Acceptable temp for rapid charging NiMH cells?

[Jax]

What might be an approximate acceptable temperature over and above room
temperature at 20C for NiMH cells to be at whilst being rapidly charged?

By "rapid" I mean a charge current of approx 700 mA which is applied to
an AA cell that might be rated at maybe 1000 to 1800 mAh.

This is the charger: http://www.vanson.com.hk/details/p3001.html

I get some gas smells (as I mention in another thread) and wonder if the
cells are overheating during charge and venting out gas.

The extra temp I see is about 12C by measuring inside the cell
"enclosure" with a probe thermometer.

 

[Roy Lewallen]

What might be an approximate acceptable temperature over and above room
temperature at 20C for NiMH cells to be at whilst being rapidly charged?

By "rapid" I mean a charge current of approx 700 mA which is applied to
an AA cell that might be rated at maybe 1000 to 1800 mAh.

This is the charger: http://www.vanson.com.hk/details/p3001.html

I get some gas smells (as I mention in another thread) and wonder if the
cells are overheating during charge and venting out gas.

The extra temp I see is about 12C by measuring inside the cell
"enclosure" with a probe thermometer.

Many manufacturers give the maximum charge temperature for their cells
on the cell data sheets at their web sites.

Roy Lewallen

 

[Jax]

What might be an approximate acceptable temperature over and above
room temperature at 20C for NiMH cells to be at whilst being
rapidly charged?

By "rapid" I mean a charge current of approx 700 mA which is
applied to an AA cell that might be rated at maybe 1000 to 1800
mAh.

This is the charger: http://www.vanson.com.hk/details/p3001.html

I get some gas smells (as I mention in another thread) and wonder
if the cells are overheating during charge and venting out gas.

The extra temp I see is about 12C by measuring inside the cell
"enclosure" with a probe thermometer.

Hmmm, that air temp reading is quite differemt to the reading I get at
home when I measure the cells surface.

The surface temp can be a whopping 110C (or 90C above ambient).

But my technique is to blame as I have only a probe thermomenter which
does not measure surface temp so easily. Therefore I wrap the newly
charged cells in aluminium foil and then to insulate against heat loss I
wrap them in a towel. The probe then takes the temperature inside the
foil wrap.

I suspect the chemical reaction inside the cell continues for some time
as the cells were most distinctly much hotter after 3 or 4 minutes of
this insulation than the hottest I have felt them in the charger and
that is when I took the 100C reading.

Anyway 110C felt far too hot for comfort so I placed the calls into the
fridge to cool them before they suffered any more damage.

 

[John of Aix]

Hmmm, that air temp reading is quite differemt to the reading I get at
home when I measure the cells surface.

The surface temp can be a whopping 110C (or 90C above ambient).

But my technique is to blame as I have only a probe thermomenter which
does not measure surface temp so easily. Therefore I wrap the newly
charged cells in aluminium foil and then to insulate against heat
loss I wrap them in a towel. The probe then takes the temperature
inside the foil wrap.

I can see what you are trying to do but wouldn't that increase the
surface temperature ( the heat being normally radiated into the air) in
a similar way to body surface temp increasing under blankets or in
clothes?

 

[budgie]

What might be an approximate acceptable temperature over and above room
temperature at 20C for NiMH cells to be at whilst being rapidly charged?

By "rapid" I mean a charge current of approx 700 mA which is applied to
an AA cell that might be rated at maybe 1000 to 1800 mAh.

As Roy pointed out, the real answer is in the cell manufacturer's
recommendations.

In designing NiMH chargers, I usually set 45degC as the safety cutoff point
unless the client wants a lower figure - 40degC is sometimes used.

A 12Cdeg rise at ambient 20degC is fine, assuming steady state (thermal
equilibrium) and - noting your later post - the cells are in free air rather
than thermally enclosed.

Obviously the temperature rises much more rpaidly as the cells reach full
charge. While the SOC is low, the elevation should be fairly inconsequential
even in a one-hour charger.

 

[Dead Paul]

What might be an approximate acceptable temperature over and above room
temperature at 20C for NiMH cells to be at whilst being rapidly charged?

By "rapid" I mean a charge current of approx 700 mA which is applied to an
AA cell that might be rated at maybe 1000 to 1800 mAh.

This is the charger: http://www.vanson.com.hk/details/p3001.html

I get some gas smells (as I mention in another thread) and wonder if the
cells are overheating during charge and venting out gas.

The extra temp I see is about 12C by measuring inside the cell "enclosure"
with a probe thermometer.

Ahem,
Stand Back coz I am going to shout this:

YOU CROSS-POSTED TO FOUR NEWS GROUPS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[dead paul]

Stand back 'cause I'm gonna shout this.

YOU'RE A GODDAMNED RETARD. YOU'LL NEVER BE A NETKOPP.

Me a netcop? You stupid moron.

SO SHUT THE **** UP, DIPSHIT!

Eat my turd you moron

--
HERETICS IV. Mr. Bernard Shaw. By Gilbert K. Chesterton

In the glad old days, before the rise of modern morbidities, when genial old
Ibsen filled the world with wholesome joy, and the kindly tales of the
forgotten Emile Zola kept our firesides merry and pure, it used to be thought
a disadvantage to be misunderstood. It may be doubted whether it is always or
even generally a disadvantage. The man who is misunderstood has always this
advantage over his enemies, that they do not know his weak point or his plan
of campaign.

 

[frischmoutt]

Sir, Sir !

Obviously, your internal temp exceeded the threshold.
First, may I suggest you to put your head in the fridge for 2 or 3 hours in
order everything comes cooler before you attempt a new charge ?
Second even though you disagree with somebody, you should keep polite. For
example writing your insults using only one letter over three should have
led to the same result and made the post more funny to read. You might also
have used the ROT13 code.

We'd appreciate you correct the sentences with the suggestions above and
repost.

Thank in advance and best regards

 

[frischmoutt]

This exactly the answer I was expecting. It confirms that you should put
your entire body in the fridge and remain here at least one night.
You'll have fresh ideas the day after.

 

[Roy L. Fuchs]

This exactly the answer I was expecting. It confirms that you should put
your entire body in the fridge and remain here at least one night.
You'll have fresh ideas the day after.

Dude, your retarded, top posting ass is worse than Jeffery Dahmer.

At least he didn't advertise on the net. Get help, son.

I wouldn't remain at your place one second, much less one day.