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I see there are a number of questions regarding this but none made it clear to me, so I'll risk being virtually stoned and go ahead and ask it again.

I have a 12V battery which powers some 12V components, however I also have a bunch of other components that require 5V, so I will get a buck converter. On it there is a Vin+, Vin- as well as Vout+ and Vout-. My 12V circuit has only a + wire, the - is connected to ground (which happens to be the metal case of my work), so I have 12V + wire going into Vin+ on the converter and Vin- is connected to ground. On the other side I would like also to have Vout- connected to ground so that it's easier to connect my 5V components without having to deal with wires but it's bugging me because I'm essentially connecting Vin- and Vout- on the converter and if that was okay then why would they even have put Vout- on there?

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it's bugging me because I'm essentially connecting Vin- and Vout- on the converter and if that was okay then why would they even have put Vout- on there?

You probably have an isolated converter.

If you need to maintain galvanic isolation between the input and output (for example, for user safety), then you would not connect VIN- and VOUT-.

If you don't require isolation, then it's perfectly okay to connect these together.

By providing separate terminals, they give you the choice whether to use the converter in an isolating configuration. If they only provided one COMMON terminal, you'd have no choice and wouldn't be able to isolate input from output if you wanted to.

If your converter is not an isolated design, then they might just provide separate terminals for convenience in wiring.

Edit The photo you shared is almost certainly not an isolated design. They are probably providing separate input and output terminals for your convenience only.

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