Thread: low voltage light dimmers.

It's a good question. My sparky says yes. I have a meter here, I'll hook it up over the weekend and see what happens.

I also watched Carbon Cops on the ABC the other night and they had these low energy fluro globes for downlights. Supposed to use a bit over half the power of a 50w halogen. Not sure of the cost or if they're available for 12v.

Hi Silent,
The trouble with the compact flouros is that you can't dim them and its hard to get funky under the white glare that flouros give off.

The low energy flouros that you mentioned may be different from the compacts but I don't think that they could be dimmed as they don't have a filement.

Any how it will be interesting to so what results the meter gives.
Cheers.

Stay away from the cheaper units as well as the transformers they use to step down the voltage tend to humm... I'm guessing this would mess with the serenity of the moment too.
Cheers
Max

The trouble with the compact flouros is that you can't dim them

Good point. I was thinking of getting a few more dimmers in, as we have 6 banks of 4 downlights in the place but only two have dimmers, so when they're on, they're on and it's 200 watt hours every hour (quick calculation: 3 cents per hour per bank of 4).

So if dimmers are about $20 each and I dim all the lights 50%, then it will take about 1300 hours to pay them off. Now that's a lot of getting funky!

I have been giving this subject a bit of thought lately .... senility perhaps.. but I recon that I usually have the lounge room lights set at below 25% of their brightness... I don't know if that equates to less than 25% of their power consumption.

When you conect your meter up Silent make some incremental adjustments and see what results you get.

If it is the case you may be able to justify their existence if you have them dimmed low, or is it the transformer that chewing the juice?

Questions, questions, questions....

I usually have the lounge room lights set at below 25% of their brightness

Ditto

I don't know if that equates to less than 25% of their power consumption.

I think that the transformer loses a bit of energy in the form of heat. Not sure about the dimmers. My sparky reckons the lights use less power when dimmed (that seems logical) but couldn't say whether it was proportional to the amount of light being emitted.

The meter I have is an old analogue meter and I time the rotor with the stopwatch then extrapolate out to kWh. It's a bit rudimentary but I should be able to spot a difference if there is one.

The biggest hassle is getting up in the ceiling and hooking the lights up to a powerboard so I can insert the meter.

Sorry Silent that does sound like a big hassle...so just think of it as an advancement of science. Increasing our awareness and understanding of global warming issues.

There probably isn't a Nobel prize in this one but you may get a warm fuzzy feeling somewhere. ..Also as you have done a lot of your own wiring I hope that is the only feeling you get crawling around in your ceiling!!!

Cheers

When I finished installing the flue for the fire I said "right, that's the last time I'm getting up there for a while".

Bloody science...

Well it's a compromise for sure. In our recent reno we put compact fluro's in the kitchen where the lights are on a lot and dimmable low voltage lights in the dining room.

Also made a point of buying the top of the line electronic transformer. So hopefully the combo of a good transformer and the dimmed lights helps.

The trouble is the quality of fluro light is not the greatest. The light people we spoke to said that dimmable compact fluro's should be on the market "soon".

I'll be intersted to see your test results too.

i have not done any scientific stuff to prove this but from my observations on my home downlights they do not make much improvement in the power bill.
i think you will find that the heat generated by these lamps and dissipated to ambient atmosphere would account for a lot of the wasted power, compared to the fluoro type lamps.
further, i am sure i have seen dimmable fluoro's somewhere in my travels around the hardware departments
i have found a considerable saving in power bills since converting to fluoro lamps, (not dimmable) difficult to quantify in figures as we have had a lot of variables in the equation over the years, but certainly the bills are now lower.
hope this helps.
joe

Hi There

My father is an electronics engineer and says the answer is yes. He has just replaced all his down lights with 25w globes instead of the 50s ... there were tooo many installed as it was. By doing this and replacing all teh normal globes with CFs he calculates hge has reduced the consumption to 25% of what it was. Of course there are some losses and your lights are probably negligable compared to some other appliances ... every bit helps though!!

If memory serves me right. The power consumption of your light circuits remain the same when you have them dimmed. A dimmer is just a resistive load placed in series with the lamp and as its resistance is increased so is the voltage drop across the dimmer and hence also across the lamp. Less voltage across the lamp equals less brightness but the current consumption is the same in all parts of the circuit...
It's been way too long since I went to bloody trade school

By the way, you can get flouro dimmers but they are a special type, some people have them fitted into the pelmets above curtains etc but I haven't seen anything like this for the compact flouro's

Not an expert but doesn't Ohm's law state that current = volts / resistance, so if resistance increases and volts remains constant, current will decrease?

http://en.wikipedia.org/wiki/Electrical_resistance

But I've just found out that they don't work by adjusting the resistive load, they work by switching off and on:

Solid-state light dimmers work by varying the "duty cycle" (on/off time) of the full AC voltage that is applied to the lights being controlled. For example, if the voltage is applied for only half of each AC cycle, the light bulb will appear to be much less bright than when it get the full AC voltage, because it get's less power to heat the filament. Solid-state dimmers use the brightness knob setting to determine at what point in each voltage cycle to switch the light on and off.

Typical light dimmers are built using thyristors and the exact time when the thyristor is triggered relative to the zero crossings of the AC power is used to determine the power level. When the the thyristor is triggered it keeps conducting until the current passing though it goes to zero (exactly at the next zero crossing if the load is purely resistive, like light bulb). By changing the phase at which you trigger the triac you change the duty cycle and therefore the brightness of the light.