Automatic Light Dimmer On A Timer

[Alex Brown]

I have succsesfully built an automatic timer which slowly turns my lights on over a 2 hour period from dark (off). Then, in the evening they turn off over 2 hours for the night. I am running two blue t5's and 2 daylight t5's and will be soon running a DIY LED strip to add the shimmer effect back onto my reef.

This unit in theory will work with any existing lighting, as long as it has a UK, USA or Euro plug socket on the end of your lights (the AC socket). I havnt tried it with MH, LED or T8 - but it should work just the same.

I was wondering if anyone else has done this, and if anyone might be interested in purchasing such a unit? I am able to make them in bulk, for a price in the region of £50-£70. My unit will dim up to 700w of lighting per dimmer.

Thanks

 

[Schmill]

I presume you are doing this by a gradually switch on / switch off of the tube 1 at a time, or are you actually dimming the tubes?

I didn't think you could dim the tubes, and if you did it wasn't good for them?

 

[zedd]

I'm interested Alex, but I'd need some more info about the unit. Any pics?

Thanks.

 

[keenonfish]

dimming tubes isn't very good for them but is possible. Have you designed your own switching circuit OP or is it some sort of module that you are controlling?

I would like to know how the unit would dim MH lighting though

 

[rabbut]

It will work fine with LED's

It would work OK with Florescent tubes, but you have to essentialy build your own balast/buy in a specialist balast to drive the tube if you want it to be reliable, and you shorten the tubes life in doing the dimming, so... You can get balasts what will dim tubes already, predominatly for the professional sound and lighting industory (Ex. Professional rigger speaking here...) but they are still fairly poor for tube life expectancy. Flo's aren't intended to be dimmed Using a standord balast and fiddeling with the input current will eventually cook the balast and/or the tube, not good...

Many professional dimmer racks now have the facility to dim a Flo on stage, but they are mostly primative "on/off" dimmers. You can get ones that dim a lamp, but they are few and far between, and their use is even more rare...

It would be very difficult to make work on a halide unit. Running the lamp cool will be murder in the lamps innerds, hence the lamp life will be sevearly reduced The issue will be sparking the lamp, and then maintaining a current that is suffice to keep the lamp going, without the lamp warming up to operating temperature too quickly. The same will apply to the switch off. You will have to reduce the current to cool the lamp, but not sufficiently for it to stall out. The ammount of current required for that will vary on the ambient temperature arround the lamp and the individual lamp itself, so the balast would need to be "inteligent" and sence what the lamp was doing from the two contact pins only aswell as actually feeding power to the lamp... Try restricting power to a halide balast, and it will literaly cook itself. Magnetic ones would probibly get hot enough to start a fire I would be very wary about using a dimmer on a halide TBH

All the best
Rabbut

 

[raptorrex]

dimming tubes isn't very good for them but is possible. Have you designed your own switching circuit OP or is it some sort of module that you are controlling?

I would like to know how the unit would dim MH lighting though

for fluorescent and metal halide you need specific dimming, capable ballast units, whatever control units you use. these are expensive, to say the least.

unless your dimmer includes a new ballast for the £50-70, its an expensive way to destroy your current lighting set up!

 

[Gun]

Hmm..yeah, I was hoping I could set up a dimming to moonlight system in my shed. Though, after reading rabbuts advice it now seems to be an expensive option and a potential fire hazard.

It would seem the best option for me now would be 'strip lights switch off, moonlight switches on'. Maybe on a timer.

 

[rabbut]

LED Moon lights are easily dimmable, as are any other form of LED lighting. They take DC power at a low current and usualy low voltage. Simply create your wireing loop of LED's in parallel (so that is one fails, you don't loose the entire loop as you would with series wiring) and connect the loop to an appropriate DC transformer, via a large Capasitor and resistor. When the loop is switched on, the capasitor will gradually charge up, increasing the LED's outputs proportionately to the charge stored on the capasitor, and the Resistor will reduce the current through the circuit, such that when power is switched off the capasitor will discharge as slowly as it charged, through the resistor, assuming you keep the nutral cable connected to the nutral/earth of the supply from the transformer.

You will need to use a slightly larger transformer than the LED's are rated for, as voltage will be "dropped" across the resistor when the circuit is in use, thus less PD is available to the LED's for outputting light.

