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| 18650 beginners guide/introduction |
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| Rick Law:
Beside charge protection, you also need over discharge protection. If your battery is over-discharged to say 0.0V, your battery is dead. In fact, discharge to below 2.6V is not healthy for a LiIon battery. Reviving a 0V battery is possible, but it would be like reviving a race-horse and the horse can now limp with 2 legs while dragging the other two. Search the web, you will find "battery protection modules." They typically cut out at 2.4V-2.6V and don't let the battery discharge below that. Some battery protection modules also protect against shorts (over current), over voltage charging, etc. |
| spec:
--- Quote from: Rick Law on November 21, 2018, 03:24:06 am ---Beside charge protection, you also need over discharge protection. If your battery is over-discharged to say 0.0V, your battery is dead. In fact, discharge to below 2.6V is not healthy for a LiIon battery. Reviving a 0V battery is possible, but it would be like reviving a race-horse and the horse can now limp with 2 legs while dragging the other two. Search the web, you will find "battery protection modules." They typically cut out at 2.4V-2.6V and don't let the battery discharge below that. Some battery protection modules also protect against shorts (over current), over voltage charging, etc. --- End quote --- "race-horse" :-DD You read on the web that if you try to charge a LiIon battery that has a terminal voltage of less than xV that they will explode, you will be killed, your house will burn down, and the world will end. People just love to be dramatic :) But you just said that the battery would be fatally damaged. I would suggest that the situation is not even as bad as that. Perhaps the wording should be, 'if you let a LiIon battery terminal voltage drop below the battery manufacturer's specification, you stand a chance of degrading the battery'. One problem with a low terminal voltage battery is that most dedicated LiIon battery chargers will refuse to charge them, often with dire warnings, so you have to bring the terminal voltage up manually with a constant current from another source. Once the terminal voltage has risen above the lower limit you can then put the battery on a normal charger to complete the charge. About the damage done to a LiIon battery with a low terminal voltage. For a start it is obviously not advisable, because the manufacturer says so, and they are the authority. There can be no argument there, but what about practice. To start with, I have often wondered how the battery manufacturers make LiIon batteries without burning the factory down. When they first make a LiIon battery, isn't the terminal voltage 0V by definition? I must admit that I have not looked into this and may have missed a fundamental point. Perhaps a battery manufacturing expert can advise. Over the years I have been involved with batteries and chargers of pretty much all types. And I have done many experiments, including discharging LiIon batteries below the cut off point and also over charging them above the specified voltage. In most cases it made very little difference to the subsequent battery performance. But it does depend on how long the battery is kept at a low terminal voltage and all the experiments were done with a charging current of capacity/10. In one experiment 10 LiIon batteries were left for a year at a below recommended voltage. After a year, the batteries were given three normal charge/discharge cycles and every battery performed normally. Also, I regularly pull 18650s from laptop and power tool packs and the batteries are in all states of charge and terminal voltage. But after three charge cycles most recover, apart from the one battery that failed and made the pack unusable. Of course the terminal voltage is important, but equally important is charge current and ultimately the limiting factor, as with most electronic components, is internal temperature. Just briefly, because I may cover this aspect in my original post: there are various LiIon battery charging regimes, ranging from aggressive to benign. An aggressive regime is high current charging, high terminal voltage and low cut-off voltage. This is the regime used in many consumer products, especially mobile phones, laptops, E-cigarettes, and battery powered tools, because long battery duration and fast charging are key selling points. But it is a triple whammy and gives the battery a hard time. As a result, they do not last long. At the other extreme you get a benign regime as used in Tesla electric cars for example. And the reason is that Tesla guarantee their batteries so they cannot afford to sacrifice battery life. A typical benign regime would be to charge to 4V and discharge to 3V. With this regime you would get around 70% to 80% of capacity, but a vastly longer battery life. The point of all this, is that there is a lot more to LiIon batteries than never exceeding a terminal voltage of 4.2V and never going below 2.7V. |
| 6PTsocket:
Another thing to note if buying new cells, some are slightly longer than 65mm because they already have the protection module built in. This also detirmines the maximum discharge rate for that cell. You will see cells listed as protected and unprotected in places like the Battery Junction catalog. If you are building your own multi cell pack there are control boards for various numbers of unprotected cells. See ebay for an idea of what is out there. Sent from my SM-G900V using Tapatalk |
| nemail2:
Hi, thanks for all your replies! I have these batteries, unfortunately I didn't find anything on the internet about them. They seem to have some balancer board integrated. The red one is the same as the black one but without the outer plastic (I removed that). https://owncloud.ne-mail.net/s/3jmTYBpdpfx8J2X/download?path=%2F&files=20181121_222438.jpg https://owncloud.ne-mail.net/s/3jmTYBpdpfx8J2X/download?path=%2F&files=20181121_222445.jpg https://owncloud.ne-mail.net/s/3jmTYBpdpfx8J2X/download?path=%2F&files=20181121_222455.jpg Will have to read everything a few times and google more and watch the video to master the batteries eventually and build my first practical things up (like DC-DC converter (step up/down) for powering things). |
| thm_w:
That is good they have the protection circuitry already installed, I would leave it in place and use the pack as is. Probably provides overcurrent and over/under voltage protection already (you can see some control IC and a mosfet switch). |
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