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Discussion Starter · #1 ·
Thanks to this awesome product, I was able to test every USB 'Micro B' cable in my possession with various chargers. Highly recommend!

Buy it at adafruit.com

TL;DR Use a short, high quality cable, avoid power outlets with lots of interference. If your cable is loose, charging current stays down for safety reasons.
Best results: This "premium cable"

Don't waste your time "charging" inadequately.
Use case: my phone dies faster than it charges in my car while using GPS w/ 2.1A charger... time to research what is going on!!!

What is it? "USB Charger Doctor" (UCD)
3-7V, 0-3A USB passthrough device which measures voltage AND current.

Samsung Galaxy S3 w/ ~60% battery remaining (2yr old, i suppose my USB port could be a bit worn, but I did get 1A on 2 cables with 3 chargers).

Observed Charging currents:
  • 1A
  • 0.65A
  • 0.45A
  • 0.25A
  • 0.1A
  • 0.000A
Voltage fluctuated between 4.5 and 5.1V, didn't seem to affect my results much. If the voltage dropped much lower then 4.5V or higher then 5.3V I would be concerned.

Chargers tested:
  1. Samsung OEM 1A wall charger
  2. USB 2.0 powered hub (2A transformer), maxed out at 0.65A.
  3. Desktop USB 0.5A
  4. Monoprice 5000 mAh 2.1A battery pack maxed at 1A (phone limit)
  5. PNY 2.1A USB Car charger maxed at 1A (phone limit)
Cables tested:
  1. Monoprice "premium" 3ft cable w/out ferrite core *1A*
  2. Monoprice "regular" 10ft cable w/ ferrite core *Sadly 0.5A*
  3. Samsung OEM cable *BAD*
  4. Random 1ft cable *1A*
  5. Random 6ft cable in car (wired under dash) *0.5A*
  6. MHL HDMI w/ USB power cable ~12ft *0.65A*
Outlets tested:
  1. Wall outlet 1 *BAD*
  2. Wall outlet 2
  3. Wall outlet 3 w/ Power bar 1 w/ Logitech Z-5500 speaker system (off) *BAD*
  4. Wall outlet 4 w/ Power bar 2 w/ home theatre tv and computer
  • The outlet used matters!! Shocking!! Wall outlet 1 and Power Bar 1 couldn't get more then 0.25A out of any of my cables, with Samsung OEM charger. Moved to another room in house (Outlet 2) and I got 1A no problem. Power bar 2 had no problems either.
  • Cables wear out / break without visible damage! My Samsung OEM cable is now useless, even though phone showed as connected and charging, UCD showed only 0.1A/0.25A!!! Cable was still snugly fitting, reinsertion did not increase this number with 1A charger.
  • New 10ft cable from Monoprice did NOT charge > 0.5 A with Samsung 1A charger.
  • If you jiggle the cable and it slightly loses connection, the current drops down for safety (presume), I did NOT observe the current ramping back up to 1A (even with a good cable), had to remove, wait 5 seconds, and re-insert.
  • USB powered hub: 0.65A (MHL cable / premium cable). 1A is unlikely as phone recognizes USB mode instead of AC mode.
  • Monoprice's USB battery pack: 1A (w/ premium cable / short cable)
  • USB car charger: 1A (w/ premium cable / short cable), all others <= 0.5A!! Wiggled (eg: bump in road) my 6ft 'car' cable, and it dropped to 0.25A and did not go back to 0.5A! Let alone, not getting 1A with my current cable Yay! Figured it out!
  • Some people have reported car chargers not crossing the "data -+" lines, so phone only charges at 0.5A, UCD helped confirm 1A possible with that charger
  • MHL cable w/ AC adapter still capped at 0.65A
    Phone may die while streaming HDMI
  • Android needs USB Data+- wires present.... This Adafruit 3-way charge cable did NOT charge my phone. Blackberries appear not to care.
Hope that encourages others to replace their cables / chargers / buy this amazing product!

pps: I can't wait for USB 3 "C" connector
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