Disassembly of USB charged batteries

[SIZE=+3]Disassembly of USB charged batteries[/SIZE]



I have reviewed these two batteries and wanted to see how the electronic was made. I expected them to be about the same inside, except Lumitop must have two charge chips (There is a jump on the usb charge curve) and MecArmy must have one.



The usb charge circuit and protection is placed at the top of the battery.



[SIZE=+3]Lumimtop[/SIZE]





First step is to get rid of the wrapper.



The cell inside is without any wrapper, this means the battery has slightly less diameter.



The backend of the battery has a extra metal plate, this makes the battery more robust for tail springs.



The front is an extra metal top with the electronic inside.



There is two connection with flat metal strips between the battery and the top (No surprise). The electronic can be pushed out of the metal top (More or less).
The shrink wrap helps with holding the top in place, when I had cut it the top was fairly easy to remove.




The top has the circuit board and a piece of plastic to keep the circuit board in place.



There is 5 chips on the circuit board. Two 57b3 (TP4057) charger chips and 3 CT2105 protection chips.
The charge chip has a 2400ohm resistor, this gives 0.41A charge current for each.
Each protection chip is rated for 3A at 25°C, it has an over temperature shutdown at 120° (Very nice).





The led is not aimed out the hole, but up from the circuit board, i.e. the light seen in the hole is the reflection from the black plastic.



With the circuit free I did some measurement:

• Circuit battery discharge current at 4.2V is 5.7uA
• Circuit battery discharge current at 3.2V is 5.5uA
• Circuit battery discharge current at 2.8V is 5.5uA
• Circuit battery discharge current at 2.4V is below 0.01uA (Overdischarge protection tripped)

[SIZE=+3]MecArmy[/SIZE]



The MecArmy gets the same treadment.



Here the original NCR18650B wrapper has not been removed, making the battery slightly thicker.



And there is no protection metal place at the bottom, making the battery slightly shorter.



The top looks the same.



This time I could push the circuit board out.



The top part of the original wrapper has been removed.
The outer ring is minus and the center is plus, any short between is very bad. When assembling these batteries they must be very careful with the plus metal strip.




The metal top and the plastic piece looks exactly the same as above.



This circuit board only has one charge chip and 3 protection chips, both are same type as above.
The charger chip has a 1800ohms resistor, making the charge current 0.55A





The top was rather difficult to remove, it looks like it was soldered to the circuit board.



With the circuit free I did some measurement:

• Circuit battery discharge current at 4.2V is 5.6uA
• Circuit battery discharge current at 3.2V is 5.3uA
• Circuit battery discharge current at 2.8V is 5.2uA
• Circuit battery discharge current at 2.4V is below 0.01uA (Overdischarge protection tripped)

[SIZE=+3]Conclusion[/SIZE]

The protection circuit is one chip, not a chip and one or more external dual mosfets, it makes the circuit slightly more compact. It would probably be better to use white plastic for the insert, instead of black, it would have made the leds brighter when looking into the two holes.
The Lumintop with the two charge chips charges faster and will also last better in light with a strong tail spring.

Both batteries looks well constructed and the low discharge current will not affect the lifetime.



[SIZE=+3]Notes[/SIZE]

Lumintop review MecArmy review

The calculated charge currents do not exactly match the measured values, this is due to tolerances in the chip and on the resistors.

A look inside some 18650 cells:
Disassembly of UltraFire 9900mAh 18650 battery
Disassembly of some UltraFire batteries
Disassembly of cheap 18650 battery

The protection with a protection chip and external mosfet transistor can be seen here:
The Anatomy of a bottom Protected LiIon Battery

Interesting. Do you think the Lumintop has a slightly superior overall mechanical construction?

SubLGT said:

Interesting. Do you think the Lumintop has a slightly superior overall mechanical construction?

Click to expand...

I will rate the Lumintop as the superior design, but it is only relevant in some circumstances.

This is Great! Thanks for the teardown. Waiting for the Lumintop to become available (at BG) and hoping in will fit in a SC62w. The parasitic drain though does mean these are not good to store for years, they should be users or topped up to storage voltage. I like these for single cell EDC lights for people not really familiar with 18650 cells and don't want to have to have a charger for them. Of course a light with a build-in charger might be better for them, but those are usually bigger lights.

StandardBattery said:

The parasitic drain though does mean these are not good to store for years, they should be users or topped up to storage voltage.

Click to expand...

The standby drain will run the battery dry in about 50 years, that is not really something to worry about, even if you store the batteries for a couple of years.

HKJ said:

The standby drain will run the battery dry in about 50 years, that is not really something to worry about, even if you store the batteries for a couple of years.

Click to expand...

You may have a point, but from storage voltage combined with self discharge you'll drop below safe level long before 50years... but OK 2-3 years maybe you're OK so I can stock a spare if needed. Sometimes special batteries sit for a long while as the more common variety are used.

StandardBattery said:

You may have a point, but from storage voltage combined with self discharge you'll drop below safe level long before 50years... but OK 2-3 years maybe you're OK so I can stock a spare if needed. Sometimes special batteries sit for a long while as the more common variety are used.

Click to expand...

Storage level is around half charge, i.e. 20 years is acceptable (With the battery's self discharge not as much).

I have seen a lot of laptop battery packs, genuine ones, which was never used, but protection circuit drained them down to 0.8 volts.