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DC High Voltage Breakdown Rating Of

Discussion in 'General Technical Questions and Answers' started by N0PGR, Sep 28, 2010.

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  1. N0PGR

    N0PGR Ham Member QRZ Page

    Well for me I'm looking for is....

    How much DC Voltage can pass through

    PL-259 and SO-239 and BNC , F , N......

    and so on


    As far as Coax Cable

    I have seen numbers applied to

    RG-58 of 1900VRMS
    RG-59 of 2300VRMS
    RG-8[PE] of 4000VRMS
    RG-213 of 5000VRMS

    and if you could imagine

    RG-6 of 2700VRMS

    Good and plenty I say


    Wouldn't VRMS imply a AC Voltage

    What about DC High Voltage

    I have seen opinions for

    DC breakdown Voltages of

    RG-58 @ 10KVDC
    RG-59 @ 30KVDC
    RG-213 @ 50KVDC

    So what is the actual DC rating



    So why all this business


    I'm building a large multi band V/UHF amplifier

    Using multi PA decks

    With one LARGE HV Power Supply

    I need to get 1800 to 2300 Volts of B+ to all the decks

    { safely ;) }

    Besides, haven't you had a thought on this

    subject before at one time or another

    Thank you

    Terry N0PGR

    Last edited: Sep 28, 2010
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    For detached amplifiers/power supplies I use high voltage wire, not coax. HV test probe cable is easy to find rated at 5kV DC, and much higher if you wish. Some of the silicone rubber insulated stuff is good for 20 kV+ and it's cheaper and more flexible than coax.

    For B+ I use either Millen 7kV connectors (very commonly found and available, and cheap) or MHV connectors.

    I wouldn't use type UHF or BNC or N, as those can be too easily confused for antenna connections.

    My grounds and B- returns are separate: A couple of paralleled ground wires run in the multi-pin connectors that are used for LV, filaments, switched AC, metering and other stuff; plus the third prong in the AC power cord provides a solid utility service return. I usually bring B- out separately from "ground," as it floats slightly above ground (not much, usually floated by the plate current meter shunt resistor and a fault diode) so I can meter plate current in the B- return path.

    The DC voltage rating for cables should always be somewhat higher than the AC RMS voltage rating, by at least a factor of 1.414. I just avoid using coax for B+ because it's too easily confused for antenna wiring, especially if a guest operator has to de-bug something when I'm not around.
  3. N0PGR

    N0PGR Ham Member QRZ Page

    Cheap is the is the key

    Noted 7mm solid core spark plug wire can be used also

    Have coax

    Poked out there on the net for these

    Millens about $10 each

    MHV about $10 each

    Thats getting up there

    $100 for B+/B- connections

    and that is w/o wire

    Nice , sure is......

    Have PL-259/SO-239 just in the drawer

    Thought about mixing up the connectors

    Got to be a work around for that

    So if one were to use the 2300VRMS you should be covered then

    For this thing RG-213 type will be used

    Flexibility , not an issue

    Terry N0PGR

    Besides, kind of like the idea of
    ground shielded B lines

    Say if one got nicked or cut
    Keeps it inside cable​
    Last edited: Sep 28, 2010
  4. N0PGR

    N0PGR Ham Member QRZ Page

    I found something rather interesting ​

    {holy fix oversized pictures}

    Answered my own question finally

    And Thanks to John Doran KV0L

    Terry N0PGR

    Last edited: Sep 28, 2010
  5. KB4QAA

    KB4QAA XML Subscriber QRZ Page

  6. KE3WD

    KE3WD Ham Member QRZ Page

    Using the same connectors for the deadly high tension lines as you do for your Antenna and input connections is a recipe for disaster.

    Don't think that you would never make a mistake sometime.

    "Never say 'never'"...
  7. W5RB

    W5RB Guest

    What's with the bizarre format ? It's like you're using a template for a wall poster of the Desiderata , and it's ..... distracting .
  8. AG3Y

    AG3Y Ham Member QRZ Page

    If I remember my math properly, you take the RMS values you have listed above, and multiply by 1.414. That will give you the peak of the AC voltage, which should be the same as the maximum DC voltage that the cable is rated for !

    WD has good advice. Use special HV cable rather than coax. A life is PRICELESS ! ! !
  9. K7NI

    K7NI Ham Member QRZ Page

    I have seen modified coax connectors like the ones pictured used on a Hi-Pot tester.

    Regular PL-259, SO-239 and BNC connectors are rated for 500 Vpeak. N connectors are rated for 1500 Vpeak
  10. K8ERV

    K8ERV Ham Member QRZ Page

    I think there are too many variables to come up with one figure. Instantaneous breakdown? Long term breakdown? How clean are the surfaces, etc.

    I worked in a lab that applied 50kv (briefly) to RG-8 in a pulse generator.

    TOM K8ERV Montrose Colo
  11. WB3BEL

    WB3BEL Ham Member QRZ Page

    This issue about using PL259 for HV connections has been beat to death many times.

    It really is more of a safety issue than anything else for HV below 5KV.

    I would strongly recommend not to use these kind of RF connectors for carrying dangerous HV. You yourself might forget and plug something incompatible or dangerous together by mistake. Or a guest operator, or someone handling your estate etc.

    Sure good connectors might cost a bit more, but how much is someones life worth?

