# Power Supplies

#### Mazaag

Joined Oct 23, 2004
255
Hi guys,
I had a stupid question with regards to power supplies.

When power supplies are labeled, they are usually labeled with both Voltage and Current, or say Voltage and Power.

My stupid question is as follows:

When a power supply says " 5volts, 6A" what does that actually mean ? like its supplying a voltage of 5 volts and 6 amps? but doesn't the current depend on the resistance of the load or whatever I connect up to the power supply ?

Thanks guys, I know its a stupid question, but i'm sorta blacking out.

#### Papabravo

Joined Feb 24, 2006
20,980
Originally posted by Mazaag@Mar 17 2006, 01:02 PM
Hi guys,
I had a stupid question with regards to power supplies.

When power supplies are labeled, they are usually labeled with both Voltage and Current, or say Voltage and Power.

My stupid question is as follows:

When a power supply says " 5volts, 6A" what does that actually mean ? like its supplying a voltage of 5 volts and 6 amps? but doesn't the current depend on the resistance of the load or whatever I connect up to the power supply ?

Thanks guys, I know its a stupid question, but i'm sorta blacking out.
[post=15102]Quoted post[/post]​
What the spec means is that the output will be pegged at 5V plus or minus some tolerance for any amount of load current from 0 Amps up to and including 6 Amps. At a load of more than 6 Amps different supplies will do different things, but for sure the output is no longer guaranteed to be 5 volts plus or minus some tolerance.

A current limited supply may shut off very abruptly if the current limit is exceeded. Another supply may supply 6.5 Amps at 4.61 Volts or 7 Amps at 4.28 volts. The supply gives more current, but at a lower voltage and the maximum power remains the same.

#### hgmjr

Joined Jan 28, 2005
9,027
Originally posted by Mazaag@Mar 17 2006, 12:02 PM

When a power supply says " 5volts, 6A" what does that actually mean ? like its supplying a voltage of 5 volts and 6 amps? but doesn't the current depend on the resistance of the load or whatever I connect up to the power supply ?

Thanks guys, I know its a stupid question, but i'm sorta blacking out.
[post=15102]Quoted post[/post]​
Greetings Mazaag,

The current stated on the power supply refers to the amount of current that the supply is rated to deliver to the load. As you stated, the percentage of that available current used is governed by the load to which it is connected.

hgmjr

#### windoze killa

Joined Feb 23, 2006
605
Originally posted by hgmjr@Mar 18 2006, 04:20 AM
Greetings Mazaag,

The current stated on the power supply refers to the amount of current that the supply is rated to deliver to the load. As you stated, the percentage of that available current used is governed by the load to which it is connected.

hgmjr
[post=15104]Quoted post[/post]​
The current rating on a power supply is normally the maximum "continuous" current the power supply can deliver to the load. There are sometimes other ratings which may include peak current ratings. Your 5V 6A power supply may have a peak current rating of 10A. This current will only be for a short period of time, maybe half a second or so.

As Papabravo stated what can happen when you exceed the rating may vary. Reduced volage, shutdown and unfortunately in some poorly designed ones it may even let the smoke out.