Save some power to do actions after the current is cut

Using Arduino General Electronics
1

Hello there,

I want to build a ceiling lamp that physically "opens" itself with a small stepper motor (or maybe a servo) when turned ON.
The lamp is only connected to main power, controlled by a regular switch on the wall.
quite usual thing up to here.

Now my problem :

I want the lamp to close itself right after the power is cut. So I need :

  1. To detect the power loss quickly.
  2. And more importantly save, somehow, enough power (@12V) to keep the system working (including of course, the motor + the light dimming off...) during the closing phase of the lamp (lets say 10 sec).

I did some research about this, and generally the guys who want to do this kind of thing are only looking for a way to backup some data onto the EEPROM @ about 2.7V without any physical action.... but I want a spinning 12V motor for a couple of seconds + a fairly bright light! thats quite a different requirement.
Of course the energy storing device should be charged enough within seconds to perform the closing action fully.

I suppose a lithium battery (or better NIMH? ) could do the trick, or maybe a supercapacitor, but I have to mount an array of those to reach 12V...
But supercaps+step up module is a quite tempting option, no?

Any practical ideas?

If it is REALLY unpractical, I suppose I will have to go for a soft logic switch somewhere on the wall...

2

The motors will eat up your stored electricity, which may not be be up to the task of 'closing the lamp'. Steppers under load are current hogs. Maybe instead use the motors to hold the lamp open while it's powered, against a geared down spring, which closes it mechanically when the power turns off.

Keeping a LED alive for a few seconds is much easier, especially if it's supposed to fade to off.

3

yep that's what I thought.

For the spring yeah, good idea, but it may be difficult to gave a slow and neat closing move using this kind of mechanical potential energy, but nice idea though.

It may be an overkill, but a 12V NiMH @ about 1000mAh battery pack could works, yeah?
easy and fast to charge and relatively safe.

4

Benn:
... it may be difficult to gave a slow and neat closing move using this kind of mechanical potential energy, but nice idea though.
...

Sure you can. Use some clockwork, or a pneumatic damper. Or both.

Benn:
...
It may be an overkill, but a 12V NiMH @ about 1000mAh battery pack could works, yeah?
easy and fast to charge and relatively safe.

Do you want to have two power systems, one being a battery that you will have to replace at some point?

5

ChrisTenone:
Do you want to have two power systems, one being a battery that you will have to replace at some point?

Yep this is the idea. I can access easily to the lamp, so swapping batteries every 2 years or so won't be a problem.

I will investigate the pneumatic dampers, good idea.
Or maybe a weight suspended to a string with a system of pulleys to demultiplicate the effort, that may work.

the form factor of the lamp will be like a cylinder : a inner semitransparent and light emitting and a outer part opaque (brushed metal?). the inner one will come out under the larger one.

6

Cool - I imagine a 'steam punk' look to the lamp, which is why I'm thinking it should look mechanical.

7

I am a big fan of steampunk, but for this project I was more on the ORDNING from IKEA for the outer cylinder

or something like that if I found better elsewhere (without holes...).

the inside cylinder will have to be lightweight obviously, so Japanese paper probably.