Despite their limited use for testing wall chargers and power banks, USB inline testers let you compare power sources. In three videos, we take you through their features, and we also try an inline USB electronic load.
When testing a USB charger or power bank, you can connect a phone or other device and see if it charges. That’s nice, but if you need more data or suspect a failure, you need to interrogate the power lines. While it’s possible to do that with a breakout board, some resistors, and a handheld or bench multimeter, you can use an inline USB meter for very little money.
If you check online, you’ll find dozens of inline USB testers. We tried two from Eversame, available from Amazon and other online sellers. You’ll find what looks like identical products sold under different brand names. Figure 1 shows the two meters and the electronic load.
These inline meters not only measure voltage and current, but they also calculate a USB port’s output power, amp-hours, watt-hours, and load resistance. They also provide chart recorders for voltage, current, and output voltage ripple. Their screens also provide arrows that indicate current flow from input to output. In two of the videos below, we take you through the menus. In a third video, we try out an electronic load, which lets you vary the load so you don’t need a set of fixed resistors. We tried fixed-resistor loads, too.
Both inline testers feature USB-A and USB-C ports, while one adds a micro-USB input port. You’ll also need some cables, and you may require USB breakout boards for connecting to other equipment, such as an oscilloscope. Because UCB-C chargers and power banks produce up to four output voltages, you’ll need something to force them to the desired output voltage unless the default 5 V is sufficient. I used an attachment board that has a set of DIP switches and a two-terminal block for connecting a load, shown in Figure 2. It’s shown connected to a single 10 Ω, 10 W power resistor. For a higher current, we have four resistors connected in parallel to make a 2.5 Ω, 40 W load.
Packaged USB inline tester, Model J7-c
Figure 3 shows the Eversame 2-in-1 Type C USB Tester Color Screen LCD Digital Multimeter Model J7-c, $16.14 on Amazon.
For a low cost, you get a device that’s useful for testing sources such as phone chargers and power banks. You can also use it to see the current a device draws. It has USB Type-A and Type-C input and output connectors. You can plug it directly into a charger or power bank, or use an extension cable, which will result in additional power losses. You’ll likely need a cable to connect the load shown to the Type-C output port in Figure 2.
The color LCD screen is small, and the text, other than the primary voltage and current readouts, is downright tiny. A single button lets you scroll through several screens (see video), including two chart recorders. One chart recorder plots output voltage and current, and the other shows voltage ripple.
Larger screen, no package
Figure 4 shows the Eversame USB C Power Meter Tester, Voltmeter Ammeter Load Tester, $23.39 on Amazon.
This USB inline meter could use some packaging, as it’s just two boards screwed together with spacers. It looks like someone assembles these in a back room. That makes the tester somewhat fragile compared to most other USB inline testers on the market. The good news is it’s easy to take apart. There’s no part number on the product, nor in the Amazon listing. The meter comes with a USB-C to USB-C cable. This tool adds a micro-USB input connector for passing power from an older power bank that has such a connector.
After using the J7-c, I appreciated the larger screen. Four buttons let you select the screen display, change settings, and rotate the screen left or right. That’s handy should you connect it to a wall charger and find that the screen is upside down or sideways. As the video shows, you also get the chart recorder, power, resistance, watt-hour, and mA-hour calculations. In the video, you’ll see the readout screens and settings menu.
What’s a circuit without a load?
Fixed loads have their purpose, but they’re fixed. You get what you get, no more and no less. Dynamic loads, such as connecting a power source to a phone, can give you some insight into charging, but the load changes are out of your control. A variable load lets you change the current drawn from a charger. Figure 5 shows a
Drok USB Load Tester, Electronic Load Test Resistor Module 25W LD25 USB and Type C Interface, $14.95 on Amazon.
With this electronic load, you can vary the current that the load draws from the power source and thus test your source under differing conditions. If you need a programmable dynamic load, you’ll have to spend more money or design your own.
The Drok load can sink up to 4 A. Our tests couldn’t go nearly that high because that’s more than any of our power sources can deliver. It might be worth trying it with a bench power supply some other time.
The load includes USB-A, USB-C, and micro-USB connectors. There’s an LED display that indicates current drawn, and it can indicate power. A temperature sensor and a fan keep things cool. The digits illuminate in sequence, which makes it difficult to see all of them on the video. To the human eye, they appear to be constantly lit. The board has an on/off button and a setting button that sets the display from amps (default) to watts.
Future work
In future articles, we’ll use these tools, an oscilloscope, and USB breakout boards to compare several chargers and power banks. We will also teardown the Eversame USB-C Power Meter Tester, Voltmeter Ammeter Load Tester, the one with no model number, to see how it displays activity on the data lines.
Related EE World content
Phone chargers produce EMI: We compared four
USB Type C standardization – what you need to know
A look at USB Type-C in power-only applications
How USB Type-C connectors hold the key to maximizing data speeds and power delivery
The three “C’s” of USB Type-C: connectors, controllers and cables
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