lithium ion - If Li-Ion battery is deeply discharged, is it harmful for it to remain in this state unused?

It is well known that Li-Ion batteries should not be deep discharged.

But sometimes they do discharge deeply. Is it OK for the device to remain in such state for a long time (and recharge again only when the device is needed again after a year) or it should be charged back as soon as possible?

In other words, the battery was discharged deeply. Now I need to know the best way to prevent further damage to the battery. Should I recharge it immediately or leave it in a deeply-discharged state until I need it again?

Does deeply discharged battery have higher or lower self-discharge compared to normally charged battery?

Answer

No, it is not OK to have a Li-Ion deeply discharged at all.

Here is why: When discharged below its safe low voltage (exact number different between manufacturers) some of the copper in the anode copper current collector (a part of the battery) can dissolve into the electrolyte. The copper ions (atoms?) then in turn can stick on to the anode during charging by chemical reduction and cause dendrites. The dendrites might cause a short circuit inside the battery. So basically discharging too much is as bad as charging too much. But the dendrites caused by overcharging is formed out of lithium.

Normally the battery pack should have some sort of supervisory circuit that disconnects the cells from the charger or load when the cells are above or below the recommended voltages.

Question 2:

Does a deeply discharged battery have higher or lower self-discharge compared to normally charged battery?

A deeply discharged battery might have a higher self-discharge due to the above mentioned damage.

From what I can see in the data sheet provided by a large manufacturer (under NDA) the best relative (%) capacity retained is at somewhere around 50% charge and at low storage temperature.

batteries - Storing a possibly damaged Li-Ion battery

I replaced the battery of my mobile phone earlier this day. Because of adhesive, narrow spaces etc it happened that I slightly bent the old battery during removal (see sketch below).

    top view     v---contacts                            side view
----------------[]-                                              _________ 
|                 |                              _______________/  _______| "bottom"
|                 |    contacts on this side >   |________________/
|                 |                                                       
|                 |                                             |<--1cm-->|

|                 |
|                 |
-------------------
      "bottom"

Sorry for the bad sketches, I stored the battery away to (probable) safety and didn't take any pictures beforehand. The bend starts about 1cm away from "bottom" and at the very bottom the battery is not more than 1mm elevated. There is no visible damage of the hull.

I cannot dispose the battery before friday and hearing of all the troubles regarding Li-Ion and LiPo batteries I am a bit worried now.

It is a 2300 mA Li-Ion mobile phone battery and at the time of removal it was probably around 20-25 % charged.

I have limited options for storage, no garden available. I thought about burying it in a glass jar filled with sand (would be available) in order to make it impossible for a fire to start (least possible amount of air available) - but the tightly closed lid would make it impossible for fumes to escape and the jar might explode from pressure?

I could also wrap the battery (or jar) in some fireproof blanket (like they are available for kitchen fires) and just hope for the best.

Do I have to worry at all? I know that LiPo-batteries like they are used for racing cars or model planes can be dangerous when damaged, but what about phone batteries? How should I store it in order to be safe until friday?

How fast would I notice any possible danger, if the battery would have been damaged? I watched it for about 3 hours before storing it away (it's in the jar of sand at the moment, with the lid open) and nothing happened. Does that mean that there will not happen anything anymore?

How can I duplicate Apple's tiny USB power adapter?

I'm designing a project that controls 110VAC (plug in, socket out), and also has a microprocessor inside. I'd really like this project to not need a wall wart to get it's 5V, so I want to include a small DC power supply inside.

Apple's USB power adapter looks like a great small design that I can fit inside my case. I'm guessing this is a switching power supply but I can't find any teardowns or schematics anywhere.

Does anyone know how this thing works? I know I could make my own 110V->5VDC supply from a bridge rectifier and some caps, but I'd like to also be super safe. What's in the Apple brick?

microcontroller - What is the simplest and cheapest way to interface with USB?

If I wanted to make a simple device that communicates with my computer, say maybe a switch that could mute my computer when turned on and off and plug it in via USB, what would be the cheapest and easiest way to accomplish this?

Using the core of a toroidal inductor as the core for a toroidal transformer?

As the title says, I have quite a few toroidal cores that I have gathered over time, and would like to reuse them, do they also work as transformer cores?

Answer

Toroidal cores are the best in term of power transfer because no flux is lost with its shape. Depending on the size, Toroidal cores can be used for different application. transformer is one of them. The voltage depends on the turns ratios. You obviously can add many turns to it if it's small size.

Why do computers only use 0 and 1?

Why do computers only use 0 and 1? Won't the addition of other numbers such as 2 or 3 speed up computers? Also, 2 and 3 can be used to shorten the bit-length of integers (2 and 3 can be used to end an integer, so that the number 1 only needs one two bits.)..

Why is binary computer more preferred?

NPN Transistor switching two loads with common ground

I have a 12V siren (speaker that includes a driver) that has two positive leads, one for steady sound and one for a yelp sound. There is also a shared negative lead.

I want to control both sounds from two Arduino output pins. I currently have this schematic but I'm not sure how to hook up the other positive lead.

Answer

Instead of switching the common ground, you want to switch each of the positive connections independently and keep the common ground tied to ground. Something like this:

The SIREN and YELP lines are intended to be driven by 0-5 V digital outputs. This will put very little (well under a mA) load on the digital lines. When YELP is driven to 5 V, it will cause Q3 to turn on as a 10 mA current sink. This becomes the base current of Q1, which can then acts as a high side switch that can support up to 10 mA times its gain. Figure you can count on Q1 and Q2 having a gain of at least 50, so they can switch up to 500 mA as this circuit is drawn. This is all you need if the yelp and siren inputs to the sound unit draw 500 mA or less at 12 V.