Hi, I am new to this group. As per subject I am working on a project that
would allow me to have a smoke alarm in my room and I would never need to
change the batteries. I have it partially finished now. I used a 7809
voltage regulator to regulate the voltage from 12 rechargeable nimh
batteries so the voltage going to the smoke alarm is a reliable 9 volts. I
used a .33 micro farad capacitor and a 1 micro farad capacitor on the
regulator, with a heat sink and it works beautifully. But I am not done, the
current draw from the voltage regulator even when there is no load is a
constant 5 milliamperes so the nimh batteries only last a couple of weeks
apparently, and I want a more permanent solution. So I remembered an old
article in a misplaced (I cannot find it right now) model railroader
magazine that let a nicad battery charge off of the train power supply as
the train is being used and that allowed the train's front light to stay on
even if the train is receiving no electricity. So it all boils down to me
needing you guys to at least point me in the right direction for circuits or
information on how to recharge those 12 nimh batteries (or nicad if
necessary) while the smoke alarm is working so that when the ac power shuts
off as it does in most places in the U.S. every once in a while, then the
batteries supply the electricity to the smoke alarm until the ac power comes
back on or the batteries run out of juice after a couple of weeks. This
shouldn't be too hard of a project for me so any help could speed my
progress tremendously. Thanks, and let me know? By the way - I have tried a
lithium 9 volt battery in my smoke alarm and despite the instructions saying
it lasts for up to 10 years it only lasted 9 months. I think thats because
the shelf life is 10 years but the device life is much less.

If you've a permanent supply available, why run off of the
batteries in the first place? Place a diode between battery
output and permanent supply. Have permanent supply 9.7V
such that the diode is reverse biased while permanent power is applied.
When permanent power goes away, diode becomes forward biased.
Circuit operates off of battery supply.


--
sincerely,

Russell Powell

Artisan Components
SR. FAE - U.S. Central

469-438-6589





"Daniel Morrow" wrote in message
om...
Hi, I am new to this group. As per subject I am working on a project that
would allow me to have a smoke alarm in my room and I would never need to
change the batteries. I have it partially finished now. I used a 7809
voltage regulator to regulate the voltage from 12 rechargeable nimh
batteries so the voltage going to the smoke alarm is a reliable 9 volts. I
used a .33 micro farad capacitor and a 1 micro farad capacitor on the
regulator, with a heat sink and it works beautifully. But I am not done,
the
current draw from the voltage regulator even when there is no load is a
constant 5 milliamperes so the nimh batteries only last a couple of weeks
apparently, and I want a more permanent solution. So I remembered an old
article in a misplaced (I cannot find it right now) model railroader
magazine that let a nicad battery charge off of the train power supply as
the train is being used and that allowed the train's front light to stay
on
even if the train is receiving no electricity. So it all boils down to me
needing you guys to at least point me in the right direction for circuits
or
information on how to recharge those 12 nimh batteries (or nicad if
necessary) while the smoke alarm is working so that when the ac power
shuts
off as it does in most places in the U.S. every once in a while, then the
batteries supply the electricity to the smoke alarm until the ac power
comes
back on or the batteries run out of juice after a couple of weeks. This
shouldn't be too hard of a project for me so any help could speed my
progress tremendously. Thanks, and let me know? By the way - I have tried
a
lithium 9 volt battery in my smoke alarm and despite the instructions
saying
it lasts for up to 10 years it only lasted 9 months. I think thats because
the shelf life is 10 years but the device life is much less.

Russell Powell wrote:

If you've a permanent supply available, why run off of the
batteries in the first place? Place a diode between battery
output and permanent supply. Have permanent supply 9.7V
such that the diode is reverse biased while permanent power is applied.
When permanent power goes away, diode becomes forward biased.
Circuit operates off of battery supply.


