Warning! Don't use Firewire charger.

[Greg61]

Hi, I have one of the last Firewire capable iPods and have a Belkin car charger hooked up with a Firewire cable. I plugged the iPhone into this and just heated up, no charge.

I talked to Apple and said not to use the Firewire cable, as its a higher powered connection that the iPhone is not set up to handle.

Just thought I'd throw this out there!

 

[yotaguy]

Hi, I have one of the last Firewire capable iPods and have a Belkin car charger hooked up with a Firewire cable. I plugged the iPhone into this and just heated up, no charge.

I talked to Apple and said not to use the Firewire cable, as its a higher powered connection that the iPhone is not set up to handle.

Just thought I'd throw this out there!

umm I use an apple fire wire charger with my iphone. I have no issues and it charges fine. Im pretty sure firewire and USB both use the same 5v power.

note: iphone will not transfer data through firewire.

 

[loudestnoise]

I just don't understand why people would even use Firewire chargers. It makes no sense. I have both USB and Firewire from iPods, but I don't understand why you would even try it.

 

[radiantm3]

I use a FW cable to charge my phone as well. No issues so far.

 

[loudestnoise]

It seems there are varying reports of success and failure. So OP's dramatic warning seems a little unneeded.

 

[radiantm3]

I just don't understand why people would even use Firewire chargers. It makes no sense. I have both USB and Firewire from iPods, but I don't understand why you would even try it.

Because some people have firewire cables lying around from old ipods. I charge my phone in different locations. Why spend 20-30 bucks for apple USB cables when I have FW cables and ac adapters lying around?

 

[loudestnoise]

A very valid point, I'll be sticking to my USB chargers.

 

[Royale w/cheese]

Because some people have firewire cables lying around from old ipods. I charge my phone in different locations. Why spend 20-30 bucks for apple USB cables when I have FW cables and ac adapters lying around?

My thoughts exactly.

 

[radiantm3]

A very valid point, I'll be sticking to my USB chargers.

If I had more of them, I'd use them instead.

 

[KD7IWP]

My 3G iPod will charge through firewire, even when my Powerbook is closed and sleeping. With my 5G iPod it will NOT charge through USB when my Powerbook is closed. So I preferred Firewire since it seemed silly to have the computer on just so it could charge the iPod.

 

[mrbrown]

Mine works just fine.

As far as I'm aware, both the Firewire charger and the USB charger output the same voltage to the iPhone.

 

[Scarlet Fever]

hows about some more info on this.

My FW Charger says the output is 12V, and my 5th Gen iPod says it's rated 5-30V at 1A Max.

What does the iPhone say in the small print on the back?

 

[AirmanPika]

Also using a firewire charger here. Don't feel like buying another USB cable when I have a perfectly good firewire one.

 

[cookiejuice]

Just got back from Italy and my luggage got lost with my iphone charger in it (oops). Anyways I found my 2nd gen ipod firewire charger and starting using that on my phone. I left it in for 20 minutes and got scared because my phone got quite warm/hot and it never gets warm when charging. Naturally I have taken it off and now I am just am praying that my battery has not been harmed in any way.

 

[ZBoater]

I tried my firewire cable and AC charger from an 3G ipod, and my iPhone blacked out. I had to reset it to get it to work again.

Those chargers put out 12V. The newer USB ipod adapters, and the iPhone adapter, put out 5V. I am not an electrician, but it seems odd to me that a 12V input would work just as good as a 5V input.

On a $600 phone, it just aint worth it.

 

[AirmanPika]

I wonder why some chargers work fine and some don't. My firewire adapter is from an iPod Photo and I use the actual ipod dock so that I can stand my phone up while still in the case I got for it. Are all the larger firewire adapters 12V?

 

[DylanG]

I've been charging with a FW adapter since the phone was new. I looked at the charger and it is rated 12v. FWIW, the printed manual says to only use a USB charging device.

I haven't seen any ill effects but I'm going to stop until I know for sure.

 

[alywa]

I used a firewire - wall charger while on vacation. Worked fine. I will check the specs when I get home.

That said, at home I've been using the USB charger that came with the phone. My car (12v) adapter iPod charger did charge the phone, however. I'm sure it steps down the power, I just don't know how much.

