PortaPow USB Power meter teardown
I don't have a proper USB power meter so after searching around, I settled on getting the Portapow from online.
I have just received it so, what better way to not turn it on, and take it apart.
This is what is contained in the box.
No paper instructions or manual included but they can be found online.
But the device is simple enough to use that the buttons and functions are mostly self explanatory.
The first thing I noticed was that there was a piece of dirt (FR4 burr) on the inside of the LCD screen.
It turned on right out of the box. A slide switch on the left switches it on or off, they opted not to use a soft touch tact switch. Not a big clunking power switch but it hard switches the power to the uC.
With the power switch off, there is no indication if it is charging but there is power being drawn.
The back cover is simply snapped on. No screws so it was very easy to open.
I don't know why they used a small barrel connector for the 5V supply. Why not use a mini or micro USB so there is no need to look for the special charging cable included. It will be less of a hassle too if you lose the original cable.
The wattmeter connector used a special kind of barrel connector with three coaxial contacts, similar to some laptop chargers.
Positive is the center pin, current is measured on the negative line.
The banana jacks are the very cheap kind. I was hoping for atlease a better quality one but it will be an easy change if you wanted.
The LCD is one of those clone Nokia monochrome dot matrix screens. It is simply snapped on to the PCB. The bottom part appears to be cut off.
The back of the LCD display.
The main uC is 8051 based. I assume it has onboard ADCs as there appears to be no other special circuitry. U01 looks to be an op amp.
The wattmeter jack is soldered to the PCB but it looks bad since they appear to have used lead free solder which didn't wet well so I resoldered it.
A whole board look.
What looked like a solder splatter is actually a bodge. The resistor pad is connected to a via nearby.
Inside of the moulded case front.
LED backlight is blue. I don't like it so I'm changing it to a different color.
I would have wanted white but I don't have a high efficiency one so I used true green, still much better than blue.
And here it is. Looks much better IMO.
Now it is assembled. Seems to still work.
I connected it to my voltage reference.
1.000000V output verified on a 7 digit bench multimeter.
When the probes are reversed, there is a slight difference to the reading.
And now, for the 10.0000V output.
And again, with the leads reversed.
Now for the amps function. My ammeter has also been verified against a calibrated unit. Accuracy is acceptable for my use.
It can also measure reverse amps (displays "-" ) but the amphour reading still counts up.
And a bonus.
I also bought a Matek USB power meter so we compare both on the same load.
A more detailed review can be found here.
Here it is displaying volts.
Some things I would have liked would be a charging indicator when the unit is off. When on, the battery level indicator counts up and the backlight stays on. It would've also been nice if the mAH reading goes up with positive current flowing and counts down when flowing back, useful for monitoring battery SOC. Also, the buttons are kind of protruding which is ok for easy activation but the reset button works instantly so if you accidentally bump it, the readings are cleared. I would have liked the reset button to have a short delay (long press to activate) so that accidental bumping won't clear the readings.
The Portapow USB power meter has decent accuracy, features are also nice and I like the internal battery so that the energy readings do not disappear when USB/test power is lost. It is more accurate than the inline USB power meters but you'd need to fumble with the cables so it is more for those where accuracy is more important. For those quick checks or eyeballing the ratings, I can use the Matek USB meter for ballpark figures.
29 May 2017:
It still gets some use from time to time but one thing that annoys me is that it has no indication when charging if the unit is off.
I jut had to mod it.
Near the power jack is this 6pin SOT-23 chip which has the same pinout as an LTC4054 but has an extra pin which is the inverse of the charge indicator pin, in other words, it goes low when charge has terminated. I could not tap off the charge indicator pin as it is connected to the uC and could pose problems when pulling up while the uC is off.
A 680R pull up resistor is added between the VCC (pin4) and the charge terminate pin (pin5) and the LED is connected between pin5 and batt- which is a ground plane with solder resist scratched off nearby.
Since pin5 is an active LOW, open drain pin, when charging, it is Hi-Z so VCC flows through the resistor then through the LED to batt-. When charging terminates, pin5 is shunted to batt- so the LED turns off.
With the unit turned on, it is a slightly noticeable but can't be seen in the pic.
If the unit is off, the amber LED can be seen well indicating it is charging.
Another shot at an angle with the LED light more visible.
I had an idea where to get high efficiency white LEDs. I scavenged a bunch of broken cellphone/tablet LCD screens for their backlight LEDs.
Found six that have the terminals near the front face (emitting side) which would make face-down mounting possible. The wide package was also about the perfect size!
I like this a lot better than either blue or green!
Looks bluish in the picture but is a nice pure white in reality.
With the charging cable plugged in, there is a slight orange tint (more visible in actual) on the battery icon corner because of the added amber charge indicator LED. Perfect!
Page created and copyright R.Quan © 06 Dec 2015.