NiMH Batteries Hissing

[speedy_w_beans]

I have several 3000 mAh NiMH stick pack batteries that are about three years old. They've been used quite a few times, and even when I wasn't running cars I'd still cycle them through discharge and charge once every two months just to keep them alive.

This weekend my son and I were driving outside a lot and I had about six batteries to charge. Last night I discharged them all to 5.4V; this morning I started charging them at a 1C rate. They all accepted 2900-3100 mAh. They were all warm (but not excessively hot) at the end of charging.

Four of the six packs charged as usual -- they were 100% quiet. Two of the packs surprised me; as they approached peak charge one of the packs made a few very quiet popping noises, the other pack let out one or two quiet popping noises and one moderate, "psss" for a half second. Again, the temperatures of these packs were not abnormal.

I have to assume these two packs were venting a little. Should I be concerned about this? I was thinking about TA-Mark's posting about a NiMH explosion he had experienced (http://www.tamiyaclub.com/forum/index.php?showtopic=68988entry481294), and thought I should ask.

[Zac_F83]

I have heard of NICD's hissing but not NIMH's -I would think they're just venting pressure or expanding from heating up?

[XV Pilot]

I have also heard similar noises from mine from time to time, with no ill effects. As far as I know, it is a natural consequence of the charging process, and the batteries have built-in vents for this reason. Unless the batteries are getting excessively hot or hissing for an extended period, I wouldnt worry.

[94eg!]

I've had several matched Nimh IB4600 race packs that would always pop & hiss when they were on the charger (since new). Never had a problem (other then the fact they were only worth racing for a couple months). I asked other racers the same question and was told "If it happens, it's just the way it's gonna be". Not necessarily a good thing, but not really bad . As long as they are venting, they are NOT building up dangerous internal pressure. It's when the vents get blocked (bad soldering) or damaged that the cells can go boom.

If you're not 100% confident in them, then you could consider retiring them. Personally I would still use them, but only charge outdoors (away from my car).

[beefmuffin]

i'm a big chicken when it comes to batteries. if it hisses or pops, i consider it out of commission. might still be fine, but the hissing and popping indicates - something - so my philosophy is to act on that information by retiring that battery. have only had this happen once.

[TA-Mark]

As 94eg says, they should be fine to use. My explosions were caused by dust blocking the vents and the cells not being able to vent like they should. Built up big pressure and BANG! If you can hear the hiss, then the vents are working normally.

[speedy_w_beans]

Thanks guys for the replies. Since they're not getting hot, taking a full charge, and venting properly I'll definitely keep using them.

I was concerned because this was the first time I had heard any of these noises, so if it was the beginning of the end for these packs I just thought I should know.

[94eg!]

FYI: When you take charge temps, check each individual cell. Sometimes 1 cell is weak and gets hot before the others. This is assuming you're taking temps with a gun of some sort.

[Wooders28]

As 94eg says, they should be fine to use. My explosions were caused by dust blocking the vents and the cells not being able to vent like they should. Built up big pressure and BANG! If you can hear the hiss, then the vents are working normally.

So should I put some small holes in the duct tape I have wrapped around some stick packs that had the shrink wrap damaged???

[TA-Mark]

So should I put some small holes in the duct tape I have wrapped around some stick packs that had the shrink wrap damaged???

Duct tape isn't that good of a seal I wouldn't think. As long as the wire end is still open like it is with the shrink around it is plenty.

[94eg!]

Danger is pressure inside the cells. Not between duct-tape and the cells. No worries from tapping up your packs.

[Tamiya1/10]

You guys got it all wrong, again. Batteries hissing, sure.

Its his mrs. telling him to put the darn toys away, get inside, do the dishe and take the garbage out. Or thats what my wife sounds like when she wants something done around the house. hhhiiiissssssssss.

[stevepi]

I had some which used to crackle. Modify a plastic sandwich box by putting a slot int it that way the battery is in the box with the charger outside. This is a safe way to charge them. But as always excessive heat or noise for the sake of £20 is it worth it?

[hammerstien]

lol blew 2 4.8v batteries today in my mardave both vented cells in middle of race not a good day