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Author Topic: Fuse in Negative lead  (Read 10036 times)
N1DVJ
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« Reply #30 on: October 24, 2010, 03:39:56 AM »

I had a friend do the trick with the spare battery.  He put a big deep cycle in the back of his little econocar, don't remember what it was.  He was always fighting noise on the power, so he bypassed it.  He'd get a week or so and then hook the battery up to charge it.  

Just 25 cpus?  I think more, but the extreme would be back around 1989 or so, I saw a report where a German group had taken a car and totally computerized it.   They did EVERYTHING via computer and networks.  Even things like the tail-light assemblies.  There was a main power bus in the vehicle and then a data bus.  Hit your brakes, and a command packet went out that said 'brake light on'.  If the processor in the taillight assembly detected no current draw, it would pulse modulate the other lights in the assembly and respond with a packet telling the main computer the taillight was out, causing a warning to come up on the dash.  The test vehicle was an Audi if I remember right, and the reports said they saved almost 300 pounds in vehicle weight.

It was ahead of it's time...  
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K0BG
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« Reply #31 on: October 24, 2010, 07:20:01 AM »

Not really. The Cadillac Allante had a buss-driven, common-power system back in 1990s. It didn't work very well, however.

Lots of folks try isolating their batteries because they have all sorts of RFI issues. Suddenly the RFI goes away, and they're convinced they've found the solution. Well, the truth lies elsewhere.

As a result of my web site, I get about 50 photos of installations every month. The database is currently about 700 MB. Less than 20% are posted to the Photo Gallery. Why? Far too many installations are dangerous, near dummy loads, wired as if a 9 year old did it, etc. Some of the worse ones are in the Hall Of Shame Album. Probably the most pathetic part is, most of them brag about the DX they've worked, or the low SWR they have. And, they universally complain about ignition RFI and/or interference to some on-board device. It doesn't take a rocket scientist to figure out why.
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K5LXP
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« Reply #32 on: October 24, 2010, 11:10:46 AM »


> the smaller accessory ground from the battery to the chassis
> could become overloaded and fail.

The factory one in my car is at least a 10ga, if not 8.  Easily capable
of 50A with a negligible drop (<1' long).  If the car doesn't have a
ground jumper like this, it's simple enough to add one.

And AA4PB, I agree that except for light duty a self tapping screw
would not be a suitable grounding technique.  Was just making
the point that just because a fastener isn't in a handy spot doesn't
mean you can't add one. 


> If you change the voltage drop across the accessory ground
> (in essence the metering shunt),

Putting your load on the terminal side of the battery would bypass
a low-side shunt, not a connection on the chassis side.  All of the
vehicle loads are referenced to chassis, and so should any added
accessory loads like a radio.  It would seem that low side sensing
like this would necessitate a chassis connection over a terminal
connection even more.


> we make things even more computer based, we're all going to be
> hard-pressed to operate any kind of mobile. Let's hope not!

They key game-changer was the creation of the 42V system but I'm
not aware of anyone that's actually done it.  Hybrids are another
story.  The good news is hams aren't the only ones interested in
accessory power and it's only a matter of time before techniques
or hacks are known to deal with future unique charging systems.

Meanwhile, for 12VDC negative ground I'm grounding to the chassis...  :0)


Mark K5LXP
Albuquerque, NM
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K1CJS
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« Reply #33 on: October 27, 2010, 01:09:27 PM »

There's no need to reinvent the wheel.  You've got one fuse in the negative lead at the battery.  You've got the individual rigrunner fuse for the radio fuse.  the fuses in the power cables are redundancies which can be easily--and safely--eliminated.  End of story.  73!
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K0BG
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« Reply #34 on: October 27, 2010, 04:01:01 PM »

Well, Chris, that's true only if the wiring is done correctly. Without a schematic, we're sort of guessing.

Part of the issue is the RigRunner® itself. The term, RigRunner, has almost gained the status of the term Mack Truck, in that it has become universal verbiage (not necessarily specific to brand). Some so called rigrunners (note lower case) have their chassis connected to the actual ground connection. This isn't ideal if you stop and think about the ramifications. Thus, there is another problem which might rear its ugly head. If the chassis is connected to the negative lead, and the battery's accessory ground fails, then the rigrunner becomes the path of least resistance. What we need to start thinking about, isn't the rigrunners themselves, but how they are installed.

As you are no doubt aware, I have a web site dedicated to mobile operation. Aside from short, stubby antennas, the vast misunderstanding about what is, and is not a ground plane, wiring is the next biggest issue. Far too many just do not get the picture. It just makes me wonder where it is all going to culminate. Hopefully, not in a vacuum!

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K1CJS
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« Reply #35 on: October 28, 2010, 05:30:03 AM »

Yes, Alan, you're right--and I should have said it like that.   --IF-- the wiring is done correctly.

