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Author Topic: Rechargeable Battery Stench....  (Read 6029 times)

Offline mafew

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Rechargeable Battery Stench....
« on: 03/01/2008 10:00:51 »
I was wondering if the smell emitting from my batteries when they're being recharged is harmful?

-Matthew Johnson Winooski, VT USA


 

Offline techmind

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Rechargeable Battery Stench....
« Reply #1 on: 03/01/2008 11:05:26 »
I don't know what sort of batteries you're referring to - can you clarify?
Ordinary NiCd / NiMH household rechargeables shouldn't emit any gas (apart from a tiny amount of hydrogen perhaps) or make any smell when being recharged. If they are, then you're probably harming the batteries quite severely.
Are you sure it's not the charger itself? You wouldn't expect that to make a smell unless it was overheating anyway.
 

Offline mafew

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Rechargeable Battery Stench....
« Reply #2 on: 03/01/2008 14:47:45 »
Thanks, they're definitely NiMH batteries and use one of those fifteen minute charges they've come out with in the last few years.  There's a fan built in to help cool the things due to their getting really hot in the the process.  I think the fan is what enables them to be able to charge so quickly without getting dangerously hot.   I have smelled this odor coming from them over the years I've used them though....even in the slower charger models.  I wish I could give some more detailed description of the smell, it's very strong.  I guess New Jersey is the closest smell I can think of.    -Matthew
 

Offline techmind

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Rechargeable Battery Stench....
« Reply #3 on: 03/01/2008 15:02:04 »
Ah ha. I've never charged such batteries faster than about a 3-hour charge.

The general principle is that (very) fast charging is mostly okay as long as the main charge is cut immediately the batteries are full. If the charger attempts to put more current in once they are fully charged then (a) the batteries rapidly heat up since they cannot chemically absorb any more energy, and (b) they vent hydrogen gas (which will, over time, reduce the capacity of the battery).
Modern chargers monitor the battery temperature and/or voltage profile during charging to establish when they are "done".

That said, a 15-minute charge is very fast. Can you identify whether the smell begins when charging begins, or only happens toward the completion of charging? Are the batteries you are using actually rated for a 15 minute charge? The rate at which gas can be liberated internally within the cells (especially under fault/overcharge) goes up with the charging rate, and if the battery vent is not designed for a high enough rate there may be a safety (explosion) issue to consider. Take care!

Does the fan cool the batteries, or charger electronics, or both?

Edit to add:
I've just done a Google search and found Energiser and Rayovac brand 15-minute chargers. I was not previously consciously aware of their availability.
Doing the maths, to charge a 2500mAh battery in 15 minutes you're going to be putting in over 10 amps (which is a lot for a small consumer-electronics device) and I wouldn't find it at all surprising if the charger got hot (and consequently smelled a bit) along the way.
If the batteries themselves ever got too hot to touch, then I'd start to worry.
« Last Edit: 03/01/2008 15:15:34 by techmind »
 

Offline mafew

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Rechargeable Battery Stench....
« Reply #4 on: 03/01/2008 15:29:18 »
  Hi, and thanks very much for your detailed reply.  I do own the Rayovac version of this 15 minute charger and they do get hot enough to the touch to burn my skin.  The fan cools the batteries and the unit it self, it draws the airflow over the batteries from underneath. Most of the charger itself consists of the fan housing. 
  When I first bought the unit I was excited about the 'new shorter charge time', but suspicious after the intense smell and heat; that it might be reducing the lifetime of the batteries (I have sets NiMH AA size that've lasted me 4 years).  The other suspicious and horrible thing is that I got suckered into buying it from Wal-Mart, on a whim.  I try not to buy anything from there, but I was walking through with a friend and spotted it.  The devil voice whispered in my ear and here I am today, asking about possible noxious fumes.  I wonder if anyone else has caught a whiff of these things when they're charging....I should google it.  Thanks again, you've helped me isolate heat as the probable source. 
« Last Edit: 03/01/2008 15:31:27 by mafew »
 

Offline techmind

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Rechargeable Battery Stench....
« Reply #5 on: 03/01/2008 15:53:36 »
A fairly detailed (technical) overview of NiMH battery technology and how best to use them -as recommended bythe manufacturer- can be found here:
http://www.duracell.com/oem/Pdf/others/TECHBULL.pdf

Or the Energizer (Ever-Ready) version:
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

By the way, a note on rechargeable terminology: a charge rate of "C/3"  means a charge current of the Capacity divided by 3, i.e. nominally a 3-hour charge. "4C" would mean charge (or discharge) current of 4 times Capacity, i.e. a 15-minute charge. Note that owing to battery inefficienies you usually have to charge them to 115%-130% of what the maths says!
 

Offline mafew

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Rechargeable Battery Stench....
« Reply #6 on: 04/01/2008 07:04:55 »
Thanks again!  Very helpful.  -Matt
 

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Rechargeable Battery Stench....
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