It should be at least warm. You are dropping 7V.

but it's not dropping any voltage...I'm still getting almost 11v on the output...

 

Are you certain you have 12v at the input terminal? Certain the ground pin is grounded? Do not assume just because it is connected. Perform voltage and continuity checks (make sure you turn the power off for that one ).

 

And you are measuring the voltage across the load resistor?

hmm...not sure what you mean. I've put the resistor from the ground pin to the output pin...still measuring almost 11v on the output...
How do I make sure I'm measuring "across the load resistor"?

 

but it's not dropping any voltage...I'm still getting almost 11v on the output...

But it should be so hence it should be at least warm. And if you have 11V or so out you must have 12V in so at least check you ground and make certain it is connected. Though if it was not I would suspect 0v out.

 

Where did you get said 7805s? If you got them from eBay there is a chance they are not 7805s at all. They could simply be resistors or pretty much anything else.

yes, I think they are from ebay....hmm...don't like the sounds of that!

 

hmm...not sure what you mean. I've put the resistor from the ground pin to the output pin...still measuring almost 11v on the output...
How do I make sure I'm measuring "across the load resistor"?

He means, are you measuring from the output pin to ground (across the resistor) ?

 

yes, I think they are from ebay....hmm...don't like the sounds of that!

There is a chance they aren't 7805s at all. Are you from the States and nearby a Radio Shack? Time to make a trip.

 

hmm...not sure what you mean. I've put the resistor from the ground pin to the output pin...still measuring almost 11v on the output...
How do I make sure I'm measuring "across the load resistor"?

How are you measuring the output voltage? You have to leads from your voltmeter. Where, exactly, are you putting each of them?

 

I tried changing around the input/ground/output..doesn't make any difference on the voltage reading. I tried 5 different 7805 modules (all purchased at the same time on ebay)...same results. I tried using 9v input, and it still reads almost 9 volts. It's as if it isn't actually doing anything....

 

There is a chance they aren't 7805s at all. Are you from the States and nearby a Radio Shack? Time to make a trip.

From Winnipeg...Canada. Radio Shack doesn't exist here anymore....well, it does, but it doesn't sell electronic components...

 

How are you measuring the output voltage? You have to leads from your voltmeter. Where, exactly, are you putting each of them?

I'm putting the red lead , which is plugged into the V.ohm, ma port to the output wire. black lead to ground.

 

set to read dc volt 20

 

From Winnipeg...Canada. Radio Shack doesn't exist here anymore....well, it does, but it doesn't sell electronic components...

You have a place like this in town and you are buying from eBay?

http://www.tiptopelectronics.com/

 

10 regulators for $7.80

at same store Tip Top Electronic Supply / Active Tech
106 King Edward Street W., Winnipeg

http://www.active123.com/780510-Voltage-Regulator-Fixed-5V-1A-Pkg10-Prodview.html

 

Oddly enough, I went back in order to test things using a buck converter...tried the 7805 again, and they all worked. I didn't change anything as far as I know, but they were all reading 5.06 v. Strange things are afoot!! And yes, it did get really hot. Probably too much of a concern to use it in the project I have in mind. I want to light up an old staircase using a 12 v 5050 warm white led's (the strips that I can cut every 3 led's). There are 15 stairs, so I will have 15 segments of 3 led's. My goal is to have the lights triggered by an infrared sensor going across the top and bottom stair, which will be controlled by an Arduino. I didn't realize how hot the 7805's got....I would be worried about that kind of heat starting a fire!! So the buck converter, which doesn't seem to get hot, is probably a better option anyways...unless someone has a better option/soloution? (I want to run the 12v from the power source to the lights, but also convert to 5v to use to power the Arduino)
Thanks for everyone's help and input....I really do appreciate it. Although I love tinkering around with electronics, I have more desire than knowledge...but I'm working on that!!!

 

Where did you get said 7805s? If you got them from eBay there is a chance they are not 7805s at all. They could simply be resistors or pretty much anything else.

It looks like he knows what he is doing. I have to second the notion of bogus chips.

 

Did you know the Arduino can handle 12V? It has an onboard regulator. It's a different pin than the 5V input, but it might eliminate your problem.

 

A few measurements on a L7805CV from ST, shows the following output voltages:
Normal operation, 12 Volt input and two 100nF decoupling capacitors: 4.98 Volt
Floating GND on L7805CV and voltmeter as load: 11.5 Volt
Floating GND on L7805CV and 1 KΩ parallel with voltmeter: 8.5 Volt

 

Per Kjeldgaard's post above, the weirdness could be the result of an intermittent connection on your breadboard, and in particular an intermittent connection to the ground pin on the regulator.

 

A few measurements on a L7805CV from ST, shows the following output voltages:
Normal operation, 12 Volt input and two 100nF decoupling capacitors: 4.98 Volt
Floating GND on L7805CV and voltmeter as load: 11.5 Volt
Floating GND on L7805CV and 1 KΩ parallel with voltmeter: 8.5 Volt

Can you expand on the decoupling capacitors? I didn't put any capacitors into my circuit....perhaps that's the root of my problem...what are decoupling capacitors? Where would they go?
Sorry for the ignorance, and thanks for the info!