how current affects circuits

[veenife]

hi... otherday i was goin to play keyboard and notice that the power suppy had its cable broken... so i looked for a new supply at home... i connect it to the keyboard and the thing worked totaly fine...
but just out of curisity...

the original supply is 12v with 2 A

the new suppy though is of 12v but with just 300mA

... what is actually going on there with current.... how can the keyboard still work with a much lower current like that??

Cheerios!

 

[pradhan.rachit]

Majority of the current flowing in the keyboard will be consumed by the power amplifier.

The current capability of the power supply will decide the power handling ability of it.

P = VxI

So for 1st one, P = 12V x 2A = 24 watts

whereas for the 2nd one,

P = 12V x 0.3A = 3.6 watts.

As far as your supply can handle the requirements of the keyboard, it will function properly.

 

[barry]

If your keyboard draws less than 300mA, then you're fine; if it requires more, you're doomed. The rated current of a power supply only tells you the MAXIMUM current it can supply, not how much it WILL supply; that depends on the load. Your keyboard should(might) have a label telling you how much current it requires.

 

[Audioguru]

What happens to the overloaded WRONG power supply when it is overloaded? Will it set your house on fire? DONT DOO DAT.

 

[barry]

It will not set your house on fire.

It's output voltage will drop, an internal fuse may blow.

 

[Audioguru]

It will not set your house on fire.

It's output voltage will drop, an internal fuse may blow.

Only if the power supply is CERTIFIED to be used in a civilized country. I have a few cheap Chinese AC-DC wall warts that are not certified and they get DARN hot even without a load. No fuse, they use the wiring as a fuse.

My electrical utility company gave away compact fluorescent light bulbs for free. Some of them dripped flaming plastic and set some houses on fire. Mine just smoked. The Chinese manufacturer STOLE the certification number from a competitor and the product was never certified. No fuse.

 

[kleki]

Yes, it's completly true. You can buy some chineese products in Europe - marked with CE and with some papers - only papers. Problem with norm-conformity marking in Europe is that suppliers are making that by self. You can buy som edeivces in Asia and sell them in Europe - whan ypu have marked them with CE - everything is OK, its your responsibility. We have lot of small "one month" companies wchich are providing this problems.

@veenife - Your's keyboard is working, because You are using not so big volume. When You will try bigger - You became answer - distortions. After few minutes - power supply should be warmer. After few more minutes - should not work. Try to repair old one or buy correct.

Greetings
--
kleki