My new protected 18650 cell from MattK at BatteryJunction.com arrived yesterday and I picked it up from the post office outlet today. (Thanks for the extra gift, Matt)
Appearance: The new blue-wrapped cell is marked:
TENERGY Li-ion 18650
2200mAh 3.7V With PCB
The outline of the thin strip that connects the top and bottom of the battery for the protection circuit is clearly visible through the wrapper. The wrapper of the new cell is a dull blue color, while the wrapper of the old cell is a shiny blue. The top of the new cell surrounding the positive terminal is black, while the top of the old cell is white. On both cells, the positive terminal is not raised (no positive 'nipple').
Dimensions: As reported by others, the new cell is slightly longer than the previous ones that did not have a PCB. The old cells were 65mm long, the new cell is 67mm long. The original published length was 67mm, so perhaps my earlier speculation that the 'missing' 2mm was due to the missing PCB was correct. The new cell also has a wider diameter than the old cells. The new one appears to be about 18mm in diameter at the bottom of the cell and a bit more than 18mm at the top of the cell. I don't have a caliper for an exact measure. The new cell just barely fits in my MicroFire M2L (which I had previously modified to allow the old, thinner 18650 to fit in easily), I'll need to sand down the inside of the brass ring at the end of the battery tube a bit more if I want to use this cell regularly in the M2L.
Performance (initial): Out of the envelope, the cell measured 3.84V using my Fluke 77 series III multimeter. I prepared the four 1 Ohm, 10 Watt Wirewound resistors that I picked up from a clearance sale at Radio Shack just for this purpose. First I conneced the resistors in series, measured the resistance, then measured the current that the proteced 18650 cell could drive through the resistors. Then I removed resistors to check other values of resistance. I used two resistors in parallel to check the 1.5 Ohm and 0.5 Ohm resistances. Here are the results:
4 x 1 Ohm resistors in series, measures 3.9 Ohms, current = 0.91 Amps
3 x 1 Ohm resistors in series, measures 2.9 Ohms, current = 1.18 Amps
2 x 1 Ohm resistors in series, measures 1.9 Ohms, current = 1.70 Amps
1 x 1 Ohm resistor in series, measures 0.9-1.0 Ohms, current = 3.10 Amps for up to 50 seconds.
2 x 1 Ohm resistors in parallel, measures 0.6 Ohms, current = 4.99 Amps for 3 seconds, then 0 Amps (repeated several times).
(Note: It appears that one of the resistors is a bit below 1.0 Ohms. That's not too surprising since they are marked 10% tolerance.)
In each case I held the circuit briefly at first, then long enough to make sure the current was stable, then tried longer times. In my first set of tests I held the 1 Ohm test (3.1 Amps) for about 12 seconds without the PCB shutting off the current; in a later set of tests I held it for about 40 seconds and 50 seconds without the PCB protection triggering. I tried the test with two 1 Ohm resistors in parallel a few times and each time the current went to zero after about 3 seconds at just under 5 Amps (except for the first time where I didn't hold the circuit for more than a second).
I did a test with 1.5 Ohms last and was surprised that on the first few tests the PCB current protection triggered after somewhere between 6 and 20 seconds of just over 2 Amps, since it hadn't triggered with 1.0 Ohms and over 3 Amps. I tried the 1.5 Ohm setup again later and the PCB current protection did not trigger after 70 seconds of over 2 Amps, so perhaps the first set of tests at 1.5 Ohms were being affected by the recent triggering of the PCB protection during the 0.6 Ohm tests. In all cases the PCB protection seems to reset automatically when the load is removed.
Summary of the odd results of the 1.5 Ohm tests:
1 x 1 Ohm resistor in series with 2 x 1 Ohm resistors in parallel, measures 1.5 Ohms, current = 2.18 Amps (first tests gave about 6 to 20 seconds then 0 Amps, cutoff time varied, later test gave over 70 seconds without cutoff. I suspect the first tests were affected by the previous tests at 0.6 Ohm).
Conclusion: It seems the new "TENERGY Li-ion 18650 2200mAh 3.7V With PCB" cells have functional high current draw protection.
More analysis is necessary to determine the exact current where the protection triggers. I suspect that the trigger value is a function of both current and time, so the higher the current, the shorter a time it requires to shut off. I suspect the trigger value has a bit of memory (perhaps some capacitance) that takes some time to reset so after it has been triggered it will be more 'sensitive' for a while.
