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I have an AC/DC power supply (from the UK). It is labelled 230V/50hz. As far as I know, electric in Mainland britain is 240V/50hz. Indeed, the unit did correctly power the Korg keyboard in the UK. The DC output is labelled 21V / 1.2A. (The Korg piano is indeed labelled 21V input on the back.)

Now I have the same power supply in France. As far as I know, France is also 230V/50hz. When I plug the power supply in the wall in france (obviously using a 50 cent plastic plug adaptor - of course NOT using any sort of transformer, etc).

Using a good multimeter, in France the output from the power supply is 26 volts (around 25.9 to 26). Is that normal? Why not just 21?

(Unfortunately I never tested the output, in the UK.) Now, the electric piano is actually not working. ie, I did plug the power supply in question in to the Piano and no result, nothing comes on.

Does anyone know:

  1. Why is it showing 26 rather than 21 as labeled?

  2. Do you reckon I may have blown a fuse in the piano, due to the 26 versus 21? Or, perhaps not a fuse, just permanently ruined it? Conversely, is it likely just some other unrelated problem with the piano?

  3. To rephrase: If the piano says 21V on the back, would 26 V be too hot, or no problem, typically?

It's an expensive pro piano and a real nuisance! It is a mystery that it is showing 26V. It's almost impossible to find a replacement power supply, and, that may well not be the problem.

A further question for you experts: would an alternate supply, eg, http://www.webducommerce.com/alimentation-21v/chargeur-alim-secteur-21v-1-7a-36w-p-3485.html with a HIGHER amperage rating, actually be OK?? Should you try to match the amp rating, or us the point that it must be "at least" 1.2A in my example? Thanks again, pro geniuses!

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  • \$\begingroup\$ This belongs on electronics.stackexchange.com \$\endgroup\$
    – Dennis Williamson
    Commented Feb 16, 2011 at 17:55
  • \$\begingroup\$ For current, you the input rating is the minimum. If you can get stronger, there should be no problems. \$\endgroup\$
    – AndrejaKo
    Commented Feb 16, 2011 at 18:28
  • \$\begingroup\$ PS, for anyone looking for an answer, I also found this QA: electronics.stackexchange.com/questions/5759/… \$\endgroup\$
    – Fattie
    Commented Feb 16, 2011 at 20:35
  • \$\begingroup\$ Mains voltage in mainland Britain is 230V. Switched from 240V at the same time Europe switched from 220V to 230V. \$\endgroup\$
    – stevenvh
    Commented Jun 6, 2011 at 16:43

2 Answers 2

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  1. That's pretty normal, as it's not regulated. Voltage drops when load rises.

  2. Probably just blows fuse, but I think more likely works just fine.

  3. If power supply would be 26V regulated output, then it would be problem, probably.

Many devices tolerate much larger voltages, for example 12V laptop is fine with 16V supply.

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  • \$\begingroup\$ Both answers were superb, thank you SO MUCH. I ticked this one since it was earlier, it seemed fair! Thank you so much Olli! \$\endgroup\$
    – Fattie
    Commented Feb 16, 2011 at 20:31
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I'd guess that it's an unregulated power supply, meaning you'll see the 21V under the rated load (1.2A). 26V is its open circuit voltage.

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  • \$\begingroup\$ Just about to post this, but you saved me the typing. \$\endgroup\$
    – Kevin Vermeer
    Commented Feb 16, 2011 at 18:52
  • \$\begingroup\$ Thank you so much Pyfon!!! Thank you, thank you for that clear explanation. \$\endgroup\$
    – Fattie
    Commented Feb 16, 2011 at 20:32

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