 

[millerrh]

I asked a genius at an apple store about this exact thing since I have an extra firewire cable and wall charger lying around.

She said that they are perfectly safe to use and that is in fact what they use in the store for all iPods, even the ones that are USB only. When I asked her about the 5V vs. 12V output of each power brick, she said that is the rated output for what they are capable of, but the device is actually what draws power. So even though the brick can give 12 V of power, the iPhone won't actually draw that much and it is safe to use.

Now, all that being said, some people are saying they are getting hot and not charging, so I don't know what the deal is. Could be the genius is full of sh*t, but it seemed logical enough. I briefly tried charging mine last night with firewire just to see and it seemed to work. Never felt hot and I think my battery went up some. But I only left it on for about a half hour.

 

[DylanG]

When I asked her about the 5V vs. 12V output of each power brick, she said that is the rated output for what they are capable of, but the device is actually what draws power. So even though the brick can give 12 V of power, the iPhone won't actually draw that much and it is safe to use.

This is wrong. She's confusing amperage and voltage.

 

[whyrichard]

... so if she is wrong... chuck all my firewire chargers?


r.

 

[millerrh]

This is wrong. She's confusing amperage and voltage.

So wouldn't the phone only draw as much power as it needs P = I*V right? That includes amps. I'm no electrical engineer, but I do have a rough idea of how electricity works. Please educate us since it seemed to be working for some and not others I'd kind of like to figure out why it will or will not work.

 

[atszyman]

So wouldn't the phone only draw as much power as it needs P = I*V right? That includes amps. I'm no electrical engineer, but I do have a rough idea of how electricity works. Please educate us since it seemed to be working for some and not others I'd kind of like to figure out why it will or will not work.

Well sort of. It all depends on whether or not you have a Voltage or current (amperage) source. A voltage source (which are more typical) will try to apply the same voltage to whatever circuit it powers. A 100 ohm resistor will see the same voltage across it as a 100,000 ohm resistor. The difference is that the current drawn will change based on the load. Where I=V/R. This breaks down at heavy loads when a voltage source cannot source enough current and at these points the voltage will drop.

A current source will always try to push the same current and the voltage will vary with the load V=IR.

I'd bet that the FireWire charger is a voltage source so it will try to push 12 V at the iPhone regardless of what voltage it's designed to run at. Since the load (iPhone) is the same in both cases I'd expect the power draw to be up by a factor nearly 4 (P=V^2/R) depending on how the IC's react to the higher voltage.

The reason it might work for some and not others all depends on the tolerances of the chips involved in powering the iPhone. Apple might have reduced the chips to have an absolute maximum voltage rating in the 5-10V range (since USB puts out 5V) rather than ones that can handle up to 30 V for FireWire (from a quick Google it looks like FW puts out 30V on it's power pin with no load). Some parts might be just far enough out on the edge to work fine at 12V while others may start to get very warm and possibly fail since you're operating outside of the specified maximum voltage.

 

[DylanG]

I can't beat atszyman's technical explanation. I will add that for practical considerations, you can assume that the wall wart power supply for a consumer electronics device is going to be fixed voltage and it's necessary to match up the output voltage of the power supply with the expected input voltage of the device. I strongly recommend you don't violate this rule unless you know for sure what you're doing.

Rule of thumb:
volts output (power supply) = volts input (device)
amps output (power supply) >= amps input (device)


What we don't know is how the power supply in the iPhone is designed. I did some searching and most people are reporting that firewire chargers work fine with the iPhone. Considering that Apple has made and continues to make firewire chargers that are pin compatible with the iPhone, I'd be very surprised if the iPhone isn't intended to work with firewire power. It would be very unlike Apple to make two connectors that fit together but are electrically incompatible.

As for the people experiencing problems, it seems to be a minority and it might just be explained by the usual defect rate.

 

[millerrh]

Wow! Great explanation. Makes a lot of sense.

But Dylan, you bring up a good point as well. Would Apple really design the iPhone (or any iPod with the standard connector) to be damaged by older power supplies? I would doubt it. That would be horrible negligence on their part. But they do specify "USB power" in the manual. So you never know.