On Sunday, June 24, 2012 4:27:07 PM UTC-7, (unknown) wrote:
> On Saturday, June 23, 2012 3:08:27 PM UTC-2:30, whit3rd wrote:
> > 2>Use any-old-AC low voltage transformer, preferably in conjunction with a timer (10 hours
> > charge, then shut it off) with a series limit resistor sized so it gives  you a 90 mA charge.
> 
> Won't using a series resistor also reduce the voltage?

Yes, of course.  The implication of using any-old-wallwart is that it has to be
greater voltage than the battery, you MUST reduce the voltage or your battery will
not just charge, but charge, overheat, explode.

On Saturday, June 23, 2012 3:08:27 PM UTC-2:30, whit3rd wrote:
> 2>Use any-old-AC low voltage transformer, preferably in conjunction with =
a timer (10 hours
> charge, then shut it off) with a series limit resistor sized so it gives =
 you a 90 mA charge.

Won't using a series resistor also reduce the voltage?

For now I'm just going to replace the battery using one of the suggested id=
eas.
At some point I'd like to do one of two things:

1) Convert the device to use external power (no battery).  Run at about 1.5=
 VDC internally after using a regulator to drop from 5V DC external input.

2) Dual use...allow the device to run on external power or on battery power=
.  When connected to external power, battery is being charged.  The only ci=
rcuits I've seen for this use diodes which would probably mean sub-par oper=
ation due to voltage drop.  There's very little room inside the device, ext=
ra circuitry is probably only a pipe dream.

On Jun 23, 6:38=A0pm, whit3rd <whit...@gmail.com> wrote:
> On Friday, June 22, 2012 9:38:06 AM UTC-7, (unknown) wrote:
>
> [charge to a NiCd cell, circa 90 mA desired]
>
> > > A half-wave rectifier would provide a crude form of "pulse charging"
> ...
> > Very crude. =A0Unfortunately the product was discontinued and repair pa=
rts are nearly extinct. =A0I found a 400 mA adapter which could be used but=
 then I'd need a larger capacity cell ...
> > The stock battery has welded tabs...
>
> Two solutions:
> 1>Find a smart charger for an AA NiCad cell and clip it onto the battery =
whenever you need it charged
> ( this will require =A0you to bypass the rectifier and/or use other conne=
ctions than the socket
> on the device). =A0 Beware, many chargers only charge TWO CELLS IN SERIES=
.
>
> 2>Use any-old-AC low voltage transformer, preferably in conjunction with =
a timer (10 hours
> charge, then shut it off) with a series limit resistor sized so it gives =
=A0you a 90 mA charge.

or a dc one, doesnt matter which
walwart & resistor is the sensible option.


NT

On Friday, June 22, 2012 9:38:06 AM UTC-7, (unknown) wrote:
[charge to a NiCd cell, circa 90 mA desired]
> > A half-wave rectifier would provide a crude form of "pulse charging" 
...
> Very crude.  Unfortunately the product was discontinued and repair parts are nearly extinct.  I found a 400 mA adapter which could be used but then I'd need a larger capacity cell ...

> The stock battery has welded tabs...

Two solutions:
1>Find a smart charger for an AA NiCad cell and clip it onto the battery whenever you need it charged
( this will require  you to bypass the rectifier and/or use other connections than the socket
on the device).   Beware, many chargers only charge TWO CELLS IN SERIES.

2>Use any-old-AC low voltage transformer, preferably in conjunction with a timer (10 hours
charge, then shut it off) with a series limit resistor sized so it gives  you a 90 mA charge.

dbonnell@gmail.com wrote:
>> A half-wave rectifier would provide a crude form of "pulse charging" 
>> which (at least in more refined forms, so perhaps it helps here) appears 
>> to be better for NiCad lifespan than a straight DC charge.
>>
> 
> Very crude.  Unfortunately the product was discontinued and repair parts are nearly extinct.  I found a 400 mA adapter which could be used but then I'd need a larger capacity cell to maintain C/10 charge rate.  No problem for NiMH but impossible in NiCd world.
> 
> The stock battery has welded tabs with crimped ends that slide over rigid +/- terminals on the circuit board, holding the battery in place. I haven't seen this before and I haven't found any batteries with welded crimp-style tabs.  Could be a pain to find a replacement, so I may bypass the battery altogether and power directly at 1.5V.  Will be ugly because the existing terminals are button contacts that mate with the charging dock.

