I know, there are no dumb questions, just dumb questioners. A few days ago a question hit me. I feel I should know the answer, but when I think about it I really don’t. I have suspicions but nothing to back it up. So here is the dumb question. If you have an extension cord plugged in but nothing is plugged into the extension cord, does it use electricity? By use I mean is there a rise in usage as measured by your meter. How about if you have a recharger, like for a rechargable flashlight. It is plugged in but now the flashlight is fully charged. Is the recharger using electricity? Help me.
If there’s nothing connected at the receptacle, no electricity is being consumed.
With rechargers and such, they generally use a little even if nothing’s connected. There’s usually a transformer, and there are losses there even if no current’s being drawn from the secondary. Often chargers have an indicator light or LED which would consume some small amount of power as well.
Pretty negligable amounts in my opinion.
No it doesn’t because there is no current flow through the extension cord.
Most chargers will know when the flashlight (for example) is fully charged and stop charging however there will still be a small amount of current flowing through the charger powering LEDs, monitoring circuitry etc.
In the extension cord case, no, there is no measurable current. The charger case is bit more complicated. Most of them will draw some standby current, usually to power some sort of charge monitoring circuitry. However, this standby current will be small compared to the charging current. Many other types of electronic devices also draw a small standby current, usually because the small transformers which power them are connected to the mains as long as the device is plugged in, and draws some no-load current as a result. Some devices need this standy power, for example a TV needs to keed the IR remote detector circuitry powered so it knows when you hit the POWER button on the remote to turn it on.
If something is making a circuit in your system, then it is using electricity. Possibly at a low rate, but still using it. So if your extension cord has an indicator LED on it, then yes. If it’s just a pair of wires that extends the location of your plug, with nothing else, then the answer is no.
Rechargers use electricity, because virtually every one that I’ve seen has a transformer in it (which is itself a complete circuit). The box part that’s on or near the plug gets quite warm when you plug it in. (Hint: If something gets warm or emits light, that requires power to do, and the device is indeed using electricity)
A simple extension cord plugged in will not use any electricity, because no circuit has been completed by the cord.
Rechargers often use electricity, even when something isn’t plugged into them using electricity. How much is highly dependent on the device. Even if it’s just a simple LED thats showing you it’s plugged in and ready to charge something, it’s using some amount of electricity. I remember reading an article a while back that showed that some recharging devices still used a ridiculous amount of energy, even when not charging.
A simple way to test if a charger is using a decent amount of electricity is to feel it. A warm charger is one that’s using electricity and the heat being generated is due to the resistance within.
I have managed to put 98% of the wall warts and standby power consumers on switches in this house. Exceptions are the TV and the recording box that records the TV shows.
My non-expert guess would be that an extension cord does use some power, because it’s on AC. If the power supply were direct current, then it would only use a minuscule amount of power when plugged in or turned on. However, an extension cord must have some capacitance, so on each cycle it would be getting charged and discharged, and hence use up some small amount of power, even if nothing is plugged in. Similarly, the house wiring would have capacitance, and would use a little power even if nothing were plugged into any wall sockets. However, I suspect that the amount of power involved is very small, unless you have many kilometres of wiring connected to the power supply.
Minor nit: The glowing device that some extension cords have is a neon bulb, not an LED. Neon bulbs are about as efficient and long lasting as LED’s, but require fairly high voltage (>= 90 V) to operate. Using a simple ballast resistor in a 120V circuit, they are far more efficient than an LED would be.
The resistor used with a typical NE2 bulb is 100KOhms. 90V across the bulb leaves 30V across the resistor (yes, sine wave yada yada rms yada peak yada cutoff yadayada) so the circuit uses about 1/3 mA or 40 milliwatts…about 3 cents per month if you pay 10 cents/KWH.
The chargers and transformers mentioned above become a big deal if you live off grid. They are known as “phantom loads”.
Yes. Which is why I said “measurable” in my post; that is, not measurable in the sense that your standard household kWh meter couldn’t detect it. The cord will have some amount of capacitance between the wires, but it will be very small, and the reactive current through it will likely be on the order of picoamps, at most.