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K2SGT
04-11-2011, 02:29 AM
I USE MY MOTOROLA UHF RADIO IN MY WORK VEHICLE. ON A BENCH IT DRAWS 11 AMPS AT HIGH POWER. I NOTICED IT PUTS OUT 55 WATTS IN THE SHACK At 13.8vdc. and about 30 watts in the car. After doing many checks I found a 3 volt drop when transmitting. 14.02 down to 11.56. I am using the "power port" that is rated for 20 amps. Due to the drop in voltage there is a drop in power output. What can I do to stabilize the voltage at the radio?? I went from the alternator, to the battery, to the fuse box and there is a .5 voltage drop at best there. At the radio it is too large. Any help would be appreciated.

strook@optonline.net

N5MDT
04-11-2011, 02:33 AM
Run you a pair of suitable size wires from the radio all the way to the battery. Then see what you get. You may find an appreciable difference from using a power plug.

KA0GKT
04-11-2011, 02:47 AM
Hmmm...just crunching the numbers in my somewhat addled brain, this means that you have a power line resistance of a tad bit over 1/4-Ohm, assuming that the rig is still drawing 11 amperes at the lower voltage. Run a heavy guage pair from the battery to the radio, make it as short as possible and fuse both the + and the - leads at or near the battery (This ought to get a discussion going).

WA7PRC
04-11-2011, 03:11 AM
Use a wire size that limits the voltage drop to an acceptable level, over the distance you need to run it (including negative return). There's a nifty spreadsheet calculator (http://www.rst-engr.com/rst/jimsdata/wirecalc.xls) that takes the cypherin' out of it. Just for kicks, if you use 28 feet of #12, you just get 0.5V drop (and 4C temperature rise) at 11A load current.

Run a single wire to the battery, with the negative as short as is practicable to the chassis (the battery should have a short heavy gauge wire from the negative terminal to the chassis). Fuse only the positive wire, at or near the source. The rule of thumb is to add 20% to the maximum expected current demand (13.2A). You would select the next larger size fuse, 15A.

K0RGR
04-11-2011, 03:22 PM
Also, be aware of what the 1/4 ohm means. P=I^2 R. If the rig draws 20 amps, that's 20X20X1/4 ohm - 400/4 or 100 watts of heat being dissipated someplace! Picture what would happen if you held a 100 watt soldering iron to some part of the circuit!

K9ASE
04-11-2011, 03:34 PM
Hmmm...just crunching the numbers in my somewhat addled brain, this means that you have a power line resistance of a tad bit over 1/4-Ohm, assuming that the rig is still drawing 11 amperes at the lower voltage. Run a heavy guage pair from the battery to the radio, make it as short as possible and fuse both the + and the - leads at or near the battery (This ought to get a discussion going).this shouldn't get too much discussion going, It's covered nearly word for word on the examinations we take to get and upgrade our licenses.

K0BG
04-11-2011, 03:58 PM
The rule of thumb is to keep the voltage drop to less than .5 volts. There are a dozen sites, including mine, that have calculators for figuring voltage drop. The calculators assume there are two wires running to the battery, but often overlook the drop across fuses, and connections.

All this said, most of the time folks select the wire size for its ultimate amperage carrying capacity, not voltage drop as they should be.

Lastly, you should never use the chassis of a vehicle for a ground return. There are about a dozen reason why, not the least of which is the creation of a ground loop, which will play havoc with on-board electronics, voltage drop notwithstanding.

K9FV
04-11-2011, 04:13 PM
Lastly, you should never use the chassis of a vehicle for a ground return. There are about a dozen reason why, not the least of which is the creation of a ground loop, which will play havoc with on-board electronics, voltage drop notwithstanding.

Alan, I was thinking you were one of the folks who said not to run the neg wire direct to battery post because if the battery ground wire came loose, this would cause the radio to carry the starter motor current? I guess I didn't remember correctly. I "think" above you are saying not to ground the radio chassis ground stud to frame?

Ken H>

K7JEM
04-11-2011, 04:14 PM
I USE MY MOTOROLA UHF RADIO IN MY WORK VEHICLE. ON A BENCH IT DRAWS 11 AMPS AT HIGH POWER. I NOTICED IT PUTS OUT 55 WATTS IN THE SHACK At 13.8vdc. and about 30 watts in the car. After doing many checks I found a 3 volt drop when transmitting. 14.02 down to 11.56. I am using the "power port" that is rated for 20 amps. Due to the drop in voltage there is a drop in power output. What can I do to stabilize the voltage at the radio?? I went from the alternator, to the battery, to the fuse box and there is a .5 voltage drop at best there. At the radio it is too large. Any help would be appreciated.

strook@optonline.net

One thing to check is the connector at that "power port". In many cases, most of the voltage drop is happening right in that plug. Measure the volage drop right at the radio, and then measure it at the back of the power port connections.

You may find that simply "hard wiring" the radio to the back of the power port will decrease the volatge drop by a lot.

Joe

KB9DT
04-11-2011, 05:13 PM
Throw away the cigarette lighter plugs....use Powerpoles

W7KKK
04-11-2011, 06:28 PM
Ever looked at the size of the wire that powers some of these ports? No way will is support 15 to 20 amps in many cases.

K0BG
04-11-2011, 07:03 PM
Tom, W8JI, are at odds about this subject. All of the automobile manufacturers say to wire directly to the battery for both plus, and minus. This exactly how I do it. Obviously, there are fuses in both leads.

