Automotive battery chargers for Ipods, etc

[alia176]

I wonder if any of you know this answer: why doesn't my USB cig lighter charger able to charge ALL USB devices? For instance, it can charge my BB Pearl but not the wife's Razr or my Iphone. This thing came with my Pearl BTW. It can also charge a Motorola BT ear piece without issues.

Is this an USB 2.0/1.0 thing? Firewire?

Edumacate me!

 

[george_tlc]

USB uses the same pins on the connector for +5V and 0V regardless of USB version.

Basically all the that is going on inside a USB cig lighter charger unit is conversion from 12V to nominal 5V. Possibly the regulator circuitry that is converting from 12V to 5V is incapable of supplying the higher currents that are required to charge some of your USB chargeable devices.

USB specifies up to 500mA draw from a USB port but 'some' manufacturers will draw more than that - but that is not necessarily the problem here.

I'd guess that the cig charger/adapter that came with the Pearl was designed to provide enough current to charge the pearl, but probably well under 500mA. The devices that won't charge are likely drawing higher current that is needed by the razr etc.

Most phones etc will draw more current (up to 500mA) to charge the larger capacity battery faster. Your Pearl cig adapter is likely being overwhelmed by the higher current draw and its output voltage is dropping well below 5V and thus the charging fails.

You could just purchase a cig adapter for USB devices with a higher current rating.

cheers,
george.

 

[Fast Eddy]

USB specifies up to 500mA draw from a USB port but 'some' manufacturers will draw more than that - but that is not necessarily the problem here.

I believe there's also a low-power mode. The Moto devices may detect a higher-than-rated available current and refuse to connect to it.

 

[mkfour]

I made a USB charging port in my 80 for my phone, camera, etc..

I used a LM7805 that can put out 1 A, but my phone - Razr and camera refuse to charge. Some items may need smart charging. Some items also need to have D+/- pins pulled up or pulled down.

I'm still working on it.

 

[alia176]

My iphone would appreciate an 1amp charger it seems so I picked up a Power jolt USB cig lighter charger yesterday. It looks like it can put out 2 amp max if needed and so far it seems to be working. I hear the complaints is that using the GPS while driving around tend to deplete the Iphone battery faster than a conventional charger can put out so it ends up being a losing battle. I'll try to plug in the Pearl and BT earpiece to see if they are happy with this new charger.

Thanks.

 

[george_tlc]

I believe there's also a low-power mode. The Moto devices may detect a higher-than-rated available current and refuse to connect to it.

The low power (<100mA) is prior to enumeration (part of the USB protocol). Once a device has told the host its current requirements the host will then increase the available allocated current. Not all hosts 'care', since they can provide 500mA per port - but they will go through the enumeration process since it is part of the USB spec/protocol.

Anyhow, a device has no idea how much 'available' current capacity can be provided by the host without enumeration. The USB spec allows for <100mA on startup and devices negotiate for more.

A dumb 'host' like a 12V USB cig lighter of course have no clue about USB etc, ir just has a regulator to convert the nominal 12V to 5V. Many devices that use USB to charge don't even wire to the D+/D- data connections and just expect 5V to be available and they draw as much as they need. A few do some tricks and use D+/D- to figure out whether they are plugged into a proprietary charger (that can supply more than the 500mA USB spec). Of course this violates the USB spec, but since they are not USB devices - they are just using the ubiquitous 5V USB connector as a power source - they don't care since they will never go to USB compliance testing anyway...

Yes, I'm and EE that has had to take devices through USB compliance testing

cheers,
george.