    I think that a lot of knowledgeable guys think that the Millen connectors are not that ideal either. The SHV connector is what the savvy guys are using.
    You can search the amplifiers archives here for the gory details.

    If you want the ultimate in cheap and safe, you can get away with direct wiring PS to PA with no external connector. But its not my recommendation because for a few bucks more you have the flexibility of connecting and disconnecting the two boxes without internal surgery.
  12. N0PGR

    N0PGR Ham Member QRZ Page

    Lots of great input here....

    I agree that there are hazards

    [ie death]

    in working with high voltage

    no matter the connection.

    There is always some level, a failure

    that could happen.

    I also feel pretty good about my

    abilities to mod, make or design a wheel.

    I have taken this information seriously

    and glad to get it.

    Right know, I believe the link and pictuers

    I posted back there are my answer to the goal.

    Even been thinking of ways to make maybe even safer.

    As some have posted concerns, makes me wonder

    if they looked at the modded connectors

    and see the potential in the application.

    Positive thinking is good

    Now it is time for the

    "Man's Prayer"

    I'm a man

    but I can change

    If I have to

    I guess

    [Red Green]

    Terry 73​
  13. W8JI

    W8JI Ham Member QRZ Page

    Your messages are formatted weird.

    Anyway, most coaxial cables will handle well over 5000 volts. I typically high pot test RG400 coax to 15 kV without a breakdown (the limit of my cable tester).

    Connectors will always be the weak spot by far.

    The problem is safety. Millen connectors are also very unsafe, not even as good as a coaxial connector. If I did something crazy like running external HV leads between a supply and amplifier, I would use coax and an HVN connector system. I would interlock the system so HV could not be activated when the shield was detached.

    Whatever you do, don't use a common connector or a Millen HV connector.

    73 Tom
  14. M0GVZ

    M0GVZ XML Subscriber QRZ Page

    For the love of god - what are they teaching you lot in the USA?

    VRMS is the root mean square of the AC peak to peak signal and it means the same amount DC would need to be to give the same amount of work etc. So in short, VRMS = DC voltage.
  15. K8ERV

    K8ERV Ham Member QRZ Page

    Try: Vrms=Equivalent DC. Sounds better.

    TOM K8ERV Montrose Colo
  16. W8JI

    W8JI Ham Member QRZ Page

    The real question is what are they teaching you over there!! :)

    The equivalent for voltage breakdown is NOT RMS to DC volts. The equivalent is PEAK AC voltage to dc volts.

    If I have a 5000 volt RMS breakdown with a sinewave test, the peak is 7070 volts. A dc test would fail at 7 kV, not 5kV.

    RMS is used for work or heat. Peak is used for breakdown.

    A good PL259 installed properly would take 5000 V dc, or about 3500 V RMS, before arcing. It is only reliable to about 700 v RMS or 1000 volts dc or peak if someone is sloppy installing the connectors.

    I high pot all my cables to 5000 volts dc or 3500 AC to be sure the connectors are right.

    I would never use a Millen or UHF for a HV connector. I would use a type HVN or a special coaxial HV connector.
  17. W8JI

    W8JI Ham Member QRZ Page

    Except one problem, you told him wrong. You said RMS equaled the DC voltage, but that is incorrect when dealing with voltage ratings of components. Peak voltage equals the DC voltage.

    If that is the case, you missed the first question. :)
    Last edited by a moderator: Oct 2, 2010
  18. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    When I wire up a remote HV PS to an amp, and most of my amps are like that mostly to keep them lighter and the desktop part smaller, I do this:

    Use an AC power relay to switch the HV xfmr primary in lieu of a switch: A big relay can handle it better than most switches, unless the switch is a 20A dual pole circuit breaker or better. I just use relays.

    I break the relay coil with a switch in the RF deck, so I can turn the amp on and off from the desktop rather than at the power supply. In the multi-pin control cable between the RF deck and the power supply are a few chassis grounds in parallel. This way, it's impossible to activate HV in the power supply unless it's plugged into the RF deck and the redundant chassis ground connections are assured, because they're part of the same cable/connector set as the source that activates the HV relay.

    Then, I can use Millen connectors pretty safely, since there's no way HV can be present without the deck and PSU chassis being connected together.

    Since I still have about a dozen of the Millen connectors left (I bought about 30 of them many years ago, from Henry Radio when they were still building big amps -- and they used them all over the place), I'll probably keep using them. I do use 10kV or higher rated HV wire with a thick insulation.

    There are a few dangers using these, for sure: They're molded material and can break and crack; they don't carry a ground; and if a wire pulls out of the connector (breaks off inside where it solders to the pin), there's the possibility of having exposed HV on the end of a wire with no connector on it.:eek:

    However, none of those have actually happened to me. I'll probably keep using them, but with the design detailed above to make sure the chassis ground must be in place for the HV to come on.
  19. AG3Y

    AG3Y Ham Member QRZ Page

    Bravo, JI !
  20. N0PGR

    N0PGR Ham Member QRZ Page

    Yeah, what he said.

    I'm looking, reading and breathing.

    Lots of good stuff everyone.

    Even signed up to that AMPS mailer, great stuff there too.

    Yes interlocks of some kind will be implemented.

    Thanks again everyone, will post in the future about this project.

    73 Terry
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