USB "charger doctor" (volt+current display)

UNI-T UT61E has a drop of up to 1.1 volt when measuring mA, I would say that is significant.

The shunt resistor is not that small in all meters, especially on the mA and uA range it will be larger and a drop of 0.5 volt is not uncommon when close to maximum current in a range.

On top of that you have to add the loss in connections and cables, this is insignificant at a few mA, but at higher currents it will be significant.

For people that know their DMM and what they do, it is easy to work around some of these voltage drops (One way is to buy the uCurrent adapter from EEVBlog). Thanks nice site. I do know this stuff BTW, but its been awhile since I’ve done it.

This little USB device has a smaller range for current and I believe uses a smaller resistor with much less drop.

This little box is a x100 amplifier and some resistors, i.e. when measuring 200mA (on the 1mV/mA range) it is 200mV on you DMM and that means a 2mV drop over the resistor.

I meant the USB display device, not the uCurrent.

For example with my android phone I get around 0.1A less current with the charger doctor between…

Measured how?

With battery app, shows charging current. With device in between its correct about 7xxmA and without the current increase to 8xxmA. I have tested it several times.
If I choose a cheap cable current decreases further, sometimes funny. For example I have a retractable 3in1 cable from fasttech, mini usb, micro USB, iPad dock connector(old) and this is really garbage.

On my ipad it makes no difference, but I have a 2m cable which almost charges nothing when the screen is on, I now have measured it and current with long cable is 0.8A vs 1.8A without…I played around with a ihustle and other things.
The charger doctor is a neat device, but it is always good to have measuring tolerances and failures in mind…0.1V is still much drop

I don’t know if maybe the datalines are corrupted in the bad cables so that the devices don’t go to fast charge mode or if the voltage over the cable is so high that it doesn’t charge higher. Maybe I should check if the cable get warm…

The ucurrent reminds me on the current measuring PCB I have laying around since HKJ review. I extra ordered the amp range which has 0.1V per Amp or so, that I can use it with multimeter without calculating so much…

It was not really a review, more a "build you own current measuring device with low voltage drop" article.

Possibly less drop, than the production tolerance in individual chargers.

First rule of measuring stuff, everything matters. I would make a test rig, a dummy load on one end of a USB connection and voltage test points on both ends and do some testing.

With a 1A different I suspect you are correct and its not switching to high current mode. Stock I think USB is only good for 500 ma. but some do more.

Agree, cute device, not much of a measurement tool.

I think you might be expecting a little too much, given the price.

Works fine for me.

Same here. For the about $3, it tells me what I need.

I tested 2 iPhone 5 lightning cables. One got 500ma no matter what charger I plugged it into. The second got 750ma in all the chargers. My Galaxy S4 got 1A. Both phones were around 95% charged, so that may have lowered the current a little too.

That was testing chargers, both cigarette plug and AC. All capable of 1A or better. On a PC, I get 300ma on my S4, which is reasonable, but takes forever to charge.

Mine arrived a few days ago and I finally got around to testing it with some solar panels

2 Brunton explorer solar panels rated at 1000ma, first one gave out around 700ma and the second one around 500ma

Cottonpickers solar panel rated at 330ma gave out around 100ma

As others said it’s hard to see the display under the sun

I have opened the Case to investigate why the shunt resistor is hanging around a bit angled and it seems to be something small red underneath, maybe to give some distance to the PCB or so? Over the display there was a protection foil which I removed, not sure if this make reflections worse?
I will play with that next week as I want to add a switch to shortcut the data lines for high current charging of phone and tablet with any USB source…

estore999 did well. Ordered mine on 9/10, delivered today, 9/23.

many products made in china are not so good because the prices have to be cheaper and cheaper.

Thanks! I ordered one to get their Fast-Charge 3-in-1 Cable.

Yipes, $19 for 5 bar led, vs $3 for digital readout.

I played around with my doctor and it seems that my phone and my ipad go into high current mode if the datalines are shorted…so I soldered a big blob of solder on the 4 data pins to make them one big pin.
It has worked perfectly.