A wall-wart alternative

[Don K]

You only need 20mA of AC current to cause ventricular fibrillation. If the capacitor fails, someone could get killed touching whatever your circuit connects to.

Don

[nicksanspam]

0.0047 uF @400 V* || |

-----------||--------------------->|------------>

|| | | | | | 1.5V

120 VAC --- --- to clock ^ _ | | 10K | |

-----------www---------------------------------->

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.

Nick

[nicksanspam]

Only with constant house fires.

Nick

[meow2222]

It would be a foolish designer that enabled users to touch the output of one of these, so thats a non issue in a competent design. If for some reason they did, Y rated caps would be more appropriate than X - but still, liability like that isnt something I'd want to take on unnecessarily.

As far as fusing, if a cap shorts, enough i will flow to pop a fine wire, assuming it really is fine. A single strand of a thin stranded equipment wire etc. So the fuse concept is good.

I suppose if one wanted to improve the safety of an unsafe device (ie nonisolated supply with outputs touchable) one could put a cap in both poles and earth the supply output. Would need to ensure R is significant to avoid RCD problems.

Note this would work as a 1 cap supply, as the E connection would effectively short out the neutral capacitor. Ick.

NT

[meow2222]

It would be a foolish designer that enabled users to touch the output of one of these, so thats a non issue in a competent design. If for some reason they did, Y rated caps would be more appropriate than X - but still, liability like that isnt something I'd want to take on unnecessarily.

As far as fusing, if a cap shorts, enough i will flow to pop a fine wire, assuming it really is fine. A single strand of a thin stranded equipment wire etc. So the fuse concept is good.

I suppose if one wanted to improve the safety of an unsafe device (ie nonisolated supply with outputs touchable) one could put a cap in both poles and earth the supply output. Would need to ensure R is significant to avoid RCD problems.

NT

[meow2222]

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 supply.

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 the cap.

NT

[phatty mo]

Why not a small dc-dc converter,from your main 12/24/48V battery bank.. Safer,and probably more efficient. (takes the inverter out of the loop,atleast.)

[nicksanspam]

I don't have a battery bank.

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.

Nick

[SolarFlare]

These "hot" circuits were always accompanied by safety devices that disabled them from human contact. eg.

- polarized plugs

- cheater cords that disconnected when the back was removed

- all plastic insulated knobs to avoid metal exposure.

clock

hands and a AA battery

inaccurate timekeeping.")

but a 1K resistor

average 95 microamps

one of the 150 caps

10K resistors cost

$13.65/100. Their

12-14 minutes.

ie 1.2 Wh/year worth

Don't try this at home.

[SolarFlare]

12/24/48V battery bank..

inverter out of the

you might make the cap

does run. This circuit

hibernation.

[larry]

glue it to the face of the clock add a series resistor and schottky diode to charge the battery.

the frugal will steal the parts from a defunct solar calculator ;-)

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

[SolarFlaire]

Get an old coil for induction and put a series diode to the battery. Hang it someplace over wiring with a good load feed.

voila...self contained clock with no dangerous connection to high voltage.

the

each

(gutted

(like the

over

about

since

chassis. UL

familiar

trip at.

plug it

detectors, etc

power

[Stretch]

Nick, 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.

Stretch

[meow2222]

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 supply fail.

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.

NT

[nicksanspam]

The first old line cord I used was unpolarized...

That eats into efficiency, and it might need to change with the required current. Right now, only the cap needs to change.

Exactly what I want to avoid, with a thousand times the power consumption :-)

Nick

[SolarFlaire]

Move thre resistor

change with

to change.

the voltage down,

the power consumption :-)

[George Ghio]

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?

[Stretch]

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 life.

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 EVERYTHING!!!

Now he will have to respond to this. Probably will dig up something out of NREL :-)

Stretch

Stretch

[meow2222]

Dead batteries in smoke detectors are one of the big causes of death in house fires.

No, the batteries dont jump out and get ya, they just fail to tell you to get out in time.

NT

[meow2222]

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 alive.

That issue can be solved simply by making the CR pass enough i to power the alarm during sounding.

NT