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Author Topic: Mobile Install Power  (Read 13508 times)
N7GCO
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Posts: 147




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« on: October 14, 2012, 10:51:04 PM »

I have a Icom 706 installed in my truck with the power run directly from the battery (#4 wire both positive and negative with both fused). When ever I turn off or on the truck, I my radio momentarily stops. It seems some where I have read about a way to overcome this, but can't find it anywhere.

How can you keep the radio on when turning off and on the truck?
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AC4RD
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« Reply #1 on: October 15, 2012, 04:02:06 AM »

Personally, I don't even TRY.  I'm no expert, just another guy with a 706 in his car.  I'm concerned about the possibility of voltage spikes, and I start the car and THEN turn on the radio.  Occasionally I'll get sloppy and turn off the engine before I turn off the radio.  But I *never* start the car when the radio is on.  I've never had a problem with it, but I've heard a lot of horror stories over the years, and don't even try it.
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K1CJS
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« Reply #2 on: October 15, 2012, 05:27:17 AM »

What you're seeing is the result of power level (voltage) spikes and dips.  Did you look at the specs in the manual that comes with the radio?  It specifies the high and low voltage level that the radio uses.  The voltage level in your truck is obviously going either higher or lower than what the radio can tolerate.

What may be happening is that either the battery is getting older and has increasing internal resistance, (sulphation) or that the alternator is showing its age and is wearing out.  Best thing to do is to heed the previous poster and turn the radio on after you start your vehicle and shut the radio off before you shut the vehicle ignition off.   
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AA4PB
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« Reply #3 on: October 15, 2012, 05:29:42 AM »

I have an IC706MkiiG in the truck. It is not affected by turning off the engine but it does trip off when starting the vehicle. That is because the 706 turns off when the voltage drops below about 11.5V. The starter load on the  battery causes the voltage to drop momentarily below this level.

My previous truck (same 706) had the same problem but had room for a larger sized battery. When I installed the largest battery I could get into the space, the problem went away. Unfortunately the new truck doesn't allow space for increasing the battery size.

Actually, it's probably not a good idea to start the vehicle with the radio running anyway. The inductance in the starter can dump a big voltage spike on the power line that might damage the radio. On commercial installations we used to connect the radio to battery power through a big relay that had its coil connected to the ACC line on the vehicle so that the radio would be disconnected from DC power while the starter was engaged.

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K0BG
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« Reply #4 on: October 15, 2012, 06:04:14 AM »

While I understand the possibility of a spike caused by the starter (more likely the starter solenoid), I wonder how many folks have actually connected a storage scope to the battery, and then start the vehicle. I have, and the spike is minuscule—just a few tenths of a volt.
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WX7G
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« Reply #5 on: October 15, 2012, 12:52:45 PM »

I have a Icom 706 installed in my truck with the power run directly from the battery (#4 wire both positive and negative with both fused). When ever I turn off or on the truck, I my radio momentarily stops. It seems some where I have read about a way to overcome this, but can't find it anywhere.

How can you keep the radio on when turning off and on the truck?

The radio can be isolated from voltage dips using a diode battery isolator and a small lead acid battery. Radio Shack stocks a 7 A-H battery that would be suitable. Diode battery isolators are available at auto parts stores.
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M6GOM
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« Reply #6 on: October 16, 2012, 04:50:06 AM »

While I understand the possibility of a spike caused by the starter (more likely the starter solenoid), I wonder how many folks have actually connected a storage scope to the battery, and then start the vehicle. I have, and the spike is minuscule—just a few tenths of a volt.

Exactly. If it isn't, its because you don't have a battery connected. The battery effectively acts as a very very large capacitor and smooths out any spikes.
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AA4PB
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« Reply #7 on: October 16, 2012, 05:34:32 AM »

The SAE has measured voltage spikes exceeding 100V on a 12V automotive system. There are a set of recommended standards for equipment designed to be powered from an automotive system. The worst case scenario is an alternator load dump which can be caused by corroded connections on the battery, cables, or even inside a battery. The recommendation is that automotive electronic equipment be designed to handle such spikes. I expect that such large spikes are present only when the vehicle electric systems have deteriorated over time and the recommendations are there to ensure that electronics is not damaged during the worst case. Also, the SAE is addressing all electronics in a vehicle, many of which are NOT powered directly from the battery. Certainly spikes will be much less directly across the battery, provided the battery and connections are in good shape.

------------------------

A diode and a gel cell will keep the radio voltage from dropping while starting but it also means that you have to live with the 0.7 or 0.4 volt drop in the diode. If the vehicle battery is charged to 13.8V and you use a silicon diode (0.7V drop) then the maximum charging voltage on the gel cell is only 13.1V. If the engine is off and the vehicle battery discharges to 12V then your radio is only receiving 11.3V, which is below the limit on some radios.
« Last Edit: October 16, 2012, 06:01:01 AM by AA4PB » Logged
K1CJS
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« Reply #8 on: October 16, 2012, 05:59:02 AM »

I wonder when responders are going to read the entirety of the posts made before they offer comments--comments that say much the same thing as the comments they neglect to read.
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K0BG
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« Reply #9 on: October 16, 2012, 03:30:08 PM »

Chris, I agree with you. And I also say that experience counts!

