# Low Voltage Transformer Puzzle



## Lighting_man (Sep 2, 2007)

No run this on a 105va transformer. The losses through having a transformer of any type connected to primary with no or little secondary draw is minimal. Or of course you could use a 70va Osram mouse transformer. 70va is close enough to a 75w load to not cause any issues.


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## Ecopat (Apr 17, 2008)

Spark said:


> Hi, Hope someone can help? For weird reasons I want to use an MR16 50w downlighter lamp connected to a transformer. Due to circumstances, once in a while I may want to change the bulb to a 75w, but this may be once in a blue moon !
> 
> So I have the choice of 2 transformers to power this lamp, 65va or 105va, of course if I choose the 105va then I can chop and change bulbs as often as I would like to,(as the mini/max load range is 35w-105w) however with the 65va(max power=65w) I cannot connect a 75w: Question: "If I decide just to install the 105va and run a 50w bulb from that, would I be using up unnecessary power from the mains?, as I know the bulb will only demand what it needs, ie., 50w, but would a bigger transformer all be it not loaded to the max, maybe burn more lecy from the mains? Or would it be overall cheaper just to install a 65va transformer?, I understand there would be heat losses from the coils but surely not enough to pump up the bills!
> 
> Thank you anyone?


What are you growing then? :whistling2:


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## MechanicalDVR (Dec 29, 2007)

Ecopat said:


> What are you growing then? :whistling2:


Exactly what hit me when I read this. I guess he has a green thumb.


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## Ecopat (Apr 17, 2008)

Talking of thumbs, that sticks out a mile and a half.


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## randomkiller (Sep 28, 2007)

Ecopat said:


> Talking of thumbs, that sticks out a mile and a half.


 
Huh? Am I getting old?


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## Ecopat (Apr 17, 2008)

randomkiller said:


> Huh? Am I getting old?


By sticks out by a mile and a half, it comes from the saying " It sticks out like a sore thumb" and that thread certainly sticks out like a stoner trying to figure the best way to use lights without giving off too big a heat signature, as most cop choppers use infra-red cameras these days just by flying over residential areas with the cameras on all of the "secret gardens" show up real good.
:whistling2:


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## randomkiller (Sep 28, 2007)

Ecopat said:


> By sticks out by a mile and a half, it comes from the saying " It sticks out like a sore thumb" and that thread certainly sticks out like a stoner trying to figure the best way to use lights without giving off too big a heat signature, as most cop choppers use infra-red cameras these days just by flying over residential areas with the cameras on all of the "secret gardens" show up real good.
> :whistling2:


Thanks, it was just too early I guess, I'm normally quick.
Could also be the painkillers slowing things down.


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## Ecopat (Apr 17, 2008)

You back at work yet, how is the knee doing?


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## randomkiller (Sep 28, 2007)

Ecopat said:


> You back at work yet, how is the knee doing?


 
Oh yeah, I actually went back on Monday. It's tight/stiff but doing good thanks. I had the post op Dr. visit yesterday. Saw the pics from the surgery (inside), what a difference. The meniscus looked like a set of teeth with all the rips and he smoothed them all out. I am taking a anti inflammatory/pain pill a couple times a day, downside is the feeling of acid reflux from the pills.


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## Ecopat (Apr 17, 2008)

I guess it'll take time to heal properly, though maybe not 100%.
I hate the fact that as we get older our bodies take longer to heal and that pain is a lot more painful.
Hope you get sorted soon enough.


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## randomkiller (Sep 28, 2007)

Ecopat said:


> I guess it'll take time to heal properly, though maybe not 100%.
> I hate the fact that as we get older our bodies take longer to heal and that pain is a lot more painful.
> Hope you get sorted soon enough.


 
I do good with pain for the most part but the healing slows way down. It was the swelling getting worse daily that made me go do the surgery.


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## banquo (Mar 4, 2008)

Your transformer should be specified with no load losses, which will be constant, 24 hours a day. Using the 65VA unit with the 75W bulb will increase the load losses, because the windings aren't designed to carry the additional current, and being of smaller x-section and thus higher resistance, will dissipate more power than the larger T/F on the same load.
If the lamp will be on 24h/day, the no load losses aren't important, and the larger transformer should use less power, all other things being equal.
Of course, transformer designers don't necessarily work to the same factors of safety, and a high spec 65VA T/F might be almost as efficient as a close-to-the-bone 105VA.... e.g. I know a world leading power control supplier who uses the same SCR for 40A and 75A ratings, changing only the heat sink...
More info. here.


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## Speedy Petey (Jan 10, 2007)

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