Xiaomi Z15 aa-aaa USB Charger


  Product page @ Gearbest


  photo Screen Shot 06-09-16 at 03.05 PM_zpsnjx0ldez.jpg


  photo IMGP1322_zpswhjarsg2.jpg


Pictured is my test set up . I used two ( Three actually )  USB wall adapters , the one in the picture being advertised as being a 1A model . The other USB adapter was advertised as being 2A , interesting little tidbit , each adapter is capable of supplying half the advertised current .  Also I am using a Charge Doctor to monitor the current going to the charger . So with the 1A adapter that equals around half an amp , and with the 2A adapter about one amp of current . So that means I have a way of limiting current going to the USB charger .

2A adapter ( 1A actual )  Here we have all of 5watt to play with . Depending on the voltage state of the battery being charged , you could very well pump 5Watt into the charger ( less any losses ) . If you do your math , that is a potential charge rate of around 4+ Amps ( depending on how much power is absorbed by the charger ) and the actual voltage state of the battery . ( Yikes ! ) I did have a battery ( old ) that had a resting voltage of 0.6v , and I did use the 2A adapter and it did hit 0.97A on the Charge Doctor ... Single battery charge  ( Yes it did charge quickly )


1A adapter ( 0.5A actual )  This is much better in my humble opinion as we have some 2.5Watt to play with .  Even with half as many watt's to play with the potential is there to charge a single AA at potentially over 2A ..  Charging 2 to 4 AA would make much better sense . I am rather sure one of my USB wall adapters does 0.25A , and I would be much happier using that ( 0.25A ) , especially if I only had one or two batteries to charge .


0.5A adapter ( 0.25 actual )  This is again a better option if only charging one or two batteries as we only have 1.25Watt to play with . This means we have about  a 1A maximum charge rate for a single battery , and half that for two and half again as much for 4 .  It's good to have a half dozen USB wall adapters . 



This is a small charger , and on receiving and opening the package I was a little surprised at just how small and light this charger was . At just under 8cm long and just over 4cm wide and weighing next to nothing , I wasn't sure how well it would work or how long it would work . Well I have been put in my place I have to tell you . For such a small light FAST Charger , the first thing to amaze me was the lack of overcharging . And the second thing to amaze me was the lack of heat , the charger actually runs cool . Even @ 5 watt's , only the batteries get warm , the actual charger remains cool . Now I am not sure if the charger actually terminates or trickle charges on completion . At the moment I have no way of getting probes into such a small space to be able to monitor what is going on , but I will remedy this by making a dummy battery that is connected to an actual battery ( AA or 14500 ) and has a Amp meter and voltage meter in the circuit ( This will be in the future - perhaps weeks depending on EBay sellers )

The charger has little lights over each battery bay , and these blink slowly ( at the start ) and then quickly as you near the end . And on completion they should be a solid light , but depending on the battery ( condition ) the voltage may not reach a point where the lights stop blinking , so the charger may be trying to reach a certain voltage state ( ? ) This is why I use a Charge Doctor , It shows the current going to the charger , and when it reaches 0.01/0.02A , I know the batteries are done and there is no need to rely on blinky lights .  ( If you charge VIA USB - you really want a USB Charge Doctor )

To be honest I am not a fan of fast charging batteries , but at least with USB chargers you do have some control of just what USB power source you plug your USB charger into . Thus allowing you to control the charge rate , and if you have a Charge Doctor then you can monitor your charger on the fly . 


Power Bank


  photo IMGP1324_zpsblsatyf8.jpg


Pictured is the Z15 being used as a powerbank to feed a small Xtar charger with a 16340 . The instructions are in Chinese , so I believe all 4 batteries are being used to power any device . So with 2000mAh AA batteries , this could very well be a very small 8000mAh powerbank . The experiment I want to try is how many batteries are needed to Bank with ?  And the answer is all 4 .  3 - 2 or 1 battery installed = no Banking available . Hmmm 4 x 1.5v or should that be 1.4v fully charged nimh , = 5.6v . So at what voltage does charging ( powerbank ) end ?  5v or maybe 4.2v  ... 

It's bad news folks , looks like the bank closes at 5v , and that means there is not that much power available to charge a device with or to power a device . At best it might work for a short time as an emergency power supply for your phone or USB device .  ( depending on power demands ) If you were to throw in some Lithium or Alkaline batteries ( ? ) , as they have a higher nominal voltage , you may be able to have a longer lasting powerbank . I did throw in some Alkalines @ 1.6v to see if they would work for the powerbank mode ........ and ....... yes it works .   So a little disappointing the 5v cut off as it does not utilize the nimh batteries to their full potential . ( Nor any other AA battery - possibly Lithium could be ok ( ? ) 


Last Word


Would I recommend this charger to joe six pack ?  ........ not really ! 

I would how ever recommend this charger to anyone who is an enthusiast ( has a clue ) . If you use this charger intelligently , then it has the potential to be a great little charger . I was amazed myself how small , light and how cool it ran even at what I would call high current for AA charging . It could be used in a car VIA a sigaret lighter USB adapter , or powered by a solar panel ( due to the current potential , I would not connect it to a Computer USB port ) . The charger is insanely light weight so could be great for back packing . 

It is a fast charger , there is no doubt about that . So if you are a fan of such then you really should take a look at the Xiaomi Z15 AA/AAA USB charger .. It works , it runs cool and it recharges batteries . It worked for me ( I like it ) only because I have half a dozen USB wall adapters of varying current capability allowing me to change the nature of the beast ( tame it so to speak ) .

The powerbank feature (?) a little disappointing with the 5v cut off , but could - would - should work better with Alkalines or Lithium ( possibly ) .  The question I keep asking myself is , could it be better for the asking price ( $10 USD ) , and I just don't see it . The Z15 would need to be completely rebuilt on a larger body ( possibly ) to incorporate some sort of boost circuit to maintain 5v for the battery bank . That's more parts , a re design , more money to build and would be an entirely new product . So I can only conclude the Z15 is pretty much all it can be , and for anyone reading this the question would be is it enough ! Does it do what you want ? ( For $10 USD )

 To date I have charged over 40 batteries , amazing considering the short time ( 3 days ) I have been playing with the charger .  I would seriously recommend a USB wall adapter that limits current to 0.5A or 0.25A if you plan on using the Z15 as a primary AA charger . Especially if you charge one or two batteries at a time , as prolonged high current charging may shorten battery life .  For occasional or emergency charging the Z15 will do the job extremely well , and I can see this charger connected to a Solar panel .  There are applications where this charger could be the bees knees and it does perform as advertised .


I would like to thank Gearbest for allowing me to test this charger ..