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Science Forum Index » Electronics - Basics Forum » 12v DC power supply read 18v
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| Ed |
 Posted: Mon Apr 28, 2008 9:19 am |
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I bought a cheap 12v DC "wall wart" to operate a simple LED garage
door open alert. The circuit
has only a microswitch, a 1K ohm resistor, and 12v flashing LED.
However, the power supply
open-circuit voltage is actually almost 18v. Is this going to fry the
LED? Should I perhaps get
a 9v DC unit and hope it reads closer to 12v?
TIA
Ed |
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| Bob Eld |
| Posted: Mon Apr 28, 2008 10:04 am |
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"Ed" <jag_manR__EM*-0_V_E653@hotmail.com> wrote in message
news:K1lRj.25$3O7.19@newssvr19.news.prodigy.net...
Quote: I bought a cheap 12v DC "wall wart" to operate a simple LED garage
door open alert. The circuit
has only a microswitch, a 1K ohm resistor, and 12v flashing LED.
However, the power supply
open-circuit voltage is actually almost 18v. Is this going to fry the
LED? Should I perhaps get
a 9v DC unit and hope it reads closer to 12v?
TIA
Ed
No. This transformer will not hurt the LED.
The max current will be about 16mA which is way below the max rating of the
LED. Most LED's can take 50mA or more. Furthermore, any additional load on
the transformer will drop the voltage toward 12 Volts resulting in an even
lower LED current. The 12 Volt number is a loaded rating. |
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| Ed |
| Posted: Mon Apr 28, 2008 10:28 am |
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Guest
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"Bob Eld" <nsmontassoc@yahoo.com> wrote in message
news:LHlRj.876$1b7.453@newssvr13.news.prodigy.net...
Quote:
"Ed" <jag_manR__EM*-0_V_E653@hotmail.com> wrote in message
news:K1lRj.25$3O7.19@newssvr19.news.prodigy.net...
I bought a cheap 12v DC "wall wart" to operate a simple LED garage
door open alert. The circuit
has only a microswitch, a 1K ohm resistor, and 12v flashing LED.
However, the power supply
open-circuit voltage is actually almost 18v. Is this going to fry
the
LED? Should I perhaps get
a 9v DC unit and hope it reads closer to 12v?
TIA
Ed
No. This transformer will not hurt the LED.
The max current will be about 16mA which is way below the max rating
of the
LED. Most LED's can take 50mA or more. Furthermore, any additional
load on
the transformer will drop the voltage toward 12 Volts resulting in
an even
lower LED current. The 12 Volt number is a loaded rating.
Thanks, Bob!
Ed |
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