USB - Media Update

[neil2jo]

I have a Relay van that is a '59 plate

When bought as 2nd hand but still in warenttee the usb would not charge or recoginise my Iphone4. I took to the local dealer who said they tried a staff phone and confirm the same...umm seems a very simple test...by very simple people...based on if it does not work for me, it would not work for them!!
In addition if i use a usb stick is it fine, but after a day or two although tracks play etc, if i want to select a certain track or view folders it says 'no media found' even thought it is currently using the mp3 to play!!

So question 1 - is the usb port meant to charge and/or accept iphone 4?

Question 2 - through the menu i can choose media update, but i get an error...so i imagine i need a file on usb....does anyone have a link or similar?

[Old-Guy]

I've heard lots of tales of problems with iP__s refusing to connect and/or charge via USB ports on all sorts of devices (but not Macs!); I seem to remember reading that the cause is Apple 'tightening' the standard response time - USB is an asynchronous protocol that requires devices to respond within a certain time frame which (the speed of light), in turn limits the possible length for any USB cable.

In answer to question 1: NO (the iPhone 4 hadn't been thought of in 2009)!

I've also found that other phones and cameras are fussy about which so-called Universal USB chargers (both mains and 12V) they will charge from. The only truly universal one that I've found is a mains charger for a Nikon camera (which states "only for use with compatible Nikon cameras"!)

[Xaccers]

I believe Apple require some communication between the device and the charger (back in the ipod days, you HAD to have iTunes installed in order to just charge the ipod from a PC), while normal devices just require 5V, some will charge faster if two of the pins are shorted - can't remember which two but it tells the device it is connected to a charger rather than the USB port of a computer and so can draw more current.

[KP]

A USB port should max out at about 500ma where as a normal Wall charger can be 1-2000ma

[Old-Guy]

A USB port should max out at about 500ma where as a normal Wall charger can be 1-2000ma

The USB standard specifies a maximum of 500mA per interface. But it's quite common for laptop motherboards to use a single interface for a 'pair' of adjacent physical ports. As a result, each port is limited to a maximum of 250mA (and also runs at half-speed), this is why some devices are supplied with a USB cable with a pair of USB plugs at one end and others won't work on some laptops (because they need >250mA). External USB floppy drives are a case in point as are some USB hubs.

A bit off-topic, but relevant IMHO.