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Author Topic: Mobile Install Power  (Read 11170 times)
K1CJS
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« Reply #15 on: October 19, 2012, 05:24:49 AM »

One other thing to consider is this.  Usually the switches, fuses, etc. in a vehicle are all on the POSITIVE side of the device being powered by the vehicle electrical system, not the negative.  If the dangers of direct connection to the negative battery terminal were at all that problematic, the fuses and switches would be on the negative side.  Right from that we see that logic doesn't always hold true.

I do understand the problem about negative backfeeding in case of ground failure, but that is why installation instructions specify the negative lead from the rig be fused, negative rail isolated rig or not. 

One last thing, let's remember the actual power flow is from negative to positive, not the reverse.
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KJ4PR
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« Reply #16 on: October 19, 2012, 07:07:59 AM »

I had the same problem with my Icom V8000 a few years ago. It was the car battery going bad. Have your battery tested even if it is only a few years old. Most auto parts stores and Sears will load test it for free. Also its never a good idea to start the car with your radio on but I didn't worry too much about my VHF. It did tell me that I needed a new battery when I saw the display go blank on starting. I doubt turning the car off with your radio on could cause any damage. Good Luck.
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WX7G
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« Reply #17 on: October 19, 2012, 03:10:25 PM »


One last thing, let's remember the actual power flow is from negative to positive, not the reverse.

You are trying to be humorous I hope.
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AC4RD
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« Reply #18 on: October 19, 2012, 04:19:16 PM »


One last thing, let's remember the actual power flow is from negative to positive, not the reverse.

You are trying to be humorous I hope.

http://en.wikipedia.org/wiki/Electrical_polarity
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W8JI
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« Reply #19 on: October 19, 2012, 08:08:47 PM »

One other thing to consider is this.  Usually the switches, fuses, etc. in a vehicle are all on the POSITIVE side of the device being powered by the vehicle electrical system, not the negative.  If the dangers of direct connection to the negative battery terminal were at all that problematic, the fuses and switches would be on the negative side. 

That's just silly.  :-)

The problem has nothing to do with where fuses commonly are.

The problem is the negative buss in the radio comes out on every grounded pin or connection, including the case and antenna. This means if the negative post of the battery to vehicle chassis comes open, the vehicle current returns through the radio lead. Since the fuse is normally many times larger than the radio's internal ports might handle, or foil traces, and since a fuse takes time to open, a negative battery open can damage the radio....negative fuse or NOT.

The entire concept of connecting to the battery negative lead is **idiotic** from a design standpoint, unless the fuse can be faster and weaker than the path out ANY radio port and the radio manufacturer (or whoever tells us to connect to the negative post or lead) can assure everyone whatever connects to the radio on any radio port is significantly stronger than the fuse.

I can give an example of this problem. My IC751A has an open keyer paddle ground lead because, while the radio was in my truck, a negative radio fuse went open. The key was grounded through a random metal contact, and became the primary path for radio current. This opened the foil trace deep in the radio.

The same would have happened to a mic lead, if the mic were in ground contact, after that fuse opened.

A similar destructive failure can happen if the battery negative goes open, which can then apply positive potential to grounded jacks on the radio.

The entire concept of a negative fuse and a negative connection to the battery at the battery lead or post is just totally bizarre from an engineering standpoint.  I think the idea probably came from people not understand the other end of the system, and then just repeating a bad idea.
 
Quote
Right from that we see that logic doesn't always hold true.

Your concept was wrong.

Quote
I do understand the problem about negative backfeeding in case of ground failure, but that is why installation instructions specify the negative lead from the rig be fused, negative rail isolated rig or not. 


That silly fuse idea only works if EVERY port exiting the radio can handle more current than the fuse, and handle positive voltage. Anyone who thinks a 20-25 amp auto glass fuse (that typically takes 30 seconds or longer at 2X current to blow) will pop before a foil trace or small component is damaged, or before any wire or lead might overheat, is just not thinking clearly.

Now if the case had a solid hard ground it would save the radio and wiring, but then the lead to the battery and the fuse path would be non-functional because the resistance of that path would be significantly higher than the chassis path resistance to the battery. 

