Test/review of Miboxer C8 Smart charger

Batteries and Chargers Chargers
1

Miboxer C8 Smart charger













This is a large charger from Miboxer that can handle up to 8 cells, each with automatic current selection and lots of information. The charger supports NiMH and 3 LiIon chemistries with support for many battery sizes.











I got the charger in a cardboard box with specification on it.







The pack included the charger, a power supply and a instruction sheet.







The charger requires 12V 3A power.







The user interface is two buttons and a large display.

A short press on the SLOT button will switch between slots, holding the button down will select all slots.

A long press on the MODE button will allow adjustment of charge current for the selected channel (with short presses).

To adjust chemistry double click MODE button and then select with short presses.

The interface is easy to use and fairly logical.







All segments are shown during power on.







Display when the charger is idle without batteries.







A NiMH battery is put into slot #4, the charger has not calculated internal resistance yet.







Internal resistance is calculated and charger has selected 0.25A as initial charger current, it might be adjusted later on.

There is two numbers that toggles: The first is internal resistance and charge current (mOhm/A), the second is charged capacity and charge time.







A LiIon battery in slot #5 with 105mOhm internal resistance.







Specifications are listed on the back of the charger with small black letters.







The charger has the usual slider construction. It can handle from 28mm to 74mm, this means even the longest cells.



















Measurements charger

  • Power consumption when idle is 0.3 watt

  • Without power it will discharge a LiIon battery with about 2mA

  • Without power it will discharge a NiMH battery with about 0.2mA

  • At 0V battery voltage the charger will charge with 1.5mA and report “Err”.

  • Up to 1.9V the charger assumes NiMH

  • Above 2V the charger assumes LiIon

  • The charger will restart when a battery is inserted or power is cycled.

  • The meter is within 0.01V and works from 0.02V

Charging 4.2V LiIon



Manual charging current: Auto, 0.1A, 0.2A, 0.3A, 0.5A, 0.6A, 0.8A, 1A, 1.2A, 1.5A

Maximum actual current depends on number of batteries, charger can only deliver 1.5A with up to 4 batteries and 0.8A with 8 batteries.







I let the charger automatic select current here, it started at 1A and increased to 1.5A, the termination is at about 50mA after a nice CC/CV charging.

Display shows 3016mAh in 3:12, 64mOhm







Display shows 3194mAh in 4:40, 80mOhm







Display shows 3177mAh in 5:00, 93mOhm







Display shows 3275mAh in 3:36, 76mOhm







This time there must have been some contact resistance, the current was selected very very low and after a day and a half the charger stopped, but the battery was not fully charged (But nearly).

Display shows 3188mAh in 33:44, 407mOhm







Display shows 2984mAh in 7:42, 119mOhm







Display shows 3162mAh in 10:20, 146mOhm







Display shows 3234mAh in 13552, 197mOhm







Manually selecting 1.5A gives a fast charging and is within specifications for all newer 18650 cells.

Display shows 3222mAh in 3:36, 95mOhm







Display shows 2891mAh in 4:39, 113mOhm







Display shows 2606mAh in 4:08, 205mOhm







With manually selected current all batteries are charged nicely and as fast as possible.

Display shows 2283mAh in 4:58, 213mOhm







This old and worn down cell I tried automatic on and it charged the cell nicely.

Display shows 208mAh in 2:20, 632mOhm







A smaller cell where I manually selected the current is charged fine.

Display shows 736mAh in 1:57, 237mOhm







Here I selected 1.5A current, but the charger reduced the charger current due to the number of cells. The charging looks fine.

  1. Display shows 3241mAh in 5:16, 67mOhm
  2. Display shows 3137mAh in 4:49, 43mOhm
  3. Display shows 3305mAh in 5:01, 35mOhm
  4. Display shows 3429mAh in 5:01, 61mOhm
  5. Display shows 3308mAh in 4:56, 33mOhm
  6. Display shows 3053mAh in 4:46, 36mOhm
  7. Display shows 3310mAh in 5:03, 34mOhm
  8. Display shows 3221mAh in 4:56, 45mOhm







    With four cells I could use 1.5A charge current.
  9. Display shows 3279mAh in 3:35, 64mOhm
  10. Display shows 3204mAh in 2:49, 39mOhm
  11. Display shows 3236mAh in 2:55, 35mOhm
  12. Display shows 3220mAh in 2:52, 40mOhm







