Electronic vs Magnetic 12Vac Lightning Transformers

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Electronic vs Magnetic 12Vac Lightning Transformers

Postby bjtaudio » Sat Feb 09, 2013 5:26 pm

Here is a comparison of electronic transformers vs Magnetic Transformers and Energy Efficiency.

This article only applies to LED lamps than can be powered by 12VAC not specialized 12V DC products. While a bridge rectifier can be added to get 12VDC it is still unregulated, and may not be suitable with some 12V DC lightning products.

If you do a search on the web for advantages of electronic transformers vs magnetic for 12VAC halogen down-lights, you will find comparisons of 50Watts electronic Transformers vs the old heavy and extremely inefficient shell style iron core transformer. The problem with these comparisons, is that it gives everyone the idea that ALL iron core magnetic transformer are inefficient.

So for this reason I have created this new discussion to tell the full story.

Yes , it's 100% correct that the old style 50Watts (60VA) magnetic transformers that used to be widely available to use for powering your 12VAC down lights are inefficient. But did you know there is a new style of magnetic transformer that is smaller, extremely efficient, and extremely reliable. Its the toroidal transformer!!!

The LED driver power supply HYPE...
You may also have heard the HYPE, about how led drivers are far superior to conventional transformers, due to a regulated output voltage and or current, making your LEDS last longer..But did you know while small transformers have poor voltage regulation which can reduce LEDs life, usually due to over voltage for lightly loaded transformers. If you use a large toroidal transformer the voltage regulation is far superior and your LEDs will last the test of time. One single 150va or larger toroidal transformer can run dozens of 12v MR16 LED down light lamps, and this is the amazing advantage, is that you can use ANY wattage lamp and you can even use 50W halogens with LEDS even on the same circuit! This is truly impossible with constant current LED drivers. So you may be thinking how is this an advantage?, because it means you can change your lights to what ever you want, when you want, it doesn't have to be a particularly wattage. If a light fails and you do not have any spare lights of the same wattage you can plug in a halogen and make it do until you can replace it with the correct light when you get to the shop.

Here is a comparison of electronic/ led drivers/ and toroidal transformers.

Idle power used (no load):- Electronic/ LED drivers/ and lightning toroidal transformers have very very low power loss with no load. A well designed 150va to 500va Toroidal transformer may only draw 1~3Watts with no load, where as 150Watts+ worth of electronic transformers may use in most cases a bit more.

Minimum load:- Electronic and LED drivers typically have a minimum load, in the case of constant current LED drivers the number of LED lamps that can be connected is specific and limited. Vs A toroidal transformer has no minimum load, and due to excellent load regulation will not damage LED lamps with over-voltage as it the case with smaller transformers less than 150va.

Reliability:- Electronic and LED drivers are essentially switch mode power supplies and are made of sensitive and complex electronic components and circuits, and are sensitivity to voltage spikes and surges on the mains supply. They are also sensitivity to vibration, heat, and grime dirt, water and are easily damaged. The electronic components also have a limited life span , the typical life span may only be a few years before they have to be replaced, vs A single 150va to 500va Toroidal may last forever as there its a simple device with nothing really to go wrong, it's made up of a steel doughnut core, tough insulation and enameled copper wire.

Cost:- 150Watts worth of Electronic transformers is similar in price to a single toroidal 150VA transformer but LED drivers will cost you more but prices are coming down.

Size and weight:- Electronic transformers and LED drivers are smaller and lighter than magnetic transformers and this is good for manufactures as it saves them in packaging and shipping costs. However in most cases there is little advantage to the end consumer, as the saving in shipping is not passed on to the customer. Also a 150VA+ transformer is quite large and can not be fed through a 90mm down-light hole cut in the ceiling like a 50W transformer can, however the 150VA+ is intended to replace all the smaller units, so it best placed in the ceiling cavity centered about the lights its driving.

The conclusion:- The toroidal transformer is a better choice than using electronic transformers, as they are tough, do not suffer from minimum loads and are far more reliable. If DC 12V power is required a simple low drop out bridge rectifier can be added so most 12V DC LED products can be run off it, no need for an expensive LED driver, this is not always the case however.

