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Transformer

K

Kilowatt

Jan 1, 1970
0
Some exit lights are feed with 277 and stepped down to 120.
I always wondered if I could feed one of those transformers with 120 and
hooked it to a 277V lay in light fixture would the insulation on the
transformer windings hold or cook?
Because I valued my job I never tried it but I bet it would have worked.
 
K

Kilowatt

Jan 1, 1970
0
Sorry. But the insulation is very important. The current difference would
be the issue. The transformer would be designed to take the incoming
current it takes to run the exit light. If you put the load on the other
end.....would the windings be able to handle the current?

I take it you are new to engineering. How many exit lights have you wired
up in your engineering job?



| Some exit lights are feed with 277 and stepped down to 120.
| I always wondered if I could feed one of those transformers with 120 and
| hooked it to a 277V lay in light fixture would the insulation on the
| transformer windings hold or cook?

The transformer has to have insulation to withstand at least the 277 volts
that would be applied, wherever that 277 volts might be. Running it in
reverse to step 120 volts up to 277 volts would be applying 277 volts in
the same places 277 would be normally. So the insulation would not be an
issue.

How the transformer is grounded might be an issue.

The capacity of the transformer (rated in VA or kVA) might be, depending
on how much load you have.


| Because I valued my job I never tried it but I bet it would have worked.

I take it this is not an electrical engineering job.
http://ka9wgn.ham.org/ |
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K

Kilowatt

Jan 1, 1970
0
I understand that this is a bad thing to do. I still would like to know if
you could safely "not legally" make a 277 volt light fixture work for home
(120V) use by using one of those transformers.

You can get hundreds of 277V light fixtures from left over remodel jobs. I
am sure there are restrictions that permit you from doing this but I bet it
would work fine.

I AM NOT GOING TO DO THIS. I don't even do electrical work any more. I
don't have a transformer and I don't have a 277V light fixture. I am just
bored and would like to discuss it.
 
M

Mitch Thompson

Jan 1, 1970
0
As someone else said, the biggest issue I see is the capacity in VA of the
transformer. A 3 lamp 4 foot fluorescent fixture would have a load of 100
watts or more. An exit light may have a load of 12 watts or less. In the
interest of efficiency, the exit light probably does not have a 100 VA
transformer.

Mitch Thompson
http://autopanelboard.home.insightbb.com/home.html
Electrical Panel schedule software for use with AutoCAD
 
K

Kilowatt

Jan 1, 1970
0
He is a legend in his own mind.


| Sorry. But the insulation is very important. The current difference would
| be the issue. The transformer would be designed to take the incoming
| current it takes to run the exit light. If you put the load on the other
| end.....would the windings be able to handle the current?
|
| I take it you are new to engineering. How many exit lights have you wired
| up in your engineering job?

Of course the insulation is very important. What makes you think that I
ever said it was not. I said it would not be the *ISSUE*. The reason is
because merely running the transformer backwards puts the same voltage on
each side that it expects.

The transformer designed for 277 volts on the primary and 120 volts on the
secondary will have an insulation rating designed to handle each voltage
in the respective places, as well as whatever maximum difference will exist
anywhere in the winding or wiring terminal. Energizing the primary with
277 volts puts 277 volts where 277 volts is expected. Then 120 volts is
induced where 120 volts is expected. Reversing it, you are putting 120
volts where 120 volts is expected, and 277 volts is induced where 277 volts
is expected. As long as it is wired in reverse CORRECTLY, the insulation
it has as designed will protect it in reverse.

If you were to energize the 120 volt side with 277 volts, then you have a
problem. That will induce 640 volts on the 277 volt side, if it does not
saturate the core first, and risk overvoltage on the insulation, if it
doesn't burn out due to overcurrent first.

Since you are talking about stepping 120 volts up to 277, if you were to
get it backwards, you could end up stepping 120 volts down to 52 volts.
You'd get 18.75% of the wattage from 120 volt light bulbs that way.

