What is it that causes electric current to drop after a step up ?

In summary, the current in the wire with a stepped up voltage in the transformer with more coils is lower due to the principle of impedance and conservation of energy. The transformer is self-regulating through Ampere's Law, balancing the amp-turns between the primary and secondary. The primary current is affected by the secondary load, which in turn affects the output voltage and apparent load seen by the primary supply.
  • #1
KingCrimson
43
1
what is that causes the current in the wire that has a stepped up voltage * in the transformer , the wire with more coils * to have a lower current ?
 
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  • #2
Are you talking about a transformer?
 
  • #3
SteamKing said:
Are you talking about a transformer?

yes , after stepping up the voltage
 
  • #4
KingCrimson said:
what is that causes the current in the wire that has a stepped up voltage * in the transformer , the wire with more coils * to have a lower current ?
Impedance. Or equivalently the conservation of energy.
 
  • #5
and to elaborate on what dalespam said

or equivalently the conservation of energy.

power out = power in ( minus a some losses in the transformer )

Idealy, so if the power in on the primary side is 200V @ 1 Amp = 200W ---- power out on the secondary cannot be more that 200W and as stated it will be a little less.
So if you are stepping up from 200V to 400V ( ie double the voltage) you are going to halve the available current
so idealy, you will have 400V @ 0.5A = 200W
in the real world, you will have a little less than 0.5A

cheers
Dave
 
  • #6
davenn said:
and to elaborate on what dalespam said



power out = power in ( minus a some losses in the transformer )

Idealy, so if the power in on the primary side is 200V @ 1 Amp = 200W ---- power out on the secondary cannot be more that 200W and as stated it will be a little less.
So if you are stepping up from 200V to 400V ( ie double the voltage) you are going to halve the available current
so idealy, you will have 400V @ 0.5A = 200W
in the real world, you will have a little less than 0.5A

cheers
Dave
yea i totally understand , but i mean , physics works in order to conserve energy , so there must be some mechanism that does its job such that power is always conserved , what is this mechanism exactly , impedance ?
 
  • #7
Ampere's Law, AL. To establish core flux, magnetizing current exists in the primary. The primary is powered by a CVS (constant voltage source). Flux is determined by voltage, frequency, core area, and number of primary turns Np. Open circuited secondary current Is = 0, primary current Ip = exciting current (magnetizing current plus hysteresis/eddy current loss).

When loaded on secondary, Is becomes non-zero and generates a flux since current in a winding has a flux. This flux, per LL (law of Lenz) is of opposite polarity to the original. The core flux drops due to partial cancellation. The primary unloaded had a counter-emf nearly equal to source emf, the difference appearing across the primary winding impedance. Loaded, the counter-emf drops, so that the primary winding impedance has a voltage equal to the source emf minus a reduced cemf, resulting in larger primary current Ip. This Ip has a field and brings the flux back close to its original value so that secondary voltage is almost equal to the unloaded value.

Ampere's law AL, states that balance is achieved when the amp-turns of the primary balance that of the secondary, i.e. NpIp = NsIs. The transformer is self regulating, errors incurred since windings have resistance and leakage inductance. So the flux and voltages do not quite reach their original unloaded value, but come within a couple percent.

Claude
 
  • #8
KingCrimson said:
what is that causes the current in the wire that has a stepped up voltage * in the transformer , the wire with more coils * to have a lower current ?

I suggest that you are putting things the wrong way round. The output voltage of a step up transformer is higher than the input. The current that flows in the secondary is determined by the value of the secondary Load. So this consequential current is what counts in working out the current that will flow in the primary by affecting the emf that is caused in the primary and, hence, the apparent load that the supply sees.

The chain of causes and effects is:
Input volts - [turns ratio] - output volts - [ load] - secondary current - [turns ratio] - primary current
 

FAQ: What is it that causes electric current to drop after a step up ?

1. What is electric current and how does it work?

Electric current is the flow of electric charge through a material, such as a wire. It is caused by the movement of electrons, which are negatively charged particles. When a voltage or potential difference is applied to a circuit, it creates an electric field that pushes the electrons through the material, resulting in current flow.

2. What is a step-up transformer and how does it affect electric current?

A step-up transformer is a type of electrical device that increases the voltage of an alternating current (AC) electricity supply. This is achieved by using two coils of wire, called the primary and secondary coils, that are wound around a shared iron core. When an AC current flows through the primary coil, it creates a magnetic field that induces a higher voltage in the secondary coil, resulting in a step-up in voltage and a decrease in current.

3. Why does electric current drop after a step-up?

The drop in electric current after a step-up is due to the conservation of energy law. In a step-up transformer, the increase in voltage is accompanied by a decrease in current, as the total power output must stay the same. This is because the power input and output of a transformer are equal, neglecting any losses due to resistance.

4. Are there any factors that can affect the drop in electric current after a step-up?

Yes, there are several factors that can affect the drop in electric current after a step-up. These include the efficiency of the transformer, the quality of the materials used, and the amount of resistance in the circuit. Any losses or inefficiencies in the transformer or circuit can result in a larger drop in electric current than expected.

5. Can the drop in electric current after a step-up be reversed?

No, the drop in electric current after a step-up cannot be reversed. This is because it is a natural consequence of the conservation of energy law. However, the voltage and current can be changed back to their original values through a step-down transformer, which decreases the voltage and increases the current in a similar manner to a step-up transformer.

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