For this reason I recommend that everyone avoids buying specialized expensive all in one LED light fittings. Note: if a light fails the entire unit has to be replaced and that may require an electrician. But the marketing people say they are supposed to last 50,000Hours+? but only come with a 2~3 year warranty...will it fail just outside the warranty? YES you can bet on it..and can I get a replacement NO you cannot! " Sorry sir, we do not sell those any more.. If you want your light to match in the same room you have replace all of them AGAIN! and the electrician is required. Hence: Any power saving made is long gone.." you've been warned!"

MR16 LED 12VAC replacement lamps may not be as good as the all in one specialized fittings but they give you the option of swapping with different types and sizes and if you use a large toroidal transformer, you do not have to keep changing the power supply, no electrician needed!

Best of luck with you're next LED replacement project. :)
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby johnbali » Wed Jul 03, 2013 3:31 pm

You've excited me about the ability to use toroidal transformers for both LED and halogen lighting. I'm in the throws of designing lighting for a new open plan home and would like to instal trapeze cable lighting with LED's. I was planning to use LED constant voltage drivers but will now move to the toroidal transformers so I can change over to halogens if I don't light the final LED effect.
One important question. Could i use a 150va toroidal transformer for a 12m trapeze cable run and 8 x 8w LED's? Is there a limit on how many (and the distance) for the LED's if using the toroidal tx?
Some advice on my ideas for trapeze cable lighting would be greatly appreciated. Thanks.
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby bjtaudio » Thu Jul 04, 2013 11:25 pm

With the maximum number of LED's the limits are mainly set by the wattage rating of the transformer. For 150VA, the transformer could be run up to its maximum of 150Watts of lights. In you case 8 x 8 Watt LED's is only 64Watts, so it's fine. With toroidal transformers of 150VA in size or larger, the voltage regulation is very good, and problem of over voltage with small loads is not an issue.

The only other limit is voltage drop in your trapeze cable, in you're case a few amps over a 12meter run is not a problem. For very long runs 25m+, it best to feed the trapeze from the center to keep voltage drop low. To calculate actual voltage drop, you need to know the correctional area of the trapeze cable, and the current.

For best results try to keep voltage drop or the voltage difference between you're first light closest to the transformer and the last light at the far end within 0.5Volt for a 12V system for even light distribution.

You can verify voltage by measuring it with a volt meter at each light. You could interchange halogen with leds or even run both side by side, provided you not exceed the max rating of the transformer of course. Leds are easily damaged by heat so keep the hot halogens well away from any led lights.

Hope this helps.
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby johnbali » Fri Jul 05, 2013 1:48 am

Your reply is outstanding bjtaudio - thanks very much.
Sometimes new terminology and new technology combined can really become quite
confusing. You've managed to communicate in 'laymens' terms and that's a huge help.
I can now tackle this project with optimism, enthuisiasm and some great advice.
Very much appreciated.
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby DCvolts » Fri Jul 05, 2013 1:21 pm

Hi
Thank you for the interesting posting.
I plan to fit some LED lighting. I should like to power it directly from a DC supply.
I understand that there are several operating voltages for LED fittings and was considering dc -dc conversion for different voltage groups of LEDs as my main dc supply is 48v nominal (actual 45-58vdc).
Would you outline the pros and cons of my proposal?
I also understand that some sort of protection circuit may be required to prevent voltage surges, could you please cover this area too.

I should also like to convert existing 150w and 500w flood lights to use LED units on a dc supply. Is there a supplier for suitable components to enable this?
Kind Regards
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby jasonkaler » Fri Jul 19, 2013 11:33 pm

Hi
Thanks for the post, it is exactly what I'm looking for.
I just don't understand how the current will be limited so that the LED's don't burn out.

Has anyone tried this out?

Thanks
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Re: Electronic vs Magnetic 12Vac Lightning Transformers

Postby Jimbo007 » Tue Aug 16, 2016 1:22 pm

I realise that this is an old thread, I would just like to add a little useful information. A toroid is a significantly better option over an electronic power supply as it operates at 50 hz and can be sent over long cable lengths. The electronic supply is high frequency and cannot be sent over long cable runs as the capacitance of the cable comes into play. I had to help a friend years ago who installed 12 volt lights in his driveway and he could only buy an electronic power supply which had to be installed in the house with the low voltage being fed to the lights. The supply ran hot and the lamp filaments barely glowed. The only solution way a bridge rectifier made of high speed diodes and a low ESR capacitor on the output.
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