A wall-wart alternative

I finally got tired of replacing the 2 C-cells in a clock with a moving pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------> || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||-----------------------------------> ||
I used two caps in case one shorts and for some ground isolation. The diodes are 5.1 V zeners ($1.29 for 2 at Radio Shack) to limit the clock voltage if someone unplugs the batteries. This circuit supplies 390 microamps. I hope to avoid replacing the batteries until their shelf life runs out in 2012 :-)
This could be useful for lots of low-power stuff, eg smoke detectors.
Nick

nicksanspam@ece.villanova.edu wrote:

I finally got tired of replacing the 2 C-cells in a clock with a moving pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump

We used to use a similar circuit for powering electronic thermostats when I worked for Potterton Boilers here in Blighty. We used just one Class X capacitor feeding a 24V zener and smoothing capacitor.
I also used to use one for charging the NiCads in my caving lamp. Of course I made the classic mistake of plugging it in then picking up the crocodile clips to connect onto the battery (rather than connecting onto the battery then plugging in). Rectified 240V doesn't half hurt.
-- Malc

I used a ac adapter of the proper voltage to charge a bunch of D sixed nicads to run my answering machine during power failures. it was like a UPS uninterruptiple power supply.
my old machine would spaz with any power failure:(
The batteries went bad after 6 years, my new machine a different voltage with a battery backup of memory, so I dont use this anymore

I hope you are using rechargable batteries!
Regulart alkaline or others may dry out, overheat and start a fire!
USE ONLY RECHARGABLE BATTERIES IN THIS APPLICATION!

I like the concept, but it's hardly worth doing if you value the portability of the object and batteries can be had so cheaply.

wrote:

I hope you are using rechargable batteries!

NO!

Regulart alkaline or others may dry out, overheat and start a fire!

How much will they overheat if overchaged at 3Vx50uA = 150 microwatts? :-)

USE ONLY RECHARGABLE BATTERIES IN THIS APPLICATION!

NO!
Happy new year,
Nick

nicksanspam@ece.villanova.edu wrote:

I finally got tired of replacing the 2 C-cells in a clock with a moving pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- ||
I used two caps in case one shorts and for some ground isolation. The diodes are 5.1 V zeners ($1.29 for 2 at Radio Shack) to limit the clock voltage if someone unplugs the batteries. This circuit supplies 390 microamps. I hope to avoid replacing the batteries until their shelf life runs out in 2012 :-)
This could be useful for lots of low-power stuff, eg smoke detectors.
Nick

Caps do have a failure mode, so a series safety R is normally included with these type circuits.
If your ac supply is polarised, you'd be a bit safer putting one cap in the live than one in each pole, as the output will then be at apx earth potential, though not isolated. As it stands its semi-live.
NT

"Clark" wrote:

Looks like a shock hazard to me.

It is, but it's a current-limited shock hazard. Never pass UL, but it works. Well, until the wrong cap shorts, then someone dies. 8*|

Clark wrote:

Looks like a shock hazard to me.

meow2222@care2.com> wrote in message
nicksanspam@ece.villanova.edu wrote:
I finally got tired of replacing the 2 C-cells in a clock with a moving pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- ||
I used two caps in case one shorts and for some ground isolation. The diodes are 5.1 V zeners ($1.29 for 2 at Radio Shack) to limit the clock voltage if someone unplugs the batteries. This circuit supplies 390 microamps. I hope to avoid replacing the batteries until their shelf life runs out in 2012 :-)
This could be useful for lots of low-power stuff, eg smoke detectors.
Nick
Caps do have a failure mode, so a series safety R is normally included with these type circuits.

And at that low a current, why not ferget the caps and just use a couple of 150K resistors? The additional power loss will hardly spin your meter off the wall and you'll avoid the possible cap failure problem.
Jeff (Ducking and slinking off...)
-- Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Truth exists; only falsehood has to be invented."

If your ac supply is polarised, you'd be a bit safer putting one cap in the live than one in each pole, as the output will then be at apx earth potential, though not isolated. As it stands its semi-live.
NT

William P.N. Smith wrote:

"Clark" wrote: Looks like a shock hazard to me.
It is, but it's a current-limited shock hazard. Never pass UL, but it works. Well, until the wrong cap shorts, then someone dies. 8*|

It might pass UL, in its "double-insulated grandfather clock" :-)
Nick

I...built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- ||
Nick (nicksanspam @ ece.villanova.edu)
Caps do have a failure mode, so a series safety R is normally included with these type circuits. NT (meow2222 @ care2.com)

It should be noted that such *series capacitor* devices were outlawed for commercial products long ago in Europe. As the Big Cat notes, without a resistor to limit things, failures are usually dramatic.

wrote in message

I finally got tired of replacing the 2 C-cells in a clock with a moving pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- ||
I used two caps in case one shorts and for some ground isolation. The diodes are 5.1 V zeners ($1.29 for 2 at Radio Shack) to limit the clock voltage if someone unplugs the batteries. This circuit supplies 390 microamps. I hope to avoid replacing the batteries until their shelf life runs out in 2012 :-)
This could be useful for lots of low-power stuff, eg smoke detectors.
Nick

It seems counter-productive to build booby-traps into smoke detectors and the like.
Unlike a wall-wart, it will require special precautions not to accidentally touch anything when you go to change the battery or maybe even set the time on a clock. You will never know whether a capacitor has shorted and whether you might be killed the next time you provide a path to earth ground.
There's nothing to limit the current when capacitors fail, so that failure will cause a fire. There's no transient voltage protection, so the odds of capacitor over-voltage failure is pretty high.
Don

What is your child's life worth when they need to steal a battery for their latest toy?
That's just idiotic.
"Al Bundy" wrote in message

I like the concept, but it's hardly worth doing if you value the portability of the object and batteries can be had so cheaply.

2 Lithium batteries would be safer, cheaper, less work, last longer and much more reliable.
Just a moronic idea
"JeffM" wrote in message

I...built a charge pump like this, viewed in a fixed font:
0.047 uF @400 V || | -----------||--------------------->|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- ||
Nick (nicksanspam @ ece.villanova.edu)
Caps do have a failure mode, so a series safety R is normally included with these type circuits. NT (meow2222 @ care2.com)
It should be noted that such *series capacitor* devices were outlawed for commercial products long ago in Europe. As the Big Cat notes, without a resistor to limit things, failures are usually dramatic.

It's a fire hazard and if your insurance finds out you may be out on the street without a mortgage.
wrote in message

William P.N. Smith wrote:
"Clark" wrote: Looks like a shock hazard to me.
It is, but it's a current-limited shock hazard. Never pass UL, but it works. Well, until the wrong cap shorts, then someone dies. 8*|
It might pass UL, in its "double-insulated grandfather clock" :-)
Nick