The stuff of Kryton

An eclectic selection of technology with some cookery

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USB Charging ports – Part 1, Why are some faster?

I’ve noticed that some devices charge better on certain USB power supplies / charging ports and not others, so I thought I’d try to figure out what’s going on. Just too clarify I’m considering all “USB Chargers” as “USB power supplies” with “Charging ports” as the device plugging in (i.e. a smart phone) has the charger built in to it to charge it’s own battery.

Initial testing – is there a problem?

Initially to find out which devices drew what current on which charging ports I modified a USB lead so that the +V wire (normally Red) was Open Circuit (O/C) with both ends exposed. I then used my multimeter in current mode to measure the draw of each device on each charging ports. This confirmed my suspicions that just because it’s a 5V 2A power supply the device in question did not necessary draw 2A even if it did on other charging ports.

Basic USB test lead, Current measured with a DMM via the crock clips.

Further testing – categorising chargers

Researching further I discovered the Lygte info page on USB charging port specifications. This categorise different charging port specs the Author is aware off and helped me categorise the chargers I have.

Second USB test lead, acts as an extension lead so can be used with any proprietary USB lead. Enables current measurements and D+ & D- voltage measurements. This really needs re-designing in to a box as the data lines are only designed for 3.3V and the +V rail is 5V so a short could result in damage.

Conclusions of testing

I’d love to say there are some simple rules to follow to make my USB charging life simple but quite frankly it’s a mess. From my testing I’ve been able to establish the following random facts about devices & USB charging ports.

Devices

Modern Apple devices (Lightning port)

• Need an Apple 10W (A1357) charger to draw over 1A
• On USB DCP chargers they limit to 1A
• Modern Apple 1A chargers (A1399) are now USB DCP

Apple iPod (30Pin port)

• Needs an old Apple 1A (A1299 / A1205) to charge at 500mA
• Limits to 100mA on a USB DCP & Apple 2A

Sony Compact system camera (CSC)

charges at up to 1.4A on

• USB DCP
• Samsung 2A
• Apple 2A

##Sony Action camera charges at up to 500mA

• USB DCP
• Apple 2A
• Apple 1A
• Interestingly Charges at up to 800mA if D+ / D- are open circuit. Lots of devices simply take the current they want regardless and rely on the usb ports current limit to prevent an over load. USB power supplies

Generic chargers I own:

Either conform to:

• USB DCP
• Apple 1A
• Apple 2A

or are:

Bolse (LC058)

• “Universal” = Apple 1A (not USB DCP)
• “Samsung” = Samsung 2A
• “iPad” = Apple 2A

Belkin USB ports on 8-way mains extension lead

• 2.4A limit
• USB DCP

Anker Battery (A1211)

• PowerIQ port limits Sony CSC to 1A
• Seems to be OK with other kit.

Further thoughts:

Looking at Lygte info there is a Sony changing spec so I’d like to get my hands on a Sony spec charger and see what the camera’s do. I did once see the Anker battery set it’s ports to 3.3V on D+ & D- and the Sony CSC took 1A so I wonder if that’s the current limit Lygte info could not find out? I could not repeat this and I had a relatively high impedance current meter in series at the time which could have limited things.

Redesigning the USB test lead to make sure D- can’t be accidentally shorted to +V and possibly trash the data port of the equipment under test. This could be a rather expensive mistake!

If you’re looking at buying chargers Lygte info has a comprehensive list of reviewed chargers, although this does not cover every possible charger it can give you an idea of what to expect from each manufacturer. I certainly recommend the site.

/ license

Keywords: ELECTRONICS TECHNOLOGIESTAGS: ANKER, APPLE, BELKIN, CSC, IPAD, IPHONE, LIGHTNING, SONY, USB, USB DCP