Tom suggestion, and it does have some merit due to the fact amateur transceivers do not have isolated grounds (the negative lead is common to the chassis). That is to say, connect the ground to the chassis where the batteries accessary ground attaches. In so many words, GM & Ford tell you not to do that, however.

Whichever side you're on, there is a consensus that the ground return needs to run to the battery (post or ground). What you do not want to do, is use the chassis for the ground return.

The grounding points for the various electrical devices on a vehicle are just hit, and miss like they used to be in the old days. Any device you name, which has sensors attached to it, all share a common chassis ground. This lessens the possibility of creating a ground loop. A ground loop is a differential of current between different points. If there is a sensor ground between them, it is possible to corrupt the sensed data, whatever it is.

It pays to remember, that a modern vehicle is a rolling computer. So aside from the ground loop issues, we have to be careful about common mode currents as well.

KM3F
04-11-2011, 08:21 PM
In reference to using a seperate ground or the chassis connection, nearly every auto/truck has a ground strap from the negitive side to the engine block at some point.
Loss of a ground using a direct ground connection to the battery should never result in that lead trying to provide a major ground for starting through the radio lead.
Not that anything can happen seperatetly or some one had made changes, use of a seperate ground along with a fused and filtered positive at the battery would be the best of both ways.
If a ground lead fault would result in starter current finding another ground path, then a lot of other harness with grounds in them will also get the same result.
We all take a chance that something might develope at anytime that could result in an unintended effect, either way.
Powering anything from a cigar lighter much greater than a small device of 5 amps or greater is not a wise idea.
Look at the cigar lighter socket inside and you 'may see' it is a different design and not meant to be used for any other purpose and not compatable with a standard plug.
Very often a second socket is provided for low current devices that is designed for the purpose and are limited to 10 amps max by fuse and wire size for overall saftey due to mfger libablity.
.

K7JEM
04-11-2011, 08:55 PM
Tom, W8JI, are at odds about this subject. All of the automobile manufacturers say to wire directly to the battery for both plus, and minus. This exactly how I do it. Obviously, there are fuses in both leads.

Tom suggestion, and it does have some merit due to the fact amateur transceivers do not have isolated grounds (the negative lead is common to the chassis). That is to say, connect the ground to the chassis where the batteries accessary ground attaches. In so many words, GM & Ford tell you not to do that, however.

Whichever side you're on, there is a consensus that the ground return needs to run to the battery (post or ground). What you do not want to do, is use the chassis for the ground return.

The grounding points for the various electrical devices on a vehicle are just hit, and miss like they used to be in the old days. Any device you name, which has sensors attached to it, all share a common chassis ground. This lessens the possibility of creating a ground loop. A ground loop is a differential of current between different points. If there is a sensor ground between them, it is possible to corrupt the sensed data, whatever it is.

It pays to remember, that a modern vehicle is a rolling computer. So aside from the ground loop issues, we have to be careful about common mode currents as well.

Having installed hundreds of medium power and high power commercial radios, I can say that this is not true, nor is it accepted practice, AFAIK. Most commercial radio manufacturers only include a short pigtail for the negative lead, maybe 3 to 5 feet long at best. It is intended to be grounded near the radio, to a good ground point. That might be a bolt, but sometimes it is a self tapping screw into the body of the vehicle. Since the radio usually gets a ground from the installation bolts, this ground is usually redundant. The chassis on virtually every commercial and ham radio is tied directly to the negative side of the electronics.

An interesting test would be for someone who has done this "negative lead to the battery through a fuse" idea to try a short pigtail directly to ground, and measure the voltage drop in both cases, with the radio removed from it's bracket, and otherwise isolated from ground (no antenna connected, just a dummy load).

In reality, the negative lead back to the battery isn't going to make any difference, in most cases, so if people want to do that step, they can. I really haven't heard of any ill effects, it's just not the proper way to do things.

Joe

KN4X
04-12-2011, 02:26 AM
If the voltage drops too much when loaded, do some more investigating like check battery voltage with all accessories off, then with the a/c blower on high and headlights on high-beam. Could be a voltage regulator / alternator. Could be the battery / terminals. Might be a bad meter?

If the electrical system checks out, do a straight run of 12g wire from the battery to the radio. Fuse both sides.

Why would you fuse both sides? Imagine a scenario during which a loose battery chassis ground causes your radio, radio chassis, and antenna ground to be your starter ground. Extra-crispy rig that's not covered by warranty. I'm sure most are guilty during an install of connecting a rigs antenna first, then the positive lead and immediately hearing the rig spring to life without the negative lead connected. The rig is getting its ground from the antenna ground via the radios chassis. Always fuse both sides of transmitter power leads. :eek:

Those that say all installs will get a ground from the radio's chassis via the mount haven't mounted a radio into plastic in a shifter side plate.

K9STH
04-12-2011, 04:17 AM
BG:

The major commercial two-way manufacturers have been grounding the negative lead to the body of the vehicle through a short lead for decades. This has worked VERY well!

As JI pointed out, the standards in Europe have been changed to not allowing the negative lead to be connected to the battery! Now I don't know how long it will take for Japan to come to the realization that this is the best practice. Of course, you do realize that the majority of vehicles sold in the United States are, to a large part, designed in Japan.

