Multiple negative ground radios on a single power supply

Discussion in 'General Technical Questions and Answers' started by NQ8J, Sep 10, 2020.

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  1. W9WQA

    W9WQA Ham Member QRZ Page

    you said,,,
    "the bonding jumper was removed from this power supply"

    so when/if, the primary leaks/shorts to the secondary you have line volts on your antenna. kids playing near it in bare feet???
     
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah I was looking at the schematic of a current production LMR repeater recently and negative is bonded to chassis to circuit boards all over the place.
     
    N8YX and K7JEM like this.
  3. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    That’s true. And if using a grounded power supply (as many are per their design) you also can’t eliminate a ground loop on the house ground wiring to your antenna ground and back through the bonding wire between rods. And then there are grounded computers and USB cables, etc to radios that can also present a loop.

    But, is any of this causing a problem? It rarely does, unless something else is wrong like using unbalanced antennas with inadequate grounding and/or no common mode choking.

    Removing an internal negative ground from a power supply is dangerous unless the supply is designed with double internal insulation (and non conductive chassis) so that a chassis ground isn’t needed for AC fault safety. (It would also violate the UL safety listing of the supply, if it has one. Most Astron supplies aren’t UL listed BTW, I checked on the UL database. Nor do they appear to be designed with double insulation).
     
  4. W9WQA

    W9WQA Ham Member QRZ Page

    most electronic devices since the beginning of time have one side tied to a chassis,the other to the supply voltage be it positive or negative. obviously including positive ground radios and hot chassis tv sets....

    and computers.
    and power supplies...
     
    N0TZU likes this.
  5. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    And those that don't are specifically designed that way and approved by safety agencies for that service.

    Look at at the nameplate of a typical small power supply or TV, etc. with a two prong cord these days. They have at least one and typically many safety agency marks showing that the design was examined and tested for electrical safety (crappy, unsafe knockoffs may not have any marks or have counterfeit marks).

    Usually they also have a symbol of a box within a box (below) that indicates the use of double insulation for an ungrounded design.

    Screen Shot 2020-09-10 at 9.01.18 AM.png

    Here is the nameplate from a TV in my house showing this.

    IMG_0070.jpeg
     
    Last edited: Sep 10, 2020
    KA0HCP and W9WQA like this.
  6. KF5LJW

    KF5LJW Ham Member QRZ Page

    What are you talking about? Who said anything about removing the bonding jumper in your radio? What planet are you from?
     
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Many decades ago before we learned how dangerous it was. Computers never ever have done that or anything you buy today except car electronics. As Bob points out there are still two wire devices made today without ground. However they are double insulated as I have said many times before. If it has a metal case that you can touch will have a 3rd wire ground, and nothing inside the gizmo is bonded or using ground as a circuit conductor.
     
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    Dead wrong Bob. There is absolutely no requirement or need for a 12-volt DC power supply to have the output bonded. Prove it to yourself. Go look at a new Astron today. On the back panel is Ground Terminal with a Jumper to Negative with instructions to remove it. It took than 40 years and thousands of complaints to catch up with the modern world. Time for you to catch up too.

    A good quality DC Supply today will have have an option to Floated or be bonded to either the Negative or Positive. Whatever the application calls for. Astron PS are really low quality consumer junk. More about that in another thread.
     
  9. W9WQA

    W9WQA Ham Member QRZ Page

    so when/if, the primary leaks/shorts to the secondary you have line volts on your antenna. kids playing near it in bare feet???

    you end up with a hot chassis.

    but you cant see that.
    you are dangerous.
     
    N0TZU likes this.
  10. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    To protect against a primary to secondary short, the secondary of a supply must be bonded to grounded chassis unless the transformer (if one) and the rest of the design meets the requirements for double insulation or equivalent per safety agency listing. Unless the supply manufacturer doesn't care about listing with UL or other safety agency, and the customer doesn't care for their intended purpose.

    As I said, most Astrons are not listed according the the UL database when I looked a month or two ago. Just because Astron does something is not an indication that it's correct and safe.
     

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