Cell Number Incorrect error

B6 “Cell Number Incorrect”

Preamble

Following on from B6 based chargers, I managed to fry my SkyRC B6 Mini LiPo battery charger whilst charging a 3S LiFe battery. Now I just get an error message whenever I initiate a charge cycle.

The Frying

I was attempting to charge my Nano-Tech 3S LiFe 9.9 V 1.5 Ah 1C battery.

Nano-Tech LiFe 3S battery
Nano-Tech LiFe 3S battery

I stupidly connected the balance lead first to the 3S balance port, switched on the charger, tried to charge and got the “Check power port” or “Connection Error Check Main Port” error, because I had forgotten to connect the charge leads, d’oh!

I unplugged the charger. then connected the brown female Deans connector to black female HiTec adapter to the black male HiTec connector on the LiFe battery, and then I connected the brown male Deans to banana plugs adapter (without having the banana plugs plugged in). I plugged in the GND banana lead but, unfortunately, while I was doing that, the flying red banana lead was touching either the case or one of the balance pins in the 4S balance port (it was resting in the top left corner of the 4S balance port, so presumably it was touching the case, and thus grounding the positive terminal of the battery). I heard a sizzling sound, and there was a smokey plastic smell. I thought that I had damaged the LiFe battery at first – however after feeling the battery to check for over heating, it seemed fine.

I plugged in the red banana lead, but then, when I tried to charge, I got the following error:

Cell Number Incorrect error
Cell Number Incorrect error

There is a burnt plastic smell coming from the balance port side of the charger. I would guess that the resistive matrix used for balancing has burnt out.

Related links

Not so related links

Guys – I needed a magnifying glass, but this is what I found.
If you remove the unit from it’s case (8 screws, and 4 pushbuttons/ 2 main end cap plates) then look closely at the back of the balance plug circuit board. Mine had a track completely missing ! the 3S socket (4 pins) (The one I need the most !!! had the black, and the outer two lives, soldered to actual tracks, which -i f you trace them back, link into their corresponding cell numbers, to each of the other sockets.So the idea is that, each socket’s cell 1 joins with all the other “cell 1’s, and “cell 2’s join to all the other “cell 2’s” etc etc. But on my board, the Cell 2 pin, on the 3s socket, was only soldered to fresh air – ie – there was no track to it!!!
I cut about a 1″ long piece of wire , and bared and tinned the ends, then carefully soldered to the back of pin 2 on the 3s socket. The other end went to another “pin 2”, on one of the other sockets ( I think I used the 4s pin 2, but it’s not important, so long as you are definately on pin 2 in both cases. This simple fix, made up for the missing track on the 3s socket. The charger now does it’s job fine, without any stupid error messages. (I guess this to be a common fault with the fleabay B6 chinese copies, as I assume the whole batch will have had this circuit board printed, minus this particular track on the 3s socket. ) So I’m now about 3 weeks in, and have had no further problems. For a cheapo copy, to be fair, it’s pretty damn good, At least I think (Now that it’s been repaired)well worth the 12 squids I paid for it!

Useful reminder about clones

Videos

Taking the unit apart

I removed the four small M2.5 screws at both ends of the unit, therefore eight screws in total – leaving the fan still screwed to the left hand plate.

Then I removed the four M2.5 screws holding the PCB to the case.

The two M3 screws securing the LCD display do not need to be removed, the display is soldered to the PCB with 8 pins, and so can not be removed without desoldering. A wide “spade” soldering iron attachment is required to do this, properly (see EEVblog #397 – Turnigy Accucell 6 Charger Teardown at 13:35 to 16:41, but be aware not to damage the tracks, see 16:42 to 17:37).

Once the screws have been removed then the PCB needs to be prised (SLOWLY) from the case, as it is stuck on with some thermal conductive paste, on the MOSFET (?)

From visual inspection, it was not easy to see any burning. Unfortunately the resistive matrix is below the LCD display, and as such it is difficult to check for melted ICs. However, the smell was strongest from that area.

The resistive matrix is made up of 36 121 SMD resistors (120 Ω), in a 6 x 6 matrix. Presumably, one row is for control/comparison, and then the other five rows are for the 2S, 3S, 4S, 5S and 6S balance ports respectively:

121 SMD resistor
121 SMD resistor

Upon closer inspection, I did notice that one of the SMD 121 resistors, in the 6 x 6 matrix had deformed. It was the third IC of the third row, which would correspond with the third cell of the 3S balance port. The damage is shown in the diagram below, represented by the red dot:

B6 damaged resistor
B6 damaged resistor

So the repair would simply be a case of removing the LCD, to gain clear access to the resistive matrix, and replacing the IC.

A brainwave

However, after watching the two videos, Li-Po 3cell 11.1v cell count incorrect using Accucell 6 charger and iMax B6 Charger LiPo Cell Error Fix – Mikes Inventions, I thought that it would be wise to perform the “Battery Meter” test.

So hastily putting the case back together again, with just two screws either end, I connected the LiFe to the 3S balance port. The Battery Meter showed only two cells:

However, connecting the LiFe to the 4S balance port (again with out the power), all three cells were displayed!

I then left the LiFe connected to the 4S balance port, connected the charge cable, and started a charge. It then worked!

Putting it back together again

It is a simple enough job to put the unit back together again. The screws are of two types:

  • 2 x M3, and;
  • 12 x M2.5
    • 4 left side, 4 right side, and 4 internal

However, the thermal paste should really be re-applied to prevent overheating.

A cheap replacement

The chargers are certainly much cheaper now, as I had paid £31.50 + £3.50 for mine – after extensive searching for the genuine item. Now, SKYRC iMAX B6 Mini Balance Charger / Discharger for RC Aeromodelling Battery, US $26.87, Approximately £20.69 (normally US $31.99, save US $5.12 (16% OFF*)) and it claims to be genuine.

Conclusions

The 3S balance port part of the resistive matrix is obviously damaged. As it is the third cell which is not recognised, by the 3S balance port, the effective shorting of the battery must have drawn too much current from one of the end cells (it is unclear as to which end the cell is) and damaged the first/last of the SMD resistors in the 3S balance circuit.

It shouldn’t be too difficult to locate and replace the burnt SMD resistor. However, for the moment, I will continue to just use the charger’s 4S port, en lieu of the 3S port, as it works fine.

The possible solution of using a balance board is not required, as the B6 Mini already has a built-in balance board, and one can just use a different port.

 

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