The practice of connecting the negative lead directly to the battery has its roots in the "CB" craze of the late 1960s and into the 1970s when the Japanese entered into the mass production of "CB" radios. Since, at that time, truckers were a significant portion of the market, and since, again at that time, there were quite a number of tractor units still in use that had positive ground, the Japanese started producing radios that could be used on both positive ground vehicles as well as negative ground vehicles. They just isolated the chassis from ground and provided equal length positive and negative power leads. All that had to be done is to connect the positive (red) lead to the "+" terminal of the battery and the negative (black) lead to the "-" terminal of the battery. It did not matter which terminal was connected to the frame/body of the vehicle.

When the Japanese entered into the production of mobile amateur radio equipment they retained the same configuration of supplying the positive and negative leads the same length even though the chassis of the equipment was no longer isolated from ground.

Again, the commercial two-way radio manufacturers have been grounding to the frame/body of the vehicle since well before World War II even though the vast majority of vehicles were positive ground until the mid 1950s. This works VERY well and the Europeans have finally come to this conclusion!

Glen, K9STH

KN4X
04-12-2011, 05:58 AM
I've only had one automotive computer malfunction that I could blame on a rig. A 2m Kenwood installed in a 1992 Toyota Camry. I ran the antenna wire down the passenger side, under the plastic door jam trim. Every time I keyed the radio, the ABS brake and check engine lights would come on. SWR was great, NMO mount to a Diamond antenna. I called Toyota, and after being handed off to about 5 different engineers, one told me the cars computer was under the passenger side seat. He recommended I move the antenna run to the drivers side. Problem solved. RF issue?

I'm not a commercial radio installer, and I do not doubt that the big trunk Motorolla radios had/have a short chassis ground. I do however have experience with Asian manufactured amateur radios, and most I've dealt with prefer a direct run from the battery. Fuse everything. Better safe than sorry.

KG4PWF
04-12-2011, 08:39 PM
Hard wire directly to the battery... forget power outlets.. they are for charging toys and phones....to small ..to much for your radio.. hard wire to the battery .fused and your good to go !!!

WA7KKP
04-12-2011, 10:15 PM
Throw away the cigarette lighter plugs....use Powerpoles

Amen to that -- and if in danger or in doubt, use a mult-pole connector with several pins in parallel. I've used the beau/Cinch P306 for years, with 3 pins in parallel for each side. Never had a problem.

Gary WA7KKP

KA9VQF
04-13-2011, 10:38 AM
I’m one of the many who do not like running two wires to the battery. Partly because I’m lazy and cheap but mainly because the whole body of your vehicle is at ground potential anyway, unless you have a very old or foreign made machine you are trying to put a radio in, it is connected to the negative side of the battery anyway.

Unless the vehicle is very rusted it is the best way to ground your accessory. I have installed a lot of accessory radios and tape players in vehicles over the years and always, unless the owner is a butt head who will not listen to me, ground whatever I’m installing to the nearest spot on the chassis I can.

When I was on the fire and ambulance department in northwest Wisconsin we obtained a 5 ton truck from an army base that had already been setup to be a tanker. We paid the astonishingly low price of one dollar for the vehicle.

We went and picked it up down in the Dells area and drove It home which is a whole ‘nother story.

Once we got it home it didn’t take long to discover it was a 24 volt positive ground vehicle. Because of this we had no siren or radio to put in it.

As time passed I mounted a 120 amp alternator {huge at the time} out of a Dodge in the machine and put a separate 12 Volt battery in so we could run our light bar, siren, and radios. The body of the alternator had to be insulated from the rest of the truck.

I had to mount isolated positive and negative buss bars for the 12V system,

I could not just tag the ground for the light bar and siren to the body of the truck since the 24 Volt positive ground system used that, so I had to run two separate wires and insulate the light bar from the roof of the truck.

Having these wires run under the floor and up inside the back of the cab to the light bar caused all kinds of problems with the fire band radio when the lights were on. Running the electronic siren totally wiped the fire band radio out.

I was sure it was a ground loop problem at the time just didn’t know how to fix it since I couldn’t have the shortest possible leads.

It took some real head scratching to find a way to fix it. I tried using a choke and even bypass capacitors to filter the light bar motor noise out to no avail.

The fire chief was convinced the noise was coming from the 24V generator but I had already put bigger bypass capacitors on that and I was sure it was not the problem.

There was virtually no noise in the radio until you turned the light bar on.

Eventually I discovered that simply putting the wires inside some conduit that was bonded to both top and bottom of the cab of the truck did it.

K0BG
04-13-2011, 01:48 PM
If you take the time to measure the resistance in a modern vehicle body, you might be surprised. If we're really looking to keep the voltage drop low, you run a separate ground wire.

The point that is apparently lost here, or ignored as the case may be, is the on-board electronics. What you could get by with 25 years ago, you can't now. It isn't so much the computers themselves, but the sensors they use to control all sorts of other electronics. The three big killers, are common mode, ground loops, and RFI in about that order.

How you wire your vehicle is your business, but for me, taking shortcuts and ignoring the obvious is not the stuff of champions.

K7JEM
04-13-2011, 01:52 PM
If you take the time to measure the resistance in a modern vehicle body, you might be surprised. If we're really looking to keep the voltage drop low, you run a separate ground wire.