--
sincerely,

Russell Powell

Artisan Components
SR. FAE - U.S. Central

469-438-6589

.................................................. ...........................
not good....some electrical fires that cause total distruction of the home
cause the electicity to go off long before smoke would get to the bedroom.
If you have a death wish go ahead and run the smoke detector off 110.
John




"Daniel Morrow" wrote in message
om...
Hi, I am new to this group. As per subject I am working on a project that
would allow me to have a smoke alarm in my room and I would never need to
change the batteries. I have it partially finished now. I used a 7809
voltage regulator to regulate the voltage from 12 rechargeable nimh
batteries so the voltage going to the smoke alarm is a reliable 9 volts.
I used a .33 micro farad capacitor and a 1 micro farad capacitor on the
regulator, with a heat sink and it works beautifully. But I am not done,
the
current draw from the voltage regulator even when there is no load is a
constant 5 milliamperes so the nimh batteries only last a couple of weeks
apparently, and I want a more permanent solution. So I remembered an old
article in a misplaced (I cannot find it right now) model railroader
magazine that let a nicad battery charge off of the train power supply as
the train is being used and that allowed the train's front light to stay
on
even if the train is receiving no electricity. So it all boils down to me
needing you guys to at least point me in the right direction for circuits
or
information on how to recharge those 12 nimh batteries (or nicad if
necessary) while the smoke alarm is working so that when the ac power
shuts
off as it does in most places in the U.S. every once in a while, then the
batteries supply the electricity to the smoke alarm until the ac power
comes
back on or the batteries run out of juice after a couple of weeks. This
shouldn't be too hard of a project for me so any help could speed my
progress tremendously. Thanks, and let me know? By the way - I have tried
a
lithium 9 volt battery in my smoke alarm and despite the instructions
saying
it lasts for up to 10 years it only lasted 9 months. I think thats
because the shelf life is 10 years but the device life is much less.



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Why not just toss out the present smoke detector and get a $4.95 one from
walmart that the battery will last a year. any one that is eating the
battery in such a short time is defective anyway and probably would not go
off in an emergency anyhow. trying to conserve batteries in one is stupid
in my estimation, + a screw up could easily cost your life. John T.
.................................................. .....................
Lenroc wrote:

On Thu, 09 Oct 2003 17:00:46 +0000, JOHN T wrote:

not good....some electrical fires that cause total distruction of the
home cause the electicity to go off long before smoke would get to the
bedroom. If you have a death wish go ahead and run the smoke detector off
110. John

But the OP already says he has batteries that last a few months, and is
just looking for a way to continually recharge them. Russel just mentioned
that the OP could just feed off the wall power until it goes away, then
switch over to batteries.

If the power went out for a few months (long enough to drain the
batteries), you'd think that the OP would have other issues (like... not
having power) to worry about.

The only thing I'd worry about is making sure that if the smoke alarm _is_
working off batteries, to have some sort of signal/alarm going off to
alert you to the fact, to eliminate the risk that only the smoke alarm
would lose power...




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On Thu, 09 Oct 2003 17:00:46 +0000, JOHN T wrote:

not good....some electrical fires that cause total distruction of the home
cause the electicity to go off long before smoke would get to the bedroom.
If you have a death wish go ahead and run the smoke detector off 110. John

But the OP already says he has batteries that last a few months, and is
just looking for a way to continually recharge them. Russel just mentioned
that the OP could just feed off the wall power until it goes away, then
switch over to batteries.

If the power went out for a few months (long enough to drain the
batteries), you'd think that the OP would have other issues (like... not
having power) to worry about.

The only thing I'd worry about is making sure that if the smoke alarm _is_
working off batteries, to have some sort of signal/alarm going off to
alert you to the fact, to eliminate the risk that only the smoke alarm
would lose power...

--
Lenroc

Thanks for the simple solution Russell! I am a newbie compared with
you engineers though so what do you mean by a reversed biased diode -
that the diode is connected in reverse? Forward biased? Thanks again
for the simple solution! By the way - I need both a permanent power
supply for this smoke alarm and a battery supply in case the power
goes out because a fire elsewhere in the house melted the insulation
and caused the circuit breakers to trip, for example. Thanks!

"Russell Powell" wrote in message .net...
If you've a permanent supply available, why run off of the
batteries in the first place? Place a diode between battery
output and permanent supply. Have permanent supply 9.7V
such that the diode is reverse biased while permanent power is applied.
When permanent power goes away, diode becomes forward biased.
Circuit operates off of battery supply.


--
sincerely,

Russell Powell

Artisan Components
SR. FAE - U.S. Central

469-438-6589

JOHN T wrote in message ...
Russell Powell wrote:

If you've a permanent supply available, why run off of the
batteries in the first place? Place a diode between battery
output and permanent supply. Have permanent supply 9.7V
such that the diode is reverse biased while permanent power is applied.
When permanent power goes away, diode becomes forward biased.
Circuit operates off of battery supply.