Since both 120 volt and 277 volt circuits are typically configured with one
hot wire and one grounded (neutral) wire, such a transformer may have the
chassis grounded to the wire it expects is grounded. Back when there was
not a separate ground wire, this was often done. Hopefully you won't have
that unsafe situation.

The transformer _may_ be an autotransformer, meaning that the low voltage
and high voltage share the same winding, and the circuits are not isolated.
Since both 120 volt and 277 volt circuits are typically configured with one
hot wire and one grounded (neutral) wire, this would not be a problem. But
you may have only one neutral wire coming out for both sides. be sure your
wiring is correctly reversed and correctly grounded.

Electricity is a hobby for me, not my job. So this means I probably know
more about this than half the BSEE graduates out there (who mostly did not
study power systems). The true power engineers who fully understand their
field (not something a mere BSEE can always produce) are the ones to get
real answers from.




| |>
|> | Some exit lights are feed with 277 and stepped down to 120.
|> | I always wondered if I could feed one of those transformers with 120 and
|> | hooked it to a 277V lay in light fixture would the insulation on the
|> | transformer windings hold or cook?
|>
|> The transformer has to have insulation to withstand at least the 277 volts
|> that would be applied, wherever that 277 volts might be. Running it in
|> reverse to step 120 volts up to 277 volts would be applying 277 volts in
|> the same places 277 would be normally. So the insulation would not be an
|> issue.
|>
|> How the transformer is grounded might be an issue.
|>
|> The capacity of the transformer (rated in VA or kVA) might be, depending
|> on how much load you have.
|>
|>
|> | Because I valued my job I never tried it but I bet it would have worked.
|>
|> I take it this is not an electrical engineering job.
|>
|> --
|> -------------------------------------------------------------------------
-
| ---
|> | Phil Howard KA9WGN | http://linuxhomepage.com/
| http://ham.org/ |
|> | (first name) at ipal.net | http://phil.ipal.org/
| http://ka9wgn.ham.org/ |
|> -------------------------------------------------------------------------
-
| ---
|
|
http://ka9wgn.ham.org/ |
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---
 
R

Ross Mac

Jan 1, 1970
0
Kilowatt said:
Some exit lights are feed with 277 and stepped down to 120.
I always wondered if I could feed one of those transformers with 120 and
hooked it to a 277V lay in light fixture would the insulation on the
transformer windings hold or cook?
Because I valued my job I never tried it but I bet it would have worked.
Since the current and voltage are inversely proportional, as long as you
don't draw more than the original rated current, when used in reverse this
should work. Grounding may be another issue. And of course, code. .....Ross
:>)
 
D

DarkMatter

Jan 1, 1970
0
Since the current and voltage are inversely proportional, as long as you
don't draw more than the original rated current, when used in reverse this
should work. Grounding may be another issue. And of course, code. .....Ross
:>)
Another retarded response by the RossTard that did NOT address the
question.

The fact is that the insulation on mag wire is in the area of 1500
volts, and will not break down. Also, the rating is for Volt Amps,
not merely current. That is for "heavy nyleeze". High temp wire has
much better ratings. So it would depend on how the transformer was
constructed.

As long as the rating of the transformer is not exceeded, it should
be able to transform in either direction up to said specified rating.

Why would it not? A 94% efficient transformer at 200 VA being used
as a step up OR as a step down should exhibit the same behavior in
either direction at any given consumption rate that falls inside its
rating.

As far as using it in a structural power feed installation, I would
say that the transformer can only be used as it is designed in that
case. Which would mean NO, but that wasn't the question.
 
R

Ross Mac

Jan 1, 1970
0
DarkMatter said:
Another retarded response by the RossTard that did NOT address the
question.

The fact is that the insulation on mag wire is in the area of 1500
volts, and will not break down. Also, the rating is for Volt Amps,
not merely current. That is for "heavy nyleeze". High temp wire has
much better ratings. So it would depend on how the transformer was
constructed.

As long as the rating of the transformer is not exceeded, it should
be able to transform in either direction up to said specified rating.

