Do iPods qualify for this forum?

[TJ_Kat]

I hope it's safe to talk about iPods here. You go some places and they tear you appart if you mention anything to do with Apple.

Anyway, on to my question. I want a car lighter adapter for my iPod without paying the $40 - $120 price tag for a name brand one. That seems a bit excessive to me, but based on my research, I may not have a choice.

My first notion would be to take a data link cable and a lighter adapter, chop off the ends I don't want, and hook the power lines together. 2 problems with this plan though: a) I don't want to hack up my data cable because I still need to be able to connect to my computer. b) Buying a new data cable just to hack up would totally defeat the purpose of doing this cheaply.

My new plan, which I'm liking right now, would be to instead of connecting the adapter directly to the data cable, put a female firewire connector on the other end of the lighter adapter. That way, my data cable stays intact, and I just need to bring it with me for the car. This would have the added benefit of being usable with any device that uses firewire for power.

Of course, then there's the big problem which may scrap this project  before it even starts. Keep in mind, I did this research a while ago, so I may not have this quite right. Anyway, first, a car lighter is an inherently unstable power supply. You step on the gas, more power goes to the lighter, you hit the break, less power goes to the lighter. Fluctuations like this would destroy my iPod's battery.

Now other devices have no problem with being plugged into a car lighter; discman, cell phone, etc. Why don't they have a problem and the iPod would? Is there something in their design that allows for the fluctuating power? Is there soemthing in the power adapter that protects them (if this is the case, my project is a go)? Or is it something to do with the iPod using firewire for power?

I'm likely going to have to go redo my research to see if I understand it any better this time.

[phreak97]

im assuming firewire is running at 5v, as i dont know much about it. but if that is correct, then plugging it right into the car is going to do bad stuff right from the start. but.. you can use a voltage regulator to overcome this AND the varying power, all in one hit. get a 5v regulator, they should be pretty common at any electronics store, or if you cant find one, theres one in every snes, every genesis, and probably scores of other consoles and home electronics. regulators look just like the large transistors, but mostly start with LM if you read the labeling, and they often have i G O printed on the pcb at the base.. theyre black rectangles with a hole in the top (the top is often metal) to screw it to a heat sink, they have three pins, the pins are as follows from left to right look at the front with the pins at the bottom. In, Ground, Out. in is your ~10-15v from the car, ground is, well, ground (or negative if thats how you want it labled) and out is your now safe 5v.

having said all that, you might want to check that firewire is indeed 5v, and not 3.3v. getting 3.3v is harder, youll probably need an adjustable voltage regulator, which will probably have a different pinout. if they are 3.3, post back here and ill tell you the parts to get a 3.3v regulator setup going. (these should be standard.. i dont know why they arent.. then again, maybe they are and i just dont know about it)

[TJ_Kat]

Actually, what I've been looking for are the IEEE 1394 specifications. First, to get the pin configuration so I know which is the power, and now to get the voltage too. I've been to the 1394 Trade Association home page looking for the specs, but couldn't find them.

And I just found the adapter I plan on hacking up. Input 12VDC ; Output 6VDC. That's a start.

UPDATE: My iPod power adapter is finally dirty enough that I can read the light grey on white print. Input 100-240VAC ; Output 12V (I can't make out if it's AC or DC, but I think DC would be a pretty safe bet...)

[atom]

Does your ipod have a wall charger? Does it put out close to 12 volts dc? Simply cut the cord half way through and put a banana or din plug on it so you can swap between a lighter charger and the wall charger.

[TJ_Kat]

The wall charger is just an adapter you plug into a wall, and you plug the data cable with the firewire end into that. Hence why I'm putting a firewire connector on the lighter adapter; it'll be the car equivalent of my wall adapter.

[TJ_Kat]

It just occured to me, since I already have a steady 6VDC output, can't I just amplify the voltage to 12VDC?

[NFG]

Creating voltage is a more complicated process than decreasing voltage.  You're better off to use the 12V and reduce it.

Car adaptors generally have, at the least, some filters and regulators to control the power flow.  In addition most devices connected would be 9V, not 12V, and so they'd already be dropping the power.  THey're not using straight-through connections.

I don't really know much about power filtering, so I've got little else to offer.

[TJ_Kat]

The wall adapter says it outputs 12V. *shrug*

Actually, from the reading I did, it sounded like creating voltage would be easier than I thought. You use a transistor to create more current, and then a resistor to convert current to voltage (yeah, I know that's an oversimplification, but it didn't go into more detail.) I also read that an op amp can increase voltage - that it's basically a transistor and resistor in a single unit - but I couldn't find more information on that.

It would be nice if I could just replace the 6V regulator with a 12V one, but I don't know much about them. What kind of effect would the source voltage going below 12V have?

The other thing that crossed my mind is, why do I need to change the voltage? It's already regulated at 6V, it will still charge the iPod, just more slowly, right?

BTW, circuit diagram of the lighter adapter, in case anyone cares.

