USB Load resistor Juwei 2.5-5-10ohm


Official specifications: I bought from ebay dealer: power116

This load tries to be everything, it has 3 different resistors that can be switched in, it has 3 input connectors (USB A, mini and micro), it has 4 usb output connectors with different coding and it has a couple of white leds.
Usual the most interesting detail about this type of load is how hot they get, some power resistor has a working temperature between 200C and 300C when fully loaded.


I got it in a plastic bag, there where no specifications or user manual included.


The actual load circuit is fairly simple: 3 resistors, each with a switch and a led (The 1A led did not work). On this load there is added four usb outputs with different coding (Samsung is missing, but there are 3 different Apple coding).


On this side the micro and mini usb connectors can be seen. The white leds are also placed here with a common 2.2 ohm dropper resistor, this resistor is going to be hot.



DSC_8149 DSC_8151


Load testing

Being resistors the current will depend on voltage. The current is a bit lower than specified. The reason can be tolerance on the resistors, contact resistance in the switch and in the usb connector.


As expected the load current and power is stable with a resistor, except for a small change due to temperature.


M1: 209,1C, M2: 152,3C, M3: 84,6C, M4: 94,0C, HS1: 272,4C
The resistor with 2A gets close to its maximum temperature, it is a good idea not to touch the circuit board or the resistors while they are working.


M1: 118,8C, M2: 116,8C, M3: 83,1C, M4: 77,8C, HS1: 278,9C
The backside do also get fairly hot.


M1: 69,1C, M2: 49,9C, HS1: 86,4C
What about the white leds? They do heat the circuit board a bit, but there is one warm point.


M1: 84,8C, M2: 59,9C, HS1: 216,5C
To get a measurement of the hot resistor I covered all the leds with some fabric, then I could measure the resistor.
It is not going to have a long life at that temperature!


This load tries too many things at the same time, but do not really do any of them well.
The load part can be used, using a fan to cool the load is a very good idea.
The coded outputs can be used to check what coding a phone will accept, but I miss the Samsung coding.
I do not really know why the white leds are there and the dropper resistor gets way too hot.

The idea with multiple resistors that can easily be switched in is good enough, but this device is not very well made.