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Planning an install, help with finishing touches...

Discussion in 'Mobile Radio Systems' started by N8MLP, Sep 9, 2019.

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  1. KB0MNM

    KB0MNM Ham Member QRZ Page

    W5GX pointed out the thread, the chart would make you consider 10 gauge. Triple-insulate your firewall -through wires, and use water-tight holders for the fuses on the engine-compartment side. There are a couple of other considerations: 1. Mount everything such that it cannot move much, or be moved by airbags. To do this, you will probably be doing some drilling inside the vehicle- at least we hope that you mount the microphone holder such that you are not sending a random PTT with a somewhat dead carrier. For the drilling, invest in a good set of Cobalt Steel, not just Z.Nitride coated bits. These are less likely to be brittle and fail on curved metal ( as in under seats- it almost all is ). Be sure to watch the back of whatever you drill- air bags can inflate if you hit a wire- and can cost plenty. Watch for top-curtain bags when the speaker is mounted, or the antenna wire routed. Remote cabling- be sure your Kenwood kit is sufficiently long ( including ups and downs- eg. alongside carpet, kick-boards, or headliner ). Consider an extra run of Category 5 or 6 8-conductor or shielded 8-conductor stranded cable and the appropriate RJ-45 or Kenwood PG-5H made as an adapter. For the speaker, the Kenwood TM-D700a could sound better in my opinion using the Yaesu speaker ( approx. 4 inches on a side ) with the red square noise-filter button. You should be able to get single channel audio to sound good without changing a plug size that way. You really do not want to try to listen to two channels at once, as transmitting based upon that audio can get others confused. If you must, get two of the Yaesu speakers and an extra switch to easily turn one off rather than turn the knob. Finally, if you can still get a Brute-Force filter for your alternator and battery supply- it made sense to me. Other amateurs may say that if the vehicle is noisey, this is like a doctor covering the symptoms. I would have to agree, but that they know it can help. If you just spent around $700 for the rig, another $25.00 to $35.00 to keep the power-line clean seems like cheap insurance to me. These filters can be home-built, for better serviceability. Or you can check with Motorola or Kenwood for a pre-built unit. If you are interested in fldigi, etc. then also see the K5URU / www.wlhkj.com info first.
     
  2. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK this could get you in trouble if not done correctly. Sounds like you want a Feeder cable to a Distribution Block which is fine, but if done incorrectly could cause melted wiring, excessive voltage drop, malfunction, and a fire danger.

    To start you will need a fuse block on the Battery Positive Term Post. Many new vehicles will have a high current open terminal you can use. Just needs to be fused correctly with the right size wire. If the vehicle does not have a high current terminal you can make one with this Battery Fuse Block than attaches directly to the battery Term Post. They are good to 300 amps and fuses are available from 5 to 300 amps. They even make a Dual Fuse Block in the even you need two circuits. Blue Sea MRBF 2151.

    [​IMG]
    What size fuse and wire you need are directly related. For safety the wire size determines the maximum size fuse that can be used. Example a 12 AWG wire i slimited to a 20 amp fuse. 5, 10, 15, and 20 are OK on 12 AWF but nothing larger than a 20 amp fuse. However that may or may not satisy voltage drop requirements. if the 1-way cable distance is greater than say 10 feet. You want to limit voltage drop to 3% of less which i snot much on a 12 volt circuit because 3% of 12 volts is only .36 volts. Ne sweat, just use the table below. Determine you max load current, say 35 amps, and 1-way distance is 15 feet cable feet. You would round up and use a 40 amp fuse with a 6 AWG cable.

    [​IMG]

    For the battery return Negative do not run a wire to the battery. Use the nearest chassis Hard Point. In fact you will see Ground Terminals hidden under seat, behind panels, and in the trunk area. From the engine compartment you will have one of two wiring harnesses running to the back of the vehicle. Along the way they drop off battery to high power items like power seats, windows, locks, seat heaters, etc. The vehicle puts hardened Ground Terminals for battery return, and the wiring harness will run right bu them along the way to the back. Use the closest one you can find or a Seat Bolt.