How simple it would be if i just had to swap the L7806CV for a L7812CV

[phreak97]

normally for a regulator to work you need a couple of volts over the target, the regulator needs that to run.. so youre gonna want like 14v min going into the regulator.. your car isnt always going to be outputting that much, in fact while the engine is off, itll quite possibly go below 12v.. youre hitting the same trouble i had a while back.. you need some kind of circuit which will send the current through the regulator when above 13-14v, and straight into the ipod when below that.
i never did find a way to do it.

[TJ_Kat]

Well, I'm already considering taking out one, maybe both of the resistors to up the current (the wall adapter outputs up to 1A, and the lighter adapter only outputs 350mA). Could I replace them with a capacitor or two to help keep the voltage up, or is my understanding of capacitors totally wrong?

Oh, and on a side note, where can I find firewire jacks? I've been looking and I'm starting to think I'm going to have to get a cable and hack it up.

[TJ_Kat]

*bump*

I finally decided that if I could successfully remove the 6V regulator and install a 12V regulator, then I would also be capable of replacing the 12V one with a 9V one if the 12V one didn't work.

So, with the 12V regulator installed... I get a constant 11.96V out of my adapter regardless of the state of my car. So I'm considering this a success.

However, I'm having problems measuring amperage. Any suggestions? In theory, doubling my voltage should have doubled my amperage too, right? I would consider 700mA acceptable, however I would like 800mA to 900mA better.

[phreak97]

amperage isnt like voltage, it isnt pushed through the device, the device pulls it. so the amperage at any given time is dependant on the device connected. the amperage rating on a transformer is the maximum the transformer can handle before it either starts limiting it, or fries, depending on the transformer.

[TJ_Kat]

That's the catch. I actually have to have something connected to it to measure the amperage and that's not easy to do at the moment. Need to go see if i can scrounge up a 12V bulb, or fan, or something i don't really care about to test it.

But the reason I ask is, the adapter was originally rated to output 6V 350mA. Now, conventionally, when you increase the voltage in a circuit, the amperage increases proportionnally by the same ammount. However, I'm not sure that applies in this case because isn't the voltage in the circuit the same, and I'm only changing how much goes through the regulator? That's how I'm understanding this, and I'm not sure how that's going to affect my output amperage. Will it even affect it at all?

[phreak97]

uhh.. ok, a car can output way more than 200mA, just plug it in and be done with it.

there is no way i can think of that you are going to find out the max amperage. putting in a 12v bulb will just tell you what amperage the bulb draws, itll have very little to do with the regulator.

if you really want to find out the max amperage, put a multimeter on its 10A range, and connect it straight between ground and the output on the regulator.
NOTE: i cannot guarentee this wont harm the regulator or blow a fuse.

[TJ_Kat]

Yeah, but for the multimeter to measure the amperage, there actually has to be someting in the circuit drawing current.

But yeah, I'm tempted to just plug the damned thing in right now. There's a 500mA fuse in the adapter, and everything in it is rated to handle 1A. So... if I plug it in, and the fuse blows, I will have a satisfactory level of current. Yay for trial and error... =p

[phreak97]

if it's all rated for 1 amp, then your output should be 1A max, drawing more could damage the regulator etc.

heres another thing: some regulators can get really hot, i had one in my car a while back to supply the 5v a cd-rom drive needed. it got roasting hot.. one time i could smell the insulation tape melting.. (i do dodgy work in my car.. but the wire was soldered under the tape, so not so bad)

[TJ_Kat]

My concern isn't so much that it'll draw too much current. My concern is, that with how it's set up inside, it may not let enough current pass through.

Off the shelf, it only passes 350mA. That's not enough. I want AT LEAST 700mA, preferably 900mA to 1000mA.

What I don't know is how the "bigger" regulator will affect the amerage throughput (if at all), and how to tweak the rest of the circuit if my amperage isn't enough.

Sorry for not being clear on this. Wasn't focussing too well on the right thing...

[TJ_Kat]

I've finally gotten around to revisiting this project. Went and got myself a firewire jack, wired it all up properly, tested it to be sure I had my constant 11.96VDC passing through the right points, plugged in my ipod, and charging did NOT occure =(

I have assumed things down to two probable causes.
1 - (the one I'm hoping it isn't) that the computer sends the ipod some kind of signal on the data lines to let it know it's supposed to receive power; and that the wall adapter has some kind of chip in it that sends the same signal. This would suck as I'd have to spend more money than I care to for another wall adapter just to rip the stupid chip out of it.
2 - the amperage is too low. I fully admit, my understanding of a lot of this stuff is seriously lacking, or just outright wrong, but, how I understand it, even with the correct voltage, if the amperage is two low, it won't activate the charge process. Does that make any sense? I'm also working on the assumption that since the pre-mod adapter passed a max 350mA, by swapping the L7806CV for a L7812CV, I've effectively cut that amperage in half? Would removing one or both of the resistors before the voltage regulator increase my current?