Question regarding 28989 charger kit with 28987 lithium ion batteries
HappyHippo
Posts: 6
The charger kit came with UltraFire IRC 18650 2500mah cells. These cells have protective circuits. Are there any details on what the protective circuit does? I assume it cuts off at high voltage, low voltage, high temp, possibly low temp. I'd like to know what the conditions and the calibrations are for the protective circuit if it does indeed cut-off. Or do I have to monitor the circuit and cut if off myself? I was thinking of doing that anyway as a secondary measure (especially when the cells brazenly call themselves UltraFire). I don't know what an UltraFire is but it doesn't sound good. But I don't necessarily want to do secondary monitoring right now since it looks like the MicroChip ICs are protecting at least from overvoltage. Also, I want to get a similar set-up for a Boe-Bot (28988) but I see it doesn't come with batteries. When I order the batteries will they be the Tenergy ones, as pictured for 28987 or these UltraFire ones I just received? By the way, note that the Tenergy cells say they are 2600mah but the cells that came with the charger kit are 2500mah. Not a huge difference but directionally incorrect. It would be nice to have some kind of spec sheet for the batteries,especially since I'm paying a small premium for buying them from the good people at Parallax.
Comments
The issue of protection built in to the cells is a distraction as it might duplicate what the charger board provides.
In other words, if you are free to use unprotected 18650 cells from any source with the charger board, you might find more capacity in other cells. There is always a process of increasing the capacity of cells that is hard for Parallax to keep up with.
Above all, I think the charger board is a great value as I have been using unprotected 18650 cells without one and the results have been sudden death of Li ion cells that go below their low voltage limit. In one case, this happened on the first use of a brand new pair of 18650 cells... an expensive lesson.
So focus on the charger board.
I suspect that Parallax doesn't really want to try to compete in the fast changing world of battery sales. They just try to provide a quality cell that will work well with or without the board in order to assure satisfied customers.
None that we've been able to find. All Lion Cells come from China as far as we can tell. Supposedly the cells will open-circuit if you try to pull too much energy out of it too quickly. The Lion Boards are designed in such as way, that the cells should never experience a rapid discharge event (that's the purpose of the 2 amp mini fuse). If the cells do "open circuit" then they will be unusable (the fuse does not reset as far as I can tell. Whether or not the cells have internal protection we can't tell - that's why we put as much protection into the board as we could - keep reading...
No, probably not. Only in an over-amperage situation as far as I can tell
No. Because Lion cells do have a lot of guidelines for charging and dis-charging, the board's circuit is designed to monitor all of those parameters and turn off the cells to prevent a problem.
LOL!
The board does all the monitoring it needs to do - no worries.
a) you can't overcharge the cells - it's a completely automatic charging system.
b) not only does the board monitor over-charging, but each cell holder has an embedded temperature sensor that monitors the cell's temperature - which shuts down the charging circuitry automatically if there's a problem.
c) when you plug in a power source into the charging jack both cells are electrically isolated from each other and their outputs are disconnected from the output jacks. Each cell is then charged independently of the other, which means that there can be no "out of balance" cell charging issues (which could be a big issue). Each cell has it's own charging system that is designed to not only not overheat itself (it throttles back if needed), but also protects the cells themselves.
Of course we can't vouch for the quality of the cells (we don't make them) but we've never had a problem - I myself have used dozens of them over the years - never an issue. And when the boards did fail, it was because I was pulling more current than I should have and the fuses blew.
No it doesn't come with batteries. The Tenergy cells were our preferred device - but Tesla bought 'em all. (The Tesla electric car uses the very same cells - about 6800 of them (PER CAR), if I remember correctly). They've bought out the world's production several times that I've heard of.
Your mileage may vary
Yes, we agree :thumb: If you can find one let us know! We only know the specs that they exhibit - any datasheet material is just about non-existent as far as we can tell.
Hope this helps :thumb:
-MattG
My impression is that you can use unprotected 18650 with the 28989. Parallax just happens to sell the protected 18650 cells.
It is not the best solution if you desire one-stop shopping (which I often do).
The protected cells have an added circuit board in the shape of a small button that is added on to their ends.
Exactly. In fact we've tried numerous brands of 18650's and they've all worked.
- me too!.
Exactly. In fact, the Charger was actually created in response to the Stingray's "AA" battery pack issues. From there it morphed to a general purpose 18650 charger system that can be used to power "whatever you want". The secondary design was the BoeBot version #28988
That's one of our primary goals
-Matt-KindaLoopyToo-G
I like 18650 cells and have acquired quite a few via salvage of a retired notebook's battery pack (had 6 cells). But these were all unprotected 18650 --- and if that are used with a board such as the one Parallax provides, they experience sudden death from excessive discharge. I cannot seem to locate any protected 18650 in retail stores in Taiwan, so I foolish purchased a few unprotected and promptly destroyed an expensive pair on first use.
I presume the Parallax board includes a low voltage cutoff as well as the other protection schemes. It seems the 'button' on the protected cells also duplicates this feature.
Li Ion cells really require several forms of monitoring.
A. Temperature monitoring
B. Over-charge monitoring
C. Over-discharge monitoring
Tesla was very wise to choose a solution where every cell is independently monitored. Central monitoring can only do so much. In the case of two cells in series, this isn't a problem. But as you add more and more cells in series and/or parallel; the monitoring becomes rather nightmarish.
Of course, the real beauty of using only the protected 18650 is that you can use them occasionally in projects without the Parallax board and enjoy their long life without having to design and build your own protection scheme. When you need to charge them, you can just use the Parallax board to do so.
The protection on the board is:
a) over-current discharge (via 2 amp fuse)
b) over-charging protection (via charge controller)
c) automatic charger shutdown when cell overheats (via charge controller)
d) automatic charger shutdown if it detects a fault in the way the charge current is being received into the cell (via charge controller).
-MattG
Going below 3.2V or so discharge results in permanent damage to the unprotected cells. If you are using a LDO voltage regulator, it can happen without noticing anything until it is too late.
The next time you attempt a recharge, the battery just goes to 0 volts.
Sorry to bear bad news, but I have grown very frustrated with the unprotected 18650 cells. I am looking into buying 4 wire linear regulators with the 4th wire provided for an Enable. In that way the Enable can be attached to a potentiometer that can be set to cut off the battery before the voltage drops too low.