Test/Review of Charger and power bank Miller ML202 V4

Charger and power bank Miller ML202 V4







Miller is mostly know for the ML102 charger (V9, V8, V7, Old ), but they have a few other products. This here is basically a dual slot version of the ML102 with both charger and usb output.







The actual packing of the ML202 is only a plastic bag without any accessories.







The charger/power bank is a closed box. The cover is locked in position, but it is easy to remove it.







The charger has a micro usb power input for charging current.







And a large usb connector for usb power output.







The charger has a couple of leds inside the transparant box:

Red: Charging

Green: Battery full

Blue: Usb output is on.







The charger will only fit one battery length and that is 65mm, i.e. unprotected 18650 cell, it is possible to use both flattops and some buttom tops.











The charger can only handle unprotected flat top cells.







Measurements

  • Will discharge a battery with 1mA to 2.5mA when not powered.

  • When overdischarge protection trips the discharge current is below 0.03mA

  • Below 0.5 volt the charge current is uA.

  • Between 0.5V and 1.8V the charge current will is in the mA range (See curve).

  • Above 1.8 volt full charge current is used.





This is a nice charge curve, charge current is 1.3A and termination current is 0.1A with a good CC/CV charge profile.



The other slot looks the same.



A 2600mAh cell is also charged fine.



There is no problem running two cell at a time, but the usb charger/power supply must be able to supply 2.5A to maintain full charge speed.



Adding a resistor in series with the power supply to simulate a weak usb charger will reduce the charge current, but it do also interfere with the termination. The charger terminates to early.



M1: 30,9°C, M2: 31,6°C, M3: 33,8°C, HS1: 35,9°C
It stays very cool during charge.



M1: 31,8°C, M2: 32,3°C, M3: 31,2°C, M4: 34,9°C, HS1: 37,0°C



Here is a look at the charge current at different voltages.



The charger do not have any computer chip inside, this makes it start immediately.



USB output
  • Can be used as UPS, will draw more power from the usb input.

  • Will discharge a battery with 1mA to 2.5mA when not powered.

  • When overdischarge protection trips the discharge current is below 0.03mA

  • When drawing usb power while charging, the power is taken from the usb input.

  • Usb output is coded as USB charger (DCP)







With one battery it can supply 1A output current, but as can be seen below not for long.



With two batt the current can reach 1.25A, but it will not terminate on overload anymore.



The usb output will also work when usb input power is connected and it maintains full usb output voltage.



There is 17mV rms and 156mVpp noise. This is very good values.



There is 30mV rms and 220mVpp noise.



There is 24mV rms and 170mVpp noise. Using two batteries will reduce the noise slight.



Tear down



To look inside the box four screws must be removed.



It looks very symmetrical, but each channels is not completely separate. The usb output is controlled from U5, it handles two inductors, but is a single channel boost controller.




There is nothing on this side of the circuit board.



Conclusion

The design makes it fairly handy for a power bank (Dedicated power banks is usual smaller) and it can also easily be used as a 18650 charger.
It works fairly well, but as my test shows there are a few details that could be better.



Notes


The charger was supplied by Gearbest for a review.

Here is an explanation on how I did the above charge curves: How do I test a charger
Read more about how I test USB power supplies/charger

Thanks for the detailed review, HKJ!

Sounds like it is an adequate power bank and an adequate 18650 battery charger, with its main feature distinguishing itself from the competition being its relatively compact size and its main drawback being battery size limitation.

For those who are looking for a functional power bank/battery charger, this is a reasonably inexpensive option. :nerd_face:

I have been waiting for a long time for this review. Thank you :slight_smile:

Thanks for the review, I like the idea of these simple UPS style chargers.

How separate are the two slots? Is it safe to have one fully charged cell and one discharged cell?

Yes. Its like having 2x single slot chargers - only the output is combined. Undercharge protection, charging is separate.

Thanks for the review, I have this charger and I’m very happy with the performance, got 86% efficiency with 2x LGF1 18650s at 1A discharge rate.

Because it has LVP, when using a single cell you may not get all the energy from the battery, and often at 3.4V it will stop working. (because the voltage drops under load). The boost circuit doesn’t lower the output to reduce the current draw and keep the battery voltage above LVP like some more advanced powerbanks does. Like CV phase but for discharge.

Can anyone confirm that it actually supports up to 18V input? Almost all sellers say that up to 18V is supported and 5-12V input is recommended.

I decided to make my own short test:

  • I insterted 2 cells into ML202 V4. They were around 3.85V
  • It was measured with ZY1270 using serial output.
  • Notice that the amperage goes up with the voltage until around 5.3V (measured before the 0.5m USB cable)
  • At around 21.5V both red charging lights turned off! (it continued charging)
  • One of the red lights turned back on, later at around 5V. The other red light is not working properly anymore.
  • At the end cells were 4.02/4.03V
  • Despite one of the red LEDs acting weird it charges and discharges both sides OK.

It’s a power bank, but if it doesn’t have power applied, it discharges the battery slowly?

All power banks does that, the question is how slowly (Days, months or years). With easy replaceable batteries a few months are fine, as long as you do not store it with batteries in.

HKJ, could you please explain how can the ML-202 have separate charging and boost and then combine to one 5V? I thought you should never combine outputs like that.
I am thinking that if they can do it then perhaps I can somehow put 20 cells and 20 boost circuits for some 100W output?!

EDIT: I want to further clarify - I am thinking if I can somehow utilize half dead cells by putting a lot of them in parallel with protection circuits and use as a powerbank. So if some die (<2.5V), the output still works.

The ML202 do not combine outputs, but you can do it if you know what you do.
There are power banks that selective switches cell in, i.e. the cells do not have to be balanced.

I mean the 2 batteries are charged independently but there is a single USB output - what do you mean ML202 do not combine?

It has one controller for the output, that means the two inductors are always in sync.

Got it, thanks!

> Can be used as UPS

How “uninterruptible” is it as a power supply — does it sustain the output when the input fails, is there a blink/loss of power as it changes over?

The usb output is always generated from the battery voltage, this means that there is no “change over” time.

> up to 18v input

How about variations in input, from a solar panel — would it be usable by just attaching a solar cell, maybe for an outdoor light or camera to work unattended?

Yes it does, I tried with input voltage up to 14V and it worked fine. Most 12V solar panels have much higher open circuit voltage (~20v) but once you attach the load it normalizes, swaan tested up to this voltage with no problem. Another feature is the pass-through charging which most normal powerbanks don’t have, really useful for using with solar.