Do transformers in chargers act as a load?

  1. Due to the fact that I don't have any plans on damaging my chargers (something I am not planning to risk at the moment) I have not been able to confirm whether the transformers in chargers act as a load when nothing is charging. From what I have read, based on the design of many chargers, even when no phone/load is charging the resistance from the transformer in the charger causes it to act as a load and consume a few watts. I am asking for a confirmation of this possibly with a more in depth explanation for somebody who isn't what you would call an expert (me).
  2. jcsd
  3. davenn

    davenn 4,354
    Science Advisor
    Gold Member
    2014 Award

    The transformer will still have small current flowing through them ... some of that is just pure leakage current.
    Even just a plain transformer across the mains outlet, with no load on the secondary side, I suspect, will present a small load to the mains supply due to eddy current losses in the transformer core

  4. I think most chargers are switching regulator supplies that work over a wide range of input voltages (100V-240V, for example) They have switching losses even when no load is being drawn. Even a transformer and rectifier system will draw current with no load.

    Can you explain more about why you care?

    You can buy a power meter to determine the load. for example (there are a bunch, read the reviews)
  5. I was thinking of saying something to that effect. I don't think any phone chargers are using transformers anymore. (could be wrong)
  6. even if nothing is being charged, the transformer will still act as a load. it will burn a small amount of energy which is considered to be loss of the transformer.
  7. yes they still do. what changes is they are no longer linear. they use SMPS now a days just like a PC power supply but still transformer is being used.
  8. psparky

    psparky 884
    Gold Member

    They better still be using transformers. I'm pretty sure I don't want 120 volts held against my face.

    5 volts sounds much nicer.
  9. I guess my sloppy thinking got us here. All chargers have transformers. I was implying a linear AC transformer based system where there are some no-load losses due to the transformer, filter capacitors, etc. The switched mode systems have significant losses at no load due to the switching. Some switching circuits require small minimum loads to keep them in regulation.

    For some reason I considered linear to be "transformer based" but in reality they are all transformer based.
  10. you realize you can convert voltage without a transformer? Convert to DC, then pulse the DC current through an inductor. No transformer needed. And since the inductor would be smaller than an equivalent transformer, you save size and weight. I don't think I'd see a transformer if I opened up my phone charger.

    why can't you just have a switch that cuts off the circuit when charger drops below a minimum current? or when the battery reaches a threshold voltage?
  11. I think you would.

    I would expect that all commercial regulatory approved wall wart style chargers are transformer based. But, I have not opened any to check. I expect many have a transformer the size of a dime.
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