    The charger uses up to about 2.5A from 12V when charging at full current.
  13. Display shows 3264mAh in 6:00, 181mOhm
  14. Display shows 3135mAh in 4:54, 43mOhm
  15. Display shows 3301mAh in 5:06, 32mOhm
  16. Display shows 3283mAh in 5:03, 44mOhm
  17. Display shows 3327mAh in 5:04, 32mOhm
  18. Display shows 3108mAh in 4:57, 40mOhm
  19. Display shows 3264mAh in 5:06, 41mOhm
  20. Display shows 3206mAh in 4:55, 44mOhm







    M1: 31.0°C, M2: 33.2°C, M3: 33.8°C, M4: 34.6°C, M5: 35.1°C, M6: 35.2°C, M7: 34.4°C, M8: 32.9°C, HS1: 44.7°C

    With 8 batteries the temperature is fairly low.





    HS1: 42.5°C







    M1: 41.0°C, M2: 45.9°C, M3: 45.6°C, M4: 42.2°C, HS1: 63.4°C

    With 4 batteries both the batteries and the charger gets hotter.





    M1: 49.3°C, M2: 47.6°C, HS1: 53.5°C







    The charger uses a internal resistance check to decide the charge current and will then ramp the charge current slowly up.







    It is possible to override the current setting at any time.







    The charger turn the charge current off the check the voltage.







    Charging 4.35V LiIon







    The high voltage LiIon looks fine.

    Display shows 2931mAh in 3:32, 113mOhm





    Charging 3.6V LiFePO4







    Display shows 1256mAh in 1:51, 82mOhm







    LiFePO4 is charger to 3.6V and the charger stops when the battery is full, this looks fine.

    Display shows 576mAh in 2:03, 113mOhm





    Measuring Internal Resistance LiIon







    The results looks good and the consistency is also fine (I was a bit lazy and only checked 4 slots).







    Charging NiMH



    Charging current: Auto, 0.1A, 0.2A, 0.3A, 0.4A, 0.5A, 0.6A, 0.7A, 0.8A, 0.9A, 1A







    The NiMH charging uses -dv/dt termination, here I used manual current selection. There is no top-off or trickle charge and none is needed.

    Display shows 1782mAh in 2:14, 51mOhm





    Display shows 1715mAh in 2:08, 63mOhm







    Display shows 1707mAh in 2:10, 79mOhm





    Display shows 1705mAh in 2:04, 90mOhm







    Display shows 1783mAh in 2:12, 185mOhm









    Display shows 1681mAh in 2:18, 105mOhm







    Display shows 1775mAh in 2:11, 66mOhm









    Display shows 1743mAh in 2:15, 148mOhm







    Display shows 2258mAh in 2:50, 69mOhm







    The two high capacity batteries is charged fine with a -dv/dt termination.

    Display shows 2293mAh in 2:55, 55mOhm







    The AAA is charged fine.

    Display shows 666mAh in 1:53, 92mOhm







    Here I selected a very low charge current, this means a -dv/dt termination will not work. The charger terminated anyway and at about the correct time.

    Display shows 1725mAh in 18:43, 100mOhm







    With -dv/dt termination the charger will be slow to termination on a full cell, here it took about 15 minutes.

    Display shows 60mAh in 0:14, 53mOhm







    The automatic current selection can also be used for NiMH.

    Display shows 1744mAh in 4:01, 71mOhm







    With NiMH the charger can charge 8 batteries with full current at once.
  21. Display shows 1890mAh in 2:24, 110mOhm
  22. Display shows 1794mAh in 2:13, 52mOhm
  23. Display shows 1880mAh in 2:14, 47mOhm
  24. Display shows 1847mAh in 2:12, 51mOhm
  25. Display shows 1750mAh in 2:07, 54mOhm
  26. Display shows 1766mAh in 2:07, 37mOhm
  27. Display shows 1890mAh in 2:14, 35mOhm
  28. Display shows 1870mAh in 2:13, 41mOhm







