"Larry Jaques" wrote in message
...
On Mon, 6 Apr 2015 17:31:57 -0400, "Jim Wilkins"
wrote:


I bought one of those solar wattmeters o eBay for $14 or so and it
works well for 12v. The little ones above are USB, so they are for
5v
USB circuits only. Since Ig said 5v, I keyed on it.

I forgot to check the charging rate of the little USB wattmeter
through the solar charge controller, but will do that tomorrow.
(Where
the 'ell did I hide the little bastid, anyway?)

I turned the cable and a connector from a USB1 hub into a breakout
cable to check the AboveTEK meter with a DVM and an external resistor
load.

AFAIK USB2 ports can supply 500mA continuously, for USB3 it's 900mA.
They are protected (?) by PTC thermistors that allow higher startup
surges. I'm not about to risk my laptops or portable hard drives by
measuring these limits.

I run into them with a USB3 ExpressCard that won't run a portable hard
drive without externally supplied 5V.

-jsw