    For a Distribution Block I have no idea how many circuits you need. Blue Sea System have a wide selection. Pick one that works like these.

    [​IMG]

    [​IMG]

     
  3. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    When you're wiring for DC, the main consideration is voltage drop, not current capability, per se. The goal is .5 VDC or less. For me, I always error on the low side. You might want to read my wiring article.

    http://www.k0bg.com/wiring.html
     
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Personally I would ignore that BLOG because the information is incorrect, dangerous, and does not comply with any known electrical codes. Case in point: Look at the battery wiring diagram. It shows the Negative Return Conductor fused along with Positive. All electrical codes forbid this practice on a Grounded Systems. Grounded circuit conductors cannot have a Fuse or Switch inserted in-line because it would leave the grounded circuit conductor HOT if the fuse or switch opened. Imagine your surprise if you removed the negative fuse thinking the circuit was de-energized only to discover it is HOT.

    A motor vehicle 12 volt electrical system is a Grounded System, not floating. Only time you fuse both circuit conductors is in a Floating System not referenced to Ground or something in place of of ground like a car chassis.

    All auto manufactures publish Technical and White Paper documents and distribute to agencies like Law Enforcement, Utilities, and professional Two-Way Radio shops who install mobile radios professionally. Universally auto manufactures stress that the Negative Return Conductor should be solidly bonded to the closest chassis ground hard point as close to the radio as possible with NO FUSE INSERTED.

    Another reason aside from safety, is operational issues of voltage loss and noise. Fuses are resistors, and the last thing you want to do is add resistance as that results in excess voltage drop and any unwanted voltage by every text book definition is NOISE.

    So why do some radio manufactures fuse the negative return? Pretty much ignorance and letting executives make poor decisions trying to avoid warranty claims. In the event a shade tree mechanic or amateur removes the ground strap from the starter motor and does not replace it, the starter motor can draw current via the radio negative lead causing damage to the radio wiring.

    Install the radio correctly by using the nearest chassis ground hard point eliminates any possibility of the Starter Motor using Radio wiring to complete a missing circuit wire a moron took off and did not replace.
     
    Last edited: Sep 11, 2019 at 5:07 PM
  5. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    I won't banter with you, but there is a very good reason why the fuse remains in the negative lead. You'd figure that out if you thought about it long enough.
     
  6. W5LZ

    W5LZ Ham Member QRZ Page

    BG - I'm getting old and I'm not sure I have enough thinking time left to figure it out. Why don't you just explain it?
     
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Not much to figure out. I already stated the ill founded logic radio manufactures use. "To prevent engine starter current to using the Radio Negative return conductor in the event the engine block Ground Strap was removed".

    No banter needed because if your stance is to use a fuse in the Return Conductor is a dangerous practice. It does not comply with any known electrical code because it is dangerous. A motor vehicle electrical system ss a GROUNDED SYSTEM where one of the circuit conductors (battery negative polarity) is Intentionally and Solidly bonded to earth or something in place of earth like a chassis to facilitate operation of over current protection devices on the ungrounded circuit conductor (positive). You cannot, well not if you understand the consequences, locate a switch or fuse in the grounded return circuit conductor. Remove the negative fuse, and that black wire from the radio is now at full supply voltage on a conductor that is suppose to be neutral and referenced to ground. This is why switches are always on the Hot Conductor. If you use the grounded circuit conductor as a witch leg as soon as you open the switch, you have full supply voltage on the equipment conductor looking for ground to complete the circuit. Just hope that ground is not you

    Only time you install fuse on each circuit conductor is a Floating System where none of the circuit conductors are bonded to a reference like ground.

    On the technical side, such practice falls short again. All you are doing is adding more resistance in the power circuit than necessary on the Negative return conductor.
     

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