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I just setup a pepper seed starting shelf using a metal shelf from a Swedish furniture outlet. The shelf has no electrical contact with the 5x T8 bulbs which are hanging on plastic zip ties. The T8 bulbs do not have a ground connection, and are isolated from their own chassis. At the very bottom, I have a small box, which uses a 12V DC LED strip powered from an external power supply (xbox 360 12V brick), for the sprouted seedlings. I was testing if there is any leakage from anywhere using a multimeter and before I even installed the "sprout box" I had about 10V/AC from the shelf in respect to the earth wire in the wall outlet. I thought that was bad and grounded the shelf to earth, although electrically isolated from everything, and the voltage disappeared. Now recently after adding the "sprout box" I noticed when touching the wires leading to the LED strips, I get a light "zing" when touching the shelf. Between the xbox 360 PSU and the metal shelf is 210V/AC!!! So I checked how much current can flow and I'm seeing about 80µA, which lights an LED very dimly.

Is this something I should worry about, as it only happens if I touch the LED strip power leads?

How comes I have such crazy floating voltages? all from induction?

Should I ground the xbox psu too?

p.s. the xbox psu doesn't have an earth connector, only live and neutral.

p.s. the psu in question is an xbox 360 power brick Here is an excerpt from the link Jack Creasey suggested below

PSU info

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    \$\begingroup\$ This is perfectly normal and the reason why metal furniture is tricky. Your shelf is at earth potential while your Xbox PSU has no earth connection, which is why its GND is floating. This means both its live and neutral wire are connected to GND by a Y class capacitor in the filter circuit. As long the current is only a few 100µA, that's ok by design. It may be unexpected though. \$\endgroup\$ – Janka Feb 3 '17 at 21:58
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    \$\begingroup\$ @Janka: That looks like an answer. Want to post it as an answer? \$\endgroup\$ – JRE Feb 3 '17 at 22:32
  • \$\begingroup\$ Answers tend to be more elaborated over here. \$\endgroup\$ – Janka Feb 3 '17 at 22:46
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    \$\begingroup\$ @Janka: Yes, answers tend to be more detailed here. But facts is facts, and if they can be expressed in few words, then that's how it is. \$\endgroup\$ – JRE Feb 3 '17 at 22:51
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    \$\begingroup\$ I guess @Janka has a sensible explanation. How do I accept that as an answer? \$\endgroup\$ – jm11011 Feb 4 '17 at 15:38
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This is perfectly normal and the reason why metal furniture is tricky. Your shelf is at earth potential while your Xbox PSU has no earth connection, which is why its GND is floating. This means both its live and neutral wire are connected to GND by a Y class capacitor in the filter circuit. As long the current is only a few 100µA, that's ok by design. It may be unexpected though.

Filter capacitors inside a PSU

This (roughly) is the schematic of a LVDC PSU with the common filter caps. The Y capacitors are pretty useless when you are having no earth connection on the mains side but PSUs may come with or without earthed plugs due to local regulations so you can assume the Y caps are there even when there is no earth. This causes the inner shield to float at half of mains voltage at a very high impedance.

On the low voltage side, there may be also caps connected to the inner shielding which causes the "half on mains" voltage to be displaced on the DC lines.

For medical devices this is often not acceptable so there are regulations which force medical PSU suppliers to reduce the Y capacitance (even when there is earthing) and add a big choke coil instead for proper mains filtering.

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  • \$\begingroup\$ Is it safe to simply connect one side of the PSU output to ground? \$\endgroup\$ – immibis Feb 4 '17 at 23:43
  • \$\begingroup\$ To earth, you mean? That would do nothing to the problem because both the GND and the +12V (or whatever) line are connected to the inner shield by the EMC filter caps. You would increase the noise on the +12V line of course as it then had an additional 60VAC (or 120VAC) potential against its GND. You cannot earth both the GND and +12V output lines. The only way to get rid of that voltage is to earth the shield itself. \$\endgroup\$ – Janka Feb 4 '17 at 23:47
  • \$\begingroup\$ Yes, I mean to earth. It would orevent current from flowing when through the asker when they touch the wires because it would instead flow through the (low-resistance) bonding point. \$\endgroup\$ – immibis Feb 4 '17 at 23:49
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If you are using an Xbox power supply with an IEC connector like this:

enter image description here

then it has an Earth connection. I'd suggest it's likely you have incorrect wiring to the plug, or incorrect wiring in the wall socket you are using. This image is for an Xbox 360S

As one comment pointed out the picture is one of the two pin plugs. But you may have a 2 pin or 3 pin supply depending on where in the world you are and what local regulations were conformed to for the supply. There are also variants for what motherboard is used (which varies the connector). There are over 6 variations of power supply when you consider mains plug (2 prong/3 prong) and motherboards.
You can tell the PS connector/motherboard version apart using this:

enter image description here

Read this if you are unsure: http://support.xbox.com/en-US/xbox-360/console/power-supply

The only way to get a (mains) high voltage on your shelf is for there to be a leakage path from the mains side to the output. This could be the results of:

  1. Bad wiring for a 3 prong
  2. Bad wall wiring for a three prong
  3. A three prong PS using a two prong cable
  4. A bad power supply (2 prong or 3 prong).

You should be able to measure the voltage between the PS output (+12 Gnd and +5SB) and the wall supply mains neutral and earth pin to establish is there is a power supply problem.

It's also worth noting that the Xbox 360 power supply is never off. Although you have to short +5SB to Gnd to get +12 V....in the off condition it actually outputs >3 V to test if the motherboard is shorted (Standby).

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  • \$\begingroup\$ No... It doesn't. Look closely. That's a C17 connector to NEMA 1-15-P, without ground. You are thinking its a C13/C14, the 3 prong grounded version. \$\endgroup\$ – Passerby Feb 4 '17 at 1:55
  • \$\begingroup\$ You're right, the picture is not correct.....but I have used several of the Xbox power supplies here in the Us and they certainly do have a ground pin. I still maintain the OP is likely to have bad wiring. \$\endgroup\$ – Jack Creasey Feb 4 '17 at 3:50
  • \$\begingroup\$ Most 360 supplies do not have ground pins. You are 100% wrong here. \$\endgroup\$ – Passerby Feb 4 '17 at 3:53
  • \$\begingroup\$ I'm looking at one of my surplus hobby versions now....and I've checked the two Xboxes in my house....all with ground pins. And I worked in the MS Xbox division for several years....I don't know what to tell you. \$\endgroup\$ – Jack Creasey Feb 4 '17 at 4:04
  • \$\begingroup\$ Microsoft Xbox employee, Uhhuh. Picture, part number. Otherwise please stop giving people false information. \$\endgroup\$ – Passerby Feb 4 '17 at 4:09

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