--
sincerely,

Russell Powell

Artisan Components
SR. FAE - U.S. Central

469-438-6589

.................................................. ..........................
not good....some electrical fires that cause total distruction of the home
cause the electicity to go off long before smoke would get to the bedroom.
If you have a death wish go ahead and run the smoke detector off 110.
John

Keep reading. Russel is talking about the batteries kicking in after
the power goes out, therefore the smoke alarm should still work just
fine. On another note I would say that I am sick and tired of hearing
from fire officials that you absolutely have to buy a $05.00 battery
(my smoke alarm will only accept alkaline or lithium 9 volt batteries
and the alkalines just don't work for more than 5 months each)every 9
months or else you're doomed. My way will provide the ultimate in
safety as people often forget to change their batteries or just
disable the smoke alarm altogether because of the hassle of going to
the store to buy a battery that will probably never be truly used, at
least once a year. After all - it's such a hassle I am doing this
project aren't I?

Could someone here help me with nimh or nicad recharging specifics
(i.e. trickle charging and/or in the case of nimh smart recharging) so
I can make some headway in the project? Thanks for reading.

The battery is a non-rechargable type and is for backup only.

Put in a diode so that when the AC is cut,
the battery passes juice to the detector
but the AC supply never tries to charge the battery.

Correct. The simple method I mentioned will not charge
batteries - it will merely run off of the permanent supply
and kick-in the battery back-up if ever the permanent
supply is removed/lost. Without complete circuit schematics,
I'm making an assumption that you have some, probably
unregulated, permanent dc power available from rectified 120V
AC. With this voltage being greater then the regulated 9V battery
back-up supply by the diode built-in voltage (approx. 0.7V), you
may connect both of the supplies through the diode. You would
connect the back-up supply to the anode and the permanent ~10V
supply and rest of the circuit to the cathode. As long as permanent
supply is ~9.7V, the diode is reversed-biased (non-conducting),
hence all power to the circuit is supplied by permanent supply. If
permanent supply voltage drops, the diode "turns on" and the circuit
will now be supplied by the back-up supply....
You can also get fancy and insert a pushbotton switch that'll break
the permanent supply and bypass the detecting mechanism- testing the
battery back-up.

--
sincerely,

Russell Powell

Artisan Components
SR. FAE - U.S. Central

469-438-6589





"JeffM" wrote in message
om...
The battery is a non-rechargable type and is for backup only.

Put in a diode so that when the AC is cut,
the battery passes juice to the detector
but the AC supply never tries to charge the battery.

Even if I got a smoke detector that lasts a year on one battery is not
good enough for me. I want at least a 3 to 4 year battery life. Not
only that but me not doing this project could cost me my life because
I refuse to buy batteries up the kazoo just because the industry is
slow and monopolized. My current smoke detector has diagnostics, a low
battery warning (nudge, nudge to the other poster asking for a way for
the batteries to be checked for low power) which doesn't let me use
rechargeable 9 volt batteries because those batteries only actually
supply 7.2 volts (i.e. the smoke alarm chirps and flashes the safety
light which is a standard incandescent because it thinks the battery
power is low), and a safety light in case it goes off at night and
it's dark. Anyhow John - I am just trying to be safe to potentially
save my life but I still appreciate your comments certainly, after all
it makes me think even more. I am surprised that with all of the
diagnostics and redundancy and so on in today's electronics that my
idea hasn't become commonplace with a product like it to sell. Anyhow
later.

JOHN T wrote in message ...
Why not just toss out the present smoke detector and get a $4.95 one from
walmart that the battery will last a year. any one that is eating the
battery in such a short time is defective anyway and probably would not go
off in an emergency anyhow. trying to conserve batteries in one is stupid
in my estimation, + a screw up could easily cost your life. John T.

Correct assumption. Thanks for the additional details.

"Russell Powell" wrote in message .net...
supply is removed/lost. Without complete circuit schematics,
I'm making an assumption that you have some, probably
unregulated, permanent dc power available from rectified 120V
AC. With this voltage being greater then the regulated 9V battery