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Lab31 – 3 cell lithium-ion charger repair

By on January 2, 2019
Lab31 - 3 cell lithium-ion charger repair










My little naughty niece Astrid gave her USB charger to her father after it this week failed working. Why my brother asked me today to see if I could fix his daughter’s device because else it would be just wasted. And kids easily tend to throw things away if they do no longer work.

lab 31 lithium charger repair

It was a LAB31 three 18650 cell charger that was already half open because on the left side the top of the case already was loose. Pressing the top button made no difference at all. The right case side was still closed and I had to break it open in order to remove board and cells for further inspection.

lab 31 lithium charger fix

The nickel strips on all cells already were broken. After I reconnected the red (+) and black (-) wires to the cells by restoring the bad connection to the cell poles the device responded again when the button was pressed. Which in turn activated the 4 blue leds to show the charger power was available. Last photo above on the right already shows the plus cell side that I already spot weldered with my great SUNKKO 709A spot welder. Soldering these cells is always a bad idea! Cells may overheat and degrade in quality because of the overheating while soldering. With the risk of fires or explosions. Lithium is instable when it heats up, or when cells are damaged, get wet or are short circuited.

Or may be destroyed by an over voltage above their end charging voltage of 4.20V. Even if they are discharged below about 3.2V they also likely may get destroyed. They are very powerful and can create very large currents when they are short circuited. A few years ago an electrician told me that his pants almost catches fire by some lithium cell that short circuited when he had it in his pocket. And because I even own a single Li-ion cell charged Soldering iron that works great and heats up in seconds, the power of these 18650 cells should never be underestimated!

lab 31 lithium charger fix and repair

Above photo shows the charger board type XN-091-V1.2-RHX(CE) RS058-E 20150429 with probably one 14 pins type LDR5108 charger controller.

( But that is not certain because any chip marking was already removed. This board had two 5V USB power connectors, one 1A and the second one for 2A supply. With in the middle the Micro USB charging connector. Also known as Micro-B connector. Next photos show the other side of this charger board. Everything looked fine and because all parts were undamaged and because the charger worked again after I had restored the red and black wire connections on one cell it was time to repair the 3 cell pack with new Nickel strips and my great Sunkko 709A Spot Welder. Of which some photos also will follow.

lithium battery pcb board

lithium battery pcb board repair

I have to use a Schwabe Inrush current limiter to prevent the very high AC currents that run through my Sunkko Spot welder from destroying my 25A mainpower fuse. Destroying my main power fuse on the 230VAC power lines would certainly mean a very costly Bill from the Power Company guys (they used to be the guys from Stedin but it is now called Enexis) who then need to send an engineer to replace my blown power fuse. Something that I could easily do myself but I’m simply not allowed to do because everything is carefully labelled with a special tool they use to prevent sabotage. But this still does not explain why replacing a simple 25A AC power fuse in such cases would cost as much as 540 Euros as Stedin made me believe was normal!

And because each of my power lines only accept up to delivering 3600 Watt at maximum safely I use an Inrush current limiter. Without it my Sunkko easily would consume 4800 Watt or more, also depending on the preset welding pulses per second. (4,6 or 8 pulses/second, or 4+6, 6+8 pulses or any other pulse combination ). More pulses per second means higher currents and so higher wattage consumed.

battery welding machine

Above photo shows the green PULSE field marked select buttons on my Sunkko 709A. And on the right of the Sunkko front panel the green Power switch that shows that the Welder is switched on. The red switch next to it is switched off and only needed when I also connect my special T12 Soldering Iron in case I need my Sunkko to also solder any wires on my battery packs. The big orange rotation knob in the top middle serves to also be able to adjust the strength of the welder current in combination with the pulses selected. And in this repair I used both copper pins just below the orange rotation knob to weld my new pure nickel strips onto the 3 charger cells. But instead of these copper pins which are activated when any object moves up their arms when pressed up against, we also can use a foot pedal with the also included hand welder pistol. Next photo shows how nicely the front panel of the 709A Spot welder is illuminated by the light of the front panel Led lights. Which helps to correctly weld the batteries even in darker rooms.

lithium battery welding machine

Next photos show on the left the Plus side welded and on the right photo the min side of the cells.

