Astron PS and Your Ground

Discussion in 'General Technical Questions and Answers' started by KF5LJW, Oct 29, 2019.

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  1. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK seeing a couple of threads about DC Power Supplies got me thinking it might be time to revisit ASTRON Power Supply flaw again. Might some newbs and perhaps you. I am referring too Astron Conventional Linear DC Power Supplies from 10 up to 70 Amps. Astron does have a well-known flaw and many do not understand what to do and why. Hopefully I can shed some light on the subject.

    OK that flaw or inconsistency is Bonding the 12-volt Negative Output Terminal to the Chassis. Some models Do, some Don’t, and some In-between with a Resistor installed between negative and chassis.

    Astron is the only one that sometimes Bond Negative to chassis, no others worth having. So, what should you do? Well that depends on your station Grounding and Bonding techniques and if you followed code or some ham’s advice. So, assuming you have a coax going outside, is properly bonded to a Ground Electrode System that is in common with your AC Service Ground, , the bond inside Astrons should BE REMOVED no doubt about it.

    With 12-volt Neg bonded to the chassis, connects your coax shield to the 3rd Wire, Green Ground wire in your Astron Power Supply. This causes a nasty Ground Loop that has a few real negative results.

    1. Your 12-volt radio most likely has the chassis bonded to the Negative 12-volt input line and that Bond is in parallel with the Astron bond. That will cause AC and DC Current to circulate in the power supply and power wiring. It can wreak havoc on Audio, RF, and I/O circuits. You are unknowingly injecting noise into an otherwise clean Ground Circuit.

    2. If lightning were to Strike, gives lightning a path to travel through your homes wiring via Coax Shield > DC Power Supply Neg-G Bond > Power Supply Cord Ground Circuit Green Wire. Even in normal operations there can be circulating current between coax entrance and AC Ground, and that again is a noise you can do without.

    OK now you know why most of you should break the connection between 12 volts Negative and Ground inside the power supply. Then you might ask; Is there anytime I should have it bonded?

    Well the answer is yes, but rarely. I can only think of two circumstances where you would consider having a Bond in the power supply.

    1. Is perfectly acceptable and complies with code. That is where you have an Attic Antenna or like that is not exposed to the elements and no chance of being struck or influenced with lightning. Example a simple system of say a power supply VHF/UHF radio and antenna, or an HF rig with a dipole in the attic. With the Bond jumper inside the power supply connects the coax shield to the AC Equipment Ground thus keeping touch voltages to acceptable limits. What the ground is there for is in the event it comes into contact with AC voltage to operate a fuse , and provides touch potential reference. Other than that, the ground has no purpose or function. The AC Equipment Ground or the 3rd wire in your AC power Cords has two purposes. A) clear AC power faults, B) provide a reference to 0-voltage, thus touch potential. It has no other purpose.

    2. OK I hesitate because there is no way to make the following scenario comply with any known electrical code or best practices. OK some ham told you to set a few ground rods outside the shack for an RF ground and a place to Bond your coaxes to before they enter the shack. Either that ham operator said do not bond your RF Ground to AC Service, or you just not understand.

    So here is the problem with number 2 and why I hesitate. If your RF Ground is isolated from the AC Service Ground, and the bonding jumper inside the DC supply is OPEN, if there were a lightning strike nearby or hit your tower. there would be tremendous difference in voltage between the two grounds (AC and RF) measured in the 10’s of thousands of volts. So, where does RF Ground and AC Ground come into close proximity? Your DC power Supply. You would have a flash-over and if you are near could also flash-over. By having the Bonding Jumper installed would at least limit the Flashover, however the current surge would be several thousand amps of current. However, that is only a Cover Up and/or Band Aid that fails to address the real problem of a code violation. The correct fix is BOND the RF Ground to the AC Service Ground, and pull the jumper out of the power supply.

    When it comes right down to it, the only time you would want to consider having 12-volt neg bonded to the chassis is when you have a simple set up with an attic antenna so it is safe.

    Hope that helps some of you.
     
    Last edited: Oct 29, 2019
    W4KJG, N0TZU and N8VIL like this.
  2. AB6RF

    AB6RF Ham Member QRZ Page

    Good post, thanks for it.

    What about all the linear amplifiers with the chassis (and the coax shield) connected to the AC Ground wire?
    Same issue exists there, no?
     
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yes most likely true to my knowledge. Depends on what reference the secondary of the output transformer uses.
     
  4. AA4PB

    AA4PB Ham Member QRZ Page

    I question the part about AC and DC currents "circulating" between two parallel ground paths. It seems to me that the current would divide between the two parallel paths according to their resistance just like two resistors in parallel. In my station, all equipment is rack mounted so every piece of equipment is connected to the metal rack which is connected to the station single point ground so there are multiple parallel paths to ground.
     
    W9WQA likes this.
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    Then you do not have a Single Point Ground. It has to be either Multi-Point or Single Point.