The whole "lead to the battery negative system" is an example of pure unvarnished ignorance in electrical planning.

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One last thing, let's remember the actual power flow is from negative to positive, not the reverse.


What does that mean?

First, it is electrons that move from more negative to less negative (more positive) potential. But that has absolutely nothing to do with "power flow", and has nothing to do with fusing.

A ***proper*** fuse application would prevent fire or major damage by having the fuse protect the path properly, regardless of polarity. Ground leads are should NEVER be fused, unless the thing being fused is totally isolated from external paths or contact. This is especially true if the fuse could easily be bypassed by external connections.

This negative fuse thing is like a bad riddle. If we make the system safe by solidly grounding the radio case (and negative buss) to the vehicle chassis, then we almost certainly have much less resistance in the chassis to battery path then in the radio wire to the battery. If that is the case, and it almost certainly would be unless the battery to chassis had a high resistance defect, then we ran a useless wire to the battery.

On the other hand, if we 100% guarantee to FLOAT the radio and every radio connection from vehicle chassis, then the negative fuse system is safe and we can use it. So we go though extraordinary effort just to make a higher resistance path to the battery than a chassis path would typically have.

Now there can be exceptions to this, but the exceptions are rare compared to the much more common system where the chassis is a better more reliable path.

We don't see the vehicle manufacturer running his stereo system, lights, horn, ECM modules, or anything else back to battery negative and fusing the negative. Now we might get into systems that do that with hybrid vehicles, but standard vehicles are not built that way.

73 Tom
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K1CJS
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« Reply #20 on: October 20, 2012, 06:36:16 AM »

After all that, Tom, you just prove my point.  But before I continue--please don't take this as a personal attack--it isn't meant as such.  It's just meant to point out how one occurrence can influence a view.  

The point is that something happened to you personally, and you go on to make suppositions and offer proof that every vehicle and radio manufacturer is wrong and you are right.

Quote
I can give an example of this problem. My IC751A has an open keyer paddle ground lead because, while the radio was in my truck, a negative radio fuse went open. The key was grounded through a random metal contact, and became the primary path for radio current. This opened the foil trace deep in the radio.

In your case, Tom, the key should have been mounted in such a way that the 'random metal contact' should have never occurred.  You should have allowed for disconnection of the key before it was put aside or had it mounted and insulated from the vehicle so such contact could not happen.  In short, you didn't make provision for preventing such an incident, and now you're blaming approved installation procedure for your shortsightedness.

Granted that there are a few people who, like you, have elaborate installations in their vehicles with a web of interconnected power feeds and ground mounted items, but the long and short of it is that these people have these installations which ignore simple and safe methods of either installation, interconnections or power feed and then go on to blame generally accepted and recommended connection/installation guidelines for their problems.

Most installations have a radio (maybe two) mounted in such a way that the negative fuse will blow if any such negative connection failure should happen--and without damaging the radio itself at all.  That is the long and the short of the issue, how to safely and properly install a radio in a vehicle.
« Last Edit: October 20, 2012, 06:38:24 AM by K1CJS » Logged
KCJ9091
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« Reply #21 on: October 20, 2012, 06:59:59 AM »

Motorola does not fuse the negative and recommends against the practice. A typical Motorola installation diagram:

http://www.batlabs.com/images/lmda457.gif
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AA4PB
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« Reply #22 on: October 20, 2012, 08:45:15 AM »

Motorola does not fuse the negative and recommends against the practice. A typical Motorola installation diagram:

http://www.batlabs.com/images/lmda457.gif

You'll also notice that Motorola DOES NOT recommend returning the negative power lead directly back to the battery.

It is ONLY when the negative lead is returned directly to the battery that the negative lead should be fused. That is because if the vehicle ground wire becomes defective then heavy starter currents could flow through the negative radio power lead to other ground connections on the radio. The "assumption" is that the radio will have multiple connections to the vehicle chassis including the mount and the antenna coax. Those grounds are in parallel and the current divides between them so very likely they will handle 20+ amps long enough to blow the fuse. At any rate, the damage will be MUCH less than if you didn't have the negative lead fused. The negative lead fuse really does make good engineering sense if you are going to connect the radio's negative power lead directly to the battery. Of course it is better to use the accessory grounding lug near the battery (if one is available) and avoid the possible problem altogether.