3 cells lithium batteries repair

And to make sure they would survive any normal fall (kids often have no clue of what everything costs these days until they have to pay for it themselves), I also taped the 3 cells closely together after they were correctly connected again before I soldered the pack back onto both wires to the charger board. Next photo shows all cells and the charger board re-inserted.

3 cells lithium batteries fix

Last photo shows the Charger completely fixed and working.

3 cells lithium batteries fix and repair

Again another device fixed at almost no costs. Of course not counting time and previous investments on Spot Welder, Copper pins, Nickel strips and last but not least the special AC Power line protecting Schwabe Inrush Current Limiter. A current Limiter that after it has disabled the Power line after the level of over-current and use of power is reached also must be removed from the Sunkko Spot Welder to prevent the Limiter from internally overheating. Which strangely only can be done by also removing the Schwabe Inrush Current Limiter Power plug from the 230VAC Power line because an off switch is missing. Which otherwise makes it impossible for the Limiter to reset itself before it can be re-used again. And this cooling down may take well over 45 minutes or so before the Schwabe Inrush Limiter connects the Sunkko to the Power Line again. And also keep in mind that even if the Sunkko 709A Spot Welder isn’t actively welding it still consumes a lot of power that would make the Schwabe Inrush Limiter getting hotter if the Limiter was not disconnected afterwards. (Just moving the welding arms up creates power pulses without actually welding at all!)

But using the Spot Welder on the Power line this way is safe, welding the cells is completely safe. There simply is no better way to do a repair like this!

Happy welding and keep fixing those Li-ion packs and chargers safely!

Albert van Bemmelen, Weert, The Netherlands.

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Note: You can read his previous repair article in the below link:




  1. beh

    January 2, 2019 at 3:28 pm

    Weldon Albert.but this sunko 709 A consume to much money too. 255 USD.!

    • Albert van Bemmelen

      January 2, 2019 at 5:32 pm

      I know Beh, it of course is a lot of money. But our electronics hobby was never about making money. At least not for me since it always did cost me more than it paid. Although sometimes we looking back do regret having bought certain things but that's life! But I never spend money on wrong unnecessary and unpractical things. And I never travel or spend wasted money on expensive holidays since my last trip to London in 1986. I guess i'm just a boring but reliable guy.

  2. Parasuraman S

    January 2, 2019 at 4:05 pm

    Great job there! Saved a device, keeping the user happy!

    • Albert van Bemmelen

      January 2, 2019 at 5:40 pm

      Yes, my little niece was happy the charger could be used again. She has a bad habit to sit on her things. As a result, items in her schoolbag such as the screen of her Android tablet afterwards need to be replaced or repaired.

  3. Robert Calk Jr.

    January 3, 2019 at 1:39 am

    Good job, Albert. It would be nice to have one of those spot welders.

    • Albert van Bemmelen

      January 3, 2019 at 5:25 pm

      You could also make one like in this video if you are op for it from an old Microwave Transformer, Robert? :

      or with instructions from this video?:

      • Robert Calk Jr.

        January 4, 2019 at 1:00 am

        Thanks Albert. I will keep it in mind for the future. I really don't need one very often.

      • Albert van Bemmelen

        January 4, 2019 at 1:24 am

        I wrote the typo "if you are op for it" but I wanted to write "UP" naturally. But you knew that of course Robert.(LOL)

  4. Albert van Bemmelen

    January 3, 2019 at 5:39 pm

    or maybe one of these videos?:
    and You als can buy this Spot Welder Controller on Aliexpress:
    Here they claim to have used the best 18650 welder available:

  5. Yogesh Panchal

    January 4, 2019 at 5:26 pm

    Good Job! Albert

    • Albert van Bemmelen

      January 5, 2019 at 6:45 am

      Thanks Yogesh. On several YouTube videos they show that not all Lithium-ion charger boards are safe. Some charger boards charge with an unacceptable over-voltage. And the fact that chips are not marked with a decent chipcode like the charger board in this repair, doesn't really help to check if they are perfectly safe. In those over-voltage YouTube cases they replaced the wrong original controller chips with exact 4.20V end-voltage controller chips.


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