Pholips coolshave charger.

[Ian Field]

Recently my Philips coolshave started not giving many shaves per charge - as
luck would have it, I'd just salvaged a pack of 1000mAh Ni-Cd cells (Ni-Mh
that I have bags of won't do) from some scrap equipment.

Since it was apart anyway, the connections from the charging plug were more
easily accesible than the holes in the charger plug, so I grabbed the DMM -
25VDC charger for a single 1.2V cell.

Would anyone care to offer comments on the likely rationale of that?

Thanks.

[John Robertson]

Might be the unloaded voltage.

High voltage but very low current might be good for keeping the whiskers
from building up inside the cells. not that I know for sure, simply a guess.

What is the voltage when you plug it into the battery pack?

John :-#)#
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[Ian Field]

"John Robertson" <sp...@flippers.com> wrote in message
news:AtmdnY6DsZ6LcirI...@giganews.com...

> On 07/28/2015 11:20 AM, Ian Field wrote:
>> Recently my Philips coolshave started not giving many shaves per charge
>> - as luck would have it, I'd just salvaged a pack of 1000mAh Ni-Cd cells
>> (Ni-Mh that I have bags of won't do) from some scrap equipment.
>>
>> Since it was apart anyway, the connections from the charging plug were
>> more easily accesible than the holes in the charger plug, so I grabbed
>> the DMM - 25VDC charger for a single 1.2V cell.
>>
>> Would anyone care to offer comments on the likely rationale of that?
>>
>> Thanks.
>
> Might be the unloaded voltage.
>
> High voltage but very low current might be good for keeping the whiskers
> from building up inside the cells. not that I know for sure, simply a
> guess.
>
> What is the voltage when you plug it into the battery pack?

As I explained - it was easier to get at the connections while the shaver
was open and taking a reading from the terminals inside.

The charger was plugged into the shaver when I measured it.

[John Robertson]

No better idea other than it would appear that the ni-cad battery is
open, otherwise it would load that down and possibly get rather warm if
there is any current available.

[Dave Platt]

In article <UeStx.44972$3n4....@fx35.am4>,

Ian Field <gangprob...@ntlworld.com> wrote:

>> What is the voltage when you plug it into the battery pack?
>
>As I explained - it was easier to get at the connections while the shaver
>was open and taking a reading from the terminals inside.
>
>The charger was plugged into the shaver when I measured it.

Could it be that the charging circuit is a buck regulator? The feed
from the wall wart could be "higher voltage, lower current", which
would result in lower losses the wire.

[Ian Field]

"Dave Platt" <dpl...@coop.radagast.org> wrote in message
news:fuil8c-...@coop.radagast.org...

There is an SMD inductor on the PCB, so that's very likely.

But I was a bit surprised that they step down from as much as 25V.

If the battery runs flat, I can't plug the charger in and carry on shaving.
IMO: if they'd used a charging voltage closer to that of the cell, it would
have been trivial to make the shaver capable of operating while charging.

[Ian Field]

"Dave Platt" <dpl...@coop.radagast.org> wrote in message
news:fuil8c-...@coop.radagast.org...

As luck would have it I found the service manual, but the schematic is a
jumble with no component values.

So far I've done a first draft of re drawing the schematic, so now I can
recognise most of the circuit blocks, but it needs more tidying before I can
follow how it actually works.

My best guess is, its a distant relative of the hysteretic buck with a
synchronous rectifier, but it needs more study to figure it out.