[Closed] idiot electronics question - plugs left on

http://en.wikipedia.org/wiki/No_load_power
http://www.docircuits.com/learn/how-stuff-works-your-ever-helpful-cell-phone-charger/

In short though, transformers consume current even when not powering anything on the transformed side.

The transformer and charging led will exert a slight electrical load.

Modern chargers don't tend to have transformers, you can usually tell the difference by the weight. Transformers tend to be heavy. They are [url= http://en.wikipedia.org/wiki/Switched-mode_power_supply ]switch mode[/url] and usually use use a tiny amount of power if there is no load. Really not enough to be an issue. Basic test, is it warm? That is the only place the energy can really go.

Bit of a pet hate of mine. Plugged in chargers and TVs on standby seem to get targeted by energy saving campaigns but there are far bigger wasters of electricity in a normal home

EDIT: Both those links above are pretty out of date.

Transformer has two circuits - primary and secondary. The primary is connected when the thing is switched on, but when current tries to flow the electric fields in the transformer oppose it so nothing flows (in theory). When you connect the secondary to something it bleeds energy out of that electric field to supply whatever you've plugged in, and the field then doesn't oppose the current in the primary as much so some current flows. This all adds up of course - the energy you bleed out into your device is equivalent to the energy that's allowed to flow through the primary.

HOWEVER there are losses in the system. Because both coils have resistance some energy is bled away from the electric field in the primary to create heat. The better the transformer design though, the less heat is produced and the less current flows in the primary.

Until recently chargers and power supplies used to be big and heavy - these were transformers. Nowadays though they use a similar principle but done differenty, so they are much smaller and MUCH more efficient. In the old days a significant amount of power would be lost in transformers and in appliances on standby (old cable TV boxes I think used to use 40W on standby - as much as the typical lighting in my house) but modern stuff is far better. Your modern mobile phone charger will use next to nothing if nothing's plugged in.

Plugged in chargers and TVs on standby seem to get targeted by energy saving campaigns but there are far bigger wasters of electricity in a normal home

Yes.. people can feel like they're doing the right thing by turning off their TV at night, but then they leave the thing on constantly all day even when not watching it, using 200W.

nickjb - Member

Modern chargers don't tend to have transformers, you can usually tell the difference by the weight. Transformers tend to be heavy. They are switch mode and usually use use a tiny amount of power if there is no load.

All chargers would have a transformer. A switch mode power supply operates at a much higher frequency around 100Khz and therefore its transformer can be much smaller and lighter than a conventional transformer that relies on the 50Hz mains for its operation. They also store energy in the core which is slightly different in operation to a conventional transformer

There would be a small power loss to keep the control IC powered and some transformer and leakage losses but without a phone connected it would go into a power saving mode. Should be about 10-100mW depending on how good/old it is.

molgrips - Member

Yes.. people can feel like they're doing the right thing by turning off their TV at night, but then they leave the thing on constantly all day even when not watching it, using 200W.

Again TV would go into a power saving mode in standby which should be less than 1W for a modern TV

I think he meant that they actually leave the TV on, not just in standby.

I know my point is that the power used on standby is nothing ocmpared to the power it's using being on when no-one's watching it 🙂

Sorry molgrips, mis-read your post