If I were to use a benchtop power supply to power something like a motor or servo while controlling the motor/servo through the Arduino, would I need to connect the ground from the benchtop to the GND on the Arduino?
I'm asking because some benchtop's don't have a ground output, so how does that work?
Ground is a reference point.
I can think of a bench supply with a floating ground... but not one without something you can call "GND". Without ground you cannot measure a "potential difference" that means anything. And a potential difference (aka voltage) is what makes your motor run...
If you are saying it has pins marked + and -... then - is GND
Ok, so the - on a benchtop like this one is Ground?
correct
The "+" being obvious Positive voltage and the "-" meaning "NOT +", therefore GND... UNLESS!!! the lab supply is a +/- ground referenced "dual polarity" supply... in which case the + and - are both referenced to the 3rd GND plug. (hence... 3 power plugs, not 2) With 2 plugs... one is ground (even if it floats).
The "black knob/terminal" (negative) is your "ground". On that PSU, it is likely a "floating ground" - meaning it isn't tied to the ground terminal or chassis of the power supply. This has the advantage of isolating the powered circuit from the mains, but the potential disadvantage of allowing more noise into the circuit.
On power supplies with a separate ground terminal - that terminal is tied to the mains ground (which should in turn be tied to earth ground). Since it isn't floating, though, depending on the quality (and other factors) of the power supply you might note a voltage difference between earth-ground and positive, vs "floating ground" and positive.
Finally - note that on the power supply you referenced, without more details it isn't easily possible to say whether that negative terminal is a floating ground or not - but most likely it is.
Ok, so for a power supply like this one, the ground should always be connected to the ground on an Arduino when powering a motor or whatever, correct?
yes. Both voltages Arduino and External Power need to share a common ground (reference) or you will not get the results you want.
NOTE: OP AMPS like negative voltages... Arduino's... do not.
would I need to connect the ground from the benchtop to the GND on the Arduino?
You need two connections for a "complete circuit" so the electrons can flow.
If you have a multimeter, I'm sure you've noticed that you need both probes connected before you can read anything. If you are measuring DC and you connect the meter backwards (so the +voltage becomes your meter-reference) the meter will read negative.
Or, let's say you have a power supply with 3 voltages... +5, +15, and -15V. If you connect your meter between +15 and -15, you'll measure 30V. If you stick the meter between +5 and +15, you'll read 10V.
Or... DON'T TRY THIS, but you can touch the 120VAC or 240VAC power line in your house, and as long as you don't also touch ground, and as long as your shoes are insulating you from true ground, you won't feel anything.* Without a complete circuit, the electrons can't flow through your body.
I'm asking because some benchtop's don't have a ground output, so how does that work?
I have a bench power supply here at work. It has 5 binding-posts on the front: +5, +20, -20, common, and ground. I use the common, and I've never used the ground.
The ground terminal on the front of the power supply is connected to the power supply chassis and to the power line ground. But common (and the other terminals) are "floating" relative to ground. So for example, if I measure the voltage between +5V and ground, I don't measure anything.
Think of the Green Post (Earth Ground) as a Safety and sometimes Noise Elimination(or Causing) ground. It is not required for any of your circuits to work, typically.
But if you are using analog inputs it can some times solve or cause noise problems in your measurements when you connect the Earth Ground to the DC Return. The DC return will be connected to Ground Plane in your project. This is generally where any instrumentation cable shields are connected also. I'll just throw out the term "Ground Loops" if you want to spend an evening chasing rabbits on Google.
If you have any Line Power (Mains it called in some places, think 120-240VAC as an example) involved in your project and/or in the same enclosure - you may be required to connect the Green Post to the DC Return and any other metal, including the project case. If it is metal that someone might touch and you use line power it should be connected to earth ground for safety reasons. This is regardless of any noise it might introduce into your analog circuits. You have to solve your noise problem another way.
Probably way more info than you want or needed, but you never know who might read your post in the future and I just want to save them a lot of grief (literally). Been there.
As already stated, the GREEN ground banana jack (when present) is a safety feature. It is internally connected to the chassis of the power supply (or any piece of equipment) and the third prong on the power cord is connected to the chassis. This is so, in case something were to happen causing the 120vac to short to the chassis, while you were touching the chassis, the ac current would be shunted directly to ground, blowing the fuse and tripping the circuit breaker. Obviously, this is not likely to happen with equipment such as the supply you linked because they are made in such a way that wires don't come loose.
Great replies, thanks everyone!