    The charger uses about 1.8A from 12V
  29. Display shows 1844mAh in 2:13, 101mOhm
  30. Display shows 1834mAh in 2:12, 40mOhm
  31. Display shows 1905mAh in 2:14, 34mOhm
  32. Display shows 1879mAh in 2:15, 38mOhm
  33. Display shows 1724mAh in 2:03, 34mOhm
  34. Display shows 1813mAh in 2:09, 38mOhm
  35. Display shows 1869mAh in 2:12, 29mOhm
  36. Display shows 1847mAh in 2:03, 64mOhm







    M1: 41.4°C, M2: 46.3°C, M3: 46.7°C, M4: 47.6°C, M5: 49.6°C, M6: 48.3°C, M7: 48.3°C, M8: 43.8°C, HS1: 70.2°C

    8 NiMH batteries gets warmer than 8 LiIon batteries when charging at full current, but it is acceptable.







    M1: 49.7°C, M2: 48.5°C, HS1: 55.9°C







    The charger uses a internal resistance check to decide the charge current and will then ramp the charge current slowly up.







    Current can be changed at any time.







    As is common with all NiMH chargers the current is turned off to measure the NiMH voltage.









    Measuring Internal Resistance NiMH







    The results looks good and the consistency is also fine.









    Conclusion



    The charger works fine and has a good user interface. For NiMH and 4.2V LiIon the charger is very easy to use, just put the batteries in and it will do everything, the automatic current selection may not select the best current, but it will not cook batteries.

    To get a more controlled charge current it is easy to set charge current for one or for all slots, it is also fairly easy to select 4.35V or 3.6V charge voltage.

    Some people like to see a percent, some a voltage, this charger shows everything at the same time including internal resistance, but only for one cell at a time.



    I will rate it as a good charger.







    Notes



    The charger was supplied by Miboxer for review.



    Here is an explanation on how I did the above charge curves: How do I test a charger
2

Thanks for the review.

It looks really good but i don’t see much advantage over the C4-12 unless you need to charge a bunch of smaller cells. 0.8amps is fairly slow charge for a 18650/26650. The 1amp @ 8 cells comes in handy for NiMH batteries.

3

Hi

Thanks a lot taking the effort to provide such a detailed review!

I just bought this charger but it does not behave as I expected. The charger is not automatically increasing the current when charging 4 Li-ion cells. It stays on 0.1A all the time and after 4hrs of charging I do not see a significant charge. I use 4 Panasonic NCR18650B with button head and PCB (assembled by evva-tech.com).

Is this behavior normal? Does the charger not work well with batteries including a PCB?

In this situation, should I set the charging current just manually then?

Thanks a lot for your help! I appreciate your advice.

Regards,
Andreas

4

Automatic current is effected by resistance so unless you have low double digit resistance, it won’t ramp up to 1.5A for 4 cells. Only a few of my batteries will get 1A+ on auto so I use manual most of the time and my high resistance batteries go in the Lii500

5

It’s interesting to see the display of percent for NiMH batteries!

Do you know which charger do offer this function too?
And which would you recommend for displaying the charge level in % for NiMH cells?

I’d find this chargers:

6

I’m by no means the brightest bulb in the room concerning technical data and I like this charger.

It’s strange though because when I charge my cells, (either Li-Ions or Eneloops), and let the Miboxer C8 do it’s thing and set charging current, when the cells are full, the charging ceases.

Then after the C8 has read that they’re 100% full, I’ll put them in my Xtar SV2 Rocket charger and the Rocket will show they’re only at 86–88 and will continue to charge them at 1 amp for an additional 15-20 minutes more until it states they’re now at 100%.

Wonder which one is correct?

7

With NiMH cells it takes between 5 and 30 minutes for a charger to detect a full cell and it will show show full before, I do include a test with every charger on how fast it detects a full cell (This is not very precise, but gives a guideline).
With LiIon there is difference in charge voltage and termination current in addition to a voltage drop when the cell is removed from the charger, all this together may also mean some extra charge time. With LiIon try checking the battery with a voltmeter after you remove the same battery from C8 and SV2.

8

Thanks for that HKJ!

9

How well do 21700 cells fit in this charger?
Yep, I did read the specs and they fit… it’s just that my LittoKala fits 21700 too, but a crowbar and hammer are needed to get the cell in its slot :slight_smile:

10

I would say they fit easily into the charger, the gray cell is a 21700 and there is some space left behind it: