Test/Review of USB meter: Charge Doctor

USB meter: Charge Doctor



Official specifications:

  • 21mm x 53mm x 15mm / 0.8" x 2.1" x 0.6"
  • USB Plug: 13mm / 0.5"
  • Weight: 16.2g
  • USB 1.x and 2.x - all data speeds. Does not have USB v3 pins so USB v3 connections will automatically downgrade to v2
  • Working Range: 0~3A, 3.5~7VDC
  • Resolution: 10mV / 10mA
  • Operating Temperature: 0-60ºC


This meter exist in a couple of different versions with minor differences (SMD vs. leaded parts).


How does it look






One of the digits is used to show U or A, depending on what is shown on the display.






The difference between the version is the leaded components, they have been replaced with smd components.



Not very nice looking, the circuit board has not been cleaned after soldering. The measuring resistor can be seen here, it is marked R050, i.e. 0.05 ohm (50mOhm).



Measurements

  • Voltage is within 0.03V when unloaded (Tested from 3.5 to 6 volt).
  • Current is within 0.06A.
  • When loaded the voltage is somewhere between input and output voltage.
  • The meter uses 22.3mA current
  • Works down to 3.27 volt
  • Internal resistance is about 0.14ohm including connection resistance.
  • USB data works fine.





M1: 57,5°C, HS1: 66,9°C
Notice that the hot spot is in the connector, it has a rather high connection resistance and is getting hot.



Conclusion

The internal resistance is acceptable and the same with the precision.
With two digit resolution for both voltage and current it is a good usb meter.

It looks like there is a new generation of these on the market where the resistor is changed from R050 to R100, i.e. the resistance is 0.05 ohm higher.

Notes

How do I make the test

I have a couple of these, nice to see them tested. Thanks.

Nice…thanks HKJ, I have one that has the Volts and Amps on one display, waiting for it to flip over is sometimes a pain

Great review…thanks

Thanks Henrik. I'm glad to have this confirmed as a reasonable testing tool, although as you noted it depends on which version is received.

I don’t get the part about amps, I wanted to see if a plug in for the lighter produced 2 amps, do I need to put this in between the adapter and what I’m charging to see the amps?

Also, is there much difference from an adapter that will produce 2.0 amps, and the 2.1 amps that apple products call for, or is that pretty much meaningless?

I will probably also post a review of that unit, I do have a couple more in queue.

I have two different versions of the charge doctor, they work the same.

Yes, you have to plug it in between the adapter and whatever you are charging. Then it will show how much current you are charging with, not how much your adapter is capable of. Because these usb meters add some resistance, some devices may reduce their charge current.

If there is a difference between 2.0 and 2.1A depends on the adapter and the device you are charging. A smart adapter may reduce the output voltage when to high current is draw and a smart device may get the hint and reduce the charge current.

Henrik: Could you give us your preference between these (Charge Doctor) and the XTAR USB unit please. Any pros or cons between the two. Is one better than the other? I would really appreciate and respect your comments.

One very important parameter is the internal resistance, it must be as low as possible (Charge doctor wins there), but the Xtar has better precision and works at a lower voltage.

I prefer another one, but that review is not published yet

Excellent! I will patiently await for the report. Thank you.

I’m not feeling so patient!I almost purchased the x-tar model.Now I have to wait and see what HKJ is recommending. :~

The question is hos long you want to wait. I have done a couple of reviews more and know one of them is better, but I have more usb meters in queue for reviews and do not know how they perform. I will probably also be publishing other reviews, i.e. it might be close to xmas before I am finished with all the usb meters or maybe even next year, depending on how much other stuff I review.

With the speed I publish (One review each other day), I have to plan and write ahead. I.e. do the testing and write the reviews when I have time.

I just received 2 more of these from BIC at only $1.79 each. From the pics on the site I expected a knock off but they appear to be the same. So I ordered 5 more.
Gift time!

http://www.buyincoins.com/item/34684.html#.VClAwvldXoI

EDIT: I just checked more closely and the more recent one I recieved from BIC differs from the first one. Here are the pics
The original one I received is on the bottom, scratched up, the most recent on top. They look the same.

but from the back, there are differences. My original one looks more like what is in this review.

The one I received a couple of days ago on top and my original on the bottom.

Thanks for the review HKJ. I bought one of these some time ago (I think on Chloe’s recommendation) and find it quite useful. A silly question, but is is easy to remove the blue plastic cover without damaging it? Can it be replaced again once removed?

I do not like the one at the top, it has more resistance.

That’s what I thought. You’re talking about the switch for .05 ohm to . 10 ohm, right? These guys are always making changes for the worse.

Exactly.

Oy.

I missed that question. If you have the right tool (Spudger) it can be removed with only minor damage and replaced again.

It’s cheaper for them component wise, thus the dangers of Chinese stuff