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[N1AUP]

I understand the absolute necessity of fusing connections to a vehicle battery.  Ideally, fuses should be connected right to the battery to protect against short circuits, and resulting fires, explosions, and other catastrophes. 

In most cases, I've fused about six inches to a foot from the batteries.  I do fuse both the plus and minus, although I've heard this is not a good idea.  Ham radio companies do fuse both sides, and recommend running power directly to the power source.

I now have a Deere backhoe that I am adding a battery switch to.  Right now, there is probably about two feet of heavily protected, 2:0 cable running from the battery to the starter, and another 15 inches from the battery to a fuse, which feeds all of the electrical stuff on the tractor.  The cable to the starter is encased in heater hose to add a second layer of protection, and passes through a grommet protecting the wire from the metal frame of the tractor. 

In my new setup, the two batteries in parallel are going to feed the switch via 2 feet of 2:0.  A two foot 2:0 will go to the starter through the same heater hose and grommet, and another 2 feet from the battery to the fuse / rest of the tractor.  I'd feel more comfortable putting a fuse between the battery and the switch, but that's not how Deere does it in the instructions on how to install the Deere supplied switch. 

Curious as to everyone's thoughts.  I'm thinking that the odds of a short in a few feet of cable is pretty small, compared to a 15 foot run into the cab. 

Thanks

[W9IQ]

In a modern vehicle, you should not connect directly to the battery as they employ a coulomb counter to manage battery charging. If you connect directly to the battery, you will defeat this device and may end up with a dead vehicle battery.

When I added accessories to my tractors, I did wire directly to the battery and put a fuse in the positive side at the battery as well as a fused distribution bar in the cab. The tractors don't have coulomb counters. You do need to weigh the issues of corrosion, resistance, maintenance, etc. when considering the fusing. There are high current fuses made that attach directly to the battery post.

- Glenn W9IQ

[AI5DH]

Adding a fuse directly to a battery positive does not interfere in any way with the vehicles hall-effect sensor. It is not a coulomb counter, just a simple current meter to tell the voltage regulator what the battery charge current is so when it tapers off tells the voltage regulator the battery is charged up and lowers the voltage to FLOAT  The sensor is on the  negative, so it is a waste of time even talking about it and has nothing to do with the question.

Never ever connect directly to the battery negative. Has nothing to do with the sensor, it has to do with putting your radio in parallel with the vehicle negative wiring. Makes for a fire hazard and a lot of noise in your radio. Additionally never ever fuse the negative, connect directly to the vehicle chassis as close to the radio as possible with as short of cable as possible.

To answer your question directly, where you want to connect is just fine. Just keep the wire length as short as possible between the in-line radio fuse holder, and the tractor battery distribution block. Shorter is always better and safer.

[WA6BJH]

Obviously, we have a difference of opinion here.  I don’t know the answer, but I’d like to know what the answer is.  I wonder why all the radios come with fuses in each of the power leads.  At least the Icoms do.

[W9IQ]

The double fusing is there to protect the radio and harness in the event of a loss of chassis ground on the vehicle when the radio is connected directly to the battery. In this fault condition, some or all of the ground current that should be flowing through the chassis bonding wire will flow through the radio. The ground fuse in the radio harness will open in this condition.

I had a Jeep that had developed this exact issue - the bonding wire from the engine to the firewall corroded away and left the chassis floating. It confounded the dealer and produced interesting electrical effects in the vehicle as the load on the chassis side was increased. I bought it as is off of the dealer for half of what it was worth because they were stumped and I was confident I knew what the problem was. Twenty minutes after driving it off the lot, it was fixed.

If you are bonding the radio negative supply directly to the chassis and on the same chassis as the antenna, the fuse is probably unnecessary. But other than a reliability issue, there is little downside to having the ground fuse in place.

Regarding tying directly to the battery, there are both types of charge management systems in the marketplace. Thus the general guidance not to tie directly to the battery.

