Test/review of Miboxer C8 Smart charger

HKJ

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[size=+3]Miboxer C8 Smart charger[/size]

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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.

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

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The charger requires 12V 3A power.

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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.

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All segments are shown during power on.

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Display when the charger is idle without batteries.

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

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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.

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



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

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

supportedBatteryTypes.png


supportedBatterySizes.png
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[size=+2]Measurements charger[/size]


  • 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

[size=+2]Charging 4.2V LiIon[/size]

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.

Miboxer%20C8%20auto%20%28SA18650-33%29%20%231.png


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

Miboxer%20C8%20auto%20%28SA18650-33%29%20%232.png


Display shows 3194mAh in 4:40, 80mOhm

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Display shows 3177mAh in 5:00, 93mOhm

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Display shows 3275mAh in 3:36, 76mOhm

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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

Miboxer%20C8%20auto%20%28SA18650-33%29%20%236.png


Display shows 2984mAh in 7:42, 119mOhm

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Display shows 3162mAh in 10:20, 146mOhm

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Display shows 3234mAh in 13552, 197mOhm

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Manually selecting 1.5A gives a fast charging and is within specifications for all newer 18650 cells.
Display shows 3222mAh in 3:36, 95mOhm

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Display shows 2891mAh in 4:39, 113mOhm

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Display shows 2606mAh in 4:08, 205mOhm

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With manually selected current all batteries are charged nicely and as fast as possible.
Display shows 2283mAh in 4:58, 213mOhm

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This old and worn down cell I tried automatic on and it charged the cell nicely.
Display shows 208mAh in 2:20, 632mOhm

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A smaller cell where I manually selected the current is charged fine.
Display shows 736mAh in 1:57, 237mOhm

Miboxer%20C8%201.5A%20%288xSA18650-33%29.png


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

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

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The charger uses up to about 2.5A from 12V when charging at full current.
#1 Display shows 3264mAh in 6:00, 181mOhm
#2 Display shows 3135mAh in 4:54, 43mOhm
#3 Display shows 3301mAh in 5:06, 32mOhm
#4 Display shows 3283mAh in 5:03, 44mOhm
#5 Display shows 3327mAh in 5:04, 32mOhm
#6 Display shows 3108mAh in 4:57, 40mOhm
#7 Display shows 3264mAh in 5:06, 41mOhm
#8 Display shows 3206mAh in 4:55, 44mOhm

Temp5704.png


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.

Temp5705.png

HS1: 42.5°C

Temp5714.png


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.

Temp5715.png

M1: 49.3°C, M2: 47.6°C, HS1: 53.5°C

PoweronLiIon.png


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

CurrentChangeLiIon.png


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

ChargingLiIon.png


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



[size=+2]Charging 4.35V LiIon[/size]

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The high voltage LiIon looks fine.
Display shows 2931mAh in 3:32, 113mOhm


[size=+2]Charging 3.6V LiFePO4[/size]

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Display shows 1256mAh in 1:51, 82mOhm

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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


[size=+2]Measuring Internal Resistance LiIon[/size]

RiLiIon.png


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



[size=+2]Charging NiMH[/size]

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

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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

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Display shows 1715mAh in 2:08, 63mOhm

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Display shows 1707mAh in 2:10, 79mOhm

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Display shows 1705mAh in 2:04, 90mOhm

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Display shows 1783mAh in 2:12, 185mOhm


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Display shows 1681mAh in 2:18, 105mOhm

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Display shows 1775mAh in 2:11, 66mOhm


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Display shows 1743mAh in 2:15, 148mOhm

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Display shows 2258mAh in 2:50, 69mOhm

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The two high capacity batteries is charged fine with a -dv/dt termination.
Display shows 2293mAh in 2:55, 55mOhm

Miboxer%20C8%200.5A%20%28eneloopAAA%29%20%231.png


The AAA is charged fine.
Display shows 666mAh in 1:53, 92mOhm

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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

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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

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The automatic current selection can also be used for NiMH.
Display shows 1744mAh in 4:01, 71mOhm

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With NiMH the charger can charge 8 batteries with full current at once.
#1 Display shows 1890mAh in 2:24, 110mOhm
#2 Display shows 1794mAh in 2:13, 52mOhm
#3 Display shows 1880mAh in 2:14, 47mOhm
#4 Display shows 1847mAh in 2:12, 51mOhm
#5 Display shows 1750mAh in 2:07, 54mOhm
#6 Display shows 1766mAh in 2:07, 37mOhm
#7 Display shows 1890mAh in 2:14, 35mOhm
#8 Display shows 1870mAh in 2:13, 41mOhm

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The charger uses about 1.8A from 12V
#1 Display shows 1844mAh in 2:13, 101mOhm
#2 Display shows 1834mAh in 2:12, 40mOhm
#3 Display shows 1905mAh in 2:14, 34mOhm
#4 Display shows 1879mAh in 2:15, 38mOhm
#5 Display shows 1724mAh in 2:03, 34mOhm
#6 Display shows 1813mAh in 2:09, 38mOhm
#7 Display shows 1869mAh in 2:12, 29mOhm
#8 Display shows 1847mAh in 2:03, 64mOhm

Temp5730.png


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.

Temp5731.png


M1: 49.7°C, M2: 48.5°C, HS1: 55.9°C

PoweronNiMH.png


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

CurrentChangeNiMH.png


Current can be changed at any time.

ChargingNiMH.png


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




[size=+2]Measuring Internal Resistance NiMH[/size]

RiNiMH.png


The results looks good and the consistency is also fine.




[size=+2]Conclusion[/size]

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.



