Auxiliary Battery for HF & running power Amp.

Discussion in 'Mobile Radio Systems' started by KJ4ADN, May 12, 2018.

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  1. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    This is for Mobile use, as in running down the road, running power.

    My little 2011 Subaru Forester, I have the IC-7000 radio body mounted in the back, left side "cubical", right next to the door. The radio is grounded with #10, there's not a lot of metal within reach of it. The radio "head" is in the front of the car. Aux on the car radio's system is via a long shielded audio cable to the center console. I have #6 parallel cables running from the battery back to the radio, with snap on chokes at both ends. Also on the radio end of the #6, I have 2 caps, 50wvdc x 50,000mfd, and a tee where I've connected a 500w HF linear amp - works nicely, no problems, with all of this setup, no noise.

    The HF antenna is thru the roof, about midway past the the sun-roof and the back of the tailgate, it also passes through the roof rack for extra support (the hole has a big rubber grommet), and a short wire from the antenna to ground thru a small coil for better matching. This has worked well. OK, that's the basic setup.

    Here's the question:

    A couple of times, I've thrown some big batteries into the mix, using them to provide supplemental power to the amp, connected inline to the #10 cable... the radio is isolated to the main car battery, via a diode bridge and battery booster (then to the radio). Is there any advantage to grounding the batteries to the car frame, -and- grounding the solid state linear amp?

    The grounding "path" is a bit interesting, I wonder if I'm limiting output of the Amp, or input power.
    I plan on duplicating this with a truck, but with a larger Amp for 80 & 160m use.

    All replies are appreciated, at least they give me something to ponder.
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Go to my web site, and read the Amplifiers section.
  3. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    (under the grounding section, you have)
    "Under no circumstances, should the body and/or frame be used as the DC power ground return. Doing so on a modern vehicle is a prescription for RFI, and operational problems with the various on-board electronics. Returns should always be directly to the battery or jump points as the case dictates, and the wiring article covers the specifics. Note that using the chassis as a ground return can create a ground loop, often mimicking an RFI issue. This is why ground loops are the toughest problems to find and correct."

    Really that's part of the basis of why I asked, I want neither my radio's ground, the Amplifier's ground to be the "preferred path" for something else I might have forgotten.
    So far, I've run several hundred watts (just shy of 400w, measured), without any issues, but, with JUST the radio bonded/grounded, not the Amp. No problems, no noise, no stray RF, coax is RG-8 to the rooftop connector, which is well connected to the roof, -and- also a very short #6 bonded to a internal roof support.

    The Amp is capable of pulling 275amps. You and I know, even with the 'least path of resistance'.... there is a likely hood, something else is going to be 'included' in the path to ground (even in a minuscule way). Hence the question, if bonding the Amp & Batteries to the vehicle body is of *any* advantage to mitigate "potential" problems...
  4. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    It doesn't matter, as long as there is a return conductor (ground lead). The issues are the voltage drop, and the aforementioned ground loop one.

    Disregarding efficiency, you can get by with almost murder when you're running 25 to perhaps 100 watts, depending on the vehicle of course. But when you step up to high power (≥400 watts), things start to get dicey. If you really want to see what happens, try running legal limit in a vehicle, while underway.
  5. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    .... that is the direction this is going, near legal limit on the low(er) bands. Hence the extra batteries. Was thinking of running "#12 radials" from the antenna mount over the outside of the vehicle the first time.

    I have this vision of running a kw on 160 meters in the rain... road wet... tires wet, and sparks arcing from tire to pavement as I'l rolling down the interstate. LOL

    Mobile HAM experimentation is fun - until it fries the electronics and voids the vehicle warranty, I suppose...
  6. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    The radials won't help. There is almost nothing you can do to lower ground loss. Bonding helps, but you need to remember, that a Greyhound buss has about the same ground loss as a micro car!

    You're correct about the tires. Once upon a time, I ran four, 4CX250Bs mobile, powered by a second alternator (finding room for one under the hood of any vehicle today is all but impossible). As you increase altitude, corona becomes a REAL issue. In 1974, I blew a tire due to corona when operating atop Fremont Pass in Colorado. With an outside temp well below zero, it was no fun mounting the spare. There are other issues too, aside from the radiation standards. It is possible to generate enough current in the various vehicle wiring looms to literally burn them in two! Imagine what it would be like in a computerized, late-model vehicle?

    If you REALLY want to do this, look into buying an Aura Systems alternator—if you own a Ford F250 or larger truck that is. They offer one as an unfit package, for about $15,000. It will deliver 13 kW peak, with about 10kW continuously. The unit has a control box, that not only produces the necessary vehicle voltage, but also 120/240 VAC. There is even a 3 phase 480 VAC option. Don't laugh, I know of two, both using SPE solid state amplifiers, and Scorpion antennas. Which by the way, is the only mobile antenna out there capable of handling legal limit.
    KX4O likes this.
  7. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    .... just imagine the guy who wants to wash my windshield at a stop-light... and I key up, "LEAVE ME ALONE!!!!" Fffffzaaaap!

    Literally a rolling bug zapper! One of these is going on it.
  8. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Too bad.
  9. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    ...we shall see... I like the design & materials, especially the diameter of the coil for 80/160m operation. But, what I'm curious about is the way he makes contact with the coil, it's similar to an idea I was thinking of awhile back, he's doing it on the inside of the coil, I would have done it on the outside with little rollers on a tube.

    I've already built a pretty robust capacitance hat, mounting this monster is an issue...
  10. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Think distributed capacitance, as the coil's end caps and shorting plunger are all aluminum!

    As for the cap hat... It is not place correctly. Got to my web site and read the cap hat article.

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