# Transformers

Discussion in 'Homework Help' started by Blaise, Jul 9, 2004.

1. ### Blaise Thread Starter New Member

Jun 26, 2004
2
0
When you step down the voltage from say 230v to 12v what happens to the current? Transformers can be up to 99% efficient so presumably power out should nearly equal power in. To simplify calculations say we put 100v @5A into a 10:1 stepdown transformer theoretically the output should be 10v @50A if P=VI. This is clearly not the case. So if both voltage and current is reduced power out does not equal power in and efficiency is greatly reduced. How does it work?

I relise this is a pretty basic question but please just humour me.

2. ### mozikluv AAC Fanatic!

Jan 22, 2004
1,437
1
hi blaise,

here's the humor you were asking,

When you step down the voltage from say 230v to 12v what happens to the current? nothing

Transformers can be up to 99% efficient so presumably power out should nearly equal power in. theoritically yes, in reality no

theoretically the output should be 10v @50A if P=VI. This is clearly not the case.
you are right

So if both voltage and current is reduced power out does not equal power in and efficiency is greatly reduced. How does it work?

the difference is filled up by the core loss, copper wire loss, power factor & coil resistance

Nov 17, 2003
6,960
143
4. ### haditya Senior Member

Jan 19, 2004
220
0
considering no energy losses (which is practically impossible) the current decreases as voltage is stepped up and vice versa. which is why in step down transformers the secondary winding are thicker(so as to reduce resistance) and are thinly insulated. the opposite happens in a step up transformer