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Question about low voltage power supplies Answered

I have several wall plug power supplies. The voltage on one says 12v 300ma but on my multimeter im getting 17 volts. Why is it 17v and not 12v?

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tech-king (author)2008-01-28

what trialex said is true. this is also why, on the thread of how to convert under car neons to run on house power, i recommended against a wall wart power supply. to correct the problem and ensure an even, continuous 12 volts, you can do one of the following: install a zener diode accros the positive and ground leads to regulate power install a 7812 voltage regulator install a mosfet vcr

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Rob K (author)tech-king2008-01-28

I was going to use the power supply to run a 30 LED array. The 7812 voltage regulator might be what I need to help.

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tech-king (author)Rob K2008-01-30

30 leds in paralelle?? you may draw too many amps for a 7812. consider a zener diode

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Rob K (author)tech-king2008-01-30

I think it was around 220-240ma for what im looking at running 33 leds. I was going to run 11 3 LEDs series with 15ohm resistors. LEDs 3.9fv 20ma

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tech-king (author)Rob K2008-01-30

ohh. in that case, just use the 7812

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Rob K (author)2008-01-27

I pluged it into a 12DC fan and checked with the multimeter agin wile it was running around 13v.

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trialex (author)2008-01-27

Because it's a cheaper model and not regulated. The voltage of non-regulated power supplies typically sag under load - so to ensure they still deliver 12V under load, they produce a bit more when there is no load attached.

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