How to test USB chargers

How chargers work

To charge a battery a charger must provide 1) enough voltage and 2) enough amps to charge the battery. The amps is what “fills up” the battery to capacity. A battery capacity is measured in “amp hours” or “milliamp hours”. So a 10,000mah battery is the same as 10 amp hours. As a battery charges the voltage stays the same but the amps it draws become less and less until the amp draw reaches zero. Chargers will often have a cutoff point for the battery voltage. So when a lead acid car battery reaches 13.5vdc then the charger should cut off all voltage.

A lithium battery inside a USB powerbank has a max charge of about 4.2vdc. When the lithium battery reaches 4.2vdc then the charge circuit should cut off power. At this point the battery should be full charge, however battery capacity will slowly degrade over time. How fast the capacity degrades is based on the battery quality.

Top quality brands of lithium batteries, like 18650s, are Panasonic, LGR, and Sony. On these brands you actually get what you pay for.

The charger

USB chargers come in many sizes and specifications. The specification is they should provide 5vdc, and some amps. Chinese charges are infamous for exaggerating their specs on the amp side, this is why testing is necessary with a USB meter and a load. Learn a bit more about USB meters at “Power bank capacity”. Foreign USB chargers might say the support total output of 1 amp, when it really only supports 0.5amps.

If a charger has multiple USB ports, and it’s an Asian charger, it’s very likely the output it provides is the TOTAL amps on all ports used at once. So if a 2 port charger says it supports 2.1 amps, and you plug in 2 devices to the charger, it will supply about 1 amp on one port and about 1.1 amps on another port. This is another way sellers fool the customer.

Chargers on Ebay are often fake. Sometimes they will say “Made by Abble” or even “Made by Apple”. I also have a very good but fake Samsung charger. I could not tell the difference until I put a real charger next to the fake one. The fakes are getting quite good. I didn’t label the fake one so I had to test both chargers and the results told me which one was fake. Now I tested all my chargers and write with a light blue marker on them the max amps they will provide. Light blue works on a white and black charger case. I recommend people buy from a reputable seller.

Remember, if it’s too good to be true, it probably is.

Good charger brands

Good charger brands on Amazon are Sony, Apple, Amazon Basics, Aukey, Monoprice, and Anker. I’ve tested some of these and they all meet their stated spec.

How to test the chargers

First, you will need a USB meter, and an adjustable load. Loads where you turn the brass knob or some other knob to slowly adjust the amps the use are best. Loads where you have a switch to select 2 different loads will not tell you much.

1. Plug the charger into the wall.
2. Plug the USB meter into one port of the charger.
3. Plug the load into the USB meter. Adjust the load to 1 amp, watch the USB meter, it will tell you how many amps the load is drawing.
4. At a draw of 1 amp of current, does the USB meter still say 5vdc? Then it’s fine.
5. Slowly increase the power draw of the load by turning the knob. Keep an eye on the voltage of the USB meter. If the voltage of the USB meter drops down below 4.8vdc then the charger fails at that point.
6. If the voltage drops below 4.8vdc, reduce the load until it reaches 4.8vdc. Now read the amps on the USB meter. This is the amps (Current) the charger supports on that one port.

4.8vdc is my own cutoff point that I test with. Others may choose a cutoff of 4.95vdc or even 5.0vdc or 4.7vdc. Anything less than 5.0vdc does not meet the USB spec but batteries will still charge at 4.8vdc. That’s why I use it.

If you want to test 2 ports on the charger, you will need another USB meter with another load. You will simply put loads on 2 USB ports at the same time, read the amp outputs on both meters, and sum the amps together to determine the total amps the charger supports.

Signs of a bad quality charger

1. It has misspellings on the listing page or on the charger itself.
2. Only one picture of the device. This indicates laziness, an unprofessional listing, and lack of attention to detail.
3. Vague specs like “It meet all needs very good for you.”
4. Lack of physical measurements. I want to see if a wall charger will block the other outlet or not.
5. Bad grammar. Chinese and other ideographic languages do not translate well to English, especially their grammar. Free translation packages or websites do not work very well.

For more info see these links

1. 2013. Counterfeit charges say “Made by Abble”. https://www.techspot.com/news/51965-designed-by-abble-ul-warns-usb-chargers-bear-counterfeit-ul-mark.html
2. 2012. Big name and small brand chargers. Apple is good but not the best. http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html?showComment=1405222737608
3. A search for current USB charger reviews. https://duckduckgo.com/?q=USB+charger+review+made+by+%2Babble&t=brave&ia=web&iai=r1-1&page=1&sexp=%7B%22cdrexp%22%3A%22b%22%2C%22artexp%22%3A%22b%22%2C%22prodexp%22%3A%22b%22%2C%22prdsdexp%22%3A%22c%22%2C%22biaexp%22%3A%22b%22%2C%22msvrtexp%22%3A%22b%22%7D