Transformer power usage

S

Scott

Guest
I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Thanks!
Scott
 
On Thu, 13 Aug 2009 11:33:19 -0500, Scott <sdswetmore@gnospammail.com>
wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Thanks!
Scott
Click to expand...
An unloaded power transformer uses some excitation current, some of
which is reactive power (out of phase with the line voltage, so isn't
real power) and some amount of real power, due to core and copper
losses. A good, big transformer should have real losses below 1% of
full-load power; a junky wall-wart cauld have a lot more, and run
distinctly warm with no load at all.

If you measure line current, you're seeing the vector sum of the real
and the imaginary (out-of-phase) currents; only the real part is true
"wattage", which creates heat and spins your electric meter.

Google "transformer losses" and "transformer excitation" and "real
imaginary power" for details.

John
 
Scott wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Thanks!
Scott
Yes.
Click to expand...
 
John Larkin wrote:
On Thu, 13 Aug 2009 11:33:19 -0500, Scott <sdswetmore@gnospammail.com
wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Thanks!
Scott

An unloaded power transformer uses some excitation current, some of
which is reactive power (out of phase with the line voltage, so isn't
real power) and some amount of real power, due to core and copper
losses. A good, big transformer should have real losses below 1% of
full-load power; a junky wall-wart cauld have a lot more, and run
distinctly warm with no load at all.

If you measure line current, you're seeing the vector sum of the real
and the imaginary (out-of-phase) currents; only the real part is true
"wattage", which creates heat and spins your electric meter.

Google "transformer losses" and "transformer excitation" and "real
imaginary power" for details.

John

John,
Click to expand...
Thanks for the explanation and terminology for further reading. Indeed
the unloaded transformer was quite warm.
Scott
 
On Thu, 13 Aug 2009 11:33:19 -0500, Scott wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Pay no attention to Phil Allison - sometimes he goes off his meds.
Click to expand...

No, a transformer with no load will draw very little power. With no
load, it's merely an inductor, drawing only magnetizing current.

Of course, with the timer motor running off the secondary, it will
draw whatever power the timer motor uses, plus some losses, which are
usually negligible.

To verify this, just feel the transformer with your hand. If you can
rest your hand on it, then everything is OK.

So don't worry. :)

Cheers!
Rich
 
On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:
Scott wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Yes.
Click to expand...
No. Stop misleading the newbies.

Thanks,
Rich
 
On Thu, 13 Aug 2009 13:33:10 -0500, Scott wrote:
John Larkin wrote:
On Thu, 13 Aug 2009 11:33:19 -0500, Scott <sdswetmore@gnospammail.com
wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

An unloaded power transformer uses some excitation current, some of
which is reactive power (out of phase with the line voltage, so isn't
real power) and some amount of real power, due to core and copper
losses. A good, big transformer should have real losses below 1% of
full-load power; a junky wall-wart cauld have a lot more, and run
distinctly warm with no load at all.

If you measure line current, you're seeing the vector sum of the real
and the imaginary (out-of-phase) currents; only the real part is true
"wattage", which creates heat and spins your electric meter.

Google "transformer losses" and "transformer excitation" and "real
imaginary power" for details.

Thanks for the explanation and terminology for further reading. Indeed
the unloaded transformer was quite warm.
Click to expand...
It depends on what you mean by "quite warm". If you can hold your hand
on it for more than, say, 5 or 10 seconds, then there's nothing to worry
about.

If you could fry an egg on it, you probably have a problem. :)

Hope This Helps!
Rich
 
Phil Allison wrote:
"Scott"

I am curious.

** Weird is more like it.


Does a transformer draw (considerable) power even with no load.

** No.

Am I correct in my thinking that even an unloaded transformer would draw
considerable wattage?


** No.

Now piss off - you stupid TROLL..




.. Phil


Phil,
Click to expand...
It was not my intent to troll. Your answers are appreciated, however
terse.
Pissin' off!
Scott
 
Rich Grise wrote:
On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:

Scott wrote:


I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?


