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12-20-2013, 10:35 PM
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The Market Ticker - Reviving Over-Discharged Lithium Batteries
PROCEED AT YOUR OWN RISK. How many of you have something with an internal Lithium battery that you leave uncharged for a while and then it's completely dead -- it won't take a charge at all? If that's happened to you it happened because lithium-battery-powered things have a protection chip in them. It's there for two reasons -- Lithium cells will plate metallic Lithium out if they are ever reverse-charged (even a bit) and if they internally short they can build up e**ugh gas pressure to rupture and catch fire as well. As such the protection circuit will refuse to allow a charge if the battery's voltage falls too low for any reason. Fire is bad, by the way. But **t all of those Batteries are actually dead and only some causes of the battery being very low in voltage are dangerous. And if you're willing to take a calculated risk you can often revive these devices. Here's how. First, get it apart. This may be harder than it appears to do without destroying it. My example is a Fiio E6 headphone amp, a little square that is incredibly handy and occupies my camera bag, containing in its little sealed case a Lithium polymer battery. Second, figure out where the actual battery tabs are -- **t the wires coming off the battery to the circuit board. In this case it wasn't hard to find them; they were on the other side of the little board attached to the battery that performed the protection function. You might need to remove some tape or similar to get to them -- use care and ** metal tools (short circuits are very bad!) If you can't find the actual battery tabs this will **t work, as the protection circuit's job is to prevent you from doing what you're trying to do. Carefully inspect the battery. If it is physically compromised in any way, such as being bulged or similar, stop. Attempting what you're about to do with a physically compromised battery has a very high risk of causing a fire; the protection circuit did it's job and did it well. Don't proceed. If the inspection looks ok, measure the voltage across the actual battery terminals. There has to be voltage present. Lithium ion Batteries are typically 3.7v charged; even if the battery is only showing a half-volt it's ok. If the voltage is zero the cell is shorted; do **t attempt this as you will probably, once again, cause a fire. This is the exact situation that the protection circuit is trying to prevent. I repeat: It is utterly essential that you do **t attempt this with a shorted cell, as a short through the separator is exactly how these Batteries fail when they burst into flame. You will need a current and voltage-regulated power supply. Do **T attempt this with a power supply that can**t closely regulate output voltage and current, as again there is a major risk here if you dump a bunch of energy into a low-resistance cell. If all you have is some Batteries or something similar find someone with a bench power supply or stop right **w; the "redneck way" of going about this is extremely dangerous. Set your voltage source to 3.2-3.5v. ** more. Set the current limit to 100ma for a small cell and ** more than 500ma under any circumstance. It's important that you **t provide a lot of energy as again, you're trying to mitigate risk of a fire if there is something internal wrong with the cell that your inspection has **t disclosed. **w connect your power source to the battery's tabs, bypassing the protection circuit. For a small cell (~200mah) you only need to do this for a few (10 or less) seconds. For a larger one found in (for example) an iPod or cellphone that averages 1,500mah you need perhaps a minute or two. Your power supply, if it gives you real-time current monitoring, will show you very low current initially, then the drain will go up quite a bit (again, limiting current is really important!) and then it will begin to fall again. When it begins to fall you're done. **w measure the voltage across the battery's terminal. If you were successful you will see something around 2.5v or so, up to as much as 3v or more. DO **T attempt to power up the device, as there is very little energy in the battery at this point. (This, by the way, is the reason this procedure is reasonably safe in terms of fire risk.) What you have done is put a very small amount of energy into it to get off the "knee" in the output voltage of the cell's chemistry. **w re-secure whatever you had to remove to get to the terminals on the cell (again, make very sure there will **t be any short circuits!) and connect the device to its **rmal charging source. The unit should go into charge mode as the protection circuit will **w "see" a safe battery voltage. For the first charge, and for a couple of hours after it completes, it's a good idea to do this outdoors on a surface that, if the battery bursts and/or catches on fire it won't damage anything. I've successfully "rescued" a number of devices with "**n-replaceable" Batteries this way that were left unused for a long period of time but were otherwise "ok." This does **t work for a battery that has truly worn out for obvious reasons -- it only works for those that are dead because despite having few cycles they have fallen into disuse and the battery self-discharged beyond protection circuit limits. If you blow yourself up or catch on fire don't blame me, and read those warnings up above -- this is **t a "safe" procedure but if done judiciously it may save some piece of consumer electronics that you were otherwise going to throw out. أكثر... ??????? ??????: The Market Ticker - Reviving Over-Discharged Lithium Batteries || ??????: rss || ??????: اسم منتداك
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