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Mobile Install: Grounding

Discussion in 'Mobile Radio Systems' started by KI4KGR, Jun 9, 2018.

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  1. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Let's not get too hasty in removing the negative lead fuse.

    While rather unlikely, it is possible for the battery's chassis ground connection to fail. That could cause starter and/or load current to flow back to the transceiver and/or coax cable to ground. This issue has cropped up twice I am aware of. Once on a Nissan Titan pickup truck, and on a Toyota Tacoma. In both cases, the battery ground connection was compromised due to over tightening. I have a photo of the Titan, but can't find it. If I do, I'll post it.
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Here is the photo I mentioned above. The accessory ground isn't what I would call robust, but it is used on a lot of vehicles, not just Japanese ones. In the case I alluded to, the screw broke, but the radio ground connection (ring terminal) stuck to the battery lead connection. The fuse was inline, and blown, thankfully. I don't know enough about the Toyota case to comment.

  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Just because; "that is the way they always have done it makes it correct". Great example is many radio manufactures Fuse both Positive and Negative battery polarities which if you know anything about electrical ground systems is extremely dangerous. That goes back to the day of the 50's when cars and trucks had Positive or Negative bonded systems and radios used Floating Systems. Those days are long gone along with points and condensers. Time to get up to date.

    Additionally you are incorrect, a picture from Motorola is worth a thousand words. I have no issue if you want to use the Chassis as your return conductor in your trunk or wherever as it is not my problem, nor do I really care what you do. What I will say is use the same point the vehicle manufacture used to bond the battery to the chassis which is usually on or by the Firewall or as close as you can get to it.

  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Alan that is one of the best reasons to never use a fuse in the negative lead. Solidly Grounded means just that, no fuses or switches. You are contradicting yourself in your BLOG. CW keyer ring a bell? If you loose or somehow disconnect the fuse, most likely your radio will still appear to work in some radios. But when you key the mic you now have high current inside your radio where it was not designed to go through.

    I have a lot of respect for you and in your Blog I agree with just about everything you say with respect to mobile installations. I take a different opinion than you do with just one item on the Hall Effect Sensor. Not every vehicle has all battery return leads going through a Hall Effect sensor. Every vehicle may have Hall Effect sensors, but not every vehicle runs all returns through the sensor.

    However that is all a MOOT POINT because where we do agree and what makes it a MOOT POINT is to bond the Radio Negative Return Conductor where or near the same point the vehicle manufacture bonds the battery to the chassis. FWIW that is exactly how to instruct folks to connect the radio in your BLOG.
  5. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I'm glad to see that you now agree with negative bonding location at the chassis near the battery.

    So, I would summarize best practice as follows:

    1. Radio positive to vehicle battery positive terminal, with an inline fuse very close to the battery.
    2. Radio negative to chassis at the same point as the vehicle battery negative, or close by. No fuse needed or advised.
    3. If the vehicle has a battery management system (around 2011 or newer), check that the location for negative will not bypass the current sensor of the battery management system (shouldn't be an issue if #2 followed).
  6. K7JEM

    K7JEM Ham Member QRZ Page

    In the past, if you had a Motorola radio for a positive ground vehicle, it still came with one fuse. The fuse was in the negative lead that attached to the battery. The positive lead was a short pigtail with no fuse, that was grounded to the frame of the car near the radio. Same procedure that applied to the negative ground vehicles, except fuse and short pigtail wire were reversed. The "fuse negative and positive leads" seems to be a Japanese thing that showed up when the import radios started becoming popular. It has never been a Motorola thing or a GE thing, or promoted by any American manufacturer of radio equipment.

    I have no issue with attaching the negative lead to that point, however, many current install kits do not provide a "long" negative wire to run back to the battery, or even the firewall. I posted a picture a few posts back of a current DC install kit for a Harris (previous GE) radio. It has about 30 feet of red wire, and about 5 feet of black wire. Obviously, that is not enough negative lead to get from the back seat of an F150, let alone from the trunk of a car. As an installer, are you supposed to go and get more black wire, splice it on, and then run to the engine compartment? The designers of that radio never intended that to happen. Many Motorola radios are the same way.

    The diagram you posted looks to be a print from a "Motorola Solutions" install page. But the radio looks to be a Vertex radio, I'm not sure of which model number, but almost assuredly a Vertex. That radio brand, although now owned by Motorola, is actually a Yaesu. Yaesu started the Vertex brand back around 1990 to sell LMR equipment and get away from the Japanese sounding name, and to appeal to public safety and commercial LMR customers and dealers. So, the diagram hails back to the Japanese roots of negative lead going to the battery, through a fuse.

    A current Motorola product, the APX1500, has the wiring diagram shown below. As you can see, it differs from the Vertex wiring in that there is no negative wire that returns to the battery, and no fuse, either. This is the same type wiring that Motorola has used for decades, bonding the negative lead to a good ground near to the radio itself.

    The diagram above clearly shows the current Motorola power connector being used on their radios. The power connector on the Vertex is clearly a "Japanese style" connector.

    In any case, I agree that there should not be a fuse in the negative lead.

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