When purchasing a technically complex product, we trust the seller with our money and expect that the description of the product will correspond to reality. Large manufacturers, as a rule, make sure that the real characteristics of the products coincide with what is indicated in the description, as they care about the brand image.
However, not all manufacturers turn out to be honest with their consumers. And today I want to tell you just about one of such cases.
There was a need to repair the battery of the electric scooter, as it stopped producing the required capacity. The characteristics are indicated on the label: voltage 52 V, capacity 28 Ah.
The second line indicates the size of the cells (18650) and the assembly diagram (14S10P). That is, the battery should consist of 14 blocks of 10 cells each, for a total of 140 cells.
We remove the heat shrinkage and fiberglass insulation from the battery. So far, everything looks pretty decent.
View of the battery from the side of the BMS board. The wires are laid neatly, everything is secured with insulating tape.
Disconnect the balancing connector and measure the voltage across each of the 14 cell blocks. On all blocks, the voltage is the same, except for the 11th — there is zero on it.
The defective unit must be replaced. To do this, you will have to partially disassemble the battery, namely, remove the BMS and unsolder all the balancing wires.
We remove the side insulator and see that in each block we have not 10 cells, as indicated on the label, but 9, that is, the battery diagram is not 14S10P, but 14S9P. This would not be so important if the final battery capacity coincided with the declared one. But more on that later. We continue dismantling.
To make it easier to navigate and eliminate errors, I signed the numbers of the balancing leads with a marker.
After desoldering the BMS and balancing wires, we decompose the battery into 2 parts — in this state, it was welded. Looks like no cells were reported. Actually, the way it is.
We mark the faulty cells with a marker so as not to confuse them during dismantling, and cut off the contacts with a drill.
It turned out to be quite easy to remove the 11th block of cells, since the cells were not glued with superglue, but only held on adhesive tape, contacts and a small amount of hot melt glue. It seems that the battery was originally assembled with the expectation of future repairs.
Now you need to find a replacement. To do this, look at what is written on the cells. And here a surprise awaits us — the battery is assembled from cells with a capacity of 2500 mAh, that is, with a real 14S9P circuit, the battery capacity was 22.5 Ah, while the label says 28 Ah. Thus, the real capacity was 20% lower.
But what is even more surprising, even if the battery was assembled according to the 14S10P scheme stated on the label, its capacity would still be lower than the declared 25 Ah, not 28 Ah. That is, the seller not only removed 14 cells from the battery, but also used cells with a smaller capacity.
Well, we are continuing the repair in order to find out what capacity these pink cells have in reality, because it may turn out to be less than the declared 2500 mAh.
We did not have 2.5 Ah cells, but we have quite good DLGs with a capacity of about 3 Ah. Since the capacity of the new cells is larger, this will not in any way reduce the capacity of the entire battery, but at the same time, it will not increase it — just of these 3 Ah, only 2.5 Ah will be used.
We collect a similar block from the cells using superglue.
For welding we will use nickel-plated contacts. We cut them to the required size in the required quantity and degrease.
Before using the spot welding machine, we put on protective goggles in order to prevent sparks from entering the eyes.
Welding is complete, new cells are in place.
On the reverse side, everything is also ready.
Before connecting the balancing connector, it is necessary that the voltage on the new unit coincides with the voltage on the other units, so we recharge the new unit using the charger.
After that, we pack the battery and measure its real capacity using a wattmeter. It turned out to be equal to 23.12 Ah, that is, the real capacity of the pink cells is 2568 mAh, which means it corresponds to the declared one.
To summarize: during the repair it turned out that the battery was assembled according to the 14S9P scheme, and not 14S10P (the manufacturer did not report 14 cells), but its capacity
Be careful and don’t be deceived. Have a nice day, everyone!
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