Posted 21 November 2012 - 08:33 PM
LiveBrianD, on 21 November 2012 - 06:23 PM, said:
I'm getting a voltage drop to around 2-3V when using that. Interestingly, I got the same issue when doing this off my desktop. I've got 24A on the 5V rail, so this shouldn't be a problem, but I'm getting the same drop, measured from that USB port - perhaps this is due to the USB current limit? (however, according to software anyway, the PSU didn't blink an eye - and if the 5V rail had dropped like that, the PC would've crashed)
When I ran this off a heavier duty PSU (2A, variable voltage), at 4.5V, it was pulling around 180mA, and was brighter. (and the voltage was actually 4.5V) Sure, maybe cheap chargers can't deliver the full rating, but I shouldn't have been even close to the limits. I used a big resistor to put load on the USB charger (v=ir, r = ~7ohms), and again, noticed a huge voltage drop.
Anyway, I'll read more about this.
For the record, most of those chargers barely deliver half of what they are rated for. I found this out with my Pi. 1A chargers couldn't keep it from crashing (it only needs .7A). Then I moved to a 2A quality unit, and never had trouble since.
Also, your PC may have 24A available at the 5V rail, but your USB controller will limit the current to the ports. Usually, to 500mA.
"There is a cult of ignorance in the United States, and there always has been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.'" -- Isaac Asimov
Steam Machine: MSI 970A-G46, AMD Phenom 955 @ 4.0Ghz, 8GB Gskill ram @1600mhz, 128GB Plextor M5s, EVGA GTX 550Ti
Laptop: Alienware 14, Intel i7-4700MQ, 8GB DDR3 ram, Nvidia GTX 765M 4GB DDR5, Plextor M3 256GB SSD, 1080P IPS display, Killer GigE, Killer 1202 wifi
Hackintosh: Gigabyte H61m-HD2, Celeron G1610, 4GB Patriot ram @1333Mhz, Asus GT210, WD 1TB Black, Silverstone ES50 500watt PSU, OS-X Mountain Liion