battery-to-battery iPhone3G charger design

[blue82vette]

I have a UB1280 Universal, 12 volt, sealed lead acid, 8 Ah, battery (used in a UPS). I want to use it to take camping with me to keep my iPhone3G battery charged. I need the rate of charge to be high enough to keep the iPhone3G's battery charged, while using a GPS application, which drains the phone's battery faster than any other application.

I need someone to help me with a circuit and a parts list. I don't know much about electronics anymore.

Thanks in advance,

 

[(*steve*)]

You can't control the current (i.e. rate of charge) the phone does that.

Having said that, applying various voltages to the data pins of the iphone will indicate the power source's capacity

A simple regulator comprising a 7805 and a couple of small capacitors to ensure stability is all you need. You will also need a couple of resistors to bias the data lines so the iPhone recognises that it can charge.

You may be better of looking for a firewire charge cable as 12volts is perfectly fine for that (apparently it can use up to 35 or 40 volts depending on what you read)

 

[blue82vette]

You can't control the current (i.e. rate of charge) the phone does that.
Having said that, applying various voltages to the data pins of the iPhone will indicate the power source's capacity

[B]===> Thanks for the reply, Steve. Like I said previously, I don't know much about electronics and by that, I know how to solder. What I am worried about is putting too much voltage or current to the USB charging cord for the iPhone3G. I assumed that some regulation is needed between the power source and the iPhone's USB charging cord. Over a year ago I purchased a car charging cord for my iPhone and when using my GPS application, the phone's battery would run down. A month or so later I purchased a better one and it kept my phone's battery fully charged while using the GPS application, but the plug that goes into the iPhone broke and I tossed it. I wished I had kept it for the circuit. Since the iPhone's charging cord uses a USB plug, I need to go with that instead of a firewire plug, right? I wasn't aware that there is a firewire charging cable for the iPhone. I understand that the power pins in the USB plug is the 2 outside pins. Is this correct and if anyone knows how I can tell which pin is the + and which pin is the -, I'd appreciate that also.[/B]

A simple regulator comprising a 7805 and a couple of small capacitors to ensure stability is all you need. You will also need a couple of resistors to bias the data lines so the iPhone recognizes that it can charge.

===> First I need to know the complete values or description of each part I will need to tell the sales person at the electronics shop. I've driven seven miles to get parts just to find out he needs more information and I've got to go back home and post questions to get the answers I need, then drive back to the electronics store a second time. If I knew a shorter was to express this, I would. So a suggestion to this will also be greatly appreciated. Secondly, I need a step-by-step description on what parts to solder to what parts, to complete the charging circuit.

You may be better of looking for a firewire charge cable as 12volts is perfectly fine for that (apparently it can use up to 35 or 40 volts depending on what you read)

===> I understand I can use a 12 volt power source and possibly up to 40 volts DC. Is this correct? However, at the phone's end of the charging cord, what would be the max. voltage and current that can be put to the phone's circuit and battery, without damaging anything in the phone.

Thanks in advance,

 

[blue82vette]

Steve, I forgot to ask what the max. voltage and current should be, so I can check out the circuit before plugging it into my iPhone.

I know how to check the output voltage with my volt-ohm meter, but I need to know how to check the current output of the circuit. ;^\

Thanks much,

 

[LTX71CM]

You're probably a lot better off buying a commercially available iPhone car charger and wiring it to a 12V socket attached to your battery. At least then if it damages your phone you have a company to call. iPhones and iPods are very touchy about being charged, this is experience speaking.

Find a little regarding iPhone charging here: http://www.adafruit.com/blog/2010/08/03/the-mysteries-of-apple-device-charging-video/

 

[(*steve*)]

Yes, LTX71CM has a valid point. Get an adapter to charge your iPhone from a car cigarette lighter socket and just wire it to the battery.

The current required to charge an iPhone is about 1A max, but it depends on a couple of factors.

Make sure you get something that is designed to charge an iPhone, and not just something with a USB output. Without certain voltages present the iPhone will just ignore the charger.

Something like this is probably cheaper to buy than to make.