Electronics > Beginners
Odd output from Elenco XP-15K Power Supply
mvs:
--- Quote from: tomherrick on January 22, 2019, 03:13:05 pm ---I've taken these measurements with photos of results:
Voltage from P4 to P3 is 17.1V
Voltage from P4 to P1 is 17.1V
--- End quote ---
P4 is connected to P2, so you are measuring AC voltage from the transformer.
Have you switched your DMM to DC voltage mode to measure DC voltage at the output?
Check DC voltages across capacitors. You may post only values, no need to have them on photos.
tomherrick:
A previous respondent indicated wrote: "We don't know how you took your original measurements...", hence the photos to make it clear. I switched the DMM from VAC to VDC to take the output readings; guess I should have included the DMM selector switch in the photos.
rf+tech:
Thanks for the clear photo. That middle digit sure looked like a 3.
What is the voltage on the LM317 adjust pin, at minimum and maximum?
Please refer to the datasheet for correct pin identification.
RF+ Tech
tomherrick:
MVS, not sure how to properly measure voltage across the caps. In VAC or VDC? The only steady reading I've gotten so far is across C1 at 49.5VAC. When I switch to VCD readings I get a myriad of results that keep changing. Am I looking for AC or DC values? Should I expect the values to change/degrade?
rf+tech: On the LM317, Pin 1 is labeled ADJ. When pot is set to 0V the value is -0.57V; set to 15V it's -1.30V
rstofer:
Just to make sure everything is clear, measure AC voltage when looking at the transformer, DC voltage everywhere after the 4 diodes.
For fun, measure between blue and yellow and blue and the other yellow. They should be the same but post these as the AC voltage results. I think you did this and got 17.1 VAC but I just wanted to be certain. Pretty sure that's valid.
49.5 VAC on C1 is invalid because it is a DC voltage - it's after the rectifier diodes. I would expect a number less than 20 VDC.
Voltage across ALL capacitors is DC. They are after the rectifier diodes.
Is the regulator getting hot? One thing that will cause the DC output voltage to vary is the built in self protection from overcurrent. This will reduce the voltage substantially until overload is removed.
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