Transformer Question

[macmonkey]

Do transformers always output their specified output current? I need to power some 12V LEDs off a transformer I have. It says on it the input current is 120mA and the output is 1.2A. However, the LEDs I'm using don't need 1.2A. If I use the transformer will I be running the risk of blowing the LEDs?

Thanks in advance

 

[480threephase]

No.

The transformer will put out the same amount of current you would get if you were using a battery power supply. The current is controlled by the resistence of the LED's. Just use ohms law to make sure your voltage wont be high enough to burn out the LEDs. What are the ratings on your equipment?

 

[macmonkey]

Thanks for the reply.

The LEDs in question are **broken link removed**. There are 16 LEDs in total (I didn't buy the entire strip, just part of it).

My transformer has an input of 240V AC at 50Hz and 120mA. The output is 12V DC at 1.2A. I'm not sure what the resistor on the LEDs are because it's built into the strip.

 

[crutschow]

The transformer current rating is simply the maximum current it can deliver without being overloaded. The actual current depends upon the transformer output voltage and the load resistance.

 

[Hero999]

Assuming your LEDs don't have built-in resistors or a power supply you need to add a current limiting resistor or they'll blow.

The same would be true if you were running them from a battery - LEDs always need a current limiting resistor or some other current limiting mechanism.

 

[macmonkey]

No.

The transformer will put out the same amount of current you would get if you were using a battery power supply. The current is controlled by the resistence of the LED's. Just use ohms law to make sure your voltage wont be high enough to burn out the LEDs. What are the ratings on your equipment?

**broken link removed**
I only bought a strip of 18 LEDs.

Assuming your LEDs don't have built-in resistors or a power supply you need to add a current limiting resistor or they'll blow.

The same would be true if you were running them from a battery - LEDs always need a current limiting resistor or some other current limiting mechanism.

I know all about current limiting resistors thanks to GCSE electronics and yes, the strip does have built in resistors.

Thanks for all your replies guys, I have been running the LEDs from my transformer for the last 10 mins with no problems

 

[rezer]

Do transformers always output their specified output current? I need to power some 12V LEDs off a transformer I have. It says on it the input current is 120mA and the output is 1.2A. However, the LEDs I'm using don't need 1.2A. If I use the transformer will I be running the risk of blowing the LEDs?

Thanks in advance

A transformer is a power "source". Much like a battery or power supply, it will only provide as much current as the load requires. In the case of your LEDs, with 12Vac applied from the secondary, you will draw as much as 20mA depending on your current-limiting resistor(s), and LED circuit configuration.