car charger for Samsung phone

[rans6andrew]

Yesterday I tried to use a car charger on a Galaxy Siii mobile phone and found that it wouldn't charge the phone, the phone just kept displaying the message "USB connected". The charger has been used satisfactorily with a Samsung Ace phone. It has the same micro USB connector as the mains charger that works with both phones.

Is this a hardware issue or have I missed something in the setup of the phone?

Frustratingly, if the car power is turned off while the phone is connected to the charger, the charger draws power from the phone (the LED on the charger stays illuminated) and further discharges the phone battery!

Rans6......

[Avtrician]

There may have been a broken connection/wire some where. There is a resistor two fitted in there some where, that tells the phone its connected to a charge source, not a data source.

[henry_crun]

Rans6 - yes, a hardware issue.

It hinges on the feature known as otg or on-the-go. The Samsung Ace does not support otg but the S3 does.

The hardware difference is that a fifth pin in the usb plug is used to signal the direction of power flow. When the pin is open, power flow is into the phone or tablet for charging. When it is shorted to the 0V pin the power flow is out of the device so that it can power memory sticks or other peripheral devices.

I think your charger cable is the wrong one and has an otg plug so it will get power into the Ace (no otg protocol) but is telling the S3 (which recognises otg) to disconnect incoming power and send power outbound.

The remedy is to replace your charger cable with one that is designed for charging.

[rans6andrew]

I just had a look inside the jobby, after prising it open. The wire from the circuit to the micro USB has only two cores, ie it only has the regulated 5 volts and ground connections. Maybe the phone "expects" something clever in the other two connections of the micro USB to tell it what to do.

My sister had a similar issue with Motorola Razr phone which would not charge when connected to her computer, apparently there was some sort of software fix for this. I don't know if it was a driver for the PC end of the link or a code download into the phone. I'll see if she can shine any light on the issue.

Rans6.........

[henry_crun]

Andrew, I think your charger has the wrong micro usb plug. And it is not the 'other two pins', it is the FIFTH pin that does the otg signalling. The pins are connected within the plug itself. A short from pin 4 to pin 5. Check the usb spec. :ugh:

Try a new charger.

[rans6andrew]

I just noticed that the plug at the phone end of the thingy can be opened without destroying it and inside it there is a small circuit board with a placement labelled "R1". This placement has been shorted out (a single strand from one of the connection wires has been soldered to the other end of it, deliberately) rather than fitting a resistor.

It probably gives the phone the wrong message when connected.

I wonder what value resistor should be fitted? Unfortunately, the mains charger plug cannot be opened without breaking it.

I have the technology if I could find out what the value should be.

Rans6....

[rans6andrew]

Wonderful. The connector pin numbers are on the circuit board inside the plug, helpfully arseaboutface.

Removing the shorting wire completely has enabled charging??????

Sorted, ta for your words of wisdom pointing me in the right direction.

Rans6........