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.
Reply by ●June 24, 20122012-06-24
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.
Reply by NT●June 24, 20122012-06-24
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
Reply by whit3rd●June 23, 20122012-06-23
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.
Reply by ehsjr●June 22, 20122012-06-22
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
Reply by lang...@fonz.dk●June 22, 20122012-06-22
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
Reply by ●June 22, 20122012-06-22
> 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.
Reply by Ecnerwal●June 22, 20122012-06-22
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.
Reply by Borrall Wonnell●June 22, 20122012-06-22
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?