How do A123s Fail? (Full Version)

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Tex Gehman -> How do A123s Fail? (7/10/2007 2:21:53 PM)

My Ni cells can and do fail in short condition, and are therefore safe when using BEC. How do A123 cells fail? Same way, I hope, and not to the open condition. As I frequently use BEC and UBEC I'd sure like to know. TIA, Tex.



Brijar -> RE: How do A123s Fail? (7/10/2007 4:09:09 PM)

I haven't had any fail on me, but I think that they just start loosing performance (voltage and runtime) after the 1000th charge or so. I really don't know, but that would make sense to me.

Brijar!!!



Red Scholefield -> RE: How do A123s Fail? (7/10/2007 5:19:41 PM)


quote:

ORIGINAL: Tex Gehman

My Ni cells can and do fail in short condition, and are therefore safe when using BEC. How do A123 cells fail? Same way, I hope, and not to the open condition. As I frequently use BEC and UBEC I'd sure like to know. TIA, Tex.


There have been very few failures reported, the only one I recall was a short.



A123 Racing -> RE: How do A123s Fail? (7/10/2007 9:43:38 PM)


Shorts when using our batteries are not recommended, but in most cases the battery will survive. In most short circuit conditions
A great deal of heat is generated, in many cases this extreme heat will destroy the material (wire, solder tab, etc.) where the short occurred, thus rectifying the short circuit condition (see attached pictures). It is possible for a short to create so much heat inside the cell (which in turn causes pressure) that the safety vent opens on the bottom. This is a rare occurrence but when this does occur it is indeterminate whether it will fail open or short circuit.

If a cell or pack is shorted allow it to cool and then inspect it. As long as the cell has not “popped” its safety vent you may continue to use it as normal. The primary side effect of a cell that has been shorted without venting is that will have a shorter life span.

Power . Safety . Life

Brian

[image]http://www.a123racing.com/images/Animated-Banner_r0.gif[/image]



Tex Gehman -> RE: How do A123s Fail? (7/11/2007 12:31:09 AM)

Thanks, but my querie is more to the point when a cell fails. I've flown round Ni cells for 30 years and had several packs get sluggish, and usually it is caused by one or more of the cells going to zero volts and testing continuity with little or no resistance, ie: internally shorted. This is a safe condition for BEC operations. Other chemistries can fail to open circuit. This is bad! I want to know about my A123s. Has there been a case of a pack going to zero volts caused by internal cell failure to open circuit? Tex.



A123 Racing -> RE: How do A123s Fail? (7/11/2007 5:20:36 PM)

Hello Tex,

If you were to have a cell fall to 0.0V it would not create an open circuit. For example if you have a 9.9V pack and a cell somehow falls to 0.0 volts the pack will measure 6.6V, and continue to put out power.

Power . Safety . Life

Brian

[image]http://www.a123racing.com/images/Animated-Banner_r0.gif[/image]



Red Scholefield -> RE: How do A123s Fail? (7/11/2007 5:40:34 PM)

I think we are mixing apples and oranges here. The question addressed cell failures, not pack failures which are fairly easy to understand since they are no different than any other pack failures exhibited over the past 50 years. It is the mechanism of the cell failures that people are interested in understanding better.


quote:

ORIGINAL: A123 Racing


Shorts when using our batteries are not recommended, but in most cases the battery will survive. In most short circuit conditions
A great deal of heat is generated, in many cases this extreme heat will destroy the material (wire, solder tab, etc.) where the short occurred, thus rectifying the short circuit condition (see attached pictures). It is possible for a short to create so much heat inside the cell (which in turn causes pressure) that the safety vent opens on the bottom. This is a rare occurrence but when this does occur it is indeterminate whether it will fail open or short circuit.

If a cell or pack is shorted allow it to cool and then inspect it. As long as the cell has not “popped” its safety vent you may continue to use it as normal. The primary side effect of a cell that has been shorted without venting is that will have a shorter life span.

Power . Safety . Life

Brian

[image]http://www.a123racing.com/images/Animated-Banner_r0.gif[/image]





niteman -> RE: How do A123s Fail? (7/13/2007 12:07:43 AM)

Hi Brian,

Would like to know myself the answer to that question.

"the mechanism of the cell failures that people are interested in understanding better".

Thank you, Dan



lutach -> RE: How do A123s Fail? (7/22/2007 3:19:02 AM)

I have found the hard way that the A123 batteries are really strong and has melted the tip of my pliers. I accidently touched the other side while cutting. Good thing for rubber grips.



lutach -> RE: How do A123s Fail? (7/22/2007 3:20:23 AM)

Also, the fuse didn't pop and the pack still puts out 36 volts.



Red Scholefield -> RE: How do A123s Fail? (7/22/2007 12:11:41 PM)

So far there are several dozen A123 packs being flown by our club members. I'm waiting anxiously for a pack to go bad so I can do a teardown and see if the failure can be diagnosed.



coro_sk -> RE: How do A123s Fail? (7/24/2007 10:49:47 AM)

quote:

ORIGINAL: Tex Gehman

My Ni cells can and do fail in short condition, and are therefore safe when using BEC. How do A123 cells fail? Same way, I hope, and not to the open condition. As I frequently use BEC and UBEC I'd sure like to know. TIA, Tex.


All reported failures I have read about, have finished with shorted cell, thus they are safe for BEC.

But there were warnings about remaining energy in healthy A123 pack. Once voltage falls as cells are approaching to empty state, there is allmost no energy in them and it is possible that they get overdischarged or even reversed by consumption of servos thru BEC. Or even they may be unable to support servos for landing.



Red Scholefield -> RE: How do A123s Fail? (7/24/2007 1:00:23 PM)


quote:

ORIGINAL: coro_sk

But there were warnings about remaining energy in healthy A123 pack. Once voltage falls as cells are approaching to empty state, there is allmost no energy in them and it is possible that they get overdischarged or even reversed by consumption of servos thru BEC. Or even they may be unable to support servos for landing.


This is a given for any battery technology, when the electrons stop flowing the lights go out. [8|]



dick Hanson -> RE: How do A123s Fail? (7/25/2007 4:30:37 AM)

My external BEC setups- allow me to fly till the motor quits - I set ESC for lowest cutoff--
I measured the 4 cell pack at 10v when this happened.
the radio worked fine
also discharging th pack using 1157 bulbs -I can watch voltage go to zero thenimmediately remove load and read a surface voltage of 2.3 which is without load . then recharge



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