All the best
Rabbut

 

[Gun]

Cheers for that rabbut..not sure I understand it yet, takes me a few reads lol

My dad has just bought 4 standard 4ft ballasts (think they're called) today..looks like these are going to be used on the first rack. Two fixed or maybe suspended from ceiling, the other two running through the rack. LED's will follow the same path. Manual switching from daylight to moonlight, with maybe an automatic timer fitted at a later date.

Are the fish/plants happy enough living under standard household tube lighting? Is there any tubes you would recomend for the racks?

 

[keenonfish]

LED Moon lights are easily dimmable, as are any other form of LED lighting. They take DC power at a low current and usualy low voltage. Simply create your wireing loop of LED's in parallel (so that is one fails, you don't loose the entire loop as you would with series wiring) and connect the loop to an appropriate DC transformer, via a large Capasitor and resistor. When the loop is switched on, the capasitor will gradually charge up, increasing the LED's outputs proportionately to the charge stored on the capasitor, and the Resistor will reduce the current through the circuit, such that when power is switched off the capasitor will discharge as slowly as it charged, through the resistor, assuming you keep the nutral cable connected to the nutral/earth of the supply from the transformer.

You will need to use a slightly larger transformer than the LED's are rated for, as voltage will be "dropped" across the resistor when the circuit is in use, thus less PD is available to the LED's for outputting light.

All the best
Rabbut

While you have got the right idea it wouldn't work unfortunately! Needs a slightly more complex circuit but quite doable!


did you ever come across reverse-phase dimmers by any chance? Always wanted to know a bit more technical info about these!

 

[rabbut]

The Dimming LED circuit I described does work, as I have made one before some time ago The only way it would not work, is if you diden't factor for the voltage dropped by the resistor after the capasitor The Resistor has to be large to get a noticable dimming effect, so the voltage it drops will also be high, thus more voltage than the LED's are rated for must be supplied to the circuit, to get them to light.

Work out from the LED's specs, how much resistance you have across your LED strip. You know the resistance of the resistor. Divide the resistors resistance, by that of the LED strip, and multiply by the working voltage of the LED's to get the voltage dropped across the resistor. Add this to the opperating voltage of the LED's and you have the voltage you need to supply to the circuit

I have come across twin phase dimmers before, but not revrse phase ones, unless they have another name I do not know As to how those dimmers work from an electronics point of view, I don't know, I only had to rig them (pushing the right wires onto the right connector to get the thing to work)

All the best
Rabbut

EDIT to add:

Having thought about it, I was creating a dimmer that took a few seconds to go to full on when I last used the circuitary. To get a couple of hours dimming rate, you will need need to fiddle with it a bit.... Give me a while to think about it

 

[keenonfish]

The Dimming LED circuit I described does work, as I have made one before some time ago The only way it would not work, is if you diden't factor for the voltage dropped by the resistor after the capasitor The Resistor has to be large to get a noticable dimming effect, so the voltage it drops will also be high, thus more voltage than the LED's are rated for must be supplied to the circuit, to get them to light.

Work out from the LED's specs, how much resistance you have across your LED strip. You know the resistance of the resistor. Divide the resistors resistance, by that of the LED strip, and multiply by the working voltage of the LED's to get the voltage dropped across the resistor. Add this to the opperating voltage of the LED's and you have the voltage you need to supply to the circuit

I have come across twin phase dimmers before, but not revrse phase ones, unless they have another name I do not know As to how those dimmers work from an electronics point of view, I don't know, I only had to rig them (pushing the right wires onto the right connector to get the thing to work)

All the best
Rabbut

EDIT to add:

Having thought about it, I was creating a dimmer that took a few seconds to go to full on when I last used the circuitary. To get a couple of hours dimming rate, you will need need to fiddle with it a bit.... Give me a while to think about it

Hi Rabbut, but I don't understand how you could make a reasonable dimmer that would last more than a few seconds, give equal dimming times for both on / off and drive multiple leds. I am sure you would find the leds would turn on very quickly but will fade slowly. To fade up quickly you would have to put the resistor on the supply side of the capacitor which would then mean a rapid fade would result when power removed. Resistor either side? It would have to be a big capacitor! I would like to be proved wrong though!

Anyway regarding reverse phase it is the opposite of standard phase switching but the lamp is turned on at 0 degrees / volts and turned off somewhere through mains cycle to determine brightness. Normal household dimmers do exactly the opposite (on somewhere in cycle off at 0 phase / volts) which results in noisy filaments (big bulbs only) and shorter bulb life but the technology is way cheaper. Maybe there is another name or perhaps the tech. is taken for granted in pro gear?