Yes.


No. Stop misleading the newbies.

Thanks,
Rich


Well, it's true in some parts, it's obvious there is power being drained
Click to expand...
while not having any attached device.. There is no such thing as a 100%
power efficient xformer. As you and others can argue the point, it's
just what it is, pointless.

So, yes, the statement is true as far as the poster is concerned.

Going into details of why it happens, isn't what I think
the poster was looking for. Because to be frank about it, I'm sure
the poster does not care as to why, just closure on their assumption.

I don't know what he considers a considerable amount of power, but the
fact that it's using power, makes my statement not false!.

If the poster wants to know the technical details, as to why, i'm
sure you'll be willing to step up to the plate. Just remember, it's hard to
be on top and stay there.

So, if you want to make a mountain out of an ant hill, go for it. I'll
just sit back and be amused.
 
On Thu, 13 Aug 2009 15:09:49 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Rich Grise wrote:
On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:

Scott wrote:


I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?


Yes.


No. Stop misleading the newbies.

Thanks,
Rich


Well, it's true in some parts, it's obvious there is power being drained
while not having any attached device.. There is no such thing as a 100%
power efficient xformer. As you and others can argue the point, it's
just what it is, pointless.

So, yes, the statement is true as far as the poster is concerned.
Click to expand...
---
No, it isn't.

Without knowing what the OP means by 'considerable wattage' your answer
is, at best, irresponsible.
---

Going into details of why it happens, isn't what I think
the poster was looking for. Because to be frank about it, I'm sure
the poster does not care as to why, just closure on their assumption.

I don't know what he considers a considerable amount of power, but the
fact that it's using power, makes my statement not false!.
Click to expand...
---
No, it doesn't.

What makes your statement true or false isn't the fact that the
transformer isn't 100% efficient, it's what the OP considers to be a
considerable amount of power.

Without knowing that (and he didn't specify what he thought
'considerable' was, your answer is meaningless but will, as Rich pointed
out, confuse the newbie.

JF
 
"Scott"

For arguements sake, I would consider "Considerable" to be 50% or more of
the loaded wattage.
Click to expand...

** FYI pal - the un-loaded power loss of a 300VA toroidal mains
transformer is about 3 to 4 watts.

The un-loaded power loss of a typical 300VA E-core type is about 6 to 8
watts.

Bored with trolling yet ??



..... Phil
 
John Fields wrote:
On Thu, 13 Aug 2009 15:09:49 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Rich Grise wrote:
On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:

Scott wrote:


I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?

Yes.

No. Stop misleading the newbies.

Thanks,
Rich


Well, it's true in some parts, it's obvious there is power being drained
while not having any attached device.. There is no such thing as a 100%
power efficient xformer. As you and others can argue the point, it's
just what it is, pointless.

So, yes, the statement is true as far as the poster is concerned.

---
No, it isn't.

Without knowing what the OP means by 'considerable wattage' your answer
is, at best, irresponsible.
---

Going into details of why it happens, isn't what I think
the poster was looking for. Because to be frank about it, I'm sure
the poster does not care as to why, just closure on their assumption.

I don't know what he considers a considerable amount of power, but the
fact that it's using power, makes my statement not false!.

---
No, it doesn't.

What makes your statement true or false isn't the fact that the
transformer isn't 100% efficient, it's what the OP considers to be a
considerable amount of power.

Without knowing that (and he didn't specify what he thought
'considerable' was, your answer is meaningless but will, as Rich pointed
out, confuse the newbie.

JF
Click to expand...
Thank you for the continued response. Actually I am interested in the
'why' as well as a definitive 'yeah' or 'neigh', despite my lack of
details and tentative grasp of electronics. By my simplistic thinking,
tying each end of a wire to AC mains should draw current and use it up
as resistive heat. I believe I am underestimating the function of the
inductor of the transformer's primary.