The point that is apparently lost here, or ignored as the case may be, is the on-board electronics. What you could get by with 25 years ago, you can't now. It isn't so much the computers themselves, but the sensors they use to control all sorts of other electronics. The three big killers, are common mode, ground loops, and RFI in about that order.

How you wire your vehicle is your business, but for me, taking shortcuts and ignoring the obvious is not the stuff of champions.

Not so sure this is the case. I've never seen a sensor bothered by a radio install that uses the chassis of the car for negative return. Do you have any sort of documented case where this happened, or is this just a guess or supposition?

Joe

K0BG
04-13-2011, 02:09 PM
Yes, and yes. Probably the most interfered with device on a vehicle is the ABS system, with the transmission control circuitry a close second. These devices, almost by necessity have non common grounds on the sensors. There is a very good article written by a Ford engineer for ARC Newsletter. It appeared about 3 years ago. Perhaps I can find it, and get permission to republish at least parts of it.

It dealt with data corruption in the crash data computer (part of the transmission control system) installed on all Ford police vehicles. The final conclusion with respect to cause were ground loops due to incorrectly wired telemetrics (radios, computers, etc.).

If my mail box is any indication, the three aforementioned causes affect everything for dash board lights going crazy, the ABS applying while driving, feed back in the stereo system, and CEL (MAL) being turned on by all manner of corrupted data in the OBDII.

W8JI
04-14-2011, 07:28 PM
I would run a heavy fused lead to the battery positive, and ground the radio with a short lead to the chassis or body near the radio. This is traditionally how two-way radios are done.


The problem you have is probably not localized voltage drop, but rather accumulated resistance in the power path. That 100 watts dissipation is probably spread over dozens of feet, resulting in negligible safety or heat issues but very annoying voltage drop. I would use a proper positive fuse, connect the positive to the under-hood tap off point for all accessory vehicle positive power leads (usually near the starter relay or solenoid), and very securely GROUND the non-fused negative lead near the radio to some solid sheet metal.

End of my advice.

Now the argument part:-)

Anyone who thinks the vehicle chassis in a conventional unibody or even frame/chassis vehicle has high or even significant resistance is sorely mistaken.

Anyone who assumes GM or Ford understands radio systems and ground loops is also, unfortunately, mistaken.

I not only work on cars as a hobby, I owned a two-way radio business for a while. Living in Toledo and racing near Detroit and in northern Ohio, I hung around with engineers from Ford (primarily, because I race Fords), GM, and Chrysler. I also was a managing engineer at an automotive electronics manufacturer in the 80's.

For racing, we think absolutely nothing of using the chassis of a unibody (or the frame of framed car) car for a ground return for starter currents in some very high compression large engines. That ground path, I can assure you, is ALWAYS much less resistance than any reasonable size cable will ever provide. To do this we also bond the engine block and/or bell-housing or timing cover to the chassis with suitable large cables.

In vehicles the normal wiring, almost without exception, is to have the large battery negative lad to the engine block, bell-housing, or timing cover. It almost always goes to a permanently bolted on part that does not have a current path through bearing or moving parts to the starter housing.

The ground lead to the chassis generally takes two forms. One is a braided cable to some engine part for RFI and sensor noise mitigation, the other is a ground from the battery post to the chassis. The ground lead to the chassis is the primary path for ALL electrical accessories and lights, including the computer.

The OEM negative post to chassis lead is normally sized to have a fusing current much higher than all the intentionally installed fuse links on the wires leaving the positive supply line. What they want are the normal serviceable fuses to open first, the fuse links in wiring harnesses second (they also power things that could cause real problems if they accidentally fail open), and the ground lead as a last resort. The starter and alternator return through a very heavy cable from the engine to the battery that is independent of the other grounds. This is to keep current out of bearings, and if the positive post ever has a direct ground to minimize the path length for heating (fire).

When you ground to the battery post with a radio or accessory that is not ground independent two bad things happen. First, you almost always will increase negative path resistance.

Second, you create a ground loop that circumvents the OEM ground. Now you have added a ground path that COULD handle fault currents into the equipment location, and to every wire leaving that equipment. If you really wanted to properly fuse the negative lead, it would need to be fused for the SMALLEST conductor leaving that accessory.

I have actually seen the battery negative lead open a fuse, and the coaxial cables (RG58) to the antenna get so hot it melted. This is because the gear seeks a ground through the feedline to the antenna!!

It is a fire and equipment hazard to ground to the battery. Commercial radio manufacturers generally know this, and want to avoid setting a vehicle on fire from an open negative path to the battery. Worse yet, if the starter lead opens, starter currents now have an additional path to follow.

If I had a really high current load close to the battery, I would ground near the battery ground on the chassis but NOT with a negative fuse. I would never under any condition common directly to the battery negative or to a lead from the battery negative. I would always get the connection through the chassis.

If the load was a long distance away, I would just use the chassis. My Mustang battery is in the trunk, and the battery negative is grounded through two braids that have a calculated fusing current much less than the 00 cable that runs to the starter. Nearly all of my voltage drop is in the 00 cable. Virtually none is in the chassis. In this case the block is bonded to the chassis with multiple large cables. My car starts just like the battery is up front, and there is only a few dozen millivolts difference between the block and chassis while starting. I do the same thing with the supply for my kilowatt amplifier in my F250.

73 Tom

.

