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Author Topic: Fuse in Negative lead  (Read 8914 times)
AA4PB
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« Reply #15 on: October 21, 2010, 06:04:55 PM »

"did away with that fuse , no problem since"

No problem until you have a corroded starter lead. Then maximum smoke. What caused your negative lead fuse to blow? What would cause the most damage to the radio; 20A from the transmitter or 300A from the starter? Mfgs. put in the negative fuse for a reason.
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K0BG
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« Reply #16 on: October 22, 2010, 06:53:22 AM »

This thread could go on forever, with all the pundits eagerly defending their positions, regardless of validity. Whatever one's stance is, the fact it hasn't caused any problems, is not, in and by itself, a validation. There is science, and there is pseudo science—whichever side of the fence you're on, is clearly within the responses.
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K5LXP
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« Reply #17 on: October 22, 2010, 07:18:00 AM »

I'm not so sure this is an issue of pseudo science.

I'm in the camp of never connecting the negative *or* the positive lead directly to the battery.  This comes from years of experience in the 2-way business, and the repairs I've had to do as a result of this practice.

From a physical standpoint a battery is a nasty thing to connect a wire to, positive or negative.  Most, if not all vehicles these days have a short positive cable to some demarcation point at or near a fuse box, and that's where I connect the positive lead, away from the corrosive environment of the battery post.

The negative lead is subject to ground faults.  The negative lead fuse protects you only so far.  I have seen, and on more than one occasion, where enough current was going through the chassis of the radio to cause undesired operation and damage, but not enough to blow the fuse.  Connecting the negative lead *near* but not *on* the battery chassis connection point absolutely prevents this from happening.

My point is that while a ground fault isn't a common problem, the potential for it to happen when connecting to the negative terminal is there.  But it's not there at all if you ground to the chassis near where the battery connects to it.  The impedance difference is miniscule.  There's no good mechancial or electrical reasons to connect the negative (or positive) lead directly to the battery and there's empirical evidence to show it's a bad idea.   Pseudo science?


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #18 on: October 22, 2010, 07:43:42 AM »

It depends on the vehicle, Mark. I'd say "proper engineering" includes determining the best way to make the power connections based on what the mfg has made available in your particular vehicle.
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N1DVJ
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« Reply #19 on: October 22, 2010, 08:20:50 AM »

AA4PB has it right on.  Only I'd go further to say it depends on the vehicle AND the radio.  There is not a 'blanket one size fits all' answer for this.

And I do respect K0BG.  I regularly visit his website.  It's full of great information.  It's where I have found some great tidbits of info I wouldn't even find hints of elsewhere.  Like the caveat about 3-stage chargers.  But while I have yet to find anything patently wrong, I think he suffers from the 'know it complete' syndrome.  That is, if it ain't there, it either doesn't matter or it doesn't exist.  

In fact, I think he's right about the connections to the battery, but NOT for ALL applications.

You know, it would be a GREAT experiment if everyone involved with this heated topic checked their cars.  How about we all get a cigar lighter plug and plug it in to the vehicle.  They ground through the dash connection.  That run a lead to the ground right on your battery.  Tie that to the ground lead on your cigar lighter cable and and SEE how close your battery ground is to dash ground.  Or to body ground where you have your antenna mounted.  Just disconnect your antenna lead from your rig and measure to the shield.  Let's see how many people have vehicles with good grounding systems.  (It won't count if you have an isolated ground antenna!)
« Last Edit: October 22, 2010, 08:26:47 AM by Mike Yetsko » Logged
AA4PB
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« Reply #20 on: October 22, 2010, 09:36:14 AM »

I've used a high impedance headset with a 0.01 uF capacitor in series to track down alternator whine. It's surprising when you connect to two ground points on the chassis (sometimes not too far apart) and hear the whine in the headset.
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K0BG
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« Reply #21 on: October 22, 2010, 10:35:19 AM »

Well, I've done almost that. The lead from the front battery in my Ridgeline mobile is #2, and its overall length is just over 14 feet, and the resistance is .002 ohms. The wire is terminated at the front battery with a lug attached to the existing battery connector. Its return trip is via a 12 inch jumper which appears to be #8, to the front frame rail, and through the unibody to the rear. Measuring between the Power Pole connector on the rear, and the nearest chassis point (where a bed extender would mount to the side rail) with my DVM, measures just over 1.8 Ω. My previous vehicle, a 2001 Acura 3.2 Coupe, measured just over 3 Ω with just a bit shorter run of #4. While perhaps not telltale at first glance, drawing just over 100 amps on peaks, the resulting voltage drop certainly would be!
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K5LXP
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« Reply #22 on: October 22, 2010, 10:49:16 AM »

AA4PB:

> determining the best way to make the power connections based
> on what the mfg has made available in your particular vehicle.

I don't necessarily rely on anything the vehicle comes equipped with.  If it's lacking a connection point, I add/make one that suits the purpose.  The aftermarket vehicle electronic installation accessories that are out there cover just about any situation you'll ever encounter, or come up with something on your own.  I see some of the problems encountered is the reluctance or inexperience of the installer to not want to "cut into" something or having to take the time to route a cable to a particular location, but that's a separate issue.
 
There's such a thing as good engineering practice.  Irrespective of vehicle or radio, where you make the connections doesn't have to be installation specific.  I've put radios into a lot of different kinds of vehicles, including ones that would be considered atypical and even that didn't really change the premise here.

Just because I may have a radio with a floating chassis and no chance of a ground fault doesn't mean I could connect to the negative terminal with impunity.  I would still connect it near the chassis tie point if for no other reason than to minimize the chance of acid corrosion on the lug and wire.  By following this practice I may prevent a future unforseen ground fault through an inadvertent or unanticipated ground path through say, an added or replaced piece of equipment.  Why have a set of exceptions for different situations, when one method can be used that works for everything?  Can anyone name a situation where connecting the chassis ground near the battery-chassis connection point causes a problem? I can think of (and have experienced) numerous electrical and mechanical failure modes for terminal connected installations but only a few, less catastrophic ones for disparately connected ones.

