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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. KF5LJW

    KF5LJW Ham Member QRZ Page

    Your either blind or making it up. More accurately not seeing the whole picture. If there is a primary to secondary fault, the AC breaker feeding the DC Power Supply in your AC breaker panel is going to operate, or the 8-amp primary fuse inside the DC power supply will operate. It will be a race to see which one operates first.

    Both your AC Equipment Grounds, and DC Equipment Grounds share the same common ground electrode system. If you followed code and wired up everything correctly the moment the primary shorts out to the secondary, you will have 120 VAC on your coax shield and radio chassis just like you said. However the rest of us should have our coax shields and radio chassis bonded to the Ground Electrode System, and the fault is returned to the utility transformer neutral causing a tremendous amount of current to flow and operate your 20-amp inside your AC breaker panel, or the 8 amp fuse inside your DC Power Supply transformer primary. The race is son to see which over current protection device operates first. Double redundant protection. For some reason you have not seen that yet. Your radio system shares the same common Ground Electrode System connection.

    Last edited: Sep 10, 2020
  2. K7JEM

    K7JEM Ham Member QRZ Page

    I think you are talking about power supplies, I am only talking about radios. You implied that LMR radios are somehow isolated from the chassis, I pointed out that many, or most, have their negative traces on the boards firmly attached to the chassis of the radio. This means that the chassis of the radio is firmly and directly connected to the negative input that comes from the power supply. There would be no electrical difference between attaching your power source negative lead to either of those points, or both, if you want. In fact, in a mobile install, this is what usually happens. You attach a ground lead from the radio to a good ground point near the radio, and attach the frame of the radio to the frame of your car when you insert bolts for that install. Then another ground happens in the roof mounted antenna connection, through the coax, then into the frame of the radio. So, typically three paths for DC current to flow from the battery into that radio, each one with some share of that current.
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yes sir and that makes everything you have said after that a moot point. Works great in a car, wreaks havoc if used anyplace other than a car. Have a good day.
  4. W9WQA

    W9WQA Ham Member QRZ Page

    wrong again. the secondary is floating your way. no way for fuse to blow.
    you just cant see it. ive been saying it for months. talk with a friend.

    note,the secondary and regulator are floating like a battery, UNTIL YOU TIE THEM TO THE CHASSIS. tie to chassis, keep dangerous current form your coax. dont depend on coax to save lives or blow fuses


    ask a trusted friend...
    N0TZU likes this.
  5. K7JEM

    K7JEM Ham Member QRZ Page

    I'm not sure "wreaks havoc" would be correct. In base station use, all of the frames of all of the radios are tied together. Each radio has a separate negative power lead going back to the power supply, assuming a common supply (like a large battery system), to power multiple radios. And each radio is also tied to every other radio at the bonding ground of the coax, where it enters the building. Usually, there is an additional separate ground wire going from each radio to a common bonding point, usually a copper bar, located at some point in the building. Each of these paths (the normal black negative lead, the rack frame, the additional green grounding wire, and the coaxial ground bar) can and does conduct DC at some current level. There is never a time when the only current going into a particular radio is only equal to the current in its dedicated black power cable, assuming there are more than one radio on a single supply.
    K1APJ and N0TZU like this.
  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yep. In my Astrons for example there would be no path to blow the primary fuse in event of a primary to secondary fault, if the secondary isn't grounded.

    One cannot rely on having a load connected to the secondary to provide a path - the supply must be safe by itself.
    W9WQA likes this.
  7. W9WQA

    W9WQA Ham Member QRZ Page

    did this months ago when this marathon started, just to tweak you know who...!
    btw that was authentic heath kit wire

    Attached Files:

    VK6ZGO likes this.
  8. N8YX

    N8YX Ham Member QRZ Page

    Should I hit the lotto for large money, I'm going to have a huge solid gold ground bus constructed. Along with wide chassis to bus straps made of finely woven gold wire, with crimped on gold connectors. A heavy gauge solid conductor out to a set of ground rods driven deep, and kept conducting well via one of the commercially available wetting/conditioning mechanisms specifically designed for such.

    Will post pics of the damage afterwards.

    Haters gonna hate. 'YX gonna operate...
    KA0HCP and WR2E like this.
  9. WR2E

    WR2E Ham Member QRZ Page

    oh so cruel! :eek:;)
  10. NQ8J

    NQ8J Ham Member QRZ Page

    Why not? How would the supply be unsafe with nothing connected to it?

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