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I have the Mean Well PT-45B power supply (data sheet here). It has three channels, which should give 5V, 12V and -12V, as I understand.

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Pin 1 and 4 or 5, and pin 6 and 4 or 5 should give 12V and -12V respectably (as of my understanding).

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The issue is when I connect the power, and try to measure the DC voltage, I get wrong outputs.

Pin 1 and 4 gives -17V and pin 6 and 4 gives 7V (see pictures). There is a potentiometer to adjust the output somewhat, but If I adjust it away from center to the left or to the right, the readings get really jumpy (see gif).

enter image description here enter image description here

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3 Answers 3

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Pin 1 is on the right side of the connector which is a bit unusual, and from the pictures I guess you thought pin 1 was on the other side, so that explains the wrong polarity.

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The power supply has a minimum load on two channels, notice it says "0.4-5A" on channel 1, not "0-5A". This is common on this type of switching supplies.

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It only has feedback (and thus regulation) on +5V output, so the other outputs will be less accurate, especially if the minimum load requirement is not met.

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So you need to make sure your load draws the minimum load current if you need accurate output voltage. Probing the supply unloaded (as in the pictures) will result in too high voltage.

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    \$\begingroup\$ Thank you! The main issue was that the pins was arranged in a "wrong" (or unintuitive) order. After that it measured correct enough, even without any load. :) \$\endgroup\$
    – eivindml
    Commented Jan 16, 2020 at 13:03
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    \$\begingroup\$ The clue is really that all the voltages are 12V offset and inverted from the expected ones. \$\endgroup\$
    – jonathanjo
    Commented Jan 16, 2020 at 14:35
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Often it's a good idea to read the connector drawings from the connector manufacturer -- I used to keep the Pin-1 markers of all kinds of connectors in my notebook.

However, very surprisingly, Molex doesn't mark the Pin 1 on the KK-5.08 connectors, though they do for the KK-3.96!

enter image description here (Source: Molex drawing for KK-3.96 connector) enter image description here (Source Molex drawing for KK-5.08 connector)

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The switching power supplies don't like to work without any load - in most cases the output voltage will go too high (as you see). The current range for CH1 and CH2, shown in datasheet of yours SPS, starts from 0.2...0.4A instead of 0. Try to load your SPS (with resistors or lamps), then do the measures.

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