Braun 4737 shaver.
Ian Field
The 2 AA NiCd cells died, I've hot bags of AA NiMh cells but the shavers
charging circuit isn't having any of it and its proving a challenge to round
up AA NiCds from the spare battery box with much capacity left.
The schematic would allow me to figure out whether its possible to modify
the charging circuit to suit NiMh.
Thanks.
William Sommerwerck
between nicad and NiMH, and reject the latter. I wonder if that's really the
problem.
Although some shavers have a "quick charge" mechanism to handle
"emergencies", I suspect most are little more than trickle chargers.
Suggestion... Try running down the NiMH cells (to 1.1V or so) before putting
them in the shaver. NiMHs generally have a higher full-charge voltage, and
the charger might be "objecting" to that.
The battery failure might also be Nature's way of reminding you that shaving
is unnatural, an affront to one's manhood that should be abandoned
post-haste.
"The 2 AA NiCd cells died, I've hot bags of AA NiMh cells..."
That's probably because the cells are making contact when they shouldn't...
Meat Plow
I own a Duracell AA/AAA NiMH charger that will reject NiCads.
My Energize AA/AAA NiMH doesn't care. But it also takes 30% longer
to charge than the Duracell.
--
Live Fast Die Young, Leave A Pretty Corpse
Ian Field
"William Sommerwerck" <grizzle...@comcast.net> wrote in message
news:imd7g2$cem$1...@news.eternal-september.org...
> That must be a sophisticated charger if it can spot the slight differences
> between nicad and NiMH, and reject the latter.
It looks like all discrete circuitry, but its SMD which makes it a PITA to
trace.
>
> Although some shavers have a "quick charge" mechanism to handle
> "emergencies", I suspect most are little more than trickle chargers.
AFAIK it has one fixed charge rate, it goes into burst mode as the cells get
nearly full.
According to the user manual it isn't supposed to operate from the wall wart
when the battery is flat, but it came with a SMPSU adapter instead of the
iron-cored wasll wart as advertised - this does allow plug in and use when
the battery is flat.
>
> Suggestion... Try running down the NiMH cells (to 1.1V or so) before
> putting
> them in the shaver. NiMHs generally have a higher full-charge voltage, and
> the charger might be "objecting" to that.
The odd thing is, while the motor runs OK with NiMh cells it cuts out if the
charger is plugged in - that doesn't happen with NiMh cells fitted.
>
> The battery failure might also be Nature's way of reminding you that
> shaving
> is unnatural, an affront to one's manhood that should be abandoned
> post-haste.
You calling me infidel or something?!
William Sommerwerck
> it [sic] cuts out if the charger is plugged in -- that doesn't
> happen with NiMh cells fitted.
I'm a bit confused as to what the /exact/ problem is. Could you clarify?
What exactly is "it" that cuts out? The charging? The motor?
Ian Field
The motor cuts out.
William Sommerwerck
>>> it [sic] cuts out if the charger is plugged in -- that doesn't
>>> happen with NiMh cells fitted.
>> I'm a bit confused as to what the /exact/ problem is. Could you
>> clarify? What exactly is "it" that cuts out? The charging? The motor?
> The motor cuts out.
Thanks.
That's got me scratching my head. Why should the battery type have any
effect whatsoever on whether the charger powers the motor?
Does the motor run when no battery is installed?
Meat Plow
My Norelco when completely discharged will run very slow at first when on
AC. This lasts only for a few seconds.
William Sommerwerck
> My Norelco when completely discharged will run very slow
> at first when on AC. This lasts only for a few seconds.
Probably because the discharged battery is pulling down the supply. When the
voltage pops back up, there's enough current to run the motor.
Ian Field
Maybe someone else could try that experiment in case the improper load makes
the charging circuit go phut.
Having found a selection of AA NiCds in the bits box I charged them all and
staged "battery races" - that is put 2 cells in the shaver at a time until
the low voltage shutdown trips, each time eliminating the cell that gave up
and putting the winner back in the charger ready for the semi-finals.
The final 2 cells give a reasonable running time but it seems a bit
sluggish.
So I tried running down a pair of NiMh cells and recharging them - so far so
good.
It turns out that plugging in the charger only makes the motor cut out when
the batteries are fully charged - which actually isn't a problem.
William Sommerwerck
> which actually isn't a problem.
Dr Land wins again... "We already know the answers -- we haven't asked the
right questions."
Ian Field
There is another problem though - Braun didn't use old fashioned NiCds for
the fun of it, the NiMh cells aren't up to the motor's high current draw
while shaving.
I got about 5 shaves out of a charge - should be more than 15.
William Sommerwerck
> NiCds for the fun of it. The NiMh cells aren't up to the motor's high
> current draw while shaving.
> I got about 5 shaves out of a charge - should be more than 15.
That doesn't make sense. Like nicads, NiMHs are capable of pumping a lot of
current.
Cells vary in capacity. You can buy NiMH AA cells with 2500 or 2700mAh
capacity. I don't think nicads have ever had that high a capacity.
Ian Field
Problem is the NiMh cells get pretty warm under full load - obviously not
all of the rated 2400mAh is ending up in the motor.