recharge current for AA batteries??

[Steve Robertson]

What should the (max) charge current for NiMH AA
batteries? 10% of rated current?
What happens if the charger charges at 20%, 250mA (as mine does), will get fried??
Are the 'smart' chargers really that smart??

 

[budgie]

On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
wrote:

What should the (max) charge current for NiMH AA
batteries? 10% of rated current?

Decent "smart" chargers can do up to 1C without drama or shortening
cell life.

What happens if the charger charges at 20%, 250mA (as mine does), will get fried??

Only if you leave it charging at that 0.2C for too long.

Are the 'smart' chargers really that smart??

Are all drivers idiots? No, but a lot are. There are some smart
chargers that aren't fit to garduate from kindergarten. The essential
factor is the charge termination method(s) employed. NiMH show
voltage changes that are indicative of time to cease, but these are
less well defined than NiCd. The better ones will also use both dT/dt
(rate of temp rise) AND have an absolute temp limit of say 45C. Of
course, that latter can be a PITA if you want to charge them at a 45C
ambient.

For a simple approach - as long as you are reasonably diligent -
charge them at your 0.1C or 0.2C and keep checking their temp with the
back of your hand. You'll soon get the feel of it <pun intended>.

 

[Eric]

have a look at
http://www.batteryuniversity.com/




"budgie" <me@privacy.net> wrote in message
news:3f88d828.11536030@news.individual.net...
: On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
: wrote:
:
: >What should the (max) charge current for NiMH AA
: >batteries? 10% of rated current?
:
: Decent "smart" chargers can do up to 1C without drama or shortening
: cell life.
:
: >What happens if the charger charges at 20%, 250mA (as mine does), will
get fried??
:
: Only if you leave it charging at that 0.2C for too long.
:
: >Are the 'smart' chargers really that smart??
:
: Are all drivers idiots? No, but a lot are. There are some smart
: chargers that aren't fit to garduate from kindergarten. The essential
: factor is the charge termination method(s) employed. NiMH show
: voltage changes that are indicative of time to cease, but these are
: less well defined than NiCd. The better ones will also use both dT/dt
: (rate of temp rise) AND have an absolute temp limit of say 45C. Of
: course, that latter can be a PITA if you want to charge them at a 45C
: ambient.
:
: For a simple approach - as long as you are reasonably diligent -
: charge them at your 0.1C or 0.2C and keep checking their temp with the
: back of your hand. You'll soon get the feel of it <pun intended>.

 

[budgie]

On Sun, 12 Oct 2003 20:33:50 +1300, "Eric" <some1@clare.co.nz> wrote:

have a look at
http://www.batteryuniversity.com/

If that's addressed to me, is there something specific in there to
which you are trying to draw my attention?

"budgie" <me@privacy.net> wrote in message
news:3f88d828.11536030@news.individual.net...
: On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
: wrote:
:
: >What should the (max) charge current for NiMH AA
: >batteries? 10% of rated current?
:
: Decent "smart" chargers can do up to 1C without drama or shortening
: cell life.
:
: >What happens if the charger charges at 20%, 250mA (as mine does), will
get fried??
:
: Only if you leave it charging at that 0.2C for too long.
:
: >Are the 'smart' chargers really that smart??
:
: Are all drivers idiots? No, but a lot are. There are some smart
: chargers that aren't fit to garduate from kindergarten. The essential
: factor is the charge termination method(s) employed. NiMH show
: voltage changes that are indicative of time to cease, but these are
: less well defined than NiCd. The better ones will also use both dT/dt
: (rate of temp rise) AND have an absolute temp limit of say 45C. Of
: course, that latter can be a PITA if you want to charge them at a 45C
: ambient.
:
: For a simple approach - as long as you are reasonably diligent -
: charge them at your 0.1C or 0.2C and keep checking their temp with the
: back of your hand. You'll soon get the feel of it <pun intended>.

 

[Russ]

"budgie" <me@privacy.net> wrote in message
news:3f88d828.11536030@news.individual.net...

On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
wrote:


For a simple approach - as long as you are reasonably diligent -
charge them at your 0.1C or 0.2C and keep checking their temp with the
back of your hand. You'll soon get the feel of it <pun intended>.

I was under the impression that it was fairly safe to trickle charge at 0.1C
for extended periods.

Russ.

 

[budgie]

On Sun, 12 Oct 2003 19:58:36 +1000, "Russ" <russ_spmtrp@hotmail.com>
wrote:

"budgie" <me@privacy.net> wrote in message
news:3f88d828.11536030@news.individual.net...
On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
wrote:


For a simple approach - as long as you are reasonably diligent -
charge them at your 0.1C or 0.2C and keep checking their temp with the
back of your hand. You'll soon get the feel of it <pun intended>.

I was under the impression that it was fairly safe to trickle charge at 0.1C
for extended periods.

It is as long as the temperature rise doesn't take it above the upper
limit. Refer my last para above.

 

[Eric]

No, no I just post to nobody, I like doing that, I should really hit the
delete button instead of the send button, after each message I type.

I don't post replies saying "find the answer yourself at this URL"

But I did find that URL some weeks ago, if you wish to go there and have a
look it is up to you. they only talk about secondary cells.





"budgie" <me@privacy.net> wrote in message
news:3f89100c.25846425@news.individual.net...
: On Sun, 12 Oct 2003 20:33:50 +1300, "Eric" <some1@clare.co.nz> wrote:
:
: >have a look at
: >http://www.batteryuniversity.com/
:
: If that's addressed to me, is there something specific in there to
: which you are trying to draw my attention?
:
: >
: >"budgie" <me@privacy.net> wrote in message
: >news:3f88d828.11536030@news.individual.net...
: >: On Sun, 12 Oct 2003 02:48:14 GMT, nospam@nospam.com (Steve Robertson)
: >: wrote:
: >:
: >: >What should the (max) charge current for NiMH AA
: >: >batteries? 10% of rated current?
: >:
: >: Decent "smart" chargers can do up to 1C without drama or shortening
: >: cell life.
: >:
: >: >What happens if the charger charges at 20%, 250mA (as mine does), will
: >get fried??
: >:
: >: Only if you leave it charging at that 0.2C for too long.
: >:
: >: >Are the 'smart' chargers really that smart??
: >:
: >: Are all drivers idiots? No, but a lot are. There are some smart
: >: chargers that aren't fit to garduate from kindergarten. The essential
: >: factor is the charge termination method(s) employed. NiMH show
: >: voltage changes that are indicative of time to cease, but these are
: >: less well defined than NiCd. The better ones will also use both dT/dt
: >: (rate of temp rise) AND have an absolute temp limit of say 45C. Of
: >: course, that latter can be a PITA if you want to charge them at a 45C
: >: ambient.
: >:
: >: For a simple approach - as long as you are reasonably diligent -
: >: charge them at your 0.1C or 0.2C and keep checking their temp with the
: >: back of your hand. You'll soon get the feel of it <pun intended>.
: >
: >
: