How do I dim my 12v garden lighting?

Hi all,

First time poster here and I need your help.

I have 3 x 10W MR16 lights installed in my front steps that run off a 140W, 240V transformer producing 12 volts. Due to my own flawed design, these lights shine directly down the down-sloping front path and practically blind you as you walk up the path.

I want to dim these so they are very soft and subtle. 10W globes are the lowest I can find. The dimming does not have to be variable - I need to cut these down by at least 50%. I have installed diffused glass which has a nice effect but does not reduce the brightness. Failing an electrical solution I am thinking of trying heavily tinted glass lenses (if I can have them made).

Thanks for your help,
Jason

Have you wired the Transfomer to a light circuit and is switched from a light sw say near you front or back door or is it just plugged into a GPO (powerpoint)? which i would say you have done if you have wired it to a switch simple enough, if you have wired it to a GPO a little harder but still can be done, in saying all of this providing the tranformer states it can be dimmed most transforners will state if they are dimmable! Have you tried to see if you can get 5 W mr 16 lamps yet?bunnings will not have them you need to try a electrical wholesaler!

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Originally Posted by patty

Have you wired the Transfomer to a light circuit and is switched from a light sw say near you front or back door or is it just plugged into a GPO (powerpoint)? which i would say you have done if you have wired it to a switch simple enough, if you have wired it to a GPO a little harder but still can be done, in saying all of this providing the tranformer states it can be dimmed most transforners will state if they are dimmable! Have you tried to see if you can get 5 W mr 16 lamps yet?bunnings will not have them you need to try a electrical wholesaler!

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The sparky wired it to the lighting panel, which I assume is on the lighting circuit, and ran it to a female 3 pin plug under the house. I connected the transformer to it and ran it to the lights.

I don't know if the tranny is dimmable. It's a standard one from Bunnings - I'll check when I get home tonight. So if the tranny IS dimmable, I put a standard dimmer with my switch (by a sparky), which alters the power going to the transformer, which reduces the output voltage of the transformer, dimming the lights. Is that correct?

What if the transformer is NOT dimmable?

No, I haven't looked for 5W globes - didn't know they existed!

Thanks for replying!
Jason

Their are different types of dimmers, for different types of transformers, the dimmers are either Leading edge or trailing edge dimmers! for Either Electronic or Iron core Transformers you can tell the difference of the transformers by weight electronic is light weight where the iron core are like a small house brick in weight. Have you still got the installation sheet from the transformer it should tell you if they can be dimmed if not look it up on the web.. If it states it cannot be dimmed I would replace the transformer with another type like the ones you use for the Halogen d/lights used in houses they are typically rated at 50watts as you are only using 30 watts of the 140w unit that is currentlyavailable and install it under the house and screw it to a bearer a trany for this is about 10 bucks at a wholesaler!So in the end you will still have a switch to turn them on and off and you willhave a dimmer to control

Just replace your halogen globes with one of the many LED globe alternatives now available. Most of them are way dimmer than their halogen sisters and can be had in a range of colours....they are more expensive but they are cheaper to run and last pretty much forever....

For example http://www.superlight.com.au/cat4.html and http://shop.ata.org.au/cart.php?targ...ategory_id=326

The other alternative is to use a low wattage MR16 globe and a shim between the top of the luminaire and the substrate....try a paddle pop stick....to get the thing pointing down a bit.

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Originally Posted by patty

... the iron core are like a small house brick in weight. Have you still got the installation sheet from the transformer it should tell you if they can be dimmed if not look it up on the web.. If it states it cannot be dimmed I would replace the transformer with another type like the ones you use for the Halogen d/lights

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Oh, it's heavy - must be iron core. It is a dead-standard HPM RGL11 150W one from Bunnings. I haven't looked at the manual but the web says nothing about it being dimmable (nor non-dimmable).

Is there any way I can use it? I've already wired it all up and forked out the cash for it... Then again, a $10 electronic transformer won't bankrupt me...

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Originally Posted by SilentButDeadly

Just replace your halogen globes with one of the many LED globe alternatives now available. Most of them are way dimmer than their halogen sisters and can be had in a range of colours....they are more expensive but they are cheaper to run and last pretty much forever....

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I was under the impression they were quite bright. I'll give them a bash, failing other options. Thanks.

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Originally Posted by SilentButDeadly

The other alternative is to use a low wattage MR16 globe and a shim between the top of the luminaire and the substrate....try a paddle pop stick....to get the thing pointing down a bit.

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Nice! I reckon even a few mm would help... I'll try that too.

Regards
Jason

Just checked my HPM cat it does not say it cannot be dimmed give'm a ring 1300 369 777 to double check!

series resistors would always work.

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Originally Posted by thatirwinfella

series resistors would always work.

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Not a good idea - they waste too much energy. To what value must the current (Amps) be limited? What wattage must the resistor be? If resistors are going to be used, they should be used as a "voltage divider" & not a current limiter - & this method also wastes energy.

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Originally Posted by orange squishy

Hi all,

First time poster here and I need your help.

I have 3 x 10W MR16 lights installed in my front steps that run off a 140W, 240V transformer producing 12 volts. Due to my own flawed design, these lights shine directly down the down-sloping front path and practically blind you as you walk up the path.

