The Owan looks like it's output is floating (Not connected to protected Earth) but the Stamos may not be (Minus output possibly connected to protected Earth). So I'd connect your project like this:
That is what I was thinking, but
only if I was correct in my assumption that a power supply with a specific separate ground terminal will always be floating.
The issue is that you and your son are equating the negative and ground:
That is almost precisely what I was avoiding, and hence asking...
the fact that the Owon supply has ground entirely separate should be a clue that they’re not the same thing.
Yes, that's what led me to think that a supply without a separate ground will have a problem, because connecting two of them in this way will short circuit them, assuming that a 2 output supply does in fact have the negative grounded, which if it isn't seemed rather dangerous...
The ground (green) jack on a bench PSU is an actual earth ground (aka PE, protective earth), and 99.9% of the time you will not connect it at all. That includes this time. Leave the green jacks unconnected to anything.
Talking of which, is it not dangerous to have a lot of ungrounded equipment like this?
A bench power supply’s output is floating; it has no ground reference (circuit ground, i.e. your 0V reference). So you can (and must) place that ground reference wherever you want in the circuit. Here, you want it at the midpoint between your power supplies, so that you end up with: -15V — 0V — +15V.
You do that by taking two 15V supplies and connecting them thusly:
PS 1: negative jack = -15V, positive jack = 0V
PS 2: negative jack = 0V, positive jack = +15V
Connect the two 0V jacks together. That’s your circuit ground. Observe how in both cases, the red positive jack is 15V higher than the black negative jack. And that the difference between PS1’s negative jack and PS2’s positive jack is 30V.
If this doesn’t make sense yet, you need to go back to the absolute basics of voltage. Take two AA batteries in series and a multimeter, and start probing around every combination of terminals. You need to understand that a voltage measurement is always relative — it’s the difference in voltage between two points.
Yes, the idea that it's a relative potential difference is clear. I was wondering why could one not use a single power supply with 30v. However having tried that, it didn't work. I imagine it's that one can't divide the resistive load so it just doesn't work, you get for example 10v across negative to 0, and 20 across 0 to positive...
P.S. As Kim says, just in case the Stamos is not, in fact, a proper floating bench supply, make sure to wire them the way they show, using the Owon as PS1 and the Stamos as PS2.
This seems to imply that all "proper" supplies should be floating. As above, isn't having a lot of unearthed equipment dangerous, that's why we have earths!
Dave, This is what triple power supplies were made for.
They are typically two 0 to 30 volt supplies (around that voltage) and a 5 volt supply. They are "Floating"
The 5 volt is for TTL, Transistor to Transistor logic devices. Very common devices.
Perhaps getting one of these triple supplies will help your son in his endeavors as he progresses. The suggestions above will work but if you are going to purchase something, I would buy a triple supply. Just my opinion.
I agree, however triple supplies seem to start around €500, whereas the Owon is €100.... I'm not spending 500 on a power supply!
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