We can argue all day long about the probabilities of one potential problem or another when doing a direct connect, but the simple answer is to just not connect directly, and virtually negate any chance at all.  There is no tradeoff- no additional time, trouble, or change in performance to prevent a future issue, so why not do it that way? 


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #23 on: October 22, 2010, 11:53:28 AM »

Well, I've run across cases where there is no suitable ground lug located near the battery. Then there are those who, when they here you say NEVER connect to the battery, will attach to the nearest fuse block under the dash and ground to the closes screw near the radio. There are ways to attach to the battery that limits the amount of corrosion the wires are subjected to (although I've seen people just stick the copper wire under the battery clamp next to the post).

Based on my own experience I've have to disagree with the "one size fits all" scenario. But then everyone has their own opinion based upon their own experiences.
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K5LXP
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« Reply #24 on: October 22, 2010, 01:48:14 PM »

> Well, I've run across cases where there is no suitable ground lug located near the battery.

A drill and self tapping screw takes care of that nicely.  If someone isn't willing to drill a hole for a simple ground screw, they get what they get.  That's not an engineering problem.

I agree though, as soon as you make a "rule" about something, someone will come up with an exception.  In this case though, there's going to be darn few and considering the practices (or myths) that many hams follow this would be a huge step up.  You would have to get into some pretty unusual circumstances before it wouldn't apply.

 
Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #25 on: October 22, 2010, 03:16:43 PM »

I can! When you run high power, and you use the battery chassis ground point! If you do, you run into two potential problems (no pun intended).

First, the smaller accessory ground from the battery to the chassis could become overloaded and fail. Typically, this wire is only large enough to handle the average accessory load. Whether it fails under these conditions doesn't matter. In any case, some or all of the return would be through the drive train, and back up the starter ground connection, usually size #4. Whether this causes a problem is perhaps moot, but all you have to do is ask FoMoCo about their ambulance and police car experience in the last few years to gain a good perspective of the issue at hand. If you do, you'll have a whole-new outlook about where connections should be made! This is why Ford (and others) are so adamant about how two way and high-power sound systems are wired.

The other problem is a little more esoteric. In just the last few years, most manufacturers have routed the alternator's output through the engine CPU. This allows the ECPU to monitor voltage and current. The reason they do this is for pollution and mileage maximization, and even harshness and vibration concerns. The voltage measurement is referenced through the battery's accessory ground. If you change the voltage drop across the accessory ground (in essence the metering shunt), the readings the ECPU garners will be other than what it expects. Whether this causes concerns, or whether it lights the CEL (check engine light), is also moot. What isn't, is the data recorded to the OBD II-EOBD. As some Corvette owner's have discovered, the data recorded in the extended memory, is enough to deny warranty coverage. In our case, it really doesn't matter whether the data was true, or reported false due to a ground loop or RFI, it is still corrupted with negative results.

I'm of the opinion, that by the time we lighten up vehicles enough to meet fed-mandated mileage requirements, and 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!
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N1DVJ
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« Reply #26 on: October 23, 2010, 09:03:50 AM »

I hadn't heard about the data voiding warrantee with Corvettes, that must be fairly limited. 

But I have heard that Audi can be a pain to hams about anything that transmits with more than 3W of RF!

Compare that to Chrysler.  Somewhere around here I had an old SB that described the recomended method for installation of transmitters up to 100W.  I thought there were similar documents from Ford and GM, but maybe they were vehicle specific.
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AA4PB
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« Reply #27 on: October 23, 2010, 11:04:58 AM »

> Well, I've run across cases where there is no suitable ground lug located near the battery.

A drill and self tapping screw takes care of that nicely.
 
Mark K5LXP
Albuquerque, NM

There's exactly the problem. In my book a self-tapping screw is NOT a suitable negative lead power connection, especially for a 100W or greater power level. When I say a suitable ground connection, I mean a bolt that has a heavy (probably #4 or greater) wire not over 1-foot long going from the bolt directly to the negative battery post terminal.


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K0BG
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« Reply #28 on: October 23, 2010, 11:12:14 AM »

The ARRL has a list of most of the manufacturers here: http://www.arrl.org/auto-manufacturer-s-policies

One of the newer problems deals with both aluminum and composite body materials, and the way they're glued (literally) together. Add in the fact that some high-end vehicles have over 25 CPUs all talking to one another over data busses, and operating mobile is going to get even more exciting.
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W6RMK
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« Reply #29 on: October 23, 2010, 07:49:49 PM »

25 CPUs?  probably more than that. 

But, isn't the real solution to not use the vehicle's electrical system at all.  Put in a suitable battery to run the rig, and then charge it with an isolated DC/DC converter as needed.  Seems like from an engineering standpoint to spend $1000 on a HF radio, and then not spend a couple hundred bucks on a suitable power system is not the best plan.  (leaving aside issues of retrofitting that kilowatt rig you got for free from someone who picked it up at W6AM's estate sale )

Most cars these days, electronics and all, have pretty good radiated EMI immunity (standards vary, but basically, the E field levels i've seen when casually browsing are all well over the ANSI/IEEE C95.1 limits for human exposure... although you do have the peak vs average thing)  After all, you don't want the car dying when the highway patrol car next to you transmits, or you drive next to a fixed transmitter.


There *is* still the antenna issue, because like it or not, the car's body is part of the antenna, particularly on HF.  But that's a separate issue, and power ground/return shouldn't be part of the RF circuit anyway.
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