Puck Light Power Supply Testing

[sparkyrick]

I had a service call today to trouble shoot some puck lights, 13 of 14 were out. Not knowing if one of the two power supplies was bad, I checked the output voltage first. First unknown supply: 0V, second known working supply: 0V :rant: I tried AC, then DC, still nothing. I looked at the labeling on the power supply, input voltage 120V, 60Hz AC, output voltage 12V, 20KHz AC. Apparently my Fluke 376 can't measure a 20KHz power supply output. This is the second time I've run across this. How does one test these power supply outputs with a meter?

 

[Dennis Alwon]

Not sure why it doesn't measure it but some of those power supplies need a minimum wattage before they will work correctly. Did you change some of the bulbs? Are they all on one trany?

 

[sparkyrick]

Not sure why it doesn't measure it but some of those power supplies need a minimum wattage before they will work correctly. Did you change some of the bulbs? Are they all on one trany?

I checked the power supply that was running the one working bulb and still got 0V, even with the bulb lit!

 

[Dennis Alwon]

I checked the power supply that was running the one working bulb and still got 0V, even with the bulb lit!

I don't know why you get 0v. I don't recall having that problem. Obviously there is more than 0v if the bulb is lit.

 

[sparkyrick]

I don't know why you get 0v. I don't recall having that problem. Obviously there is more than 0v if the bulb is lit.

I don't have a frickin clue. I remember reading on a power supply that I replaced awhile ago that stated that the output voltage might not be able to be measured with a typical meter because it's operating at a higher frequency. IDK.

 

[Barbqranch]

On the Fluke 376 spec sheet, it only lists an accuracy value up to 500 hz. Your 20K hz is probably just too high for it.

 

[Aleman]

20khz. Dang, that's a new one on me. To test it with a meter that doesn't like 20khz, maybe rectify it. Just hang a suitable diode on one lead and measure away.
That will give you a basic 1/2 wave rectifier which might not be very accurate but will let you know if the thing is working. Radio Shack still carries parts and
rectifiers are cheap.

 

[sparkyrick]

On the Fluke 376 spec sheet, it only lists an accuracy value up to 500 hz. Your 20K hz is probably just too high for it.

Well, I can use my nice meter on airplane electrical systems (400Hz), but I can't troubleshoot a cheap puck light power supply

I can't blame Fluke though. They couldn't see a 20KHz power supply being used in residential and commercial lighting.

 

[gar]

150113-2144 EST

With a sine wave input I get the following results:

Beckman 4410 true RMS in AC mode 3 db point is about 80 kHz.
Fluke 27 average reading type in AC 3 db is about 130 kHz.
A Simpson 260/270 is good from about 10 Hz to a 3 db point at 1.8 MHz. In the Output mode the low end 3 db is about 30 Hz.

1N4148 with a 0.22 ufd filter and Beckman 4410 in DC low end is about 10 Hz, high is way above 2 MHz.

Try the diode capacitor approach. Note this essentially measures the peak voltage minus the diode drop.

I would guess that almost any Fluke in AC mode will read up to around 20 to 50 kHz.

What is the 3 db point? This when the voltage has dropped to the half power level (voltage to 0.707 of its value in mid band).

.

 

[PetrosA]

Unfortunately this is one of the "gotchas" that come with clamp meters. They make taking amp readings a breeze, but for specialty stuff they'll let you down. Oh, except for the really cheap ones they sell at the box stores. They can do it all. No. Really.

 

[sparkyrick]

Unfortunately this is one of the "gotchas" that come with clamp meters. They make taking amp readings a breeze, but for specialty stuff they'll let you down. Oh, except for the really cheap ones they sell at the box stores. They can do it all. No. Really.

I have a Fluke 87 and a 787 I keep at home. Guess I'll check the specs on those and see if one or both would work.

 

[PetrosA]

I have a Fluke 87 and a 787 I keep at home. Guess I'll check the specs on those and see if one or both would work.

The 87 V should work (not sure how many generations back, though). The specs are a little unclear, but they definitely give accuracy ratings up to 20 kHz for voltage. It's also able to measure frequency up to 200 kHz, but that doesn't mean it can accurately measure voltage over 20 kHz.

The 787 is only rated up to 500 Hz for AC voltage, so don't take that one with you