Voltage flow through a coil

Status
Not open for further replies.

mull982

Senior Member
Does it matter which way voltage/current flows through an AC coil? In other words, with a transformer coil does it matter which way the current flows through the coil as long as it is creating a magnetic field?

I also have another situation where we are hooking up a 120 to 120V constant voltage transformer, and on the primary side of the xfmr there are two coils. I was told when wiring the primary side with 120V to wire the two coils in parallel to allow more capacity on the transformers? Does anyone know why wiring two primary coils in parallel will result in a larger transformer capacity?

Thanks

Mull982
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
mull982 said:
Does it matter which way voltage/current flows through an AC coil? In other words, with a transformer coil does it matter which way the current flows through the coil as long as it is creating a magnetic field?
Not at all.

I also have another situation where we are hooking up a 120 to 120V constant voltage transformer, and on the primary side of the xfmr there are two coils. I was told when wiring the primary side with 120V to wire the two coils in parallel to allow more capacity on the transformers? Does anyone know why wiring two primary coils in parallel will result in a larger transformer capacity?
First, make sure both primary windings are really primary windings, rated to have the same voltage applied. If, by "constant voltage" you mean a regulating device, the second primary winding could be what I believe is called 'tertiary' winding, meant to have a capacitor attached.

If it is indeed a dual-winding primary, the coils can be connected in series for 240v or in parallel for 120v. Using both windings in either way preserves the transformer's capacity, whereas using one would halve it. The same applies to dual-secondary transformers.
 

Smart $

Esteemed Member
Location
Ohio
mull982 said:
Does it matter which way voltage/current flows through an AC coil? In other words, with a transformer coil does it matter which way the current flows through the coil as long as it is creating a magnetic field?
Well it could matter! Reverse phased primary yields reversed phase secondary.

For example, I've experienced a situation where two supposedly identical pieces of 3? equipment had their 1? 480/120V control transformers' primaries wired reverse polarity. Both had control circuits which ended up in the same local control station. Because both control transformers' secondaries had a grounded "common", there was 240V across the two circuits at the LCS.


I also have another situation where we are hooking up a 120 to 120V constant voltage transformer, and on the primary side of the xfmr there are two coils. I was told when wiring the primary side with 120V to wire the two coils in parallel to allow more capacity on the transformers? Does anyone know why wiring two primary coils in parallel will result in a larger transformer capacity?
Sounds like you have a dual voltage transformer. For 240V primary you'd connect the windings in series. For 120V primary, you are connecting the windings in parallel. SOP to achieve rated output...

You also need to be sure you don't wire the parallel primary windings in reverse polarity. The net effect is 0 output and perhaps you'll let out all the smoke :)
 
Last edited:

micromind

Senior Member
When dealing with potential xfmrs and current xfmrs feeding relays or metering (where both inputs are needed) polarity is very important.

With a basic single phase power xfmr, it doesn't matter. H1 can be hot or neutral, X1 can be grounded or not. If connecting 2 or 3 single phase xfmrs in a 3 phase bank, polarity is important.

As far as the two winding question, think of a 2KVA xfmr that has a dual winding on both sides. It is very similar (though not exactly) like 2, 1KVA units in the same enclosure. Either winding can operate in series (high voltage, low current), or parallel (low voltage, high current).

An engineer can explain this a lot better than I can, (please correct me if I'm wrong) but if you connect only one half of the input side, you'll have slightly less than 1/2 of the KVA rating. (This has to do with the winding versus iron ratio). If you connect only one half of the output side, you'll have slightly more than 1/2 of the KVA rating. (This has to do with heat dissipation).
 

drbond24

Senior Member
I'm just here because the terminology in the OP title disturbed me. Voltage does not flow. Current flows. Think of a water line: voltage = pressure, current = flow. Would you ever speak of water pressure flowing? :)
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
coulter said:
True. But not much different than a bunch of engineers talking about "load flows."
Nowadays, we use the word "load" in describing the equipment at the end of the branch circuit. But in our early days, "load" literally meant "current," and "load" was measured in amps. Therefore, load really does flow.

