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Old 02-07-2011, 12:51 PM   #1
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Electrical transformer box


what does an electrical transformer box do

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Old 02-07-2011, 01:07 PM   #2
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Changes the voltage. Most common would be to step down the voltage.

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Old 02-07-2011, 01:13 PM   #3
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A transfromer, through the translation of electro-magnetism, converts from one voltage and current level to a new voltage and current level. it can step voltage up and current down, or step voltage down and current up. For example: 120vac @ 0.08 amp = 24 vac @ 0.4 amp output. there is no (physical) electrical connection between the input (primary windings/wires) side and the output (secondary windings/wires) side. they are usually 85% efficient or so. the box houses the transformer.
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Old 02-07-2011, 04:57 PM   #4
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Electrical transformer box


In most cases the box is just a cabinet for the transformer. In some cases the box may be made of or lined with a metal that breaks up or reduces electromagnetic fields around the transformer, fields that may cause radio interference or may demagnetize credit cards and other similar objects.

A transformer on a utility pole is far enough away (high enough up) that it will almost never demagnetize a credit card or stop a heart pacemaker of someone walking past.
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Last edited by AllanJ; 02-08-2011 at 06:56 AM.
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Old 02-07-2011, 09:36 PM   #5
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New transformers are a bit more efficient, especially electronic transformers.

I wouldnt say they change current....they change voltage or phases, and provide a useable, fixed maximum current to the new voltage.
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Old 02-07-2011, 10:30 PM   #6
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I like allans answer. He is the only one that actually addressed the question as it is written. Now, if the OP wanted to know what a transformer does, then the rest of you win the cookie.
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Old 02-08-2011, 09:55 PM   #7
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Originally Posted by LyonsElecSupply View Post
I wouldnt say they change current....they change voltage or phases, and provide a useable, fixed maximum current to the new voltage.
The ratio of currents in the primary and secondary windings of a transformer is always the inverse of the ratio of voltages (which is the same as the turns ratio).

You can prove this to yourself:

Take an imaginary, perfect 240V:120V transformer and connect an imaginary 1000W load.

What's the current on the 120V side of this circuit? 1000W/120V = 8.3A.

What's the current on the 240V side of this circuit? 1000W/240V = 4.17A.
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Old 02-08-2011, 11:27 PM   #8
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Electrical transformer box


Lyon was correct in his statement. The transformer does not change current. It changes voltage. Of course, the current capacity is affected but the transformer does not change the current.
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Old 02-08-2011, 11:28 PM   #9
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but the transformer does not "change" current; It changes voltage.

Current changes because voltage changes and Volt Amps stays the same.

AC currents introduce Volt Amps.

Transformers are based on capacity by Volt Amperes.
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Old 02-08-2011, 11:36 PM   #10
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That's like saying a brake pedal doesn't stop a car, but the brake pads do.

Unless it's a Toyota!

Last edited by jlmran; 02-09-2011 at 07:13 AM.
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Old 02-09-2011, 12:06 AM   #11
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Quote:
Originally Posted by LyonsElecSupply View Post

Current changes because voltage changes and Volt Amps stays the same.
The only reason current changes is because the load changes requiring a different amount of current.

The current capacity or rating, as you said previously, is simply the max current available (without damage to the x-former anyway)
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Old 02-09-2011, 02:44 AM   #12
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Originally Posted by nap View Post
Lyon was correct in his statement. The transformer does not change current. It changes voltage. Of course, the current capacity is affected but the transformer does not change the current.
OK, you got me - my statement was not technically correct. But you're not right either. In reality, the primary CURRENT determines the secondary VOLTAGE, or so say the laws of induction. You see, it's the instantaneous rate of change of primary current that determines the rate of change of magnetic flux in the core, which is what determines the EMF on the secondary winding (and the primary, for that matter). So the first derivative of primary current determines secondary voltage. Of course, these equations can be simplified greatly if you assume an AC circuit in steady state operation. The result is the "transformer equation": Np/Ns=Is/Ip=Vp/Vs where N is number of turns, I is current, and V is voltage for primary and secondary windings as indicated by the subscript.

No matter what route you take starting with Faraday's law, you end up with a set of equations where both the voltage ratio AND the current ratio are dictated by the turns ratio, and are ALWAYS the inverse of one another. To say that a transformer changes voltage and not current is plainly incorrect, and can be proven false with an ammeter and 10 minutes of your time if you don't believe in Faraday's law (don't forget to account for the leakage inductance of your non-ideal transformer).

You may be confused because you are thinking that current in a constant-voltage system is a purely dependent variable controlled by the load resistance. That is both true and irrelevant. The ratio of primary to secondary current in the transformer will always be equal to the inverse of the turns ratio, regardless of whether the power source is constant-voltage or constant-current, or what the load characteristics are.

If you still think transformers change "only" voltage and not current, then try to come up with an example (theoretical or real-life) where the primary to secondary current ratio is NOT equal to the inverse of the voltage ratio (taking into consideration leakage inductance if it's a real-life transformer).
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Old 02-09-2011, 06:44 PM   #13
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Quote:
=mpoulton;587468]OK, you got me - my statement was not technically correct. But you're not right either. In reality, the primary CURRENT determines the secondary VOLTAGE, or so say the laws of induction
Really? then why does a transformer that is not connected to a load read 0 amps of secondary current no matter what the input voltage is? Yet (as an example using 2X1 ratio winding) a 480 volt input will still read 240 volts output? Then, if I increase the input to 960vac, I will have 480vac output yet there is still no secondary current.


and even more amazing is; when I load the transformer and draw some arbitrary current like 20 amps, the voltages remain the same. Then, when I increase the load to 40 amps, the voltage still remains the same.

So, explain to me where that primary current has altered, controlled, determined, whatever term you want to use, the secondary voltage. I seem to be missing it.

Quote:
No matter what route you take starting with Faraday's law, you end up with a set of equations where both the voltage ratio AND the current ratio are dictated by the turns ratio, and are ALWAYS the inverse of one another.
You are not transforming the current. You are transforming (for lack of a better term) the current capacity.

so, what determines secondary voltage is primary voltage and the windings ratio.

what determines secondary current is the secondary voltage and the load applied. A load will draw whatever it needs until the capacity of the transformer is exceeded. Then we have meltdown.
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Old 02-09-2011, 07:04 PM   #14
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Nap has spoken with great wisdom. Measure your responses with care before submitting.

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