Re: replacing batteries in Norelco shaver

In article <od41h1pv0n8po9320qbfgnr9ummai9drfc@xxxxxxx>,
H. Dziardziel <hdzi@xxxxxxxxxxxxxxx> wrote:

| On 27 Aug 2005 05:04:45 GMT, Jim Yanik <jyanik@xxxxxxxxxx> wrote:
|
| >> For say, 1500mAh cells
|
| A typo, "1500mAh cells" should read "1500mA."

Are you sure? 1500 mAh seems right to me. You're talking about the
capacity of the cell itself, not the discharge rate, right?

Capacity is given in mAh. Charge/Discharge rates in mA.

| Unlike NiCads, NiMh are exothermic while charging so will get
| warm, especially at this rather high charge rate..

NiCds get warm during charging too. Just not as warm, due to their
generally lower internal resistance.

| Once fully charged however the temperature (T) rises sharply after
| the very small voltage drop that indicate full charge.

Same with NiCd and NiMH cells -- it's just that with NiMH cells, the
voltage drop is smaller.

| NiCads, being endothermic are more reliably temperature end of
| charge detected since the T change is sharper. In either case,
| _hot_ cells indicate overcharging

Endothermic? No way.

Apparantly there is an endothermic component to the chemical charging
process (and I see references to that in many places) but the current
going through the internal resistance will generate heat as well, and
from what I've seen, the overall temperature _increases_ as you
charge, even for NiCds, during the entire charge cycle, even when
you're not charging at an extremely high rate. (Of course, if you're
charging at a low rate, any temperature changes are hard to detect, at
least until the cell is fully charged, where it becomes much easier as
all energy is going into heat, not just some.)

Perhaps at low charge rates the endothermic component is slightly
stronger than the exothermic heating, but if you're charging a NiCd
battery in 20 minutes -- at a 3C rate -- no way. It's going to get
warm.

--
Doug McLaren, dougmc@xxxxxxxxxx Baby carrots: vegetarian veal
.

Relevant Pages

  • Re: charging 10 cell nimh pack 6 cells at a time?
    ... and there you have a way to charge 10 nimh cells ... cell banks simulatenously. ... The nice thing about charging the pack as one group is if the ... the cells as one pack. ...
    (sci.electronics.design)
  • Re: Battery suggestions
    ... lithium cells just need to be fully charged (usually around 90 minutes ... The laptop's battery management circuits will ensure the cells ... I recommend charging the battery in the laptop overnight before you ... That way you are ensured of a full charge. ...
    (alt.sys.pc-clone.dell)
  • Re: Rayovac PS3 charger
    ... Is charging NiMh cells in parallel a good idea? ... I agree that charging cells individually is preferable. ... only presents the option to charge two AA or AAA cells in parallel ...
    (rec.photo.digital)
  • Re: replacing batteries in Norelco shaver
    ... The 1500mA was an estimated 3C charge rate for the original ... >NiCds get warm during charging too. ... >Same with NiCd and NiMH cells -- it's just that with NiMH cells, ...
    (sci.electronics.repair)
  • Re: Circuit Design Q. - battery charger
    ... bright sunlight in perfectly clear weather. ... cells so you have sufficient voltage to charge the batteries? ... will be very unlikely you will give the battery much of an overcharge. ...
    (sci.electronics.design)