.

My question is this. I figured I could resolder the pins, on my old dock, to correspond to the pins which charge the new one. The old ones were fire wire, and the new ones usb.

The main problem I see, would be that fire wire's output was 12v whilst usb is 5v. So if I resolder the pins, I need to first introduce a resistor into the circuit to lower the voltage. At least that is my idea. Granted, my understanding of electricity, is limited to the experiment set I bought at radio shack, for me and my daughter, a few months ago. Which has been a ton of fun by the way.

I know the other problem I am going to run into is amperage. The difference in amperage between the two. I am not sure what the difference is right now but I am digging to figure that out as well. I will post more as I figure it out but does any one have any preliminary suggestions to point me in the right direction.

So some initial questions:

Is it possible, using a resistor, to step down voltage from 12v to 5v?
Is it possible to step down the voltage as well as the amperage? Is it possible to step down the voltage while boosting the amperage?

Thanks for the help!

beenthere · #2 01-07-2009, 12:49 AM

You really can't use a dropping resistor, as it would only be accurate for a single level of current. A voltage regulator like a 7805 is more the thing to use. Even the Shack should carry them. You can always get a data sheet to see about the pinout (for TO-220, it's in, ground, out).

Loads use the power they need. If you stabilize the voltage, then the current will vary with charge on the internal battery. As the regulator will be wasting 7 volts, you may need to attach it to a heat sink so it doesn't get too hot and shut down.

awe215 · #3 01-07-2009, 03:27 AM

Hey, thanks for the reply.

I think I may need to start studying the manual, on the main webpage, to comprehend everything you laid out, but, reading it over a couple times it makes sense.

I wire the 12v line into the left side of the regulator, the ground(s?) to the center, and the right side to the pin on the dock. Thus giving the proper 5v to the device.

I think the heat sink can also be found at the shack. The only question I have on that, is attaching it to the regulator. My guess is, it sits on the metal tip to add to the heat dissipation.

Would you recommend the heat sink grease, they sell, as the best thing to attach it?

Again, thanks for your time.

beenthere · #4 01-07-2009, 01:16 PM

There is a hole in the tab on the regulator, so a #4 screw and nut will work fine. The handy thing about a 7805 is that the tab is also ground, so it usually doesn't need insulation.

awe215 · #5 01-07-2009, 10:16 PM

So I picked up the regulator today at Radio Shack. I can't believe how disorganized the electronics racks are over there. It was a mess but some how I dug one up. Of course they didn't have the heat sink, but, they're going to send it to me, free shipping! Can't beat that.

I am going to pull the dock apart later this evening and take a look at the innards. I am sure more questions will be popping up so I hope you don't mind answering a couple more. I really appreciate the help!

One thing is, I thought I might wire it up, test it, then wait for the heat sink to arrive to put it fully into use. Would that work, or will it get too hot too fast, and should I just wait on the heat sink?

beenthere · #6 01-08-2009, 12:14 AM

You can always see how it does. The regulator will shut down if it gets too hot - which is too hot to handle, by the way. Really warm is not a problem.

awe215 · #7 01-08-2009, 05:45 AM

There's a hole in the regulator, dear Liza, dear Liza....

So, I pulled the sucker apart and then it pulled me apart (mentally, metaphorically speaking!)

Here are some photos of the mess I made. What I gather from the little I understand...I need to put the resister in between the wire, which is coming off the board, that is labeled +9v (purple) and connect that to the 5v charging pin on the ipod dock (the little blue board I am holding in the photos).

From what I found here, it seems that I found the pin I need to solder the 5v wire to. Another question I have? does the ground go, from the board, into the regulator, then out to the ipod dock ground pin?....Sorry, I am little confused.

Another one, how do I solder things so small?

Thanks again for the help.

awe215 · #8 01-08-2009, 05:51 AM

Reading the bottom of the page, which I linked in the last post, it says:

"iPod Nano 4th Gen no longer will charge from 12 volts on the firwire pins. If you tie pins 25 and 27 together through a 10K ohm resistor while applying +/- 5 volts to pins 23 and 15 (or 16) that it will charge. If you don't tie 25 and 27 together, it won't charge"

So, I use the regulator, attach it to pins 23 and 15, then I would need to solder a 10k ohm resistor between pins 25 and 17?

If that be the case, my question about the ground on the regulator still remains. How does that work?

Thank you, kindly.

beenthere · #9 01-08-2009, 01:39 PM

Well, the grounds are all common, so they should all tie together.

I have to say that the information is a bit less than comforting. I would search further for some confirmation - say an iPod forum - before making those changes. The possibility of damage to your iPod seems slight, though, with only 5 volts applied.

The part that makes me a bit iffy is the note about +/-5 volts. He may mean +5 and ground, but an electronic person sees that as applying both positive and negative 5 volts. That bit of information needs to be verified.

I'd also send a nastygram to Mr. Jobs about the lack of hardware compatibility.

awe215 · #10 01-08-2009, 02:20 PM

I see what you mean. I hadn't thought about that.

The reason I ended up here with you, discussing these questions, is because my search on various ipod forums gave me no help. A lot of people reported the problem, complained about it, but it didn't seem there was a lot of people pulling their stereo docks apart and fixing it.

But, I could post up the info from the .ru site and see if anyone gives me some feedback on whether or not that will work. Thanks.