Safely charging Lions - Just in case

[the servents of twilight]

I am new to Lion batterys. I made the jump from NIMHs mainly because of the lights available (performance). I have 2 inexspensive chargers and 4 different size cells (all unprotected). I do understand that protected cells may be safer. I imagine that if I continue to use these lights/batteries that protected cells, when available, will be next on my list. My main concern is the risks while charging. While I am willing to take the risks. I would like to be prepared - just in case. I was wondering if I could purchase or build something in case I had an explosion. Normally I will charge batteries in my kitchen or right next to me so I won't forget to take them out when charged.

I had a battery (rechargeable drill) melt and let off toxic gases. I am not sure of the battery type, but it was about 7 years ago and it was a craftsman. I had left for lunch and put it on the charger. Someone was there and unplugged the charger when it happened.

 

[SilverFox]

Hello The Servents...,

Over charging Li-Ion cells can cause thermal runaway. This is known as "rapidly venting with flame." It is actually more like an explosion with a fire ball.

The best analogy that I have been able to come up with is the road flare. When an 18650 cell goes off, it is like lighting a road flare. The road flare lasts longer, but the flame and smoke are similar. The 18650 will have more of a "pop" that sometimes will propel it over a distance of 4 - 6 feet.

It is best to use a quality charger and to make provisions to minimize any damage should a thermal runaway occur.

I always recommend attending to the charge. If you have to leave for awhile, shut the charger off and start it again when you come back. Touching the cell from time to time will alert you to any temperature rise.

I also recommend charging on a heat and chemical resistant surface. A fire extinguisher will help minimize any damage, and some people put up a smoke alarm near their charging station.

With premium cells, it is quite rare to get one to cook off. It does happen once in a while, but you have to work at it. However, accidents do happen so it is best to be prepared.

Tom

 

[jlomein]

Is there a safe way to connect a DMM to a cell while it is charging in a charger? Would this allow you to see the cell's current voltage level?

 

[legtu]

Is there a safe way to connect a DMM to a cell while it is charging in a charger? Would this allow you to see the cell's current voltage level?

i use nickel strips(or any thin piece of uninsulated metal) in between the battery/charging terminals and use my dmm's alligator clips to hold on to the metal strip. just don't forget to set the dmm to dc voltage first before connecting the clips.

 

[barkingmad]

i use nickel strips(or any thin piece of uninsulated metal) in between the battery/charging terminals and use my dmm's alligator clips to hold on to the metal strip. just don't forget to set the dmm to dc voltage first before connecting the clips.

Are you sure putting the DMM in the circuit could not interfere with the charger terminating?

 

[legtu]

Are you sure putting the DMM in the circuit could not interfere with the charger terminating?

as far as i know, for most general use of a voltmeter or multimeter set to measure voltage, it won't and shouldn't cause any adverse effect on a circuit. i could be wrong though so lets wait for someone more electronically inclined to chime in.

 

[the servents of twilight]

Using my chargers. I have not have a cell overcharge yet. Yes, there are better batteries than the ones I currently own. I do not believe that there is a really good charger that would be 100% safe. I always charge my batteries when I am home. My main concern is a 18650 launching across the room when my charger is next to me.
.

 

[MrAl]

To help with some questions here...


Li-ion chargers are made to have at least two basic modes of operation:
1. constant (or limited) current, and 2. constant voltage.
The order in which any Li-ion charger uses is first #1 and then #2.

Toward the end of a charge cycle, the charger switches to constant
voltage. Because of this it puts a limited amount of current through
the cell, mostly because the charger becomes a voltage source
with a constant 4.200 volts and also because of the internal resistance
of the cell, and also because the cell internal voltage (not that measured
across the terminals) is only very slighly less than 4.200 volts.
This keeps the cell safe for hours, even though you may not like to leave
it on charge forever because of claims that parts of the cell could change to
an irreversible chemical state, which decreases life span.

This of course means some damage will occur to the cell, but it doesnt
mean the cell will heat up or explode.

The more advanced chargers shut off at a certain low level current
threshold making the charge process even more safe.

If you stick around for another week or so you will find a new charger
available to CPF members that works with Li-ion cells that need a
current of 300ma to 3 amps. This covers small cells as well as large cells.
The new circuit will be prototyped by another member of CPF and the
circuit and performance will be published right here on CPF so anyone
can build one up.
The features will be:
1. 300ma to 3 amp charge current (for small or large cells)
2. Secondary stand-alone overcurrent protection
3. Auto shut off at end of charge (which PHYSICALLY disconnects the cell)
4. An optional step down front end, which allows the use of wall warts
of almost any voltage output (or other power supplies like computer, etc.)
with high efficiency.
5. Low parts costs using commonly (and cheap) available parts.

Actually though, everything will be optional (you can include it with yours or
dont include it) except the 300ma to 3 amp charge current setting.

One of us will be posting details as soon as the circuit is ready, which
should be within the next week or two for the prelim, a bit longer for
results from the prototype. Perhaps a Digikey parts list to follow too
if everything can be found there.

 

[jlomein]

Thanks for the info MrAl, hopefully I will find that in this section of the forum when it is posted (unless it would be in the DIY section?).

Sounds a little complication though, I may try and pay someone to assemble it for me.

 

[MrAl]

Hi there jlomein,

Actually that's a good idea about finding someone on CPF to build these up.
If they are willing to build up several and then sell them for cost plus a little
extra for the trouble maybe they can build them for many other members too.

Anyone out there interested? You'd have to be good with soldering and
assembly and possibly make your own PC boards.

Im not sure what section would be good to announce the availability, but
i think you are right in assuming the DIY section because that's about
what it is. I'll probably mention something in this section too.

 

[LuxLuthor]

This sounds great, MrAl !!

Depending on what is involved, I might be able to help. If you are saying we would need to do our own circuit board etching in addition to soldering in components.....I don't think I am ready for that much work. If you have parts ready to solder and assemble, I could probably help with that. Let us know when you get things ready more specifically.

:thumbsup:

 

[MrAl]

Hi again,

LuxLuthor, ok sure. There are going to be a lot of small parts like
resistors and a couple ic's and stuff like that, so a pc board would
be nice, but it is also possible to build one with point to point
wiring on a perf board, as long as the connections are made right
(strong and soldered well) and some of the wire is heavy enough
to handle 3 amps (not all the wiring needs to be that heavy though
as #22 would work ok for 90 percent of the circuit wiring).

I'll post more details as soon as possible.

 

[jdriller]

Thanks for helping us with a quality charger, MrAl.

 

[MrAl]

Hi Jody,

No problem