Shorting a Li-on accidentally at 30C ?

[LEDcandle]

I was tired and the room was just dimly lit with a nightlight, so I reached for my DMM forgetting that the setting was on 10A and not voltage. I wanted to check out the remaining voltage on my 10180 (90 mah) and so I touched the leads to the batt.

3.2A or so which quickly went down to 1.9A then 1.2A within 2 seconds. It didn't occur to me yet that it was on 10A mode, so I though I didn't get good contacts on the battery with my leads, so I touched it to the battery a couple of times again.

I later realized my folly. The battery resting voltage is at 3.75v and it got slightly warm. 3A is more than 30C!! I'm wondering whether this short short-circuit would damage the battery, especially with such a high current (relative to the batt size) ?

And what exactly happens to the batt during the short-circuit? I guess If something was pulling 3A from it or if it were being charged with a pack charger with 3A, the battery is undergoing a 30C strain.

But when u short it on itself... is it charging or discharging or just passing a current in a repeated circle?

P/S I wanted to charge the battery back up to see the max resting voltage, but my damn AAA Nano bit the dust when it wasn't plugged into the socket properly. I heard a fuse or something go. Damn. Anyhoo, the AAA nano is rated around 150-200ma... is it too much for a 90mah batt?

 

[DM51]

You shorted the cell (sudden violent discharge) and if it wasn't just momentary it will be damaged. What voltage is it reading now? If it is >3.0V it is OK.

If it is <3.0V it may be recoverable, depending how low it is. It will need charging at 0.1C (9 mA - yes, only 9 mA, not 90!) until it gets back >3.0V. If it is <2,0V I suggest you don't even try, recycle it and get another.

For normal charging of a 10180, the nano is too powerful anyway at 200 mA - That is >2C. You need a coin-cell charger.

 

[LEDcandle]

Hey DM, thanks for the advice. The batt is still at 3.75v so I'm assuming it's pretty alright. I'm using the AAA Nano bought from Modamag with the Drake. I thought the charge rate was about 100ma .. apparently its 150-200.

Seems like there are no complaints from Drake owners yet... but I guess such a high charge rate will shorten the battery lifespan?

 

[DM51]

Your cell is OK. It had a nasty jolt which might have taken a few cycles off its lifespan, but it should be all right. The equivalent of getting a few grey hairs!

There have been reports that the Nano charger's output can vary. I measured mine, and it was almost exactly 200mA. I do use it for my 10280s, but I wouldn't use it for 10180s. I use a coin cell charger for those (the one in the link I gave above).

There would be a risk of the cells overheating if charged at too high a rate. This risk would increase as the cells age, and it would become a very real danger if the cells had been damaged by over-discharging them. 10180s are unprotected cells, so this is a serious concern. If the cell is below 3.0V at rest, it has been over-discharged and needs to be handled with care. It is better to keep it above 3.5V at rest.

It is best to recharge these cells after each use, even if the light has only been used for a few minutes. The light should be switched off at the very first sign of the output dimming. If you use a DMM to measure the cell after each discharge, you will get a better feel for its capabilities.

 

[LEDcandle]

I use the drake mostly on low and medium, which is like SUPER-LOW... 10ma or so So I guess I won't be able to noitce dimming :laughing: But I'll keep the battery topped off every now and then to prevent over-discharge.

Strange that modamag would provide the Nano as a recharge solution when it is not really suitable for the 10180. I guess a 2C charge rate is still not in the danger zone, and since the charger is AAA, a bunch of spacers need to be used, which might offer some resistance to bring down the current?

I would measure it but my Nano is dead. I guess I'll order another one and try out one of them coin-cell chargers too, although I don't know if they ship to Singapore. I also can't see from the pic how the charging is like. Is it plug and play or do I have to customise it a little with some DIY wiring etc..

If it charges 3 coin cells in series, for example, I could just replace that with the 10180. But if it charges one coin cell only, I'd have to fiddle with some wiring to get a +/- contact to the 10180.

 

[DM51]

Magnetic or other spacers won't bring down the current much.

The coin cell charger has a spring top which makes a good contact with any size cell. At 40 mA it would be very good for a 10180 Li-Ion (~0.5C).

I do NOT recommend charging any Li-Ion cells in series without a proper balancing set-up.

Interesting - another failed Nano - there seems to have been a slight epidemic of this recently...

 

[SilverFox]

Hello LEDcandle,

A way to check the charging rate is to start with a discharged cell. A discharged Li-Ion cell should read about 3.5 volts open circuit and resting. Put the cell into the charger and start a timer. When the charge has completed, check the timer. If it is over an hour, you should be OK.

Tom