I want to dim these so they are very soft and subtle. 10W globes are the lowest I can find. The dimming does not have to be variable - I need to cut these down by at least 50%. I have installed diffused glass which has a nice effect but does not reduce the brightness. Failing an electrical solution I am thinking of trying heavily tinted glass lenses (if I can have them made).

Thanks for your help,
Jason

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My assumptions;
1] your lamps are halogen (incandescent).
2] the 12v output is AC.
3] the transformer is mounted in a "weatherproof" location.
4] the transformer is iron core.

Possible solutions.
1] Re-install the lamps so that you no longer have the problem.
2] a "Leading Edge" electronic dimmer can be used with inductive (wire wound) & resistive loads. DO NOT USE A "TRAILING EDGE" DIMMER. Also bear in mind that these dimmers are electronic & are prone to failure.

3] buy a new transformer. Ideally, it would be a 240v to 9v (I think that 6v is too much of a reduction) step-down transformer, rated at 150VA. The lower output voltage will give a dimmer light without the addition of other components. Also, if this option is used, the transformer must be "enclosed" & earthed.

Most electrical wholesalers can procure transformers although they will charge you appropriately. Just having at look at RS Components online, I have found a transformer that would suit your application. It has two 9v output legs, which can both deliver up to 8 Amps (a total of 16 Amps). It costs $62.50 exc GST. The weblink is below;

http://www.rsaustralia.com/cgi-bin/b...eID=aunetscape

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Originally Posted by elkangorito

Not a good idea - they waste too much energy.

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With a current limiting resistor the power dissipated by the lamps and the resistor is less than the power dissipated by only the lamps but I agree, using a series resistor is an awkward way of doing it.

I would be tempted to use a suitable rectifier diode in series with the secondary on the transformer which will immediately give you half power without dissipating a whole lot of heat. They are cheap and it would be an easy experiment to try before mucking around changing transformers etc.

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Originally Posted by Wood Borer

With a current limiting resistor the power dissipated by the lamps and the resistor is less than the power dissipated by only the lamps but I agree, using a series resistor is an awkward way of doing it.

I would be tempted to use a suitable rectifier diode in series with the secondary on the transformer which will immediately give you half power without dissipating a whole lot of heat. They are cheap and it would be an easy experiment to try before mucking around changing transformers etc.

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Resistors convert electrical energy into heat. If they didn't do this, they wouldn't work. Also, all of the power losses in a circuit are additive. That is, the power consumed by the resistor plus the power consumed by the lamp equals the total power loss, which is more than if the resistor was not in the circuit.

I would not use half wave recification in this case. There are 2 reasons for this;

1] the output voltage will only be 0.45 of the RMS voltage (in this case, 5.4v, a voltage reduction of more than 50%). How bright will the lights be at such a low voltage?

2] the half wave DC pulses on the secondary of a transformer tend to magnetise the core in one direction, which will reduce the VA rating of the transformer (copper losses). If the transformer is running close to full load, applying half wave rectification can cause the transformer to be too small for the load (it'll get hotter).

Reducing the supply voltage from 12v to 9v is a reduction of 25%.

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Originally Posted by patty

Just checked my HPM cat it does not say it cannot be dimmed give'm a ring 1300 369 777 to double check!

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I called HPM - no it cannot be dimmed. The transformer will simply shutdown.

Thanks for the research, elkangorito.

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Originally Posted by elkangorito

My assumptions;
1] your lamps are halogen (incandescent).
2] the 12v output is AC.
3] the transformer is mounted in a "weatherproof" location.
4] the transformer is iron core.

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Yes to all of the above.

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Originally Posted by elkangorito

Possible solutions.
1] Re-install the lamps so that you no longer have the problem.
2] a "Leading Edge" electronic dimmer can be used with inductive (wire wound) & resistive loads. DO NOT USE A "TRAILING EDGE" DIMMER. Also bear in mind that these dimmers are electronic & are prone to failure.
3] buy a new transformer.

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1] They are brick steps that have had the light holes core drilled specifically for the purpose. I may struggle to find a compatible replacement and patching the holes would look terrible. I've invested the cash in the holes and lights so I'd like to exhaust all possibilities of using them first.

2] HPM tell me the tranny is not dimmable.

3] This is looking like my best option. I was thinking of what patty mentioned earlier and how easy it would be to run the cable to a standard household electronic dimmable transformer (I have 40 or so in the roof of my house) and mount it all in a nice sealed box. I have a spare space on my light-switch panel inside that I could install a dimmer in, then I could dim them from inside the house.

Anyone see any problems with this?

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Originally Posted by orange squishy

HPM tell me the tranny is not dimmable.

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I think HPM is saying that the transformer is not dimmable with the use of an electronic dimmer. Maybe there are some electronics in it? If so, it is not just a normal transformer - it is a power supply. Is the output AC or DC?

If you want to "dim" the transformer, you will need a standard "reactive" (not electronic) dimmer unit but good luck trying to find one.

In any case, you will need to replace the transformer to achieve your goal. If you buy an "electronic" transformer, it may be compatible with an electronic dimmer. But since you have to replace "something", I think you now have 2 options;

1] replace the existing tranny with one that has a lower output voltage (as mentioned before - 9v).

2] replace the transformer with a variac (variable autotransformer). They are more expensive than a static transformer. Look up variac on google to see what they can & can't do. I'm always wary of using autotransformers due to safety & load limitations.