Braun 4737 shaver.

That must be a sophisticated charger if it can spot the slight differences 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...

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.

It looks like all discrete circuitry, but its SMD which makes it a PITA to trace.

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.

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.

You calling me infidel or something?!

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?

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.

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.

Dr Land wins again... "We already know the answers -- we haven't asked the right questions."

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.

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.

Problem is the NiMh cells get pretty warm under full load - obviously not all of the rated 2400mAh is ending up in the motor.