WA7PRC
04-14-2011, 08:16 PM
[big snip]
My Mustang battery is in the trunk, and the battery negative is grounded through two braids that have a calculated fusing current much less than the 00 cable that runs to the starter. Nearly all of my voltage drop is in the 00 cable. Virtually none is in the chassis. In this case the block is bonded to the chassis with multiple large cables. My car starts just like the battery is up front, and there is only a few dozen millivolts difference between the block and chassis while starting. I do the same thing with the supply for my kilowatt amplifier in my F250.
Those who know Ford direct-drive starters know Tom's setup is an acid test. They pull a lot of current. My ET bracket racecar ('68 Plymouth Barracuda 340-S) uses two Group 27 batteries in the trunk, with 1/0 wire feeding the starter. The ground is through the chassis. The MoPar starter design is a gear reduction type, and cranking current tends to be less than for Ford & GM starters. Additionally, though I'm running 12.5:1 compression, the cam is so long that it doesn't build much compression during cranking. But I expect it's still around 100A.

My acid test is the 3500# electric winch I use on my pickup and car trailer. The wiring is 1/0 and the stalled current is around 175A. It also gets the ground return thru the chassis with zero issues.

K9STH
04-14-2011, 09:23 PM
The Galvin brothers, the founders of Motorola, learned about proper wiring techniques at the very start of their business. When they first started, Motorola made BC band receivers for automobiles (this was in the mid 1920s). As a demonstrator unit they installed a receiver in the luxury automobile of one of the people who financed them (a Packard, if I remember correctly). Within a few minutes of operation the wiring caught fire and destroyed the vehicle!

After that, they were MUCH more careful when installing receivers in vehicles!

Glen, K9STH

K0BG
04-15-2011, 12:08 AM
Tom, since you and I are at odds about this, why do automobile manufacturers specify connecting directly to the battery?

You also speak of fusible links. Unless I'm out in left field, those haven't been used in years due to the fire hazard they impose.

W8JI
04-15-2011, 02:37 PM
Tom, since you and I are at odds about this, why do automobile manufacturers specify connecting directly to the battery?


My somewhat educated guess, based on the people I know who were and are engineers at Ford, is they don't understand ground loops and how radios work. They wrong consider the negative path from the radio or accessory the ONLY negative path. Without knowing what is outside, they want to protect the parts they installed. If (and only IF) all current came through the negative lead using a battery connection would be a great idea for protecting the OEM wiring. A negative connection to the battery does NOT protect the gear or the wiring to the gear.... and much to the contrary actually increases the chances of wiring or equipment failures and fires in the new wiring.

For not much at all, if any at all, additional protection to OEM wiring and vehicle equipment there is a large increase in risk to the new equipment and wiring to the new gear by following the guidelines of connecting to the battery with the negative lead.

It would be entirely different, and they would be correct in their suggestions, if the aftermarket gear had a completely isolated negative return. Pretty much none does.

There are many people, some very good engineers, who do not "get their heads" fully around ground loops because they don't understand the external devices and how they behave.


You also speak of fusible links. Unless I'm out in left field, those haven't been used in years due to the fire hazard they impose.

Fusible links, while used less now that fuse blocks have been largely relocated under hood or split into higher current and lower current branches, are still a normal part of wiring in high-current areas. This is especially true in areas that can be real hazards if power drops from a bad fuse connection, or current is too high for normal fuse holders. No one wants to be in the middle of a highway with no lights or motive power, or lose alternator power, because a fuse fatigued or pins corroded.

My friend's brand new truck has at least three fuse links. My older F250 (2003) has several of them, as does my wife's 2004 car.

W0LPQ
04-15-2011, 03:53 PM
I have posted this info years ago regarding cig lighter plugs. Some use a spring that is maybe at best #22 AWG size. So if you think you can pull 15A through this thing ... go for it. You will most likely have a fire. Plus, the point contact at the end of the plug mating with a sometimes questionable cig lighter ... bad choice.

You could equate part of this to powering your radio just by holding the power wire against a small bolt. Dumb choice...

I used to have a Kenwood TM241 and used the cig lighter plug as I normally ran the radio on low power. It worked ok. Once in a noisy environment I inadvertently clicked to high power ... radio ceased to work. Then it dawned on me ... I felt the plug and man was it hot. I went back to low power and ... radio barely flickered. Arrived at destination and took plug apart ... the spring was black and ... measured about 5 ohms ... so ... obviously, this thing was toast. Wired direct to the battery with fuses ... back to normal operation.

Tom has some great ideas from experience. As does Alan ... it pays to really listen to them.

WA7PRC
04-15-2011, 04:21 PM
Rhetorically speaking, if returning the negative lead to the battery is recommended for aftermarket equipment, why isn't that done with all factory-installed equipment? Logic says they would behave the same. Then, by extension, there is no reason to return the negative all the way to the battery.

Another thing to consider is that, with modern equipment, the negative is returned to its chassis. Sometimes, there is no separate negative return lead. Simply mounting the equipment to the metal chassis by itself may provide a sufficiently low resistance negative return connection.

I'm having a blast mobiling again. Look for me around 50 KHz above the bottom of 40/20/15/10m.

KA0GKT
04-16-2011, 03:48 AM
this shouldn't get too much discussion going, It's covered nearly word for word on the examinations we take to get and upgrade our licenses.

In the past, running the negative lead to the battery has been subject of many debates on ZED. I wasn't refering to I/R drop.

