NiMh Cell Popping

[Codeman]

Last night, as I was re-charging 3 Energizer 2500mAh AA cells in my Maha C9000, I had something happen that I haven't encountered before. The cells have about 100-150 cycles on them. Well broken in, but they shouldn't be anywhere near their end of life. They didn't have a forming charge done initially, but were matched using my ZTS tester. For the first 50-75 cycles, they were charged on an Energizer CH15MNCP-4. Since that charger isn't designed for 2500mAh cells, they did get cooked a bit until I got the C9000, though none ever exceeded 140°F that I'm aware of (I do check temps regularly with an IR thermometer). They've only been used in a low-drain device, my Uniden 396T scanner, so they haven't been driven hard. Now that I've covered the history of the cells...

Right when the 2A charge completed ("done") on the last of the 3 cells, I heard a fainting "popping" sound. The best way to describe is to say it sounded like an air bubble popping on the surface of water. I was sitting about 3 ft away, but it was just loud enough to hear over the TV 8 ft away. I quickly grabbed the cell and took it outside. After a total of 5 pops that I heard (about 3 seconds apart), it stopped. The temp of the popper cell was 118°F, while the other 2 cells were closer to 130°F. I leff the cell outside overnight. My guess, at the time, was that it was venting on a very small scale. I intentionally did not smell the cell, fearing that it might venting something that I didn't want to breathe.

This morning, I went to check on it. There is no visible damage of any kind. My ZTS tester shows 100% on all 3 cells, and all 3 have 1.37-1.39 V showing after 12 hours. Had I not heard the popping, I wouldn't have a clue that it had happened.

I'm expecting a replacement C9000 sometime this coming week. Slot 1 frequently fails to detect a AA cell. It held the popper and it wasn't detected until I put it in for the 3rd try. I really doubt the charger was responsible because it has work great since January, even with the flaky slot 1 cell detection that's been going on for a month or two. Still...

I may put the popper cell in the new charger when it arrives, just to see what happens. I am, however, leary of using the cell anymore.

Has anyone else had a cell pop like this? Or, more importantly, does anyone know what would cause this?

SilverFox, do you think it's safe to continue using it, or should I just play it safe & dispose of it?

TIA!

 

[Codeman]

While re-charging some more cells today, I noticed a very faint electrical hum. Every 2-3 seconds, it would cut out for ½ sec or so, then continue. When I removed the cell from slot 1, the hum stops. I've confirmed, using the same cell, that the hum only comes from slot 1, so I guess it's time to stop using that slot. Glad a replacement is on the way!

I don't know if the popping cell is safe to use or not, but it looks like I may have been wrong in ruling out the C9000 as the root cause.

 

[SilverFox]

Hello Ray,

Let's see now, what do I think of Energizer 2500 mAh cells...

It sounds like you had a vent that was letting go. These things happen from time to time.

Once a cell vents, it seems that the vent never completely seals again. It can continue to vent some with every charge. Every time the cell vents, you loose some capacity, so if it is used in a multi cell application, you end up with a mismatched situation.

If you continue to use the cell, I would suggest using it in a single cell application.

Tom

 

[Codeman]

Thanks, Tom. That cell is on the way to the recycle center.

I should also give kudos to Maha's customer service. They shipped a replacement to me, along with a return label to return the charger I now have. Sure is nice to not be without my C9000! :thumbsup:

 

[LuxLuthor]

Try another cell in that slot, and that battery in another charger? I don't know of any other way to know if that cell has a problem. I did have an IB 1400 2/3A NiMH cell "POP" while using a Mac Torch, afterwards the light turned off.

The POP was about what a capgun would feel like if it went off inside the light. Not like a firecracker, but enough to get your attention and feel the event. That cell was SLIGHTLY expanded in size, but nothing leaking or really that noticeable. I confirmed it with an open circuit once I took the pack apart. I think this was a Mad Maxabeam produced pack, and it had worked fine for quite a while...probably charged about 15 times. I replaced that one IB 1400mAh cell, and it has been working fine since then.

 

[Codeman]

Thanks for the suggestions, LL. Slot 1 simply has troubles with just about any AA cell, though it seemed to work fine with any AAA.

Sheez...I'm glad my popper was faint. I might've freaked if it had been as loud as your's!

I have a parrot, and they are extremely sensitive to pollutants, so I'm always very cautious when I'm recharging. I'd rather lose all of my lights before him. I'm leary of putting my re-charge station in the garage, though, because I prefer to have it close by, so that I can monitor things. It's a large room, so he stays at his cage while I'm recharging at the other end. As long as I don't have a LiIon vent, he should be okay...

 

[LuxLuthor]

You don't have a fireplace to use? That is the perfect solution for me. I can sit and watch TV while the batteries are cooking.

 

[koala]

I have a number of cheap cells that vents during first break-in. They vented about the same time 3-4 hours into the break-in session. After that they were fine. It's good to know that the vents are working instead of exploding.

 

[Codeman]

You don't have a fireplace to use? That is the perfect solution for me. I can sit and watch TV while the batteries are cooking.

That's a great idea, but no, I don't have one.

 

[cam94z28]

I have a number of cheap cells that vents during first break-in. They vented about the same time 3-4 hours into the break-in session. After that they were fine. It's good to know that the vents are working instead of exploding.

How exactly do you know if a battery is venting if it doesen't make noise? NiMH batteries seem to all have a metallic smell to them. After handling them warm, my hands even smell like it for a while, kind of how your hands smell after handling pennies. I don't think they were venting though.

 

[koala]

They hiss for 5 seconds pause then repeat. Kinda like opening a coke bottle. You may see yellow residue around the positive terminal. Some batteries started to leak after they pop.

How exactly do you know if a battery is venting if it doesen't make noise? NiMH batteries seem to all have a metallic smell to them. After handling them warm, my hands even smell like it for a while, kind of how your hands smell after handling pennies. I don't think they were venting though.