Happily, the prices for USB current meters have come way down, and there are so much more choices and functions. Some examples:
Some models intermediate in price and functions
- YZX Studio, maker of the ZY1276 above, claims to be the original. Supposed to sell from 2 eBay stores but they were out of stock when I wrote this. Still available elsewhere.
- Ruideng (RD) official store on AliExpress - makes a few big models like YZX, but cheaper and with less functions. Also makes 6 similar small models in blue plastic like the one shown above, confusingly. One with a colour screen (AT34).
- Power-Z - this one is unique in that it has a much faster update frequency, almost like a mini oscilloscope they claim. Unfortunately no manual exists so no one has unlocked its true potential.
- Hidance on AliExpress sells many models but they look like rebrands. In particular, their most advanced color big display model looks like RD's.
Ok now let's talk about their features:
Voltage and current measurement
Obviously they all can do this, but their precision and accuracy can vary widely. The ZY1276 above you can see goes to a whopping 0.00001V and 0.00001A! Their maximum limit varies as well. I think for Quick Charge the max is 12 V and for Power Delivery it's 30 V.
The measurements are affected by temperature or drift or something. The PortPilot Pro displays 2 mA even at no load. Even simple meters now can zero their readings, or you can manually offset if you have an accurate reference.
Mainly useful for testing power banks (ugh I don't like that term but it's the most understood), so if you test them unattended until they switch off you don't lose your data. There should be a distinction between those that just keep a summary (time, total energy/Ah), which only needs a few bytes of memory, and those that keep the individual readings at every interval.
microUSB or Bluetooth? To computer or Android?
Charging Protocol Identification/D+D- reading
One of my main reasons for getting the PortPilot Pro was to identify the charging protocol of different chargers and why some chargers charged faster (it's not due to their current capacity). There are lots of new protocols, in particular Quick Charge 2 and 3, which the PortPilot Pro obviously can't identify. The older protocols seem to have settled on DCP and the various Apple protocols (1, 2.1, 2.4A). Some meters try to identify the protocol. Some just give the raw D+ and D- voltages, which you can use to look up the protocol. The advantage of D+ and D- voltages is it'll be compatible with future protocols and updates, unlike for example the PortPilot Pro which can't identify new protocols without a firmware upgrade. I think it's also simpler to program displaying D+ and D- than the protocol names and ranges.
Meters with this: PortPilot Pro (only a few protocols, no D+D-) I think all of the big screened ones, Hidance's LCD and OLED ones (only D+D-, no protocol names):
The ZY1276 goes one step further. All the previous meters just show you the single protocol that's in use now, not all the protocols the charger is capable of. This is an issue because new charging chips are actually capable of almost all the protocols, depending on what the device asks for. The ZY1276 can actually test each protocol in turn, and give you a list of what protocols your charger supports.
Protocol Emulation/Charge Boosting/Quick Charge/Fast Charging
Remember my iHustler and Wocol Charge Booster?
Surprisingly, this simple function isn't that common. The ZY1276 doesn't do it... that well. The PortPilot Pro did, but it needed a computer to activate it. Which is a pity, since it would be so much more useful if it could change modes by itself.
Meters that have it: you have to pay attention, most meters that have it, have an automatic mode so you're not sure which protocol it's emulating. ZY1270 is the only YZX meter advertised with it, but I suspect the ZY1276 can at least do Apple 2.4A. The BY58U has it. Some of RD's small meters too (it's annoying because their AT34 only measures D+D- and the smaller ones only emulate):
Even lots of cheap meters have this, but it doesn't seem that useful to not measure the temperature of the power supply or load, so I think they're putting it in for a different reason. Probably resistance or something changes with temperature and they need to measure temperature to compensate. Since they're already measuring it, might as well display it. Note that almost all smartphones today can also measure temperature, but very very few let you access it.
I think all the meters with big screens can plot a graph of voltage or current against time, but their usefulness is limited by the slow refresh rate. All seem to be 2 Hz, even the ZY1276, except Power-Z's meters.
After charger capacity and compatibility, I think cable resistance is the second most important factor affecting charging speed, and it's something the PortPilot Pro can't do, at least not without some modifications. To measure resistance, the meter needs an in-port for that type of cable. Most high-end meters have microUSB and USB-C in. Only 1 or 2 have Apple Lightning in, unfortunately. And they all call it 8-pin, because of copyright reasons. Measuring resistance is a bit fiddly. You have to plug the meter directly into a source and take a measurement, and now use the cable you want to measure to connect the meter to the source and take another measurement.
There are a few meters that let you plug both ends of a cable into the meter and it'll test the cable like that. The BY58U has an expansion card for microUSB:
If you want to measure output capacity and resistance at high currents, you need a stable, adjustable load. Yes it's just a bank of resistors that converts USB power into heat, but I guess it's necessary for accurate measurements. DO NOT GET THIS ONE: