Power supply phenomenon:Can't go beyond a certain voltage even when knob turned

A simple circuit with the power supply leads connected to just a single 772 ohm resistor on a breadboard. [772 ohms as measured using a multimeter].
From the videohttps://www.youtube.com/watch?v=Oc98Et_OMCA&feature=youtu.be,you can see that I can't go past 7.07 V even when I turn the knob full right.
1.Why does this happen and has it got something to do with the power rating assigned for the resistor by the supplier? 2.What phenomenon is going on here that tells the power supply not to give more than 7.07V? How could the power supply know that the resistor would blow-up if it gave more than 7.07V?

Calculation gives me a power rating of 0.645W when the voltage is at max 7.07V i.e P=V^2/R
Using 2 resistors in series surprisingly gives a power rating value of 0.798W. What's going on?

Does your psu have current limiting ?

Your PSU is current limiting - that's what the second LED is showing.

Then its current limiting.

As you increase the voltage across the resistor the current rises.

The current limit function prevents the voltage rising further.

Nothing on the psu says 'Current-limiting' but it sure acts like it.
So,when the psu starts to do the 'current-limiting' thing, this means I've exceeded the nominal current right?
With the exception of a short-circuit happening,is there any other way that I could cause an excess current flow through the circuit? for instance a fried chip in the circuit...?

I'm a novice.

The led does.

Try adjusting the right knob

Boardburner2:
The led does.

Try adjusting the right knob

Do you think thats a good thing? I'd end-up providing more amps than necessary. In-fac,this is what I did and I just now concluded that this might have been the reason I fried my bluetooth module.

Current limiting is useful for that reason.

Fried chips often go short circuit.

Just tried adjusting the right knob aka current knob. The resistor got so hot that I burnt my finger a little.
I'm not sure if I want to try adjusting the right knob with my arduino and the radio connected. Do you concur?

First knob is voltage 2nd current limiter.

So set the current dial to half way, then control the voltage, since you burnt your finger it looks fine..

Also place a 10k resistor there, which limits the current but will allow the power supply to deliver a lot more voltage without the current limiter kicking in.

MY ULTIMATE PROBLEM with the psu went something like this: My power supply was powering a circuit as shown here.
http://bayimg.com/mAoGkAAff
For some reason,when I tried to power the Aruino via the Vin pin and 12V from the power supply,the 'current-limiting' action started-> I turned the right current knob a little and eventually fried my bluetooth module.

I presume this happened because the voltage regulator inside the Arduino did not drop the voltage to 3.3V. The 3.3V was feeding my bluetooth module then. What's going wrong here?

You should set the correct voltage for your circuit too high will fry it.
Current alone wont fry it, but if it is fried it may be short circuit.
This will increase the current drawn.
If it is drawing more than rated current something is fried.

12 v is too mich for an arduino you have destroyed something.

Boardburner2:
12 v is too mich for an arduino you have destroyed something.

The Vin can take something between 6V-20V. I found a lot of discussions before trying this :Exploring Arduino: Tools and Techniques for Engineering Wizardry - Jeremy Blum - Google Books

http://forum.arduino.cc/index.php/topic,4769.0.html

The Vin can take something between 6V-20V.

Yes it is but not once you have fried it.

I presume this happened because the voltage regulator inside the Arduino did not drop the voltage to 3.3V. The 3.3V was feeding my bluetooth module then.

That seems very unlikely I am tempted to say impossible. Did you have any 5V signals connected to your bluetooth module?

What a current limit knob does on the power supply is to turn down the voltage until the set current is reached. Any attempt to turn up the voltage will be over ridden. Having that knob up to full can not damage anything. It could negate any protection that current limit offers but in itself it does not damage anything.

marellasunny:

Boardburner2:
Try adjusting the right knob

Do you think thats a good thing?

I'm not sure you should even own that power supply... you clearly don't believe in Ohm's law.

I think OP need to go brush up on his Ohms law before going any further.

Look at it like this - in Europe we have 230 Volts in our wall outlets. The outlets are fused by a 10 Amp fuse. 10 Amp * 230 is 2.300 Watts.

Just because the wall outlet is capable of delivering 2.300 Watts, you can still plug a 25 Watt lamp into the outlet without anything blowing up. The lamp (the load ) takes what it needs - not what is available.

You can look at constant current a bit like the fuse. The size of the fuse sets how much power you can use, before power if cut off (to protect the appliance and house wiring) - The constant current on a power supply can be seen the same way. If your circuit uses 1 Amp in normal operation, you can set the Constant current setting to 1.5 Amps - this way, only 50% extra power is available to fry your wiring etc. if something goes horribly wrong and you short anything out.

// Per.

The Vin can take something between 6V-20V.

The board alone can.
As you add modules you increase current . As you increase current and voltage you are putting a greater load on the regulator.
Once that blows everything goes.

If you limit input to 7 volts this becomes much less likely.

Lets put it this way, you don't need current limiting on properly designed circuits, they have there own current limiting build into themselves based on there rated voltage, they only pull what they need based on ohms law.

That current limiter is for test circuits, and troubleshooting repairs to prevent accidentally frying the device your powering when unsure of expected current pull.

If you fried your Bluetooth then either it was defective, over volted, or wired wrong to name the most likely causes.