KF5CGM
04-16-2011, 04:25 AM
Ok, I was reading here and I was wondering, I have a Trailblazer and the Fusebox is under the rear seat.
So does it make a difference when I plug my radio into the cable that comes from the battery?

K9STH
04-16-2011, 03:07 PM
You really need to run the positive lead from the radio directly to the battery with a fuse right at the battery. Going to the fuse block is generally not a good idea because of the gauge of wire that goes to the fuse block. It is heavy enough to handle the normal current requirements of the vehicle. Unfortunately, the current draw of the radio can more than double the maximum current and that will result in an excessive voltage drop as well as possibly overloading the wire to the fuse block.

Glen, K9STH

N5USR
04-16-2011, 11:34 PM
Glen, what if the fuse block includes an otherwise-unused high-current fuse? My S-10 pickup has one of those oversize blade fuses (can't remember right off, it's either 30 or 40A) with an adjacent stud for connection of a trailer braking system. I decided to use that, as I'll never be hauling a trailer with brakes and I'm also not sure how the heck to connect wiring to a side-post battery... (I did some looking at the auto parts store and didn't find anything to facilitate that - would also like to know if I missed something there...)

The fuse block in my case is under the hood just a few feet from the battery, not inside the cab.

KD0EAH
04-17-2011, 12:31 AM
ya see, ya do it like this....

Ya go down to the local weldin' shop. Find yer sef a nice big set of 4/0 or if in a pinch, some 3/0 wire.

Then ya go down to the local battery shop and ya find yersef a nice big ol battery out of a fork lift.

Now ya take that battery and you put it up on the back bumper and yaz hold it in place with enough duct take it don't move around there.

Now ya gotta remember. These here batteries are big, so ya are gonna have to go down to the steel yard and git yersef a couple hunk a iron there to tape onto the front bumber there to put some more weight back onto the front tires to be able to steer ya know. So ya may have to go pick up another box of tape or such. Now ya could use baling twine here, but that tends to come apart sooner than the duck tape does.

Now once ya git all this here done, ya kin run them there cable from the battery to the radio. Now once you git them run to it, ya gotta go git some solder and a nice gas torch. Now, yer workin with fire here, so ya may want to git a bucket o' water just in case you light the carpet or something else on fire.

Just remember, ya don't want too much heat into the wires here or you might melt the plastic coating and when you go to use the radio, you'd let out all that good smoke that's in there and ya know how hard it is to put that stuff back.



[/sarcasm]



The big thing I have observed/experienced/dealt with/learned with after market electronics in a vehicle, the factory grounds don't take into consideration all that wonderful gadgetry we go to install. As such, without a dedicated ground for it, you get all kinds of fun noises and bleed over from the electrics in the rest of the car.

so to solve the problem, just create a separate loop for all your toys and gadgets by running a lead from both the + and the - wires back directly to the battery. It just isolates it from the vehicle systems that way is my experience.

other wise, pull out the welding cables and the spreadsheets and turn it into the nasa/redneck shadetree, which is better, "i'm right/you're wrong" ya ain't doin it my way"

K2WH
04-17-2011, 11:16 AM
Hard wire directly to the battery... forget power outlets.. they are for charging toys and phones....to small ..to much for your radio.. hard wire to the battery .fused and your good to go !!!

While I agree with this, use of the cars power outlet is not as "childish" as you make it sound. Connecting directly to the battery is nice, and I have done this but, I have been very happily operating HF from the car running 100 watts using the accessory outlet. Why? Simply because I had great difficulty getting the #10 wires into the passenger compartment and, these wires are still in the engine compartment gathering road dust. So, as a quick fix, I plugged into the accessory outlet. Only had (1) problem in six years of use, a blown fuse when on 10 meter FM because of duty cycle. Using 50 watts FM or 100 watts in SSB mode, will not overwhelm the accessory socket and will work for most users since most users run only ~ 50 watts.

K2WH

KA9VQF
04-17-2011, 12:54 PM
I’ve run a 45 watt rig on a cigarette lighter plug with no problems for years. My XYL did not want a radio wired in “her” car so when we go on a trip I use my HTX-242 and a magmount in that car.

In both cars I have installed a strip of 1&”X” copper strap that’s just a tad over 12” long with 4 cigar lighter sockets in it. One wire heavy wire is run to the positive side of the battery and the strip itself is grounded to the body of the with brass bolts.

I polished the copper strap to a high gloss finish and then sprayed it with a clear acrylic after drilling it to try and keep it nice.

Having these additional sockets has been very handy. I can plug up to 4 additional accessories into them including the portable DVD player so the wife and kid can sit in the back seat and watch movies while I drive.

Sometimes I bring my laptop with me and plug it in while the wife does her doctor things and I have to wait. The clinic has free wifi.

KM3F
04-17-2011, 07:10 PM
Just a comment, if your 45 watts is a total draw, that is 14 volts x 3.3 amps = 46 watts, well under what that line will handle.
If however the total power were 2 x 45 = 90 watts (using a 50% efficiency factor for the transmitter), the total current draw would still only be about 6.5 amps so you would not have any issue.
If you were trying to draw at or near the fuse limit the fuse would have blown a minute or so after keyup.
So you did not do anything unusual with your 45 watt draw from that circuit.
As stated, a fuse has resistance. As the current flow drops voltage across it, the heat dissapation rises. When the fuse temperture limit is reached it melts at some point along it's structure. A fuse should not be forced flowed near it's rating if circuit reliability is to be had.

