# how does a transformer work?

by david90
Tags: transformer, work
 P: 303 how does a transformer work? Transformers could make 9v from a battery into say 250v but isn't that getting something for nothing? what about conconservation of energy? Does a capacitor with 9v potential discharge energy faster than a 9v battery? Can capacitors be replace with transformers since transformers can also output a high voltage from a low voltage source?
Mentor
P: 7,273
 Originally posted by david90 how does a transformer work?
A transformer relies on properties of Electo Magnetism. Essentially a changing EM field produces a current. So a AC current is applied to the primary windings, this current produces a changing EM field, which induces a current in the secondary windings. The Voltage and current produced in the secondary is determined by the ratio of windings between the primary and secondary coils.
 Transformers could make 9v from a battery into say 250v but isn't that getting something for nothing? what about conservation of energy?
No, transformers require AC, they do not work as a transformer when a DC voltage is applied. When AC is applied the ratio of Current to voltage remains the same. So a Transformer which steps up voltage, steps down current. Likewise a Voltage step down transformer steps up current. The only change in power out is losses due to the fact that the materials are real.

 Does a capacitor with 9v potential discharge energy faster than a 9v battery? Can capacitors be replace with transformers since transformers can also output a high voltage from a low voltage source?
The discharge rate of a capacitor depends on the load just as the current from a battery does, it is not an easy thing to compare.
Capacitors and transformers are complementary electronics components they each perform unique tasks and definitely cannot be exchanged.
 P: 5 the voltage is increased or decreased, depending on the number turns in the secondary coil. but Power remains constant .... so energy conserved...
P: 5

## how does a transformer work?

power(watt) = voltage(V) x current(A)
(P=VI)

the power input = power output
in a transformer

so V and I change themselves keeping the power P constant

& since Energy = Power x time

Energy is conserved
 P: 303 if I attach a 9v bat to a transformer that converts it to 1000v, would it shock me if I touch the transformer terminals? One time I connect a 9v to the output end of a transformer and touched the two prongs that go into the wall socket and it shocked me. why?
Mentor
P: 7,273
 Originally posted by david90 if I attach a 9v bat to a transformer that converts it to 1000v, would it shock me if I touch the transformer terminals?
Read my first post, no transformer will convert 9VDC to anything.
 One time I connect a 9v to the output end of a transformer and touched the two prongs that go into the wall socket and it shocked me. why?
It is really hard to say. Since I was not there to see what you were doing, likely it would have shocked you with or with out the battery.
 P: 303 Will turning the current to a solenoid or coil on and off rapidly shock u if u touch the circuit? If so why?
 P: 65 Because it changes the potential over time. Actually placing a battery would cause a change on the other side, if the battery were to run down, depending on the resistance of the circuit. It might be too small to measure. A constant VA power supply, would not.
Mentor
P: 21,886
 Originally posted by david90 Will turning the current to a solenoid or coil on and off rapidly shock u if u touch the circuit? If so why?
Touching any energized circuit could shock you. These are not experiments you should be performing unless you are competing for a Darwin Award.
HW Helper
P: 2,327
 Originally posted by david90 Will turning the current to a solenoid or coil on and off rapidly shock u if u touch the circuit? If so why?
Of course it could. You didn't specify the amount of current or the threshhold of electrification that qualifies as "shock." If you've got current, then you can get shocked with or without the solenoid.
 P: 7 A transformer is two inductors a certain distance apart, but not touching. An insulated Iron core is put through both inductors, and is used to carry the magnetic field. Like it has been said, they only work with AC current. If you have 10,000,000 Volts at 1 Amp, and step it down to 110 Volts, you get about 90,000 Amps. It takes heavy gauge wire to move a lot of amps, so high voltage is used instead so that smaller wire can be used. Remember Power(watts)=Volts*Amps As for the Capacitor question, if you have a Cap charged to 9V, and you wanted to discharge it, it would discharge at a rate proportional to the resistance in the discharge circuit. After about 5 time constants, the cap would be fully discharged. If you have a 1microFarad Cap in series with a 1kOhm resistor, the time constant would be 1E-6*1E3=1millisecond. It would therefore take 5ms to fully discharge the cap.
P: 5,611
 Originally posted by david90 Will turning the current to a solenoid or coil on and off rapidly shock u if u touch the circuit? If so why?
If you imput pulsed DC to the primary of a transformer you will get pulsed DC out of the secondary. This could give you a painful shock. From my own experimentation the shocks start to be painful around 20-25 volts if you hold one or both of the terminals loosly. Gripping them tightly may only cause a tingle, but if there is enough of a gap for a spark to jump it hurts.

If you got a shock from imputting non-pulsed DC into a transformer it came either from the initial change in the magnetic field, or the change that occured from breaking the circuit. The magnetic field has to be changing to induce current in the secondary. Steady DC, once it has come up to full strength, will not produce current or voltage in the secondary. There will, however, be a surge when you first close the circuit, and then another when you open it i.e. when the magnetic field is in a state of change. Repeatedly opening and closing the circuit to the primary with DC will, indeed, produce eqivalently repeated voltage and current in the secondary. With a nine volt imput your transformer would only have to do a little more than double the voltage for it to hurt.
P: 905
 Originally posted by david90 how does a transformer work? Transformers could make 9v from a battery into say 250v but isn't that getting something for nothing? what about conconservation of energy? Does a capacitor with 9v potential discharge energy faster than a 9v battery? Can capacitors be replace with transformers since transformers can also output a high voltage from a low voltage source?
As stated by many responders, you cannot transform a low DC voltage to high unless you make it AC first. One way this is done is by a multivibrator. (Look up info with Google.) These are used in electronic flashes. A low voltage, typically 3 or 6 volts, is "transformed" by first going to AC of a usually audible frequency (that high-pitched noise you hear as the flash is charging), rectified and used to charge up a capacitor to around 300 volts. When the flash is triggered, the capacitor is discharged into the flash tube.
P: 5,611
 Originally posted by krab As stated by many responders, you cannot transform a low DC voltage to high unless you make it AC first.
The transformer, per se, is designed to run on AC.

You don't, however, need to actually convert the DC to AC to transform the voltage. What is necessary is to keep the strength of the DC always varying. DC from chemical cells was being converted from low to high voltages (long before anyone knew how to generate AC) by means of induction coils which pulsed the DC by means of vibrating switches that turned the current off and on several times a second. Here is a link:

Induction Coils