Build a simple current limiter to charge at C/10 (80 mA):

            -------
  +6 ---Vin| LM317 |Vout---+
            -------        |
              Adj        [16R]
               |           |
               +-----------+
                           | +
                        [Batt]
                           | -
  Gnd ---------------------+

Note that Vin is _6_ volts in the above.
With a 16 ohm resistor, you'll get a bit over 78.125 mA
constant current. The resistor will dissipate ~102 mW,
so a 1/4 watt gives a good margin.   The circuit does
not "care" that there is a diode in series with the
battery inside the device, it still produces ~ 80 mA
constant current. If you drop Vin down to 5 volts, that
internal diode may become a problem as the 317 could
become "headroom starved".

You could use a higher Vin - if you do, more heat will
be dissipated in the 317.  Dissipation in the 317 is
P = (Vin - Vout) * .08  and Vout = 1.28 + Vbatt

Dissipation in the resistor is constant regardless of Vin.

Ed

On 22 Jun., 18:38, dbonn...@gmail.com wrote:
> > A half-wave rectifier would provide a crude form of "pulse charging"
> > which (at least in more refined forms, so perhaps it helps here) appear=
s
> > to be better for NiCad lifespan than a straight DC charge.
>
> Very crude. =A0Unfortunately the product was discontinued and repair part=
s are nearly extinct. =A0I found a 400 mA adapter which could be used but t=
hen I'd need a larger capacity cell to maintain C/10 charge rate. =A0No pro=
blem for NiMH but impossible in NiCd world.
>
> The stock battery has welded tabs with crimped ends that slide over rigid=
 +/- terminals on the circuit board, holding the battery in place. I haven'=
t seen this before and I haven't found any batteries with welded crimp-styl=
e tabs. =A0Could be a pain to find a replacement, so I may bypass the batte=
ry altogether and power directly at 1.5V. =A0Will be ugly because the exist=
ing terminals are button contacts that mate with the charging dock.


could find room inside for a bit of electronics? you can get many
different small flat lipo batteries and single chip chargers that just
need 5v in
but that is 3.7V nom. so you need a bit more than just that


-Lasse

> A half-wave rectifier would provide a crude form of "pulse charging"=20
> which (at least in more refined forms, so perhaps it helps here) appears=
=20
> to be better for NiCad lifespan than a straight DC charge.
>=20

Very crude.  Unfortunately the product was discontinued and repair parts ar=
e nearly extinct.  I found a 400 mA adapter which could be used but then I'=
d need a larger capacity cell to maintain C/10 charge rate.  No problem for=
 NiMH but impossible in NiCd world.

The stock battery has welded tabs with crimped ends that slide over rigid +=
/- terminals on the circuit board, holding the battery in place. I haven't =
seen this before and I haven't found any batteries with welded crimp-style =
tabs.  Could be a pain to find a replacement, so I may bypass the battery a=
ltogether and power directly at 1.5V.  Will be ugly because the existing te=
rminals are button contacts that mate with the charging dock.

In article 
<32c633ba-a958-4a5d-b6c4-48fea52c38ff@n16g2000vbn.googlegroups.com>,
 Borrall Wonnell <dbonnell@gmail.com> wrote:

> Hi all,
> 
> I have a device which is powered by a solitary 1.2V 800 mA NiCd cell.
> An AC wall charger (5VAC @ 180 mA) is used to charge the cell.  This
> is done via a simple half-wave rectifier that is built in to a small
> circuit board inside the device. The battery sees about 90 mA (true
> RMS).
> 
> It seems strange to use a hard-to-find AC power source rather than a
> commonly available DC wall adapter to do this job.  Particularly since
> the  built-in circuit simply rectifies the signal anyway.  Any
> thoughts on why a product would use this approach?

A half-wave rectifier would provide a crude form of "pulse charging" 
which (at least in more refined forms, so perhaps it helps here) appears 
to be better for NiCad lifespan than a straight DC charge.

If they wanted that and are nickel and penny pinching like Jeorg ;^) an 
"easy for them to find since they buy large piles of them" AC supply and 
a diode might be cheaper than a DC charger & parts to pulse charge from 
DC.

-- 
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hi all,

I have a device which is powered by a solitary 1.2V 800 mA NiCd cell.
An AC wall charger (5VAC @ 180 mA) is used to charge the cell.  This
is done via a simple half-wave rectifier that is built in to a small
circuit board inside the device. The battery sees about 90 mA (true
RMS).

It seems strange to use a hard-to-find AC power source rather than a
commonly available DC wall adapter to do this job.  Particularly since
the  built-in circuit simply rectifies the signal anyway.  Any
thoughts on why a product would use this approach?