KM3F
04-17-2011, 09:06 PM
Here is the sources of ASTRON power supply info drawings and mods.
Mfgers prefered Transmitting intalls and power feed methods for many makes.
For example Ford recommends a direct battery feed fused at the battery using a twisted pair if possible.
Specs for equipment design etc.
Look up 'Repeater Builders Tech. Infomation Page'.
Enjoy.

K0BG
04-17-2011, 10:33 PM
62755

Just because you haven't had any problems operating your transceiver from the accessory socket, does not mean that you should!

Note the arrow is pointing to the dashboard accessory socket, otherwise known as a cigarette lighter socket. Considering that a vehicle fire, it the most costly of all vehicle repairs, do you really think you aught to be doing what you are doing?

K2WH
04-17-2011, 10:55 PM
62755

Just because you haven't had any problems operating your transceiver from the accessory socket, does not mean that you should!

Note the arrow is pointing to the dashboard accessory socket, otherwise known as a cigarette lighter socket. Considering that a vehicle fire, it the most costly of all vehicle repairs, do you really think you aught to be doing what you are doing?

I assume you are talking to me and I agree with you that it does present a certain amount of danger. However, the accessory socket is fused as is the accessory socket plug, and the rig power leads. Any failures (short circuits) would cause one of more of these fuses. The 3 fuses are in series and coordinated properly so the car fuse blows first, the plug fuse second and finally the rig fuse last. I have no problem continuing with this setup as it has proven itself reliable and is properly protected. However my next vehicle will be wired directly to the battery which will be soon (I hope) only because I would rather use the accessory socket for other equipment like my GPS.

K2WH

K0BG
04-18-2011, 12:48 AM
Well, Bill, you're still kidding yourself. If you take the time to look up the hysteresis of most automotive fuses, there absolutely wouldn't be any argument, and you'd stop doing what you're doing.

As I said, you just might get by. How long, is subjective. Sooner or later, you're going to have a problem. Even if you get by for the next few years, even, doesn't really matter. If you don't understand the ramification, well....

WA9SVD
04-18-2011, 05:15 PM
One "problem" and item to consider is the typical "cigarette" lighter plug, and even the accessory plug availabble in many vehicles.

The "ciggie" socket ( and wiring) is NOT designed or rated for CONTINUOUS operation; it's designed for occasional, intermittent use. IOn that respect, the ciggie lighter will heat up even if the voltage are less than optimal, FAR below the voltage needed to power most Amateur Radios.
One result of that is that the wiring to the ciggie socket is NOT designed to provide the current demanded by a transceiver, most lighters will trip within 15 seconds or so, so the original socket wiring doesn't have time to heat significantly, and the manufacturers design to THIS use.

On the other hand, when an Amateur radio is connected through the ciggie socket, it can be drawing 2-3 amperes current in receive mode, but well over 10 Amperes (often 15 Amperes or more) in transmit mode. THAT current draw may well cause a problem in the wiring; not JUST an excessive current draw, but an unacceptable temperature rise in the wiring, not just from the XCVR to cig socket, but ALSO under the dashboard from the cig socket to the fuse block. THAT, can actually pose a fire hazard, should there be a short from the radio positive to ground.

K2WH
04-20-2011, 11:02 PM
Well, Bill, you're still kidding yourself. If you take the time to look up the hysteresis of most automotive fuses, there absolutely wouldn't be any argument, and you'd stop doing what you're doing.

As I said, you just might get by. How long, is subjective. Sooner or later, you're going to have a problem. Even if you get by for the next few years, even, doesn't really matter. If you don't understand the ramification, well....

As with any electrical distribution system to avoid blackouts, co-ordination of your interrupting devices is paramount. This is exactly what I have done with the protection of my accessory socket thru the utilization of the fuse TCC's. Yes they are slower than other protective devices, but the ones I have chosen are fast enough especially at 10-15x. I know of the hysteresis of automotive fuses, that is why they were changed to other types with very quick action beyond the long lag time of typical automotive fuses. Done properly, it is safe.

K2WH

W8JI
04-21-2011, 12:48 AM
It has little to nothing to do with fuse hysteresis. Here is what really goes on, and what is really the problem....

Maximum possible heat in a bad connection is fuse opening current (for the amount of time required) times supply voltage. That's as good as it gets. So if you have a fuse that opens at 30 amps in 120 seconds and it is a 12 volt system, you can have over 360 watts in a bad connection for a few minutes.

Fuse and circuit breakers almost never stop a fire from a poor series connection to a high current device.

The real problem is in the pin connections of the lighter plug. It isn't fuse type or anything else. The maximum safe current for that type of plug probably is around 5 amps. Auto manufacturers for some reason fuse for wire size, not the potential contact resistance that might occur with a bad accessory plug connection.

The only way positive to correct the hazard of using a push contact like that is to downsize the fuse to 5 amps or so, which would limit heat to 50 or 100 watts for a reasonably short period (most 5 a fuses will pass 10 amps for half a minute or so).

Pressure connections, unless enclosed in a flameproof box, are always going to be problems. On the old metal dashes a large fuse was probably pretty safe. I would never run anything over a few amps in my power point. As a matter of fact, I intentionally fused mine at 5 amps after a cord on my GPS got pinched ( I stuffed it in a joint in the dash to keep it out of the way, and it wore through) and melted down.

