6 of 7 people found the following review helpful
some empirical data, and a 2.1 amp iPad modification
, October 31, 2012
I haven't the time for a full review, but I've taken some measurements and it would be silly not to post them somewhere so here they are.
First, the standby current consumption with nothing plugged in to it at all is 22mA at 12.8V. That's pretty much unacceptable for something like this. It won't kill your battery in a day or anything, but it might halve the number of days it normally takes your battery to die. As a comparison, I've got a couple of mc34063 based super-cheap imported usb car chargers as well. They draw only 4mA, and at least half of that is to power the led (which this griffin doesn't even have). It's a nice design otherwise, but this area needs improvement. I'd like to see <2mA. This is quite possible.
It puts out 5.05V with no load with 8-15V input. This is ok but it would be nice to see a higher output (like 5.25V) to make up for losses in the charging cable. The voltage will have dropped some by the time it reaches the phone and it may not charge as fast as it otherwise could. Actually, I had to crack open the case to get accurate voltage readings for the remaining tests because every single one of my usb cables drops several hundred mV with an amp or two flowing, and that includes a little 1 foot extension cable.
It is capable of providing its full rated current of 2 amps without any voltage droop. Past 2 amps, the voltage starts increasing some and is nearly 5.5V by the time it craps out and turns off at nearly 3A. I ran it at 2.5A for a few minutes and it started to turn off again so I don't think it would be able to charge an ipad at 2A (see below) and a phone at 500mA+. Even with the input voltage cranked up to 15V, it just won't do 2.5A.
The efficiency is quite good. It's about 84% at 500mA, and 87% at 1A and 2A. This is much better than the other chargers I have, but it will still heat up. At 1 amp it's dissipating less than a watt. That's not too much and in most cases it probably won't get too hot, though certainly warm. At 2 amps it's dissipating over 1.5 watts. That's still quite good for this sort of stuff, but it is a fair amount of heat for a tiny thing stuck inside a dash so I'd expect some overheating in some of the worst cases out there. I certainly won't be using it in my car at 2 amps unattended during a 110 degree texas summer day.
Also, it has been mentioned that the device is wired incorrectly for high-current charging. This is not entirely correct. It is wired for charging apple devices at 1 amp or less. D+ is at 2V and D- is at 2.7V. This is the correct configuration for instructing an apple device to charge at up to 1 amp. This configuration works for apple devices, but it does not work for everything else. I have tested an iphone 4 and it charges at about 650mA. That's the same as when I plug it in to a real iphone wall charger, and certainly more than the 100mA or 500mA that it would charge at on an incorrectly configured charger. However, a galaxy nexus charges at only at about 440mA. That's much less than the 700mA it usually charges at with the wall charger it came with.
For those who wish to charge an ipad at 2 amps with this, I expect that this could be accomplished by reversing the voltage divider resistors on the D+ and D- pins inside the charger. Putting 2.7V on D+ and 2.0V on D- (rather than the other way around, which is how it comes out of the box) should instruct apple devices to charge at up to 2.1 amps. They're 0603 surface mount resistors and you might have to remove the vertical pcb to make room to get to them, but it's quite doable. This is safe to do as long as nothing is plugged in to the second port at the same time. Actually it's probably safe regardless, but the charger will shut down if too much current is drawn. The voltage doesn't sag at all - it just shuts off suddenly.
EDIT: I have completed the voltage divider modifications I discussed and have posted images containing instructions on how to do it. I don't have an iPad to test with but based on my observations I have no reason to doubt that it works. While I had the thing open I had a look at the build quality. This is not imported garbage. I like what I see and am therefore adding one star to my original 3 star rating. I cannot award the fifth and final star given the 22mA standby current consumption and the undisclosed lack of support for non-apple devices.