    What is troubling you about AC and DC Current flowing other than it should not be happening? If you draw it out, you can clearly see why. You are forcing DC current onto ground circuits when you bond the 12 Volt Negative to Chassis ground in the DC Power Supply. With your Radio connected, bonds the negative again to chassis creating a parallel Ground Loop. So now you are putting normal load operating current onto your grounds which is a big No No. It is all because your Power Supply Negative is bonded to chassis and the chassis is bonded to the green AC Equipment Ground Wire to AC Service Ground. Loops back around on your coax because it is bonded to the same electrode system the AC Service is using. You create a Perfect Storm to make man made noise and handicaps your radio.Your shooting yourself in the foot during a butt kicking contest so to speak. Good Luck.

    This not something new or unknown. In fact has been known for at least 3-decades because that is how long I have known about it. Lot of hams have learned from experience and a well known issue. Having the 12-Volt Negative Terminal in the Power Supply bonded to the chassis is just setting you up for a lot of trouble like noise and unnecessary currents circulating looking to poke some fun at you testing your patience trying to figure it out.

    The Negative can and will be bonded to Ground down stream from the DC Power Supply at your Radio and/or Gizmos which is just fine and does not create a Nasty Ground Loop. If done inside the DC Power Supply, you create a Nasty Ground Loop because the Chassis is bonded the the AC Green Wire Ground wire going back to your breaker panel and to AC Service Ground.

    Lesson 2

    Where does RF Ground Start?

    Answer. The Output Connector used to terminate coax too. Which just happens to be where 12-Volt Negative is bonded to Ground via your coax if you have it bonded correctly to ground electrode system when it exits the shack.he DC Power Supply is the dividing line between AC Safety Ground and RF Ground. This is where the myth comes in that thy shall have separate grounds for RF and AC. It is a complete misunderstanding and applied incorrectly by thinking that means the outside dirt Grounds should be isolated. That is wrong. The Separation is the DC Power Supply and is the magic of a Transformer providing electrical isolation between Input and Output. AC world on the Primary Input side, and RF World on the Secondary Output side. That is where you Isolate the AC and RF Ground. Get rid of that jumper bonding the two grounds together crating a Ground Loop. .
     
    Last edited: Oct 29, 2019
  6. AB6RF

    AB6RF Ham Member QRZ Page

    I'm not talking about the secondary side.
    For safety reasons, in every single tube amplifier the chassis is connected directly to AC green wire ground.
    (see the screen shots for just couple examples, AL-80B and Alpha 91)

    [​IMG]

    [​IMG]

    And of curse the coax shield is also connected to the chassis.

    It creates exactly the same situation as bonding 12V power supply negative to AC ground, i.e. connecting the RF ground (= coax braid) to AC ground at the station and also at the coax entry point ground bonding.
     
    W9WQA likes this.
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    In my station, it is inevitable that the 0V screw terminal on the rear of the ASTRON RS-35M is tied to earth ground, regardless of what is happening inside the Astron itself! This happens because one end of the black power cable running between the Astron and my IC7300 is internally bonded to the IC7300 chassis. You have no choice about this!

    The IC7300 chassis (PL259) is common to the tuner chassis, the Linear chassis, the tuner chassis, the Wattmeter chassis, the antenna Rotor control box, and the RF coax entry panel and its external ground rods. In other words, everything touched by coax is already bonded together, and bonded to the outside RF/Lightning grounds, both near the building and at the tower base. A special case is the my desktop ham computer. Its chassis is "bonded" to my IC7300 both by a USB cable, as well as a ground strap.

    The Linear, the Astron, the computer, the Rotor control box all have a green-wire in their respective AC-line cords, so each of those also are "bonded" to the electric utility ground system via the in-wall building wiring, in addition to being grounded to my RF ground mecca.

    Since the computer, the Amp, the rotor, and the Astron all have RF bypass caps on L1, L2, and N inside their respective Line Cords, then any Common Mode current that enters your station on any feedline will head for the lowest impedance RF ground that it can find. Best RF design practice is to provide a lower impedance one than the default path through the in-wall house wiring. That is why I provide an RF ground mecca right outside my building...
     
    Last edited: Oct 29, 2019
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  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    I understand that like every other piece of equipment that has an AC power cord will have the chassis to ACEG. No different than a toaster or a DC Power Supply. However that does not mean the secondary of the Transformer is bonded to chassis.
     
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    And it matters not at all for the reasons in post #7.
     
  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    Sorry but you are wrong, you have a choice to do it right or wrong, you chose wrong. I understand the Negative is bonded to chassis in your ICOM like most any other radio as already explained.

    You radio Ground comes from the Coax by the fact it should be bonded to Ground where it exit/enters the shack. There is only one place where your Outside RF Ground and AC Ground come in close proximity to each other is the DC Power Supply. It is the only place where both can be bonded together. Leave the Bonding Jumper out like every other DC Power Supply does, and you break the bond. The Primary side of the Transformer is bonded to the AC Ground, and the Secondary side is isolated and floats. The Secondary is bonded to earth via your coax going outside.

    No different than a utility transformer where you are isolated from the utility and their ground. Any sparky knows what I am talking about.That is why I am going over the flaw with Astron Power Supplies going over a very old well known issue you can fix. A lot of hams are unaware of the issue.
     
    Last edited: Oct 29, 2019

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