- Glenn W9IQ

[AI5DH]

Obviously, we have a difference of opinion here.  I don’t know the answer, but I’d like to know what the answer is.  I wonder why all the radios come with fuses in each of the power leads.  At least the Icoms do.

No opinion, just facts.

Stop and think about how a vehicle battery is factory wired. The negative from the battery term post  is connected to the chassis of the vehicle with a Bonding Jumper. The vehicle chassis is the negative conductor and ground conductor fopr the vehicle electrical system to save valuable weight and space.  Plain and simple fact.

Now think of how your radio is connected and how your radio is wired internally side. The negative input power lead to your radio is electrically connected inside to the radio chassis and coax shield. Simple fact any ohmmeter will prove.

Put the circuit together in your minds eye and see what circuit you created The vehicle Bonding Jumper is terminated to the battery negative term post and chassis. Your radio is terminated to the battery negative term post with the negative radio power wire and to the chassis with your radio coax shield. Your radio is in parallel with the vehicle Bonding Jumper. Your vehicle now has two parallel bonding jumpers. Your radio is now a Bonding Jumper in parallel with the vehicle Bonding Jumper putting your radio in a ground loop. Simple fact you can prove with an amp meter. .

What do parallel circuits do? Answer = Both parallel conductors conduct and share current  A potion of all vehicle current flows through your radio including engine cranking current. Simple fact of Parallel Circuit Laws.

Anyone can prove this with a Clamp-On or In-Line Amp-Meter. Turn your radio OFF. Clamp an amp-meter onto the radio negative conductor or coax shield. Leave radio OFF. Start the vehicle and observe current. When you crank the engine you will see 10 to 20 amps of current. With the engine running you will see an amp or two of vehicle current. Turn on all vehicle accessories to max power levels. Things like head lights, fans, heated seats, power window/seats, stereo, flashers, brake lights. As you turn them on, you will see more current increase as you turn things on going through your radio.  Simple fact, that is what parallel circuits do.

Now turn ON you radio and note current. Example you may see 3-amps on the negative. Now move the clamp-on amp-meter to the radio positive lead and note current. You will see the positive current is much lower than the negative, and now you know why? Simple fact.

Now for a fun and educational experiment you will never forget. Pop the hood open  and disconnect the vehicle bonding jumper from the chassis end termination. You are simulating what a mechanic might do if working on the electrical system, or perhaps wear and tear where on the vehicle bonding jumper disconnecting while driving. Leave the radio negative wire connected directly to battery negative term post. Now get in the car and turn on your radio. Being directly connected to the battery, it will work normally. Now put the key in the ignition and turn it ON to accessories position. Strangely enough all the vehicle bells and whistles turn on and come to life. Humm!

Now for the really fun part. Get a copy of Deep Purple's, Smoke On The Water tune playing on your vehicle stereo for special effects. Now crank the engine and get educated. 

Why did the cabin of your vehicle fill with acrid smoke, and why did not your radio positive wire get burned up along with your coax shield and radio negative wire?

When you figure it out, you will know why radio manufactures supplied two fuses. They supply two fuses in the event sammy hammy installs the radio connecting the negative directly to the battery to save their dumb arse from a vehicle fire and equipment damege. No extra charge for all the noise issues it creates putting your radio in a ground loop.   Two-way radio shops, fleet radio technicians, and even custom auto stereo shops learned decades ago to never connect anything directly to the battery negative term post when they burned up radio wiring decades ago. Also the reason why there are dozens of white papers and web sites on the subject. Has ZERO to do with a hall-effect sensors. Do what two-way radio shops do with the second fuse, throw it in the parts bin. Last thing you ever want to do is place a fuse in the negative or any grounded circuit conductor. If you pull the negative fuse connected directly to the battery does not kill power to the radio because the coax and chassis are still connected.

No opinion, just facts. 

Are you sammy hammy? 

