Regulator getting (too) hot?

Hey,

I'm wondering if the voltage regulator on my arduino board (DFRobot clone) is getting too hot.. I have a 12V 200mA wall wart, and when I leave it powered with this wart, after an hour or so the regulator is hot to the touch. Gets painful if I leave my finger on the caps for 10~20 seconds.

Is this normal, within tolerances.. supposed to be?

I have a IR receiver, 20x4 LCD, small buzzer, 5mm red LED and the asynclabs wifi shield 2.0 connected to it, not sure how much power each of these things take.. but it can't be a whole lot.

Using a 7v- 9v wall-wart rather than a 12v (which may be kicking out 15v + if its unregulated) should reduce the temperature the regulator runs at. It does get hot if you're running much more than the plain arduino from a 12v input.

Your Wi-Fi shield alone draws 230mA when it is transmitting, more than the rating of your power supply. Your regulator would have a lot less work to do if it's input voltage were lower. You should consider a lower voltage, higher current wall wart.

Don

I suggest a trip to a local second-hand/thrift store. I picked up a switching supply 9V 1.2A for $2USD. You will want to use 9V or slightly less so the regulator doesn't have to dissipate the rest of power through heating up. But as pluggy said, 7V is absolute minimal. Below that the regulator is not able to regulate and outputs something less than 5V. Just be careful if you don't need 1.2A, find one with less current rating. Less current under shorting condition when you mess up will save you from grief.

Gets painful if I leave my finger on the caps for 10~20 seconds.

I would say that is just about OK. For a discussion of what power you can draw from an arduino regulator see:- http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Read through your article, it does make some things clear. Though what caught my attention is, I also have a 12V 500mA wall wart.. but the regulator gets a lot hotter (and faster) with this wart than with the 200mA rated one. Since floresta mentioned the wifi shield takes 230mA when transmitting, this exceeds what the 200mA wall wart can supply? (or should I be thinking it is equivelant to 340mA at 7V?)

As for regulated / unregulated.. from the info in mikes article, aren't all AC/DC convertors regulated?

Thanks for the help thus far!

from the info in mikes article, aren't all AC/DC convertors regulated?

No. The vast majority are not. Regulated power supplies cost more to make.

Though what caught my attention is, I also have a 12V 500mA wall wart.. but the regulator gets a lot hotter (and faster) with this wart than with the 200mA rated one.

When the 200mA supply was overloaded it's output voltage probably dropped below 12v. This left less than 7 volts to be dropped across the regulator on the Arduino board. Since the 500mA supply was not being overloaded it's output voltage was closer to 12v so the regulator on the Arduino board had more work to do and got hotter faster.

(or should I be thinking it is equivelant to 340mA at 7V?)

No. It doesn't work that way.

As for regulated / unregulated.. from the info in mikes article, aren't all AC/DC convertors regulated?

You should look for a supply rated for120/240V, 50/60Hz input. It will most likely be a more efficient switching power supply with a regulated output voltage.

Don

Look here - mpja.com (in the US). Can get a 5V 4A regulated switchmode supply for $6. Am using one now, works great.

Geuss I'll keep an eye out for an appropriate wall wart. Thanks for the insight.

http://www.mpja.com/prodinfo.asp?number=18520+PS $6.95 Input: 90-132 VAC 60Hz Output: 5VDC @ 4A Specifications/Features: Switching plug supply with overvoltage & current limit protection. Non-Polarized 2 blade input. 6ft output cord with 10mm X 5.5/2.1mm ID Right Angle coaxial plug Center +. UL/canada/usa/listed. RoHS compliant .

Plugs right into the Deumilanove power jack.

Plugs right into the Deumilanove power jack.

5V ?

Yes - good catch, I forgot I have a separate panel jack that I plug this into, then connect to the VCC pin from there as the promini I am powering is installed into my project. http://www.mpja.com/prodinfo.asp?number=18549+PL

For prototyping, I use the wallwart that came with the deumilanove. 9VDC. 50mA. I don't see any 7.5V or 9V supplies listed there with 5.5mm/2.1 plugs, would have to go up to one of the 12V supplies for that. http://www.mpja.com/prodinfo.asp?number=18469+PS