NiMH cells emit smell of gas

  • Thread starter Thread starter Jon D
  • Start date Start date
J

Jon D

I have a rapid charger with a fold down cover. When I charge a couple
eof AA or AAA cells there is a smell of gas in the chamber under the
lid.

Seems to me that the cells are getting overcharge and are venting.

This is a charger with a sensor for "negative delta-V" to edermine the
end of the charging. The cells are about 10 to 15C above room
temperatre.

Is the charger cooking my cells? Or is the smell noticeable because of
the enclosed battery compartment?
 
I have a rapid charger with a fold down cover. When I charge a couple
eof AA or AAA cells there is a smell of gas in the chamber under the
lid.

Seems to me that the cells are getting overcharge and are venting.
Yes


This is a charger with a sensor for "negative delta-V" to edermine the
end of the charging. The cells are about 10 to 15C above room
temperatre.
Click to expand...

Possibly the cells had vented previously and the seal is now
open. I would throw them away, then wonder why they'd
gotten hot enough to vent previously. Some Delta-V chargers
only have a Delta-V detection but not temp monitoring, so if
a cell were fully charged and an event like AC power flicker
occured at long enough duration to reset the charger, it
might then start charging at the fast-charge rate again, but
there will be no Delta-V to detect since the cells were past
that stage already... so if they get too hot, they vent
which was better than an explosion.

At the very least if you continue to use that charger, you
might not want to fold down the cover to increase passive
cooling. There are other things you could do like pointing
a fan at the cells but it seems a hassle instead of just
seeking a different charger, IF it seems the charger doesn't
have the temp cutoff feature.

Is the charger cooking my cells? Or is the smell noticeable because of
the enclosed battery compartment?
Click to expand...


No with undamaged cells and proper charging (not
overcharging) there is no gas escaping to be building up in
the compartment.
 
Jon said:
I have a rapid charger with a fold down cover. When I charge a couple
eof AA or AAA cells there is a smell of gas in the chamber under the
lid.

Seems to me that the cells are getting overcharge and are venting.

This is a charger with a sensor for "negative delta-V" to edermine the
end of the charging. The cells are about 10 to 15C above room
temperatre.

Is the charger cooking my cells? Or is the smell noticeable because of
the enclosed battery compartment?
Click to expand...
Not all cells can be rapid-charged, some have just too high impedance
for that, as result they would heat up and went.
Good rapid chargers come with the cells designed for rapid charging,
or must at least have a list of recommended cells.

Regards,
Evgenij
 
Jon said:
I have a rapid charger with a fold down cover. When I charge a couple
eof AA or AAA cells there is a smell of gas in the chamber under the
lid.

Seems to me that the cells are getting overcharge and are venting.

This is a charger with a sensor for "negative delta-V" to edermine the
end of the charging. The cells are about 10 to 15C above room
temperatre.

Is the charger cooking my cells? Or is the smell noticeable because of
the enclosed battery compartment?
Click to expand...

deltaV doesn't work very well with NiMH cells because NiMH voltage
either doesn't drop or drops only a very small amount when full charge
approaches.

Some chargers are much worse than others. The best use not only deltaV
but also temperature, temperature difference, rate of temperature
rise, and, as a last resort, time.
 
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