I am confused about the following: in my lab, we all run electromagnets off of pretty beefy power supplies. Everyone else grounds their supply. Mine is floating. I do not have even a remotely good understanding of why they ground theirs. I don't see the advantage of it. Also, I want to use a decoupling capacitor (I think that is what they are called), to provide some additional stability. Everyone talks about connecting these between Vcc and Ground. Based on my understanding of how these work, I do not know why I should not be able to put one between the + and - terminals of my supply. Is there a reason I should not?

In short, I don't understand why I would want to ground my power supply and I don't understand why I cannot just put a capacitor between + and -.


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    \$\begingroup\$ I'm confused - everyone talks about decoupling VCC and GND, but you don't want to decouple + and -, which are effectively VCC and GND? \$\endgroup\$ – Greg d'Eon Apr 9 '15 at 16:01
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    \$\begingroup\$ What kind of voltages and currents are we talking about? Are the supplies constant current or constant voltage (regulated)? And do you have a photo of the setup? Grounding is typically safety or noise related. A capacitor across the magnet is just across the supply output- could have interesting side effects if it's a constant current output. \$\endgroup\$ – Spehro Pefhany Apr 9 '15 at 16:04
  • \$\begingroup\$ 100V, 50A (max) ran in constant current mode. \$\endgroup\$ – nosirrahcd Apr 9 '15 at 16:43
  • \$\begingroup\$ I am looking to reduce noise in my field. \$\endgroup\$ – nosirrahcd Apr 9 '15 at 16:43
  • \$\begingroup\$ How do you know the noise comes from your magnetic field? \$\endgroup\$ – Andy aka Apr 9 '15 at 17:46

What sort of noise? RF interference or core hum.

If you can hear noise from your magnet then it is very possible that filtering your supply could help but as @SpehroPefhany said in a constant current circuit addind a simple capacitor it may pose problems, they can mimic negative source impedances and having a coil and capacitor connected may cause oscillation. Grounding is unlikely to reduce acoustic noise but may help with radiated RF that might be coupled onto the power leads. Placing a few turns of the coil wires in parallel through generous toroidal cores near your supply may assist with RF radiation as might using overall screened cables (run the cables in a metal conduit).

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