USB "charger doctor" (volt+current display)

I ordered mine off eBay on 8/15, and got it yesterday. Seller was onzway2010, and cost $2.83 shipped. I have a bunch of multimeters, but this is cheap small and easy.

The main reason I got mine was to check the cheap USB chargers that say they put out higher current. We all know how accurate the specifications are for cheap Chinese products. I have a few to test, one of them is this one:
http://dx.com/p/215107

So far I tested my OEM Galaxy S4 AC charger, I got 1.3 amps. I also tested the S4 on my computer’s USB port, and it’s at 0.32 amps.

I also tested my mouse that has some lights on it. With all of them off it uses 0.04A, and with all of them on, 0.11A.

I do wish it had 3 significant digits, but 10ma resolution will be good enough for the price I paid. I also wish it had a button to switch between V and A. Most of the time I only want amps.

I ordered mine to test out solar chargers. I'll be reviewing one soon, and it'd be nice to have an easy way to determine the output.

As long as you test in bright sunshine you will probably be OK.

The past couple of days here (since I got my parcel) as luck would have it has been mostly overcast.

I thought solar panels were supposed to generate close to their rated voltage even in poor conditions, but giving very low currents. Now I'm not so sure if this is correct.

These meters only read from 3V upwards and when testing on some of my small panels with 5V USB output, I couldn't seem to get any display at all. Perhaps it depends on the load I apply.

Also, quick heads-up - the display is very, very dim when trying to view it outdoors. You might need to use an extension cable and put the meter in box of some kind or shroud it in your palm in order to be able to read it.

Mine arrived today.

Been using it on my Samsung Galaxy Note 2 charger:

5.25V and 1.60A when Note 2 is switched off. Nearing full capacity it has dropped to 0.3A, voltage varies between about 5.25V and 5.30V

Now dropped to 0.25A…

I bought one too but have no way to know how accurate it is. How do you measure the accuracy of it?

Depends on how accurately you want to measure the accuracy. :wink:

Generally you will need some known reference to test it against, but if you don’t have a good understanding of measurement chances are you will do some part of the measurement wrong, or introduce errors.

Don’t worry about it, might be a good way to go.

Like I said it measures with a resistor so it may change thechargingprocess on some devices…so watch out the current with device in between could be lower than without…

Nothing is going to directly use the “about” 5v from the USB to charge a battery, so a 0.125v drop should make no difference other than “maybe” a couple percent less max current draw, nothing anyone would notice, or most could likely measure.

Most meters use a shunt, a very small resistor placed in series, then measure the voltage drop and calculate the current flow from that, so nothing unusual about the method.

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).

http://www.eevblog.com/projects/ucurrent/ 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.