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Open Roads Forum  >  Tech Issues

 > Checking voltage on LED power supply ?

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JoeH

Apollo Beach,FL

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Posted: 01/11/21 07:04am Link  |  Quote  |  Print  |  Notify Moderator

Not RV related per se, but figured someone here would know. I recently purchased a set of LED lights to put some path lights to avoid tripping. Hooked up the lights and everything works fine.
Next, I decided to put a strip of 5050 led's on some stairs. The strip LED's have + and - markings and are 12v . The output from the power supply for the path lights is also 12v so I figured I'd hook into that. I got out the meter and I get nothing when I check the voltage, yet the lights work. Check the meter with a different power supply I have for some other lights and it reads 12v as it should. So, why would the new power supply indicate no voltage and yet at the same time, successfully light up the 12v LED lights?


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jkwilson

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Posted: 01/11/21 07:48am Link  |  Quote  |  Print  |  Notify Moderator

AC or DC?


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enblethen

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Posted: 01/11/21 07:50am Link  |  Quote  |  Print  |  Notify Moderator

Reverse your meter leads may show voltage.
It could also be the way diodes are placed in the circuit.


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Tom_M

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Posted: 01/11/21 08:58am Link  |  Quote  |  Print  |  Notify Moderator

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


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wopachop

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Posted: 01/11/21 09:37am Link  |  Quote  |  Print  |  Notify Moderator

JoeH wrote:

I got out the meter and I get nothing when I check the voltage, yet the lights work.
Conformal coating.

I didnt exactly understand your entire post but type that into Google.

JoeH

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Posted: 01/12/21 06:01am Link  |  Quote  |  Print  |  Notify Moderator

Tom_M wrote:

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


Nope-- meter stays on "0" regardless of being on AC or DC.... but the LED lights out in the yard work. Strange

Gdetrailer

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Posted: 01/12/21 08:28am Link  |  Quote  |  Print  |  Notify Moderator

JoeH wrote:

Tom_M wrote:

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


Nope-- meter stays on "0" regardless of being on AC or DC.... but the LED lights out in the yard work. Strange


Post a pix of the power supply with the model number..

I suspect it is a high frequency switching supply and has no or little filtering on the output.. Most meters will not read at all or properly 15Khz-30khz frequencies which most switching supplies operate at which could explain why you can't get a reading but the lights work.

JoeH

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Posted: 01/14/21 06:03am Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

JoeH wrote:

Tom_M wrote:

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


Nope-- meter stays on "0" regardless of being on AC or DC.... but the LED lights out in the yard work. Strange


Post a pix of the power supply with the model number..

I suspect it is a high frequency switching supply and has no or little filtering on the output.. Most meters will not read at all or properly 15Khz-30khz frequencies which most switching supplies operate at which could explain why you can't get a reading but the lights work.


I'll get a pic soon---- sounds like you might have solved it.

jkwilson

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Posted: 01/14/21 08:03am Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

JoeH wrote:

Tom_M wrote:

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


Nope-- meter stays on "0" regardless of being on AC or DC.... but the LED lights out in the yard work. Strange


Post a pix of the power supply with the model number..

I suspect it is a high frequency switching supply and has no or little filtering on the output.. Most meters will not read at all or properly 15Khz-30khz frequencies which most switching supplies operate at which could explain why you can't get a reading but the lights work.


Even with poor filtration, the output of a switch-mode supply is still DC and could be measured with any DC volt meter.

JoeH

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Posted: 01/14/21 10:42am Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

JoeH wrote:

Tom_M wrote:

Switch your meter to AC and check. Most likely one supply is AC and the other is DC.


Nope-- meter stays on "0" regardless of being on AC or DC.... but the LED lights out in the yard work. Strange


Post a pix of the power supply with the model number..

I suspect it is a high frequency switching supply and has no or little filtering on the output.. Most meters will not read at all or properly 15Khz-30khz frequencies which most switching supplies operate at which could explain why you can't get a reading but the lights work.


Quit raining and I went out to get a pic-- it is AC output but no reading on meter.
[image]

* This post was edited 01/14/21 11:14am by JoeH *

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