MFJ-4275MV Tripping GFI circuit breaker

Discussion in 'RV Operating and Camping' started by WQ6N, Jan 1, 2020.

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  1. WQ6N

    WQ6N Ham Member QRZ Page

    RV is parked with a dedicated 30amp 120vac GFI protected source. All is fine, until I connect the MFJ-4275, which trips the circuit breaker. Thinking this was a problem with the shared circuit, I wired in a separate 20amp GFI breaker just for the power supply. This new circuit also tripped when the power supply was turned on.

    Any non-GFI protected source works fine.

    Has anyone else experienced this issue?

    73, JohnF
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sounds like the problem is actually in the MFJ power supply. If it has capacitors across the AC input that have any leakage to ground at all -- boom. The GFIs usually trip at just a few mA.

    Why not try a different power supply?
    K0UO and SM0XHJ like this.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Maybe the power cord is not wired properly.

    Does it work if you lift the ground on the AC plug ?
    K0UO likes this.
  4. WQ6N

    WQ6N Ham Member QRZ Page

    It is the power cord that comes with the unit. Works fine on any non-GFI outlet.
    I might just replace the 20amp GFI with a standard circuit breaker and be done with it.
    The only other power supply that I have is a homebrew 100amp computer server PS that I modified for ham radio. Have not tried it. It is pretty noisy with the 3 fans going.
    Thank you for the input folks. Happy New Year
  5. SM0XHJ

    SM0XHJ Ham Member QRZ Page

    That the GFI trips directly when you connect that power supply to AC mains is a clear indication that you have an electrical fault in that power supply. You clearly have too much current going through ground (chassis and safety ground lead in this case). That could be a dangerous situation, and I suggest you track down the source of the problem before you use that power supply again (especially in a non-GFI circuit). If you, for example, were to connect that power supply to an ungrounded outlet, that ground fault current will likely go through you instead (yes I know the plug should prevent you from doing that, but that hasn't stopped people in the passed...).
    As for the cause of this; I see two possible reasons. Either MFJ added too much capacitance to the mains filter in that PSU, or one of the filter capacitors in the mains filter has failed. They do advertise the PSU to be extra protected from RFI, so that might be a hint.
    (A third possible option, which I hope you have ruled out already, is water intrusion.)
  6. WG5GK

    WG5GK Ham Member QRZ Page

    The switching power supply draws high current when 1st powered on to ramp up the capasitors. Also the power supply is rated at 75 amps (70 amps continuous) meaning it uses 7.5 amps or more at 120vac under full load plus system overhead to do the ac to dc power conversion. GFIs are made to turn off fast.

    My suggestion is to run an extension cord from the power pedestal to the power supply to offset the rush current to charge the capacitors.

    WQ6N and K0UO like this.
  7. WQ6N

    WQ6N Ham Member QRZ Page

    During the house remodel, I had the general contractor install a 240vac 15amp circuit in the radio room.
    I changed the MFJ-4275MV over to 240vac by re-configuring the existing connector and rear power selector switch.
    The PS is solid as a rock. This was a good decision.
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    GFCI circuits are extremely simple and even easier to troubleshoot. Assuming the GFCI breaker is operating correctly, the problem is in your power supply. Some ham radio operators and some equipment manufactures think Ground is a circuit conductor. They do all kinds of stupid things like install filters between Line - Ground or Neutral - Ground. Result is you inject small amounts of AC line current in the Equipment Grounds.

    Fortunately the GFCI is smarter than the equipment manufacture and some hams. It knows it is dangerous and generates a lot of noise if you dump line current and noise into Equipment Grounds. So it trips like it was designed to do. The GFCi is doing exactly what it is suppose to do; Protects you from yourself. Your Power Supply is LEAKING current into Equipment Ground.

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