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# transformer 110v to 12 volt ?

Fri 27 Apr, 2012 05:08 pm
I have a 3oo Watt 110V to 12 Volt tranformer for my landscape lighting. My question, if I only connect a 50 watt load, am I still drawing down the full 300 watts, or just the 50 watt load. Probably a simple question, but not sure which is correct.
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Type: Question • Score: 2 • Views: 792 • Replies: 13
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1
Fri 27 Apr, 2012 05:24 pm
@goodwoody55,
The load is what you will draw. So in this case you will be drawing 5o watts. Think if it this way, a 60w light bulb doesn't get brighter if you put in a 20 amp circuit vs a 10 amp circuit.

You also have to allow for load from the wiring. Standard rule of thumb is your load should be 80% of the rating or less. That is assuming you've used the correct wire size for the length and load you are running.
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BillRM

2
Fri 27 Apr, 2012 05:34 pm
@goodwoody55,
At a guess you would be drawing around 60 to 70 watts as small transformers had fairly large losses.

Place your hands on the transformer case and it will be warm from the losses in the windings and the core.

Footnote as you increase the load toward the transformer maximum the percents of the total power loss inside the transformer will go up in a slightly non linear manner
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Ragman

1
Fri 27 Apr, 2012 05:42 pm
@goodwoody55,
What you propose is scenario where you simply are placing a lighter load on a capable step-down transformer. Having a lesser wattage demand could make the transformer run a bit cooler and more efficeintly. If it were the other way around, you'd be heating up the xfmr and creating a problem by tripping the circuit-breaker or fuse..or worse...letting all the smoke escape from inside the xfmr.
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engineer

1
Fri 27 Apr, 2012 10:38 pm
@goodwoody55,
Your transformer is rated for up to 300W. It will use whatever the load is actually drawn, not the max rating.
BillRM

0
Fri 27 Apr, 2012 11:48 pm
@engineer,
Quote:
It will use whatever the load is actually drawn, not the max rating.

Plus a fairly large loss in the windings and in the flux heating the core by generating loop currents in such a small transformer.

2
Sat 28 Apr, 2012 09:16 am
@BillRM,
A large loss? Most transformers have a less than 5% loss.
BillRM

0
Sat 28 Apr, 2012 11:09 am
Not small transformers and anyone who need proof of that fact just place your hands on a small transformer under load.

Large transformers used by the electric companies had less then one percent lost however we are not talking about such.

2
Sat 28 Apr, 2012 11:42 am
@BillRM,
BillRM wrote:

Not small transformers and anyone who need proof of that fact just place your hands on a small transformer under load.

Large transformers used by the electric companies had less then one percent lost however we are not talking about such.

Put your hand on a 1000w transformer at full load then put your hand on a 6ow incandescent light bulb. Which is hotter? Then do the math.
BillRM

1
Sat 28 Apr, 2012 02:24 pm
You do know how heat work I assume in that a bulb who energy need to only heat an ounce or so of materials with a low special heat is not the same as heating up a 20-30 pounds or so metal transformer who materials have high special heat and a must larger surface area.?

BillRM

1
Sat 28 Apr, 2012 02:42 pm
Footnote as a child I used to play with winding my own transformers and also playing with placing the output of one toy train transformer into the output of another and running household electric devices at difference voltage levels.

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1
Sat 28 Apr, 2012 02:58 pm
@BillRM,
Quote:
You do know how heat work I assume in that a bulb who energy need to only heat an ounce or so of materials with a low special heat is not the same as heating up a 20-30 pounds or so metal transformer

You mean that heat acts differently if the black body is of different material? You better contact your local physics department and tell them that.
BillRM

0
Sat 28 Apr, 2012 04:35 pm
Poor baby you do not even know it take different amounts of energy per unit mass to raise different materials a given numbers of degrees!!!!!!!!!!

You know the name black body but you do not understand anything but the name not the concepts.

Good going making a fool of yourself in such a very open manner.

Footnote to others the reason that with the advent of cheap solid state devices that power supplies had gone away from simple 60 hz transformers to switching power supplies is that 60 hz transformers are heavy and have a must greater power lost for any given power output.

Ok parados I am looking forward to you making more of a fool of yourself.

2
Sat 28 Apr, 2012 08:32 pm
@BillRM,
Quote:
Poor baby you do not even know it take different amounts of energy per unit mass to raise different materials a given numbers of degrees!!!!!!!!!!

When did I say that?
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