Rectifier diode with low Vf

[Franc Zabkar]

I'm rebuilding a module from an "eternity lamp" of the type that is
used to illuminate headstones. It is based on a 74HC14 Schmitt trigger
which drives a red super bright LED, giving a flickering candle
effect. The power comes from two 1.2V 600mAh NiCd cells which are
charged by an 8 cell (4V) solar panel. Unfortunately the battery pack
and electronics are sealed in silicone rubber. As a replacement
assembly costs AU$165, and as it would have to be replaced every 2
years with no guarantee of continued availability, I've decided to
build my own. Naturally I plan to house the batteries separately. I've
identified most of the components, but there is one rectifier diode,
possibly a germanium or Schottky type, which is used to prevent the
NiCds from discharging into the solar panel. It is about the size of a
1N4001, with a black body, and has a Vf of 0.12V as measured with my
multimeter. The only digit I can reliably discern in the part number
appears to be a trailing "0". There is no visible logo. Can anyone
suggest a suitable replacement? BTW, the original part was destroyed
in the process of removing the silicone rubber.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Lionel]

On Thu, 07 Aug 2003 21:44:15 +1000, in
<dsn3jvcs88i20o58rbhmju0j1remnc6862@4ax.com>, Franc Zabkar
<fzabkar@optussnet.com.au> said:

I'm rebuilding a module from an "eternity lamp" of the type that is
used to illuminate headstones. It is based on a 74HC14 Schmitt trigger
which drives a red super bright LED, giving a flickering candle
effect. The power comes from two 1.2V 600mAh NiCd cells which are
charged by an 8 cell (4V) solar panel. Unfortunately the battery pack
and electronics are sealed in silicone rubber. As a replacement
assembly costs AU$165, and as it would have to be replaced every 2
years with no guarantee of continued availability, I've decided to
build my own.

Just a thought: If you're prepared to rebuild anyway, why not design in
a LiIon battery pack instead of using NiCads? Lithiums have a much, much
greater lifespan than NiCads, especially with the shallow
charge/discharge cyles they'll get with the solar charger setup you've
described. I suspect that you'd get many years of life that way.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[Lionel]

On Thu, 07 Aug 2003 21:44:15 +1000, in
<dsn3jvcs88i20o58rbhmju0j1remnc6862@4ax.com>, Franc Zabkar
<fzabkar@optussnet.com.au> said:

identified most of the components, but there is one rectifier diode,
possibly a germanium or Schottky type, which is used to prevent the
NiCds from discharging into the solar panel. It is about the size of a
1N4001, with a black body, and has a Vf of 0.12V as measured with my
multimeter. The only digit I can reliably discern in the part number
appears to be a trailing "0". There is no visible logo. Can anyone
suggest a suitable replacement? BTW, the original part was destroyed
in the process of removing the silicone rubber.

Sorry, I forgot to mention the diode in my previous response. Go ahead &
use any old Schottky diode as a replacement. If it can cope with a
couple of hundred milliamps, it should be fine. I'd pull one out of an
old computer power supply. Just check the vF first. Failing that, just
grab a cheap Schottky from Dick Smith, Tandy or Jaycar.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[budgie]

On Thu, 07 Aug 2003 21:48:27 +1000, Lionel <nop@alt.net> wrote:

On Thu, 07 Aug 2003 21:44:15 +1000, in
dsn3jvcs88i20o58rbhmju0j1remnc6862@4ax.com>, Franc Zabkar
fzabkar@optussnet.com.au> said:

I'm rebuilding a module from an "eternity lamp" of the type that is
used to illuminate headstones. It is based on a 74HC14 Schmitt trigger
which drives a red super bright LED, giving a flickering candle
effect. The power comes from two 1.2V 600mAh NiCd cells which are
charged by an 8 cell (4V) solar panel. Unfortunately the battery pack
and electronics are sealed in silicone rubber. As a replacement
assembly costs AU$165, and as it would have to be replaced every 2
years with no guarantee of continued availability, I've decided to
build my own.

Just a thought: If you're prepared to rebuild anyway, why not design in
a LiIon battery pack instead of using NiCads? Lithiums have a much, much
greater lifespan than NiCads, especially with the shallow
charge/discharge cyles they'll get with the solar charger setup you've
described. I suspect that you'd get many years of life that way.

A charging circuit for Li-Ion to enable them to deliver any sort of
lifespan is NOT the trivial exercise that a NiXX "get by" charger is.
Under the KISS principle, and having designed commercial Li-Ion
chargers, I would leave this as a Nickel job.

 

[Franc Zabkar]

On Thu, 07 Aug 2003 22:36:30 +1000, Lionel <nop@alt.net> put finger to
keyboard and composed:

On Thu, 07 Aug 2003 21:44:15 +1000, in
dsn3jvcs88i20o58rbhmju0j1remnc6862@4ax.com>, Franc Zabkar
fzabkar@optussnet.com.au> said:

identified most of the components, but there is one rectifier diode,
possibly a germanium or Schottky type, which is used to prevent the
NiCds from discharging into the solar panel. It is about the size of a
1N4001, with a black body, and has a Vf of 0.12V as measured with my
multimeter. The only digit I can reliably discern in the part number
appears to be a trailing "0". There is no visible logo. Can anyone
suggest a suitable replacement? BTW, the original part was destroyed
in the process of removing the silicone rubber.

Sorry, I forgot to mention the diode in my previous response. Go ahead &
use any old Schottky diode as a replacement. If it can cope with a
couple of hundred milliamps, it should be fine. I'd pull one out of an
old computer power supply. Just check the vF first. Failing that, just
grab a cheap Schottky from Dick Smith, Tandy or Jaycar.

I've decided to use a 1N5817 Schottky rectifier. It appears to be the
best I'm going to get. As for the LiIon battery, I can't seem to find
any 2.4V versions, only 3.6V or 7.2V. Anything other than 2.4V is not
an option since I am constrained by the solar panel. I wouldn't know
how to properly charge them in any case. I might go with NiMH cells to
give me the extra capacity during lengthy cloudy periods.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Lionel]

On Fri, 08 Aug 2003 02:11:46 GMT, in
<3f33065f.3493985@news.cantech.net.au>, budgie
<budgie@nowhere.cantech.net.au> said:

A charging circuit for Li-Ion to enable them to deliver any sort of
lifespan is NOT the trivial exercise that a NiXX "get by" charger is.
Under the KISS principle, and having designed commercial Li-Ion
chargers,

Yes, fair point.

I would leave this as a Nickel job.

Well, even using NiMHs would be a big improvement over NiCads, & they
trickle charge just fine.