[size=+3]Notes[/size]

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
 

Gauss163

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Miboxer C8 Smart charger: [IR tests on 1st 4 slots] The results looks good and the consistency is also fine (I was a bit lazy and only checked 4 slots).

It's puzzling why you tested only the first 4 slots when your tests show that is the last 4 slots that deserve closer inspection. Namely, your auto-current tests on the SA18650-33 gave IR of 64,80,93,76 mΩ on the first 4 slots, but 407,119,146,197 mΩ (much higher!) on the last 4 slots. Something seems seriously wrong with the last 4 slots (unless those are 8 different cells and by sheer luck only the healthy cells ended up in the first 4 slots - not very likely).
 

HKJ

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It's puzzling why you tested only the first 4 slots when your tests show that is the last 4 slots that deserve closer inspection. Namely, your auto-current tests on the SA18650-33 gave IR of 64,80,93,76 mΩ on the first 4 slots, but 407,119,146,197 mΩ (much higher!) on the last 4 slots. Something seems seriously wrong with the last 4 slots (unless those are 8 different cells and by sheer luck only the healthy cells ended up in the first 4 slots - not very likely).

They where 8 different cells, but I doubt that they where that different, the problem is most likely variable contact resistance. With the very good result on the first 4 slot I did not really see any reason to test more slots with resistance measurements, I do not believe my result are due to fault RI measurements.
 

Gauss163

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They where 8 different cells, but I doubt that they where that different, the problem is most likely variable contact resistance. With the very good result on the first 4 slot I did not really see any reason to test more slots with resistance measurements, I do not believe my result are due to fault RI measurements.

The only way to rule out that there is some design flaw in the final four slots is to test them too. Why not spend a few more minutes to test those slots too in order to give potential buyers peace of mind? Not to mention that it could be enlightening to understand exactly what is the source of those large discrepancies.
 
Last edited:

HKJ

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The only way to rule out that there is some design flaw in the final four slots is to test them too. Why not spend a few more minutes to test those slots too in order to give potential buyers peace of mind? Not to mention that it could be enlightening to understand exactly what is the source of those large discrepancies.

It is not a few more minutes, but maybe an hour. Each slot is 40 measurement and if anything moves I have to redo them.
 

Gauss163

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It is not a few more minutes, but maybe an hour. Each slot is 40 measurement and if anything moves I have to redo them.

But if it is a design flaw like poor contacts on just those slots or some charger-internal culprit then it only takes a handful of tests to confirm that, e.g. you could simply compare the IR measurement of slots 5 thru 8 to slot 4 on a typical cell. There's no need to do the added resistance stuff since the cause is less likely to be due to differing linearity.
 

Gauss163

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Btw, did you do some of those auto-current tests in parallel, i,e. some slots in use at the same time? If so, then possibly there could also be overload/timing issues at play, e.g. maybe it can only do so many IR tests at the same time without overloading, or some related problem.
 

HKJ

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Btw, did you do some of those auto-current tests in parallel, i,e. some slots in use at the same time? If so, then possibly there could also be overload/timing issues at play, e.g. maybe it can only do so many IR tests at the same time without overloading, or some related problem.

I did not and I would not expect any problems doing it (It is very simple to handle/avoid that type of problems in software).
 

Gauss163

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I did not and I would not expect any problems doing it (It is very simple to handle/avoid that type of problems in software).

I wouldn't assume that "simple" problems are always solved correctly - esp. on budget chargers (e.g. recall the various problems on the early versions of the Opus BT-C3100). Even some more expensive chargers (e.g. SkyRC MC3000) handled some "simple" design points poorly in early versions.

I suppose another possible explanation is that you had at one point sorted the cells based on health (IR), so then the highest IR cells got tested last in slots 5-8, and the super-high value in slot 5 was a fluke due to very poor contact. But I would think you would have already mentioned if they were sorted by IR. So I still don't see any plausible explanation other than some problem with those slots.
 

HKJ

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Thanks for the great review - as always ;)
Which of the current 8-slot universal chargers would you recommend for which purpose?

If you want support for LiIon there is only two to consider: this and GyrFalcon.
The GyrFalcon supports more battery types (4.30V LiIon) and can charge with 1A on all 8 slots
This shows mAh and IR, but you have to press a button to change between slots. The automatic current selection can be discussed.

I do not like the Nitecore, I prefer a display to see what going on and more control with charge current.

They both have acceptable user interfaces (A readable label on the back with a short explanation would have been nice), but I will mean this charger has slightly easier UI.

I am slightly (It can only be slightly because I do not like to press a lot on a button to see all values) in favor of this charger due to mAh and IR (I have not seen 4.30V batteries recently).
 

NiMHi

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Thank you very much for all the testing you are doing HKJ!

This charger looks rather nice, but I would also like a refresh (discharge-charge) option for NiMH LSD batteries.
Also a proper mAh measurement from discharging is better than from charging I think.
 

lotusseven

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Re: Test/review of Miboxer C8 Smart charger - Issues

I just got one and started charging nonstop for about 5 days a bunch of 18650 batteries harvested from cordless drills . I did a quick voltage check to separate cells for voltage above 3.6 .Charger or batteries never got warm .After about 275 I notice cell capacity read never got above 435mah. I doublechecked previously charged cells and they only read like 49ohms and 400mah which originally charged correctly to 4.20v 52ohms and 2235mah . I confirmed 20 cells with another setup I use and it checked out spot on . Anybody have this issue?? 5days straight should not be an issue its a power supply and a converter!! also never got warm !!
 

hammerjoe

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Re: Test/review of Miboxer C8 Smart charger - Issues

That sounds like a similar issue I saw with a miboxer c4 with nimh. It stops charging at around 1.43 because it thinks they are full.
 
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