[W9IQ]

Anyone can prove this with a Clamp-On or In-Line Amp-Meter. Turn your radio OFF. Clamp an amp-meter onto the radio negative conductor or coax shield. Leave radio OFF. Start the vehicle and observe current. When you crank the engine you will see 10 to 20 amps of current.

Dereck,

I have never seen a vehicle where the starter ground is obtained through the bonding jumper or the chassis. The bonding jumper generally is between the block and the chassis while the starter gets a heavy gauge wire between the battery and the block. In this case you will see no cranking current through the radio or the bonding jumper.

- Glenn W9IQ

[AI5DH]

Glen I crown thee you king of the Straw-Man arguments. You deny parallel circuit laws, and think hall-effect sensors play a part. Do the experiment, disconnect the vehicle bonding jumpers and see what happens.

[W9IQ]

Not a chance of that, Dereck. I value the electronics package in my vehicles - I won't perform your Red Green experiment. As you say "in your minds eye" envision the correct wiring of the vehicle.  I also don't wire my negative connection to the battery.

And no, I didn't disavow parallel circuit analysis. You simply fabricated a parallel path that does not exist to the extent you described it (i.e. 10 to 15 amps during cranking).

BTW, I would think by now you could catch the correct spelling of my name.

- Glenn W9IQ

[WA6BJH]

Well, Motorola—who should know about installing electronics in cars—seems to have a difference of opinion on this matter, too.  For installing one of their computers in a car, they recommend connecting both cables directly to the battery.  For their radios, however, they recommend grounding the negative lead to the chassis.

So, there!

[AI5DH]

Well, Motorola—who should know about installing electronics in cars—seems to have a difference of opinion on this matter, too.  For installing one of their computers in a car, they recommend connecting both cables directly to the battery.  For their radios, however, they recommend grounding the negative lead to the chassis.

Perhaps because you do not understand the difference between how they are wired internally. The computer negative power input is electrically isolated from the chassis,  and the radio is not isolated.  When the computer power is routed directly to the battery, there is no ground loop created. Do that with your radio radio, and you are in a nasty ground loop in parallel with the vehicle Bonding Jumper. The computer is isolated and does not have any vehicle current flowing through it. Your radio has vehicle current running through it having a party with your radio signals. It is that simple. 

FWIW older Motorola radios like the Micor, Mitrex, Syntor models and some higher end commercial radios today like L3 Harris instruct installers to run negative to the battery. They also  supply isolation bushings for the radio mounting hardware to keep the radio chassis isolated from the vehicle chassis. The radios chassis are isolated from DC Negative input. The only ground the radio sees is where the coax shield terminates too the vehicle chassis. They do not provide a second fuse because it is a Ground System, where only the un-grounded circuit conductors are required to have fuses. To install a fuse on a grounded circuit conductor like DC negative or AC Neutral is not permitted by electrical codes and dangerous to do so with no benefit or upside.

Really simple stuff, so there back at you. 

[AI5DH]

Not a chance of that, Dereck. I value the electronics package in my vehicles - I won't perform your Red Green experiment. As you say "in your minds eye" envision the correct wiring of the vehicle.  I also don't wire my negative connection to the battery.

There you go again Glen with a Straw-Man arguments beating your elitist chest trying to have the last word. You asked for what you are about to receive. The whole mind's eye experiment example was to demonstrate just how stupid simple the circuit is. No one in their right mind would do something that stupid it if they have an ounce of basic circuit fundamentals. You could not stand for anyone to say different and had to bet your chest and divert attention with a Straw-Man argument.

The current sensor you and the green alien squawk about have nothing to do with the topic. If you are anyone would give it two-seconds thought knows that to be true. How many hams connect their radio directly to the battery Glen? I would say 50% or more. None of those vehicles have any trouble with the charging system, neither do those who terminate to the chassis. Never occurred to you huh? Hams who terminate negative directly to the battery, have nose problems, not vehicle charging issues.

