Charging my iPod's discharged battery

I have an old and venerable 30G iPod Gen 5 which has served me well for a few years.  It's had a new battery, a new logic board and a new rotary switch, but it works fine.  Until a week ago, when I switched it on and it didn't respond.  The battery was flat, so I plugged it into the charger and waited overnight.  Then I left it a whole week.  The battery remained uncharged - even after a week of being connected to its charger!

Now I have noticed on previous occasions that the iPod will deep-discharge the battery if it is left unused too long and then not even a normal USB charger will rescue it.  Until recently, I have been able to get round this by using the iPod interface on my Becker car radio, which always seemed to be able to wake up the iPod and charge it.  But I've changed the radio in my car now and the new one doesn't do quite the same job.  So.  Do I just replace the iPod battery or do I look to try and charge the iPod some other way?  Being reluctant to give up on a technical problem I chose to try to charge the unit another way - after all, if the Becker could do it so should another charger - if it charges the same way and, what have I got to lose?

The Becker iPod interface is not based on USB, so its design is not constrained by the specifications of USB.  I therefore suspect that it is capable of providing more power to the iPod than a USB port and therefore has more chance of getting the charging circuit in the iPod to start charging a deeply discharged battery.  Since, by now, a number of laptops and chargers had been tried and failed to charge my iPod I had a look on the Internet to see what else I could learn.

I rapidly found that the specification for USB power was that the USB voltage is nominally 5v (more specifically, no more than 5.25 V and no less than 4.75 V (i.e 5V±5%)).  A USB outlet should also be capable of providing upto 500mA too.  So I knocked up a charging circuit based on my bench power supply, an old USB lead and a digital voltmeter.  I then put 5V across the power leads of the USB cable and connected the iPod lead between the power source an the iPod.  Guess what?  It didn't charge the battery!  So I carefully adjusted the voltage of the power supply until it read 5.25V.  Still no charge.  Perhaps my battery was dead after all!

Back to searching the Internet.  It turns out that just supplying the power is not enough: there also has to be a signal to the unit being charged that charge is available and this was what was missing from my simple circuit.  Not one to give up lightly, I looked at the Internet again, this time looking for DIY USB chargers and chanced upon this indestructible project which seemed to answer my problems.  Turns out I was supplying the right voltage; I just wasn't turning the charging circuit on in the iPod.  It seems that the iPod looks for a voltage pattern between the two data leads to identify a valid, dormant USB port before turning on the charging circuit.  The indestructible says that you need four resistors arranged as a bridge so that 2.7V is present on D- and 2.0V is present on D+.  I set up four resistors on a breadboard and went to work.

And for those who want to know exactly what I connected up here is a schematic:

Once this was set up I switched on and plugged the iPod into the makeshift charger.  Within a few seconds I got a warning message on the iPod that the battery was very low - success!!  The iPod had woken up at last and was beginning to charge up..

Now I have enough juice in the iPod to bring it back to life, I have transferred the iPod to a proper charger and it is now charging merrily as I write this blog.

The morale of the story?  Well, there are three:
  • Don't let your iPod get as deeply discharged as I did mine
  • Don't assume that 'any old USB charger' will do - if one doesn't work, then try another.  Or try a computer.  Or another lead.
  • Don't assume that a dead iPod is a broken iPod.

1 comment:

  1. How you brought back to life your iPod was certainly amazing! It is true that some people think that, when a gadget is not starting up, there’s something wrong with it. But, sometimes, the problems are just with how the battery works. That’s why it’s important to care of it too.