How much excess power do transformers draw?

Question

Hello everyone

My last question may be a little misleading and I couldn't respond to my own question so please forgive me when I rephrase it again.

I have a 65w stepdown Input230/240 AC, Out: 115V AC. 65VA transformer and I wanted to know if I should be concerned about how much electricity the transformer draws just by the fact that it is plugged into the wall socket even when the hardware connected to it is not on.

I don't need an exact figure. Just a layman's terms as what your typical transformer would draw. An absolute average idea of the average transformer.

If I turn the transformer off, all my appliances will need to be reset when I turn the transformer back on again.

So does an average one consume as much as a light bulb, or say... something much more.. like a computer etc.

I just need a general idea. Thank you.

Answer 1

Transformers are generally 85% efficient. But for no load applications, series in an ammeter and you'll know the answer for a specific transformer.

Answer 2

As jack w correctly says, transformers are among the most efficient machines around; more than 99% efficient. The slight warmth you feel when you touch a transformer is the energy wasted as heat. So a 65 watt transformer wastes less than a watt of power when it isn't putting out any power. At the price we pay for power here in NZ, that's not much more than 1/100 of a cent an hour. So the money you waste per day by leaving it plugged in wouldn't even buy you a dog turd.

Answer 3

AC transformers are on of the most efficent machines there is. With no load on the transformer, heat loss is the only use of energy. With no load, the transformer isn't doing any work.

Answer 4

No-load losses are primarily due to the so-called "iron losses", i.e, hysterisis and eddy-current losses, and to a smaller extent, I-square-R losses. They vary quite a bit, but you can use a ballpark estimate of 5% to 15% of your transformer rating. Estimate between 5W to 10W of losses for your 65W transformer.