How to check the voltage of a USB port charger

The USB port, first seen on Windows 95 personal computers, has now been adopted universally for data transfer and for powering electronic equipment. Mobile phones, tablets, webcams and digital cameras, car dashcams and satnavs, e-cigarettes and any number of rechargeable electronic items all use a 5V charger as a power source. In the past, it seemed like every mobile phone and tablet on the planet came with its own mains adaptor, resulting in millions (if not billions) of mains chargers being put into circulation. What a waste!

These days a common 5V USB mains adaptor is treated more like a general-purpose charger. Some types have dual (or more) 5V outputs to charge several devices at once. All mains chargers are not alike though, and very cheap ones (commonly sold online for a pound or two), are made in China costing next to nothing but they can be very badly made, breaking open after getting stuck in the mains socket, or poorly insulated and cause a fire hazard. Some have exploded causing injuries and house fires. My advice is to avoid cheap unbranded chargers completely and I’m wary of cheap counterfeits too.

How to monitor a USB charger

It's best to be mindful of the current demanded by a mobile phone, tablet or whatever you’re charging. Smaller ‘switched mode’ USB chargers are maybe good for 1.0 - 1.5 Amps or so, and care is needed not to overload them. Tablets can draw more charging current than a typical smartphone.

This USB Detector monitors voltage (blue) and current (red). Outputs are the top and bottom leads. [Click to see]Very few chargers tell you when charging is complete, so I was pleased to find a USB Digital Voltmeter/ Ammeter that shows both voltage and current flow on a digital LED display. Also it’s a dual-output one, so now I can charge two devices from one USB port. The plug-in USB Voltmeter/ Ammeter I’m talking about will help ensure you don’t overload your charger, but (just as useful) it will show you when charging is complete, because the current drops to zero.

To use, simply plug the USB Voltage/ Current meter like a dongle into the USB port, then plug your device(s) into it using standard USB cables. The meter is self-powered by the USB port. The voltage (typically 5V or a bit less) and the total current drawn will clearly be shown.  It’s re-assuring to see what’s going on, and once the current falls to nil you’ll know charging is complete and you can unplug the charger.

I’m using this handy little device all the time to check charging of a rechargeable dashcam, sat nav and tablet. It can also be used to test the voltage of USB ports on laptops or PCs.