How to ground the case of a multiple output power supply?

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How to ground the case of a multiple output power supply?

Postby ggedamed » 15 Mar 2011, 10:58

I started to make a power multiple outputs, an "eco" one (see pictures). It will feature 4 9V DC outputs and one 15V/18V or ±15V/±18V (not decided yet), using reclaimed transformers and LM317 regulators.

My question is: do I connect the case to the ground? If yes, which one? :scratch:

Thank you.

P.S. I know I have to reinforce and isolate the case. Will do.
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Re: How to ground the case of a multiple output power supply

Postby mysticwhiskey » 15 Mar 2011, 12:47

Assuming you're powering the transformers from the mains supply, then the case should be grounded to the main's earth for safety. Don't forget to add a fuse too. You don't need to ground the regulated DC outputs to the case, and in fact it's desirable not to if you want isolated outputs to prevent hum from any ground loops. Use isolated DC jacks if this is the case.

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Re: How to ground the case of a multiple output power supply

Postby ggedamed » 15 Mar 2011, 16:01

Thank you.
I thought this might be the answer, problem is that in my country only mains sockets with earth are in the kitchen (overpopulation control? who knows...). I don't play in the kitchen, which means no shielding. Is there anything I could do in this case?
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Re: How to ground the case of a multiple output power supply

Postby Hides-His-Eyes » 15 Mar 2011, 16:58

Pray for your safety...

I don't think there's much you can do. Leave it ungrounded. Better yet, insulate the inside with some kind of firm material that won't easily be nicked by a wire. Or better yet indeed, build it in a plastic enclosure.
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Re: How to ground the case of a multiple output power supply

Postby DrNomis » 15 Mar 2011, 17:44

You could ground the DC side of the supply to the case by connecting a 100 Ohm resistor in parallel with a 100n capacitor from the circuit ground to the casing, something that is done in the current version of the BK Butler Tube Driver, also, as has been stated in one of the other posts in this thread, make sure that you have securely connected the Mains Earth wire to the case, this prevents the case from becoming live if a fault occurs in the mains transformer primary-winding, and also include a suitably rated mains fuse in the Mains active wiring to the transformer primary.... :)
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Re: How to ground the case of a multiple output power supply

Postby johnnyg » 22 Jan 2012, 13:36

Hides-His-Eyes wrote:Pray for your safety...

I don't think there's much you can do. Leave it ungrounded. Better yet, insulate the inside with some kind of firm material that won't easily be nicked by a wire. Or better yet indeed, build it in a plastic enclosure.


I know this topic is old hat. But the best would be to try and fashion the unit as approximating 'Class II': http://en.wikipedia.org/wiki/Appliance_classes#Class_II So a solid plastic enclosure like HHE suggests surrouding some kind of metal faraday cage to help reduce any interference perhaps.

The household appliances you get in the UK with a plastic pin in place of the metal earth pin on the plug (and just two wire cable) used to perplex me before I learnt something about this kind of thing.
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