I am sorry I did not measure the current while it was powered but
unloaded. I will take some measurements this weekend for my own
curiosity. I am fairly certain what I saw was simply high resistive
losses due to the aging steel core.

For arguements sake, I would consider "Considerable" to be 50% or more
of the loaded wattage.

Thanks!
Scott
 
Rich Grise wrote:
On Thu, 13 Aug 2009 13:33:10 -0500, Scott wrote:
John Larkin wrote:
On Thu, 13 Aug 2009 11:33:19 -0500, Scott <sdswetmore@gnospammail.com
wrote:

I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?
An unloaded power transformer uses some excitation current, some of
which is reactive power (out of phase with the line voltage, so isn't
real power) and some amount of real power, due to core and copper
losses. A good, big transformer should have real losses below 1% of
full-load power; a junky wall-wart cauld have a lot more, and run
distinctly warm with no load at all.

If you measure line current, you're seeing the vector sum of the real
and the imaginary (out-of-phase) currents; only the real part is true
"wattage", which creates heat and spins your electric meter.

Google "transformer losses" and "transformer excitation" and "real
imaginary power" for details.

Thanks for the explanation and terminology for further reading. Indeed
the unloaded transformer was quite warm.

It depends on what you mean by "quite warm". If you can hold your hand
on it for more than, say, 5 or 10 seconds, then there's nothing to worry
about.

If you could fry an egg on it, you probably have a problem. :)

Hope This Helps!
Rich

Indeed it does Rich.
Click to expand...

I could maintain contact for 10 to 15 seconds after it had been plugged
in for more than 6 hours unloaded. I imagine the corrosion spots on the
edge of steel laminate core of the transformer may indicate resistive
losses.

Thanks!
Scott
 
Phil Allison wrote:
"Scott"

For arguements sake, I would consider "Considerable" to be 50% or more of
the loaded wattage.


** FYI pal - the un-loaded power loss of a 300VA toroidal mains
transformer is about 3 to 4 watts.

The un-loaded power loss of a typical 300VA E-core type is about 6 to 8
watts.

Bored with trolling yet ??

.... Phil
Click to expand...
Phil,
Thank you for the details. This is the kind of information I was hoping
to find.

Only trolling for info,
Scott
 
Scott wrote:
I could maintain contact for 10 to 15 seconds after it had been plugged
in for more than 6 hours unloaded. I imagine the corrosion spots on the
edge of steel laminate core of the transformer may indicate resistive
losses.
Click to expand...
Resistive losses are losses due to the resistance of the windings (Joule
effect). Losses in the core are due to magnetic hysteresis of the
material and eddy currents induced inside the laminates. The effect of a
surface defect on these losses is probably negligible.

v.
 
John Fields wrote:

On Thu, 13 Aug 2009 15:09:49 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Rich Grise wrote:

On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:


Scott wrote:



I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?


Yes.


No. Stop misleading the newbies.

Thanks,
Rich



Well, it's true in some parts, it's obvious there is power being drained
while not having any attached device.. There is no such thing as a 100%
power efficient xformer. As you and others can argue the point, it's
just what it is, pointless.

So, yes, the statement is true as far as the poster is concerned.


---
No, it isn't.

Without knowing what the OP means by 'considerable wattage' your answer
is, at best, irresponsible.
---


Going into details of why it happens, isn't what I think
the poster was looking for. Because to be frank about it, I'm sure
the poster does not care as to why, just closure on their assumption.

I don't know what he considers a considerable amount of power, but the
fact that it's using power, makes my statement not false!.


---
No, it doesn't.

What makes your statement true or false isn't the fact that the
transformer isn't 100% efficient, it's what the OP considers to be a
considerable amount of power.

Without knowing that (and he didn't specify what he thought
'considerable' was, your answer is meaningless but will, as Rich pointed
out, confuse the newbie.

JF
Oh well,.
Click to expand...

Don't give enough;
Give to much;

What's the difference. Seems that some one can always find
fault.
 
