Looking at the rated current.

[Classik]

I asked a simple question, purposefully. I got answers.

A DC source outputs 9V at 3A (e.g).

You have an electrical device that operates on 9V. The label on the device reads: 9V input max.

Answers provided by some people:

1. Connect the device directly to the source. The device will absorb only its own working current.
2. You are wrong. If the device operate within a current range of ...say 500 - 800mA the source will damage it.

There were many strange answers.

 

[WIP]

Do you have a question?

 

[Classik]

Actually the question is: do you really need to consider the current from the source before operating the device. I got those two responces

 

[WIP]

Electric current is the result of voltage applied to a resistance (dc) or impedance (ac) load.

The amount of available current at the source has nothing to do with the current used by the load except that of its own limit which, unless controlled by an OCPD (over-current protective device), approaches infinity.

Consider your home. The available current at your service entrance is considerably higher than the current used by any one device or the sum of all the electrical devices in your home and yet, none of the devices uses any more current than what they need at the moment.

A device's current rating indicates what level of current it can safely handle without generating excessive heat and usually relates to the full load amperage. In other words, if the device is running at its maximum performance and duty cycle, it will likely use or draw the current specified by its FLA.

In the case of inductive loads like motors for example, FLA is the amount of current the motor will draw when it is operating at its rated horsepower and frequency. If you lock the rotor or stall the motor, the current demand will increase rapidly to very high levels and will eventually damage the motor.

Does this make sense?

In a nutshell the answer to your question is no with one exception. If the device you are using needs more current than the supply can deliver, it will not function properly. Typically, the result is a blown fuse or opened circuit breaker because these are the usual limiting factors.

 

[tim-from-pa]

I asked a simple question, purposefully. I got answers.

A DC source outputs 9V at 3A (e.g).

You have an electrical device that operates on 9V. The label on the device reads: 9V input max.

Answers provided by some people:

1. Connect the device directly to the source. The device will absorb only its own working current.
2. You are wrong. If the device operate within a current range of ...say 500 - 800mA the source will damage it.

There were many strange answers.

I'm an electronic technician. The folks that stated #1 are correct. Those who stated #2 haven't the slightest idea what they are talking about, but probably you will find such (#2) people are the ones that do all the talking as if they know what they are talking about (as with most areas of life)

 

[WIP]

I'm an electronic technician. The folks that stated #1 are correct. Those who stated #2 haven't the slightest idea what they are talking about, but probably you will find such (#2) people are the ones that do all the talking as if they know what they are talking about (as with most areas of life)

You are correct sir.

 

[Classik]

Yeah but only the thermostat. ;-)

How about LEDs?