I don't even know for sure how many mobile transceivers I have used over the years. The first all solid state was an Atlas 180. There have been about 20 since that one, including the IC-7600 I've used for the last 60 days. All of them were wired directly to the battery. No chassis ground. No protective diodes, zener or otherwise. No big Farad caps. No isolated batteries. Nada! I have never suffered a failure caused by starting the engine, with or without the radio on. While these facts do not account for every single failure everyone else has had, it is a very good indication that proper wiring is the key.

As for the ASEE or the SAE, the only reference I can find for measured spikes with respect to a 12 volt automotive application is 50+ years old. We have to remember that modern vehicles are literally computer controlled. What about the spikes they experience?

All of this boils down to a simple fact or two. Every single automobile manufacturer on the planet, plus the big four (Alinco, Icom, Kenwood, and Yaesu) all recommend that two way radio equipment be directly connected to the battery or jump points as the case may be. I guess that every amateur in the world knows something they don't know!
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K1CJS
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« Reply #10 on: October 17, 2012, 04:27:32 AM »

...All of this boils down to a simple fact or two. Every single automobile manufacturer on the planet, plus the big four (Alinco, Icom, Kenwood, and Yaesu) all recommend that two way radio equipment be directly connected to the battery or jump points as the case may be. I guess that every amateur in the world knows something they don't know!

I would think instead, Alan, that people who have done their own installations have had experiences happen to them that reinforce their opinions.  All too many of them, however, ignore commonly held beliefs.  These include but aren't limited to battery interaction with the fed circuit, (capacitive effects) connections of the negative lead from the transceiver, antenna mounting, (ground at the antenna) ground loops and bonding of the various metallic car parts.

All too many of the comments made don't take these things into consideration at all--they just reference the individual's experiences without regard to car and or rig manufacturers recommendations OR commonly accepted installation practices.  Too many of an individuals beliefs are based on a single incident happening compounded by the lack of any damage to their car or their rig when their alternative way of installation is followed in later installations.  All too many of those people will argue until they're blue in the face--and all of their argument is based on the one incident compounded by their reasoning that "That is the way I've always done it!"

No two people will ever agree with each other 100 percent of the time, but to continually recommend ignoring approved installation practices and pushing their own way of doing things because of one or two isolated happenings isn't doing anyone a service, it's just showing everyone that that individual is bullheaded and worse, that that individual has absolutely no regard for other people's property and equipment that well could be damaged because someone listened to them and did their installations contrary to the specified recommendations of the manufacturers.

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W8JI
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« Reply #11 on: October 18, 2012, 07:33:57 AM »

The idea of connecting the negative lead to the battery is idiotic, and always has been, in a standard negative ground system in a device that has a grounded negative rail. A direct battery connection of negative is just begging for damage.

This is very logical to see, if someone actually looks at the system.

My best guess is the silly idea started with floating ground two-way systems, like old Motorola radios with isolated negative busses inside the radio, and carried over without thought into devices with chassis connected negative rails.

That aside, the ICOM is live inside when connected to mains. Like many radios today, the PA section and many other components (PLL unit in the 706) have power connection to the battery with or without the radio power switch "on".

If you had a 100V spike, whether power was on or off would be a moot point for expensive PA section transistors. As a matter of fact, ALL of the high current components are across the battery wires without much protection, while the 13.8 switched buss is the only one likely to be unaffected by a transient.

If I was worried about starter induced over-voltage spikes, which pretty much are a non-issue, I'd have a high current disconnect relay between the radio and battery hot.

IMO, only a fool grounds a device with an internally grounded negative buss directly to a negative battery post or post connector. It does not belong there in common systems, because it obviously sets the installed system up for problems if a negative battery lead develops any significant resistance.

73 Tom
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KB7FSC
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« Reply #12 on: October 18, 2012, 07:25:30 PM »

Hi Tom,

I read your post and it was a bit of an epiphany to me.  Thank you.  I need to reconsider my mobile installation methods.

Is it safe to assume that most of the modern built (past 10 years) mobile ham equipment is using a grounded negative rail?

Also, are you connecting your ground lead for your mobile installations to the engine block, fender, or somewhere else?

73,

Wane - KB7FSC
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WX7G
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« Reply #13 on: October 18, 2012, 09:01:49 PM »

Tom, the radio cable directly to the battery does seem like a potential hazard. Like you say, if the battery negative cable loses integrity the starter current, etc. will take the path of the radio negative cable. So, connecting the radio to the end of the battery negative cable is the best way to do it.

But! As Alan, K0BG, says on his webpage, the negative cable should be fused. This takes care of the cable carrying excessive current should the battery negative cable lose integrity.

« Last Edit: October 18, 2012, 09:18:52 PM by WX7G » Logged
K1CJS
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« Reply #14 on: October 19, 2012, 04:49:32 AM »

...As Alan, K0BG, says on his webpage, the negative cable should be fused. This takes care of the cable carrying excessive current should the battery negative cable lose integrity.

BOTH cables should ALWAYS be fused.  Not having one fused is another idea that comes along contrary to recommended installation practices.  The theory that that practice causes problems because of voltage drop and other insertion problems is just that--a theory.   

As was said, some people have their own ideas, most of the time because of some practice that they've always followed because of a single incident that... 'happened to them.'
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