AC power limiting circuit

[Heeran]

Okay, I have contacted a PTC resettable fuse manufacturer, they issue is, the trip current is twice the hold current, so how would I specify my requirement for this application. The different input voltages will require different PTC fuses, but I need these different fuses to still work for 0 to 9 watts and trip from 10 watts or above. Any suggestions?

 

[davenn]

you wont get a PTC with that sort of accuracy

 

[Arouse1973]

What about a simple light sensor fitted into the light fitting. The change in brightness that a sensor will see is likely to be quite significant between larger wattage standard bulbs. Or maybe a temperature sensor of some kind.
Adam

 

[davenn]

that's good alternative thinking, Adam

 

[BobK]

Except that I think he is trying to enforce use of LED or CFG as opposed to incandescent lamps.

Bob

 

[davenn]

but a higher wattage CFL or LED light is still going to produce a higher light output
that may be detected, would definitely be worth the experiment

 

[Gryd3]

Except that I think he is trying to enforce use of LED or CFG as opposed to incandescent lamps.

Bob

If a small circuit is being constructed to monitor light or heat output, we might as well go so far as to suggest using a small shunt resistor in series with the load. The shunt will drop a voltage based on the current flow and could trigger the circuit to disconnect from power

 

[Arouse1973]

The benefit of a light sensor is it could also be used to stop people leaving the light on in the day when the light in the room is bright enough. saving even more power.
Adam

 

[BobK]

The two lights that can be used is the LED or CFL light bulb long as the 10 watts and bellow because both these options come in much higher wattages.

The idea is not to keep people in the dark, but to enforce use of high efficiency lighting.

Bob

 

[davenn]

yes that's correct, so Adam's and my comments still stand
detect the higher light output from a higher wattage globe

The users would be warned as such, that is a higher wattage globe is used,
they wont get light. It will ensure they obtain the correct globes if they " don't want to be in the dark"

 

[Bluejets]

Why not just remove the ability to change the lamp.

i.e. use a "wired fitting" .

Many different types available such as LED.

 

[BobK]

yes that's correct, so Adam's and my comments still stand
detect the higher light output from a higher wattage globe

The users would be warned as such, that is a higher wattage globe is used,
they wont get light. It will ensure they obtain the correct globes if they " don't want to be in the dark"

How does a light sensor reject a 40W incandescent that puts out less light than a 10W LED?

Sorry, but a light sensor is not the answer.

Bob

 

[davenn]

yeah so true

OK I'm out of ideas

 

[(*steve*)]

My concern is the reason this is being designed, and whether that might render electronics a little moot.

The idea appears to be to limit the wattage of a light fitting to "encourage" efficient lighting. However, the problem is that normal power and normal lighting are very simple to wire up, so removing the electronics is a trivial process.

I agree that an integrated light fitting or even a special plug might work, but if someone wants more power they will easily be able to defeat it.

I'm thinking third world provision of cheap lighting and making it hard for the power to be used for anything else. That's not going to work. Even if you supply load limiting at the entry to the premises, you can't stop people just clipping onto overhead wires (Yes, Ive seen that -- it's endemic in Mumbai and Delhi as two examples).

 

[Arouse1973]

How does a light sensor reject a 40W incandescent that puts out less light than a 10W LED?

Sorrif a standard bulb is fitted.
, but a light sensor is not the answer.

Bob

If the LED light runs from DC which I think most do. Then the 50Hz signal produced by a standard lamp could also be detected and switch off If a standard bulb is fitted.
Adam

 

[Gryd3]

If the LED light runs from DC which I think most do. Then the 50Hz signal produced by a standard lamp could also be detected and switch off If a standard bulb is fitted.
Adam

I think we are overcomplicating things.
Would it be too difficult to hook a comparator up to a shunt resistor and have it trigger a relay? The relay could be a double throw relay, so you have the lamp on the NC contact, and you loop the NO contact back to the coil on the relay. Once the relay is triggered, it holds itself on, which would hold the output off until power was removed.

 

[Heeran]

Hello, I really do appreciate all the assistance and ideas that has been proposed. Would it be possible to have a PTC made as per these specifications.

Eg: 240Vac - input. 10watts trip. Would this PTC be able to operate for zero to bellow 10 watts and trip at ten if we do not take the hold current into consideration. This way I can get a manufacturer to produce PTC according to my inputs and trip currents.

Secondly, a possible low current AC micro circuit breaker.

 

[Bluejets]

#22 Davenn said not accurate enough..... starting to go in circles here.
I don't know of a "micro circuit breaker" but even if there were, lighting will have some degree of inrush at startup which will defeat your proposal.
Even then, people tend to find ways around so-called energy saving devices when it suits them so in my opinion " flogging a dead horse" comes to mind.
Just wire in a 10w led fitting and hope for the best. Latest ones we've been using have terrific light output so I doubt anyone would want to "hack" it.