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WX7G
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« Reply #23 on: October 20, 2012, 10:03:41 AM »

The take away from this discussion is:

1. Connect the radio negative lead to the far end of the battery cable
2. Do not connect the radio negative lead directly to the battery
3. A fuse in the radio negative lead is not needed

That is pretty simple and takes care of all failure modes.
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KCJ9091
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« Reply #24 on: October 20, 2012, 11:43:42 AM »

Motorola does not fuse the negative and recommends against the practice. A typical Motorola installation diagram:

http://www.batlabs.com/images/lmda457.gif

You'll also notice that Motorola DOES NOT recommend returning the negative power lead directly back to the battery.

It is ONLY when the negative lead is returned directly to the battery that the negative lead should be fused. That is because if the vehicle ground wire becomes defective then heavy starter currents could flow through the negative radio power lead to other ground connections on the radio. The "assumption" is that the radio will have multiple connections to the vehicle chassis including the mount and the antenna coax. Those grounds are in parallel and the current divides between them so very likely they will handle 20+ amps long enough to blow the fuse. At any rate, the damage will be MUCH less than if you didn't have the negative lead fused. The negative lead fuse really does make good engineering sense if you are going to connect the radio's negative power lead directly to the battery. Of course it is better to use the accessory grounding lug near the battery (if one is available) and avoid the possible problem altogether.



I guess that's what i get when I try to keep it short.  That is the practice I was referring to,  connecting to the battery end of the negative cable.  Chassis ground is the requirement.
« Last Edit: October 20, 2012, 11:45:59 AM by KCJ9091 » Logged
N6AJR
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« Reply #25 on: November 08, 2012, 02:21:50 PM »

usually I end up with both the pos and neg cables going to the battery, but I also run a braid from the neg post on the battery, to the chassis right aat the battery, and a ground braid  from the radio  to the floor  ( using a self tapping sheet metal screw) and from the shield side of the antenna to the chassis. This gives a pretty good  shot at having no problems in the neg side of the  setup.  I'm just sayin
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K1CJS
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« Reply #26 on: November 09, 2012, 05:56:11 AM »

The take away from this discussion is:

1. Connect the radio negative lead to the far end of the battery cable
2. Do not connect the radio negative lead directly to the battery
3. A fuse in the radio negative lead is not needed

That is pretty simple and takes care of all failure modes.

If this is taken and used exactly as stated, it doesn't take care of all failures.  It makes no difference if you connect a device directly to a battery terminal--or to an end of a cable connected to a battery terminal.  If the path of least resistance is through that wire from the rig to the negative battery terminal--wherever the connection is made, you're still going to have the same result.  You still should have the negative lead fused.

The best solution is to have a blown fuse indicator--an LED and a large value dropping resistor--across that fuse, but the fuse should still be there.
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AA4PB
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« Reply #27 on: November 09, 2012, 07:19:50 AM »

On my vehicle the negative battery terminal has two factory wires. A heavy wire going directly to the engine, near the starter motor and a smaller wire going to a large stud on the chassis. I connect my radio ground wire to that stud without a fuse. Short of the stud breaking off there is no way for vehicle system currents to flow back through the radio's ground wire.
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W5DXP
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« Reply #28 on: November 10, 2012, 05:55:09 AM »

It seems some where I have read about a way to overcome this, but can't find it anywhere.

Vehicle audio sound systems have already solved a similar problem. I had my GMC pickup wired for my IC-706 by an audio sound system firm. They ran two #10 wires (fused) directly from the battery through the firewall to the center console. I had them install an 8 farad capacitor at that point. That cured all of the voltage drop problems that I previously had when I was running my IC-706 from the aux cigarette lighter.

http://www.hifisoundconnection.com/Shop/Control/Product/fp/vpid/2888326/vpcsid/0/SFV/30046
« Last Edit: November 10, 2012, 06:01:59 AM by W5DXP » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
AA4PB
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« Reply #29 on: November 10, 2012, 06:42:01 AM »

You don't think maybe the #10 wires contributed a lot to fixing the voltage drop problems?
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