Why would it not? A 94% efficient transformer at 200 VA being used
as a step up OR as a step down should exhibit the same behavior in
either direction at any given consumption rate that falls inside its
rating.

As far as using it in a structural power feed installation, I would
say that the transformer can only be used as it is designed in that
case. Which would mean NO, but that wasn't the question.

Read the reply....I said it "should work" but also said it probably would
not be code...You said the same thing and embelished it....what else is new
here....get life punk.....
 
D

Don Kelly

Jan 1, 1970
0
Kilowatt said:
He is a legend in his own mind.
---------------
Actually Phil is right on target. In theory the transformer doesn't care
which side is the supply. In some cases where corners are cut to save cost,
there may be a small difference in practice but the transformer will work
quite happily.
--
Don Kelly
[email protected]
remove the urine to answer
|> -------------------------------------------------------------------------
|> -------------------------------------------------------------------------
 
B

bushbadee

Jan 1, 1970
0
Your correct but there will be a little less (proportionetly) magnitizing
current when the coil closest to the core is the one energized.


Don Kelly said:
Kilowatt said:
He is a legend in his own mind.
---------------
Actually Phil is right on target. In theory the transformer doesn't care
which side is the supply. In some cases where corners are cut to save cost,
there may be a small difference in practice but the transformer will work
quite happily.
--
Don Kelly
[email protected]
remove the urine to answer
|> -------------------------------------------------------------------------|> -------------------------------------------------------------------------
 
B

bushbadee

Jan 1, 1970
0
We are each experianced with different types of transformers.


Most of my transformers seldom got to a full killowat, except in a couple
high powered converters.
Most of my transformers are sitting out there in space rather than on store
room shelves or on power poles/
I also have done quite a few magamps, which if properly applied can be
useful in todays circuitry.
I even have some of them in space.
I made use of their open circuit volt second accumulation ability to
extremely reliably control voltage ouput of converters.
They can be quite small at high frequencies, wound on 1/8 mil cores.
The others that I designed include a batch of current measuring transformers
for short circuit shutdown.
By detecting peak currents with them, you can make the output of a converter
or other power supply notch way back during over load. The peak current
remains constant but the pulse width contracts to reduce the output
voltage, while the peak current allowed remains the same.



| Your correct but there will be a little less (proportionetly) magnitizing
| current when the coil closest to the core is the one energized.

Usually, the lower voltage coil is the one closer to the core. The reasons
for that include less wire length (resistance) for the winding that has the
higher current. I suppose, also, that higher voltage is easier to deal with
getting connected if it is on the outer coil. The typical distribution
transformer for utility service is step down, and all that I have ever seen
(on the inside) have the high voltage on the outer coil.
http://ka9wgn.ham.org/ |
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D

Don Kelly

Jan 1, 1970
0
| Your correct but there will be a little less (proportionetly) magnitizing
| current when the coil closest to the core is the one energized.

Usually, the lower voltage coil is the one closer to the core. The reasons
for that include less wire length (resistance) for the winding that has the
higher current. I suppose, also, that higher voltage is easier to deal with
getting connected if it is on the outer coil. The typical distribution
transformer for utility service is step down, and all that I have ever seen
(on the inside) have the high voltage on the outer coil.
 
B

bushbadee

Jan 1, 1970
0
When I designed hv torroids (1500 volts) on small cores we also sector wound
them for the same reason.
They were used for traveling wave tube power supplies.


 
D

Don Kelly

Jan 1, 1970
0
Unfortunately, when I mentioned EHV transformers, the LV winding would likly
be in the 13-200KV range and the high voltage winding in excess of 200KV
with power ratings up to the GW level.
Different animal and subject to considerable overvoltages due to switching
surges and lightning.
Same concept though.
--
Don Kelly
[email protected]
remove the urine to answer

bushbadee said:
When I designed hv torroids (1500 volts) on small cores we also sector wound
them for the same reason.
They were used for traveling wave tube power supplies.


 
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