The thing I object to is when a person tries to correct "load flow" to "power flow," with their basis being "load does not flow." My reply is that power does not flow either. At the end of a long trip, a person might ask how many miles it took to get there. But they would not ask how many miles-per-hour it took to get there.
 

coulter

Senior Member
charlie b said:
... But in our early days, "load" literally meant "current," and "load" was measured in amps. ....
I can honestly say those "early days" were before I got started 40 years ago.

But the analogy you used is a good one.

carl
 

coulter

Senior Member
charlie b said:
... Therefore, load really does flow.

The thing I object to is when a person tries to correct "load flow" to "power flow," ....
I haven't ever corrected anyone. But when the phrase "load flow" is used, I get this picture of the cables looking like a snake that just ate a pig - a bunch of motor shaped lumps bumping their way down the cable to the end use.

Kind of makes me smile a bit.

carl
 

rattus

Senior Member
Strictly speaking:

Strictly speaking:

Power does not flow; current does not flow either.

Power is the time rate of energy flow.

Current is the time rate of charge flow.

But, we all knew that didn't we?

Never heard of "load flow", and I am the oldest one around! Maybe I wasn't listening.
 

drbond24

Senior Member
rattus said:
Power does not flow; current does not flow either.

Power is the time rate of energy flow.

Current is the time rate of charge flow.

But, we all knew that didn't we?

Never heard of "load flow", and I am the oldest one around! Maybe I wasn't listening.

Actually, I disagree. An ampere is one coulomb per second, which is the flow of charge. Therefore, current is the measure of the flow of electrical charge.
 

rattus

Senior Member
drbond24 said:
Actually, I disagree. An ampere is one coulomb per second, which is the flow of charge. Therefore, current is the measure of the flow of electrical charge.

As long as we are nit picking:

Electric current is the flow of charge--no units needed.

The coulomb is the unit of measure of charge.

The ampere is the unit of measure of current which is equivalent to one coulomb per second.
 

rattus

Senior Member
drbond24 said:
:grin:

To flow or not to flow, that is the question. Which of your answers do you fell more strongly about? :wink:

Both! They are both correct.

We say and understand "current flow", but strictly speaking it is the charge that flows. You know that.

How about "AC current" or "Alternating Current current"?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
rattus said:
How about "AC current" or "Alternating Current current"?
Sorry, but right now I'm trying to read my VIN number on the LCD display at the ATM machine.*




* Don't ask why my VIN would be on an ATM. Hey, I don't get paid for this, y'know. (Good thing!)
 

drbond24

Senior Member
rattus said:
We say and understand "current flow", but strictly speaking it is the charge that flows. You know that.

I guess what I'm saying is that 'current' and 'charge that flows' are exactly the same thing.

Just for kicks, I looked up 'current' on dictionary.com. One of the definitions is "something that flows, as a stream."
 

mull982

Senior Member
micromind said:
An engineer can explain this a lot better than I can, (please correct me if I'm wrong) but if you connect only one half of the input side, you'll have slightly less than 1/2 of the KVA rating. (This has to do with the winding versus iron ratio). If you connect only one half of the output side, you'll have slightly more than 1/2 of the KVA rating. (This has to do with heat dissipation).

Can anyone explain why this is?
 

rattus

Senior Member
drbond24 said:
I guess what I'm saying is that 'current' and 'charge that flows' are exactly the same thing.

Just for kicks, I looked up 'current' on dictionary.com. One of the definitions is "something that flows, as a stream."

You are right, but substitute "charge flow" for "current"; then you are saying "charge flow flow". That is my nit picking point.
 

bcorbin

Senior Member
Exactly. It's like saying speed moves. Speed doesn't move. Speed is the measure of how fast you are moving.

This was actually one of the first little quizzes I gave my first semester circuits class. We established that strictly speaking, traditional current is measured as the rate of flow of positive charge. This was a real eye-opener to some of the students.
 
Status
Not open for further replies.
Top