On Fri, 14 Aug 2009 14:15:36 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Fields wrote:

On Thu, 13 Aug 2009 15:09:49 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Rich Grise wrote:

On Thu, 13 Aug 2009 11:49:26 -0400, Jamie wrote:


Scott wrote:



I am curious. Does a transformer draw (considerable) power even with no
load.

I have a cheapo, unregulated 88W 120VAC to 12VAC transformer/timer
(landscape lighting) in which the timer had failed. I also happened to
have a small 120V photocell switch (activates in darkness). When I
removed the timer mechanism, I noted the timer motor was running off of
the 12V side of the transformer, meaning the transformer was always
energized.

With the photocell wired in-line prior to the transformer, there is a
small power draw (<0.25W) during daylight hours, but not what I imagine
the transformer was drawing. Am I correct in my thinking that even an
unloaded transformer would draw considerable wattage?


Yes.


No. Stop misleading the newbies.

Thanks,
Rich



Well, it's true in some parts, it's obvious there is power being drained
while not having any attached device.. There is no such thing as a 100%
power efficient xformer. As you and others can argue the point, it's
just what it is, pointless.

So, yes, the statement is true as far as the poster is concerned.


---
No, it isn't.

Without knowing what the OP means by 'considerable wattage' your answer
is, at best, irresponsible.
---


Going into details of why it happens, isn't what I think
the poster was looking for. Because to be frank about it, I'm sure
the poster does not care as to why, just closure on their assumption.

I don't know what he considers a considerable amount of power, but the
fact that it's using power, makes my statement not false!.


---
No, it doesn't.

What makes your statement true or false isn't the fact that the
transformer isn't 100% efficient, it's what the OP considers to be a
considerable amount of power.

Without knowing that (and he didn't specify what he thought
'considerable' was, your answer is meaningless but will, as Rich pointed
out, confuse the newbie.

JF
Oh well,.

Don't give enough;
Give to much;

What's the difference. Seems that some one can always find
fault.
Click to expand...
---
When there's fault to be found, or for refusal to admit to a fault, of
course.

Why should it be any other way?

JF
 
vic wrote:
Scott wrote:
I could maintain contact for 10 to 15 seconds after it had been
plugged in for more than 6 hours unloaded. I imagine the corrosion
spots on the edge of steel laminate core of the transformer may
indicate resistive losses.

Resistive losses are losses due to the resistance of the windings (Joule
effect). Losses in the core are due to magnetic hysteresis of the
material and eddy currents induced inside the laminates. The effect of a
surface defect on these losses is probably negligible.

v.
Thanks. My bad choice of words. I was thinking the surface corrosion
Click to expand...
may have increased the magnetic losses through increased eddy currents
and produced more heat. I am probably wrong about that, since the
resistive element accounts for the majority of the losses and probably
heat. It just seemed odd to me that something that runs that hot without
a load was wired to be energized all the time, and was hoping its age
contributed to the heat.
Scott
 
On Fri, 14 Aug 2009 13:39:34 -0500, Scott wrote:
vic wrote:
Scott wrote:
I could maintain contact for 10 to 15 seconds after it had been
plugged in for more than 6 hours unloaded. I imagine the corrosion
spots on the edge of steel laminate core of the transformer may
indicate resistive losses.

Resistive losses are losses due to the resistance of the windings (Joule
effect). Losses in the core are due to magnetic hysteresis of the
material and eddy currents induced inside the laminates. The effect of a
surface defect on these losses is probably negligible.

Thanks. My bad choice of words. I was thinking the surface corrosion
may have increased the magnetic losses through increased eddy currents
and produced more heat. I am probably wrong about that, since the
resistive element accounts for the majority of the losses and probably
heat. It just seemed odd to me that something that runs that hot without
a load was wired to be energized all the time, and was hoping its age
contributed to the heat.
Click to expand...
Like I say, if you can put your hand on it, it'll be fine. They design
those things right on the bleeding edge, because if you can save a penny
apiece on a million units, that's $10,000 in your pocket. :)

Cheers!
Rich
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top