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power supply for qrp rig

Discussion in 'QRP Corner' started by KD2RON, Apr 22, 2016.

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  1. KD2RON

    KD2RON Ham Member QRZ Page

    The rig has the following requirements: DC 10-14 v , 15 max. 360mA rec, current max 3A-3.7 A.
    Can I use a jell storage battery from tractor supply? Can I use my 12 v power supply I have for my Alinco HF when I want to operate from my back porch or is it better to stay with battery power .
    Sorry if these are dumb questions but this is new to me and I dont want to make any stupid moves and damage my new rig. Any help appreciated.
  2. AA4OO

    AA4OO XML Subscriber QRZ Page

    Either a 3-7ah gel battery or your HF power supply would work fine with the proper connectors.
  3. KD8DEY

    KD8DEY Ham Member QRZ Page

    You could also get one of those cheap battery maintainer solar panels from Harbour freight, and add a regulator to increase operating time if under battery power "out in the field"
    under full light without load it puts out over 20v BUT is within range of your typical Regulator IC
  4. KC3RN

    KC3RN Ham Member QRZ Page

    IIRC, your rig is the MFJ 9240. It's really not too fussy about power. It will actually operate with as little as about 8.5 volts, but at a reduced output level. 13.8 volts from your power supply will give you just shy of 7 watts out.

    It's a nice little rig. I was running mine last night.
  5. KD2RON

    KD2RON Ham Member QRZ Page

    Thanks for your help, I dont want to damage my, for me, an expensive and excitiong new toy. Looking forward to trying new bands and making portable antennas. QRP adds a new dimension to thre hobby.
  6. W5BIB

    W5BIB Premium Subscriber QRZ Page

    Along these same lines... I'm using a "wall-wart" (1 amp-13.5 volts) to run my HW-9. My question is: The prongs on the wall-wart are the same size, meaning it can be plugged-in either way.
    Just to be safe, I used a VTVM to check which of the wires showed "hot". It's a temporary power source, but I'm just wondering what would happen if I inadvertently plugged it in "up-side down"? Would damage occur to the HW-9 ?
  7. KC3RN

    KC3RN Ham Member QRZ Page

    Yes. Reverse polarity is bad.
  8. KD2RON

    KD2RON Ham Member QRZ Page

    Are wall warts of the correct voltage safe to use with a qrp rig assuming your polarity is correct?
  9. KC1JLM

    KC1JLM Ham Member QRZ Page

    I am curious about this as well. I plan on using one for my 40m one watter as a temp power source......
  10. AG6QR

    AG6QR Premium Subscriber QRZ Page

    A properly engineered two-pronged wall wart will be isolated, so that the low-voltage DC output isn't directly connected to either of the two AC input prongs. I've owned hundreds of wall warts that are properly isolated, and I've found one that wasn't; I got rid of it. If the adapter is isolated, it makes no difference which way it is plugged into the AC socket. Of course polarity matters on the output (DC) side, but it makes no difference on the input (AC) side.

    As long as the output is isolated, regulated, of the proper voltage, and at least capable of delivering the amount of current the rig requires, it should be OK to run a QRP rig on a wall wart. I've done so on many occasions.

    Some switching wall warts (and they're almost all switchers these days) can be electrically noisy at HF. This can make it hard for a receiver to hear anything over the wall wart's noise. Sometimes the problem is small and can be corrected by ferrite chokes, but sometimes it's easier to swap the wall wart out for a higher quality one. Either way, a little electrical noise doesn't cause any safety concerns or any permanent damage to a radio.
    KI5WW likes this.

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