The other thing that should garner our concern is whether or not we're talking about the thing that our words tell others we're talking about.  As you said, the term 'rigrunner' is used today for all too many different--and some very poorly made--substitutes of the real thing.
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W5WSS
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« Reply #36 on: October 29, 2010, 12:20:58 AM »

Sooo let me get this right "if" one places the proper fuses in the proper wx proofed fuse holders "at" the source/Optima yellow top used as the automotive battery (one proper fuse in the negative line and another proper one in the positive line) and the radio is insulated from the frame at" the radio sitting on carpet and rubber feet strapped down with cloth non conductive strapping to the hump if you will and also repeating the same fuses "at the rig how is this a problem? The path of least resistance to ground is via the 4ft of #4 that is going directly to the battery.Then in this case Why would we worry about the shielding path via the coaxial cable? The corrosion caused by the glass mat battery is minimal. I Do not turn the radio on until after starting the engine. And I turn it off prior to shutting off the engine. I am for a dedicated and isolated circuit. I have not found any reason to ground the rig to the car frame where it is resting on the hump no common mode no erroneous operation the rig is an Icom 718 the added fuses do not cause very much voltage drop as measured "at the rig" I use a THP Hl-450b amplifier connected to the sameOptima yellow top and all done the same way I am confident this is the best way to take all the ground faults out of the equation in the first place.
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N1DVJ
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« Reply #37 on: October 29, 2010, 06:21:04 AM »

Well, first off, it makes no difference if you turn the rig on or not, probably, because the rig PROBABLY only switches the hot lead.

And you are probably already grounding the rig, via the chassis, through the coax, to your antenna grounding poing...

Now, is your chassis ground the same as your power ground?  Depends on the rig, and things attached...
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K0BG
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« Reply #38 on: October 29, 2010, 10:39:21 AM »

Don't be so sure you don't have common mode following over the coax cable. That's a function of the ground losses,and has very little to do with grounding (earthing). Ground plane? That's the issue, however.
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K5LXP
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« Reply #39 on: October 29, 2010, 11:36:46 AM »



> The path of least resistance to ground is via the 4ft
> of #4 that is going directly to the battery.
> Then in this case Why would we worry about the shielding
> path via the coaxial cable?

Because then your path, maybe not of least resistance but perhaps low resistance should that #4 become compromised, can be from the negative terminal of the battery through the chassis of the radio along the shield of the coax, to the grounded antenna mount.  If you're using a mag mount, your argument would stand as mag mounts don't have a DC path to ground.  That's easy for VHF/UHF, but what about HF?  You don't find many DC-isolated HF mobile antennas so you'd have to come up with your own isolation scheme that doesn't impact RF performance. 


> I Do not turn the radio on until after starting the engine.
> And I turn it off prior to shutting off the engine.

That won't matter in the case of a ground fault, the switch won't help you a bit.  If isolated, the only real concern would be voltage droop during starting and overshoot by the alternator but with a good low Z battery and modern charging systems, I wouldn't consider that much of a risk these days. 


> I am for a dedicated and isolated circuit.

That's fine, if you can be absolutely certain it's isolated and will stay that way.  You have to take specific measures to do so and at the same time take measures to prevent inadvertent/unintentional compromise of that isolation.  For instance, you can take pains to isolate the DC feed, insulate the radio mount from the frame and use a mag mount antenna but then unintentially ground it with an accessory like an external powered speaker or APRS interface.  Then there are the issues of using an isolated ground in terms of RF, where resonances can occur and cause RFI or other undesired operation.  I agree, you can ground it or float it but floating is a whole lot harder to do, especially when the equipment was designed and built with grounding in mind.


> I am confident this is the best way to take all the ground
> faults out of the equation in the first place.

That's another way to look at it and in fact I'm involved in the design of commercial/industrial systems that sometimes use a combination of grounded and floating power and RF I/O in the same unit.  But it takes careful consideration to pull that off and there's rigorous testing (and even regulatory standards) to ensure some obscure failure mode won't compromise the isolation.  The chassis/bonding method is safe and readily implemented and I wouldn't recommend going the isolation route unless one really know what they're doing, and has a *specific* need to do so.  At best it doesn't offer any real advantage over grounding/bonding in ham automotive installations and is more trouble to do, so it wouldn't be my first choice.  Seems like an awful lot of trouble to go through just to avoid moving the negative supply cable an inch or two from the chassis tie point.


Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #40 on: October 29, 2010, 12:27:41 PM »

I agree with Mark. There are so many Pin 1 problems nowadays, it's hard to find a piece of equipment without one designed in! Designing one out, takes talent!
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W5WSS
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« Reply #41 on: October 29, 2010, 09:12:07 PM »

It wasnt any trouble at all.  If anyone needs any advice here feel free to ask. Catch you on the air. 73
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W5WSS
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« Reply #42 on: October 30, 2010, 07:03:15 AM »

Take a look at the pic in eham of my hill top mobile antenna it uses elevated sloped radials and shield is not tied to the carbody via a conventional mobile antenna that pushes against the car body at the antenna mount nor to the earth notice the plastic stakes where the bottom radial wires attach, also notice the antenna is attached up on top of an insulated wood pole that holds the antenna. I knew this and it was no trouble to isolate the rig to One single circuit that is the path of least resistance. To the battery only. But hey my case is different but very easy.
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