WARNING on USB Charging Ports!
Just wanted to post a warning to everyone who has the built in USB charging ports on their camper/RV. We have a 2017 Grey Wolf 29BH that has 6 of these through out the camper, 3 of which are in the b...
Forum Discussion
bob_nestor wrote:wa8yxm wrote:
As I recall the "Standard" for USB ports is 500mA or 1/2 amp
My phone can suck 2 or more amps off a well designed charger/adapter via the USB cord..
NOW. a WELL DESIGNED USB port WILL limit the current... but the key word is WELL DESIGNED.. Not ever designer even knows HOW to limit current (i do but hey. I paid attention in DC Theory)
For USB 1.x and 2.0 the power is 0.5A; for USB 3.0 it is 0.9A.
And that's only after the device asks the host nicely. IIRC the initial current is 100ma or some such low number.
The USB PD protocol (power delivery) allow for up to 100 watts delivery, I believe it' 24 volts at just over 4 amps, but again, that's for the device to request and the host to say yes or no. Devices that support PD usually do 9v at 3a for safety regarding the battery.
The Qualcomm QuickCharge protocol allows for 36 watts, 12v at 3a, which most newer LG and Motorola mobile devices support.
There's other protocols out there, too numerous to mention.
USB 3.1 gen 2 power transfer gets really complicated, as power transfer is reversible, the device can power the host, example docking your ultrabook to a large format monitor via USB-C connector, and the monitor backfeeds power to the laptop. Those circuits are crazy with buck-boost or SEPIC topology on both sides, and fancy chips out the whazoo to figure it all out.
