My smoke detector draws 7 uA = 60x370C, which makes C = 315 puffs, eg 2
0.001 uF 400 V caps in series, Digikey's P1058-ND, $11.43/100. They also
sell 12 V zeners suitable for 9 V batteries, 1N5242BDICT-ND, $13.65/100.
0.0047 uF @400 V*
|| | | |
| | 1.5V
120 VAC --- --- to clock
10K | |
can trickle-charge a Seth Thomas quartz clock with hands and a AA battery
("Replace every 12 months or in case of suddenly inaccurate timekeeping.")
The trickle-charged battery might last 10 years.
The battery current jumps when the second hand ticks, but a 1K resistor
and a 10K microfarad smoothing capacitor reveal an average 95 microamps
= 60Hzx2xsqrt(2)x120VxC, which makes C = 0.0047 uF, one of the 150 caps
in Digikey's $29.95 M400-KIT-ND. Their P10KBACT-ND 10K resistors cost
$15.86/1000... 1N5231BD1CTND 5.1V zener diodes cost $13.65/100. Their
number is 1-800-344-4539. Most orders are shipped in 12-14 minutes.
This circuit uses about 1.5Vx95uA = 142 microwatts, ie 1.2 Wh/year worth
$0.000125 at 10 cents/kWh. It's probably illegal. Don't try this at home.
These "hot" circuits were always accompanied by safety
devices that disabled them from human contact.
- polarized plugs
- cheater cords that disconnected when the back was
- all plastic insulated knobs to avoid metal exposure.
But youve then got a battery alarm, not a mains/battery one. Whats the
point of running a mains supply to it if it wont work off the mains
I always wondered about using miniature audio transformers for mini
psus, get it ringing at eg 500Hz with a series cap. Wont have enough
insulation to be touch safe though. But maybe custom tfs could work.
But not worth it, as the bigger 50Hz transformer would be cheaper than
You have to supply bleeping power, relying on the battery would be
unsatisfactory. In which case it'll draw bleeping power al the time,
but since its almost entirely capacitive, and a house's total load is
normally lagging, this will in fact reduce overall current consumption.
A tiny tiny bit.
witty, but missing the point. Think about reliability and redundancy,
how very little you'd save by not using a transformer, the cost of
routing mains to the alarm, and consider the significant loss in
utility of a system that will fail if battery OR mains power supply
fails versus a system that will only fail if battery AND mains power
So yes, to be worth doing it will need to draw bleep power
continuously. It wont add to the bill or the current consumption, as
whole house loads are normally lagging.
If your main inverter doesn't run 100% of the time, you might make the cap
larger to charge the battery more when the inverter does run. This circuit
itself is unlikely to make the inverter come out of hibernation.
glue it to the face of the clock
add a series resistor and schottky diode to charge the
the frugal will steal the parts from a defunct solar
Nick, put equal value cap and resistor in series with each
line and your diodes in a small box with ac plug (gutted
wall wart- there's justice?) then run small cable (like the
old earphone cable) up to clock. Paint red insulator over
any "hot" parts in clock. The "power" cable will be about
as dangerous as any current small appliance "leakage" since
most have .045 mF caps from EACH power lead to chassis. UL
specifies an allowable leakage level. 5 ma sounds familiar
since that's the level that GFI's are supposed to trip at.
There's a thought, wire it any way you want to, then plug it
into a gfi ;-) hook all your clocks, smoke detectors, etc
together and use just one gfi. the gfi will use more power
than you're saving.
have a good new year -larry / dallas
All the parts should be in the HOT side for safety. Move thre resistor
from the bottom leg(neutral) to the top (hot) leg. Make the resistor
bigger. Safer would be to use a small transformer to step the voltage
down, then just put a diode in the secondary. That is what most large
manufacturers who don't want to get sued do these days.
What we have is a battery powered electric Grandfather clock. That's
stupid enough on it's own. Still, it's too hard to wind up a real
Grandfather clock once a week.
But then Nick in his infinite silliness got tired of replacing the
batteries every year. How tedious it must have been.
Is Nick lazy or just sad?
Nick just likes to reinvent the wheel, whilr ignoring all advances is
safety made along the way. When we are dealing with milliamps or
microamps in the charging circuit, efficiency hardly seems an issue.
Now on a battery only system, efficiency has an effect on battery
He is using a non-rechargible battery that will be ruined by his
recharging scheme. At these current levels, it won't blow up or catch
fire, it just won't work when he needs it. It is a goofy thing to do
for a once a yerar or twice a year battery change.
Strange way to gain efficiency. Reinventing what has already been
invented is rarely cost effective. You can buy something off the shelf
that works for less than you can cobble together some kludge that will
not work reliably. And for a smoke detector, reliability is
Now he will have to respond to this. Probably will dig up something
out of NREL :-)
How is describing an old CR psu reinventing anything?
We know that isnt so. All those household appliances on standby drawing
milliamps nedes a whole power generating station to supply.
The CR supply uses less money and materials in construction too. In
this case it also saves battery replacements
- more material and energy waste
- lives saved as a result of the battery still being available to work
I wasnt aware that microamp charging would damage non rc cells. Is this
true, can you offer a reference?
whats goofy about saving lives?
in what way is it strange?
there is no reinvention here
not so. Go ahead and give us a link to one thats cheaper than this.
Yes, and my one complaint about Nicks application sits here. If either
mains or battery fails, his detector wont sound. Imho if youre going to
the trouble of running mains to the detector it makes more sense to pay
the small extra and ensure it will sound if either mains or battery is
That issue can be solved simply by making the CR pass enough i to power
the alarm during sounding.
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