 

And no, I didn't disavow parallel circuit analysis. You simply fabricated a parallel path that does not exist to the extent you described it (i.e. 10 to 15 amps during cranking).

Like I said you are denying parallel circuit laws diverting attention away with a Stew-Man argument beating your elitist chest again in in a subject you do not fully understand.

BTW, I would think by now you could catch the correct spelling of my name.

Is that short for Glennette? I am sorry, I thought your were a man. My apology mam.

[AA4PB]

Electrical codes (NEC) do not apply to vehicle circuits. In home wiring the ground is not permitted to carry any operating current, the return path for operating current is via the neutral only. In a car there is no neutral - only power and ground and the ground carries the operating current. The reason for a fuse in the negative power lead on a radio when it is connected directly to the battery is in the event of a high resistance or open connection on the vehicle's negative battery connection. If that connection were to open then large currents from the vehicle (possible hundreds of amps from the starter) will attempt to flow through the radio negative lead to other radio ground connections like the coax shield or mounting brackets. The radio negative lead fuse will open at 20A in order to prevent damage to the radio negative wire, internal radio connections, and antenna coax.

On newer vehicles there are usually grounding connections near the battery and this makes the best place to connect the radio's ground wire (without the fuse). It is located close to the battery so the radio's current has a stable low-resistance path to the battery and doesn't depend on multiple joined pieces of chassis metal in the vehicle which could have high resistance or inject noise into the radio power circuits. It also keeps the smaller gauge radio ground wire away from the corrosive effects of the battery acid (as compared to a direct battery connection).
 

[N1AUP]

I think my initial interest was hearing about how much unprotected wire should exist from the batteries to the fuse.  In the backhoe's case, there is no fuse on the two foot wire length between the battery and the starter.  The cable is pretty well protected - wire insulation, thick heater hose, and a serious grommet in the metal wall that the wire has to pass through.  For whatever reason, Deere did not put a fuse in this line.  I'm guessing that the thinking was that it was unlikely that a short would occur in such a heavily protected, 2 foot length of wire.  Whereas, the cable feeding the other stuff runs all over the machine, is accessible to the operator (whereas the starter cable is pretty isolated from anything), and provides far more possibility of a short.  Even so, I'd feel more comfortable if there was a fuse or fusible link in that starter cable.

Second, regarding the discussion on where to run the negative lead of the radio, it's a fair thing to think about regarding what would happen if the radio case was grounded, the radio
's negative lead went to the battery post, and the normal vehicle ground disconnected itself in some way.  You would indeed see huge amperage running over that pretty small negative wire.  A fuse in that line is then a very good idea.

Running that negative lead to the vehicle chassis would solve this, but would also add one more failure point to the install.  Radio - negative power lead - chassis connection  -  another chassis connection  -   wire braid  -  connection to the negative post of the battery.

I think what I'm going to do is run the negative lead of the radio back to the battery, but bond it to a decent chassis ground near the battery.  And then make sure the lead from the negative battery to the chassis is tight, clean, spiked with a bit of silicone grease to keep the connection solid.  And make sure both the positive and negative leads of the radio are fused appropriately.

This sounds like a good plan.

Finally, let's try to keep the emotions out of these posts.  Everyone is making good suggestions, and I'm finding it enlightening to read everyone's arguments to support their ideas.  It's radio, not any bearing on anyone's worth as a human being.

[N1AUP]

Well, Motorola—who should know about installing electronics in cars—seems to have a difference of opinion on this matter, too.  For installing one of their computers in a car, they recommend connecting both cables directly to the battery.  For their radios, however, they recommend grounding the negative lead to the chassis.

So, there!

I think I'd feel better about using a 10 gauge wire back to the battery area, rather than relying on rust-prone, steel body parts, fasteners and such to conduct the electricity.  Again, a decent compromise seems to be that you run the negative lead of the radio to the battery compartment, fuse same, but connect it to the chassis, near where the battery's negative attaches to the body / frame.