Author Topic: wall wart power types  (Read 512 times)

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mighalpern

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wall wart power types
« on: March 08, 2016, 12:04:34 AM »
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Ok so I am brain storming about the power supply for my 12 volt rated LED's. 
One wall wart has an output of 9 volts DC and does ok.  Then I found a wall wart that output is 8 volts AC.
I tried it and it worked as well.  So now I'm confused.  I have a bone head idea about the two types and their uses, but this has me stumped. 
 I can light up my LED's and my 12 volt grain of wheat bulbs.
Can someone tell me why this is working.   

peteski

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Re: wall wart power types
« Reply #1 on: March 08, 2016, 12:29:22 AM »
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Incandescent bulbs will work fine with AC and DC power. All your household ligthbulbs were powered by 125V AC.
LEDs only light up when the voltage is higher at the anode then at the cathode. Only then the current will flow and the LED will light up.  If you use DC power, and hook up the positive lead of the supply to the LED's anode and negative to the Cathode side (also using a resistor in series with the LED of course) then the current will flow and LED will illuminate.  If you hook it up in reverse, the LED will not conduct any current and will stay dark.

AC power from wall-warts flips polarity 60 times a second (60Hz)  If you use that power source to light up the LED, the LED will light up every time the AC polarity is correct for that LED circuit (which is 30 times a second).  Because of persistence of human vision the LED still look like it is illuminated, but in reality it flickers 30 times a second.  And since it is not lit 50% of the time, it will not glow as brightly as if it was powered from a similar voltage DCC supply.  To demonstrate that the LED is flickering, take the lit LED in your hand and swing it left and right very fast. That will show you that the LED is not on all the time (you will be able to see the strobing effect).

I prefer to use DC power for the LEDs. One of the reasons is that white and blue  LEDs have very low maximum reverse voltage rating. When the AC polarity is in the reverse cycle (the LED is not lit) the voltage might be exceeding the reverse voltage rating and the LED could be damaged.
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mighalpern

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Re: wall wart power types
« Reply #2 on: March 08, 2016, 01:27:56 AM »
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peteski;
thanks for the explanation.  makes sense on the incandescent bulbs.
 I had a feeling about the AC cycling and powering it halve the time.
I was not thinking reverse current, so thanks.  i will stick with the 9 volt DC wall wart

glakedylan

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Re: wall wart power types
« Reply #3 on: March 08, 2016, 05:53:04 PM »
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Peteski
this information is very helpful
i always appreciate your knowledge in electronics
thanks for posting!
sincerely
Gary

Incandescent bulbs will work fine with AC and DC power. All your household ligthbulbs were powered by 125V AC.
LEDs only light up when the voltage is higher at the anode then at the cathode. Only then the current will flow and the LED will light up.  If you use DC power, and hook up the positive lead of the supply to the LED's anode and negative to the Cathode side (also using a resistor in series with the LED of course) then the current will flow and LED will illuminate.  If you hook it up in reverse, the LED will not conduct any current and will stay dark.

AC power from wall-warts flips polarity 60 times a second (60Hz)  If you use that power source to light up the LED, the LED will light up every time the AC polarity is correct for that LED circuit (which is 30 times a second).  Because of persistence of human vision the LED still look like it is illuminated, but in reality it flickers 30 times a second.  And since it is not lit 50% of the time, it will not glow as brightly as if it was powered from a similar voltage DCC supply.  To demonstrate that the LED is flickering, take the lit LED in your hand and swing it left and right very fast. That will show you that the LED is not on all the time (you will be able to see the strobing effect).

"the gift is today ... the promise is tomorrow ... the freedom is that yesterday is past"

peteski

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Re: wall wart power types
« Reply #4 on: March 08, 2016, 06:57:41 PM »
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Peteski
this information is very helpful
i always appreciate your knowledge in electronics
thanks for posting!
sincerely
Gary

You're welcome. That's what forums like this are all about.
--- Peteski de Snarkski

-"Look at me, I'm satirical!!!"
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Cajonpassfan

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Re: wall wart power types
« Reply #5 on: March 09, 2016, 07:22:55 PM »
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You're welcome. That's what forums like this are all about.

Than, and we like to look at your avatar :D
Otto K.