 

[raptorrex]

Hi Rabbut, but I don't understand how you could make a reasonable dimmer that would last more than a few seconds, give equal dimming times for both on / off and drive multiple leds. I am sure you would find the leds would turn on very quickly but will fade slowly. To fade up quickly you would have to put the resistor on the supply side of the capacitor which would then mean a rapid fade would result when power removed. Resistor either side? It would have to be a big capacitor! I would like to be proved wrong though!

Anyway regarding reverse phase it is the opposite of standard phase switching but the lamp is turned on at 0 degrees / volts and turned off somewhere through mains cycle to determine brightness. Normal household dimmers do exactly the opposite (on somewhere in cycle off at 0 phase / volts) which results in noisy filaments (big bulbs only) and shorter bulb life but the technology is way cheaper. Maybe there is another name or perhaps the tech. is taken for granted in pro gear?

i must admit, though i am no exert, the above is how i understand things. to dim LED's you need a pwm module, so the led's are at full power when switched on. the unit provides rapid pulsing, so the LEd's spend less time on than off, thus the light emmited is reduced. other methods will work, but not for long.

ps sorry for the delay, the forum keeps giving 505 error when i try to post

 

[Rooster]

LED "dimming" is possible in a couple of ways... PWM, where the LED is turned on and off very quickly... more off than on = "dim" !
Or you can reduce the current, easily acheived using a resistive ladder, or electronic variable resistance.

Would like to know more of the OPs gadget.... please ?

 

[rabbut]

Hi Rabbut, but I don't understand how you could make a reasonable dimmer that would last more than a few seconds, give equal dimming times for both on / off and drive multiple leds. I am sure you would find the leds would turn on very quickly but will fade slowly. To fade up quickly you would have to put the resistor on the supply side of the capacitor which would then mean a rapid fade would result when power removed. Resistor either side? It would have to be a big capacitor! I would like to be proved wrong though!

Well, large capasitor, large resistor in that order worked to fade on over about 10s and about 30 for off. I thought that upscaling the resistance and capasitor size initialy would lead to a longer fade-on time, but quickly realised that the large post-capasitor resistance would lead to a VERY large supply voltage being required, thus making it impracticle in a DC circuit...

I am trying to remember the sizes of the resistor and capasitor I used for it now, but I don't have a circuit diagram or the circuit itself to hand ATM...

I am interested in why it worked, if it wasn't supposed to...

Anyway regarding reverse phase it is the opposite of standard phase switching but the lamp is turned on at 0 degrees / volts and turned off somewhere through mains cycle to determine brightness. Normal household dimmers do exactly the opposite (on somewhere in cycle off at 0 phase / volts) which results in noisy filaments (big bulbs only) and shorter bulb life but the technology is way cheaper. Maybe there is another name or perhaps the tech. is taken for granted in pro gear?

Well, TBH, I don't probe how the gear works, unless it doesn't work A 650W 415V lamp does hum, but very quietly, to a point where you cannot hear it when the room arround you isn't silent. 1000W lamps hum more noticeably, but you would still need to be stood next to the lantern to which the lamp is fitted to hear it. I remember asking a collegue why that was, and the respoce was nothing to do with the dimmers, more the filaments EMF field as a result of the current flowing through the lamp caursing the filament and anything loose and magnetic near the lamp to vibrate, caursing the slight noise. Nothing was mentioned about the fact that the lamp was being switched on and off 50 times a second with phase switching in the dimmers came into the explaination...

In short I do not know how the pro dimmers work, I just know how to use them. If I ever came across one that was bust, then, being twin phase mains, I would likely have a professional electrician in to look at it. Twin phase will kill instantly in almost every case if you come on the reciving end of a jolt of it, so I would not touch the inside of a dimmer unit unless I knew what I was doing in there. Any transformer can in practice store a charge for a while after use, and is one of many potential hasords within the unit that I would be concerned about... Lanterns and the rest of the rig where you are basically wiring a plug, plug socket and extension lead without a fuse (They are in the dimmer unit either as standord fuses or as RCD's) I can cope with more than happily, but gubbins within a dimmer is a bit beyond where I am comfortable to go with electricals.

A healthy person can take a jolt from normal mains, so long as it isn't directly across the heart (jolt revieved from the right hand/arm and grounded through the right leg is relatively safe in most cases, but painful. Been there, done that, wrote the book and collected the T-shirt ), but twin phase mains isn't as forgiving apparently (I haven't been shocked by it yet, so couldn't tell you )...

All the best
Rabbut