Use Ipod Mini without battery

[zackattack]

My Ipod Mini's battery wore out and I wanted to use the ipod only in the car. Thinking of that, why have a battery if its always going to be plugged in? So I took apart the ipod removed the battery and the circuit will not allow the Ipod to turn on. So I tried connecting the wires that connected to the battery... still no luck. however, there are 3 wires, a red, a black, and a white. If i connect all 3 wires together it starts up for a 1/10th of a second and turn off and does this repeatedly. Simply connecting the circuit to replace the battery is not enough. I have researched many different forums with no actual solution present. I have a couple of ideas though,
1. Use a capacitor/supercapacitor in place of the battery.
2. Use a series of resistors/thermistor to trick the phone into thinking a battery is still present.

There is something that this battery is doing to the circuit that I am not aware of that is deeper than simply getting charged and running the Ipod. If that is the case, it seems dumb to me that that step cant simply be overrode.
Any ideas? Thanks

[pebe]

I am not surprised that the Ipod would not work when you shorted out all three leads. You put a short circuit on the charger output!

If you are only going to use the Ipod in the car, then why not leave the old battery in?

The battery is only a single cell 3.7V Li-ion, so the red and black are its two terminals There is possibly a thermistor connected between the black and white wires that senses when the battery warms up at the end of its charge. The Ipod would then stop charging.

[zackattack]

Yes, but if the battery is dead then the ipod will not turn on. which is the problem i ran into. Is there some way i can trick the phone into thinking the battery is still in?

[pebe]

On your old battery, can you measure the voltage between the red and black wires?
Check that there is no voltage between the black and white wires. If no voltage, then can you measure the resistance between those two wires?

[zackattack]

Im not sure what that will help you with. lets pretend and make up a number. Im really looking for some type of circuit design to trick the ipod into thinking there is a battery when there isnt one. knowing the specifics in terms of the exact type of resistor/capacitor is irrelevant until i know the general design for the circuit.
Example: we must design a method to lift a rock off the ground.
1. we decide to use a rope/pully system.'
2. we decide the strength of the wire/pully needed.

we dont do 2. before 1., which is what you seem to be asking me. if not then just help me with the general circuit design and i apologize for misreading you.

[pebe]

I wouldn’t waste my time or yours by asking irrelevant questions, so I regard your remarks as somewhat inappropriate – especially as you were unwise enough to put a dead short on the charger!

I didn’t know what sort of battery your Ipod used so I looked for spares on Ebay and found it was 3.7V. That means it is a single cell Li-ion type.

In order to fool the Ipod, it is necessary to know which type of charger it uses. I can think of two ways the internal charger for a single cell might work:
1. It could supply a constant 4.2V to the cell and monitor the charging current; switching off when the current dropped to a low value, or
2. Provide a fixed charging current and use a thermistor in the battery to sense when the battery was fully charged and therefore getting warm.

A single cell only needs two terminals so the third wire either connects to a thermistor, or just to an internal link in the battery if the Ipod only needs to establish that a battery is present – so I needed you to measure the leads so I could know which.

I needed to know the battery voltage so that I could see its state of charge to establish whether the battery really had failed or whether the charger had stopped working.

Now, if you can provide that information, I may be able to help you – if you won’t, I cannot. I don’t care one way or the other.

[zackattack]

The charger 5 volt.
The white wire is indeed a thermistor.
The battery is marked at 3.7 volts so it would make sense if the battery is charged by the 5V but then at the same time supplies the circuit with 3.7V.

A couple of ideas just rose, it is possible to get a complete charge on the battery while playing music, which would mean the battery would have to be charging at faster rate that it is draining. which would mean the Ipod needs to be dropped from 5V to 3.7V and perhaps a slight resistor as well.
Perhaps a voltage regulator at 3.7V? and some kind of resistor?
Is the thermistor required of the circuit in order for functionality?

[pebe]

I am not familiar with the charging circuit in a Mini Ipod, but from what you say it looks as though the battery is charged from a 5V source, through a series resistor to limit the charging current. That assumption accords with the fact that there is a thermistor in the battery that the charging circuit measures to decide when the battery is fully charged.

That being so, you could first fit a resistor in place of the thermistor. The thermistor changes with temperature so measure its value at normal room temperature and use a resistor of that value. The charger circuit will then think that the battery has not reached the end of its charge and will continue to output.

That on its own may fool the Ipod, but if it doesn’t it may be that the Ipod, itself, is always fed from the battery and the battery monitoring circuitry expects to always find a battery voltage of 3.7V to 4V. But without the battery that may rise to something nearer 5V and the monitoring circuit may feel that is too high and shut the Ipod down. If that is so, in addition to the resistor, try fitting a 3.9V 3W zener diode in place of the battery. If you want a drawing for clarity, then just let me know.

Because I am making several assumptions about the Ipod charging circuitry, I cannot guarantee that will work, but I think it’s worth a try.

I would be interested in how you get on

[zackattack]

Ok, thanks for your help. I will try a few methods. perhaps a couple of different methods will work. It could be a while until i get the materials to make this work. however, once i do get it to work i will post here and most likely make a video on youtube about it. I then would like to try the same thing with cellphones, for I have seen many forums of people asking how they can run their phone without a battery. that fix could be more complicated though, and for newer ipod since the system current flow is much higher and lower at times, where as with the ipod mini it is more stable.

[Edison1987]

Even I noticed the same thing. I handle my Ipod in a similar way as yours. I use the iPod as a radio and I often turn the volume to max and connect it to a desktop headphone amplifier. The battery doesn't run more than a few hours when used in this way with some time.

Thanks,
sim free mobile phones uk