Top critical review
81 people found this helpful
Only for Apple devices
on January 28, 2012
A quick summary of this product before I get into the details:
Likely great for dedicated Apple device users that has all the power it claims (simultaneously 2.1 Amps on one port with 1 Amp on the other for a total of 3.1 Amps output combined, but under performs DRAMATICALLY for non-Apple devices due to protocol issues for USB chargers. It gets 3-stars because all it claims to support is Apple devices.
Now for more details...
A little background on USB charging for those who don't know:
The USB power spec is for 0.5 Amps at 5 Volts... or 2.5 Watts. This was great up until the last couple years when devices have gotten really power hungry, particularly smartphones and tablets and to a lesser extent dedicated GPS's. Some of these devices use over 2 Amps, particularly the tablets like the iPad (or in my case the HP Touchpad).
Manufacturers of these devices therefore had a dilemma. If they had their devices pull more than 0.5 Amps, they risked damaging the power source, which could be a computer, that was only prepared to source 0.5 Amps. Thus the manufacturers have used tricks to determine whether their device is connected to an unknown source, at which point they purposely only draw 0.5 Amps, or to the dedicated charger that was provided with the device, where they can draw all the power they need.
There seem to be two common tricks used. The first is to short the two data-wires together in the charger. This is what most non-Apple devices do. Since a computer or older device wouldn't have done this, the device can assume it is safe to draw all the power it needs.
Apple seems to have taken a different approach, one that I don't fully understand but know can be seen by the fact that the data lines are neither open nor shorted when the charger is plugged in, and is more sophisticated and probably superior, because I suspect it allows the device to know exactly how much power it can use.
While Apple taking a better approach might be nice in concept, it's created chaos in the USB charger product category. What is the non-specific charger to do? They can't support both.
Kensington chose to go the Apple route for the 2.1 Amp port. I don't own any high-power Apple devices, so I can't say for sure, but I suspect this unit performs well with Apple devices. Using electronic equipment I was able to draw 2.1 Amps when putting a fixed load on this USB charging port. However, when I connect any of the 3 high-power devices I have (HP Touchpad (2 Amps), Motorola Triumph Android phone (0.85 Amps) and the LG Optimus Slider (0.7 Amps)), none of them drew all the current they could have, because they were expecting a shorted set of data-lines.
The 1 Amp port on this device is a bit of a quandry however. It didn't have the signature on the data lines of either the Apple protocol or the shorted lines. It appeared to have them open... which was a surprise and I believe a mistake (although I can't be certain with Apple products). The results for my 3 devices however were identical to that of the 2.1 Amp port.
To highlight the positives, I can say this, I was able to draw all the power the product claims it can source using fixed loads. As my above explanation makes clear, it is the DEVICE, not the charger, that chooses not to make full use of the available current (Amps). So by using power resistors I could test the actual capacity of the device without dealing with the data-line issue.
As such, I was able to draw both 2.1 Amps from one port and 1 Amp from the other, simultaneously. I can not say the same for the other charger I have tried (and I have two in shipment to test).
Thus this device gets 3 stars because it only claims to support Apple devices and without any to test I have to assume it would work great for them. It also can deliver the current it claims. It is likely a 5-star product for sole apple users.
However, for non-Apple users, I STRONGLY encourage you to look elsewhere for your Car USB power needs. The other device I've tried is the "PowerGen Dual USB 2A Heavy Duty Ouput Car Charger" (http://www.amazon.com/gp/product/B00622AG6S/ref=oh_o05_s00_i00_details). It has other problems (the 2A port doesn't have the data lines shorted and it only sources a TOTAL of 2A, not 2A on one port and 1A on the other), but at least one port (the 1A, which can really do 2A by itself, see my review over there for more details on that) on that has the data lines shorted to get the full power with non-Apple devices.
I've ordered two additional devices:
- "Ultra Compact High Output Dual USB Car Charger - 2.1A Output" (http://www.amazon.com/gp/product/B00470C35E/ref=oh_o01_s00_i00_details)
- "Bracketron Universal Dual USB Car Adapter (UGC-298-BL)" (http://www.amazon.com/gp/product/B0056VNVV8/ref=oh_o00_s00_i00_details)
Hopefully one of the two of them will be able to deliver to their specs for my devices.