73 Tom

WA9SVD
04-23-2011, 12:50 PM
I don't remember if anybody pointed out that each fuse will also create a slight voltage drop, and the MORE fuses used, the greater the voltage drop, particularly on transmit.

K9PHT
04-23-2011, 06:41 PM
I just recently installed a IC-706MKIIG and a ICOM 2820H in my new 2010 F150 truck. The ICOM radios main units are installed under the back seat area of extended cab truck. I ran #4 GAUGE cable (left over from RV POPUP cable upgrades) from my BATTERY connection to a BLUE SEA COVERED FUSE BLOCK and used a 50AMP fuse here. Then I continued the #4 GAUGE cable thru the firewall into the truck and down the floor cable duct area under the doors to the back seat area. there I terminated the BATTERY CABLE and SHORT FRAME GROUND to a BLUE SEA covered TERMINAL BLOCK. This is where I connect the 12VDC cables from the IC-706 and IC-2820 radio units. Then I ran the CONTROLLER CABLES under the rug to the front console area where the two CONTROLLER HEADS are mounted. Neat installation if I say so myself haha.. I get full RF power out from my IC-706.

WA9SVD
04-23-2011, 09:31 PM
I just recently installed a IC-706MKIIG and a ICOM 2820H in my new 2010 F150 truck. The ICOM radios main units are installed under the back seat area of extended cab truck. I ran #4 GAUGE cable (left over from RV POPUP cable upgrades) from my BATTERY connection to a BLUE SEA COVERED FUSE BLOCK and used a 50AMP fuse here. Then I continued the #4 GAUGE cable thru the firewall into the truck and down the floor cable duct area under the doors to the back seat area. there I terminated the BATTERY CABLE and SHORT FRAME GROUND to a BLUE SEA covered TERMINAL BLOCK. This is where I connect the 12VDC cables from the IC-706 and IC-2820 radio units. Then I ran the CONTROLLER CABLES under the rug to the front console area where the two CONTROLLER HEADS are mounted. Neat installation if I say so myself haha.. I get full RF power out from my IC-706.

WHat distance is it from the positive battery terminal to the fuse block?

W8JI
04-24-2011, 12:45 AM
I just recently installed a IC-706MKIIG and a ICOM 2820H in my new 2010 F150 truck. The ICOM radios main units are installed under the back seat area of extended cab truck. I ran #4 GAUGE cable (left over from RV POPUP cable upgrades) from my BATTERY connection to a BLUE SEA COVERED FUSE BLOCK and used a 50AMP fuse here. Then I continued the #4 GAUGE cable thru the firewall into the truck and down the floor cable duct area under the doors to the back seat area. there I terminated the BATTERY CABLE and SHORT FRAME GROUND to a BLUE SEA covered TERMINAL BLOCK. This is where I connect the 12VDC cables from the IC-706 and IC-2820 radio units. Then I ran the CONTROLLER CABLES under the rug to the front console area where the two CONTROLLER HEADS are mounted. Neat installation if I say so myself haha.. I get full RF power out from my IC-706.

The important things for safety are where the negative lead connects (it should be to the vehicle chassis) and using the smallest possible size fuse for the job. A 50 amp fuse might be a tad large unless your gear actually draws near 50 amps. My extra large 2/0 or 3/0 copper cables into the radio room run from a 50 ampere breaker, because 45 amps or so is the very most I draw with all radios and all amplfiers running on the worse case mode. :-)

73 Tom

AF6OD
04-25-2011, 05:20 PM
I USE MY MOTOROLA UHF RADIO IN MY WORK VEHICLE. ON A BENCH IT DRAWS 11 AMPS AT HIGH POWER. I NOTICED IT PUTS OUT 55 WATTS IN THE SHACK At 13.8vdc. and about 30 watts in the car. After doing many checks I found a 3 volt drop when transmitting. 14.02 down to 11.56. I am using the "power port" that is rated for 20 amps. Due to the drop in voltage there is a drop in power output. What can I do to stabilize the voltage at the radio?? I went from the alternator, to the battery, to the fuse box and there is a .5 voltage drop at best there. At the radio it is too large. Any help would be appreciated.

strook@optonline.net

You did not mention your vehicle year, my 1971 pickup has a huge wire for the lighter, maybe 14 ga. My 2004 Toyota has maybe 18awg could even be 20awg.

Try running a wire from the Bat. to the radio using a #12awg to reduce the voltage drop.
I used the formula from K0BG website which takes more then just wire resistance into account. and 15 feet of 18 awg with fuses would be 1.075 Ohms
15 feet of 12 awg would be 0.28 Ohms.

There seems to be some interesting debate on vehicle grounds too.:D ( First I'm not an electrical engineer, or even play one on T.V.) But have a good knowledge on the topic. FWIW SAAB does run separate ground wires back to a central location in the engine bay for all connections. Similar to your house grounding system. Chevy/Ford/Dodge/Toyota/etc. do not. I have noticed that on larger vehicle's they will run a separate ground wire to the rear so the tail lights and what not don't have to travel the length of the body/frame back to the battery. I suspect voltage drops were dimming the bulbs more then the engineers liked?

I have noticed that most engines have more than one ground wire from the engine to the body too. I will see braided wire and stranded wire used, so they must be trying to accomplish more then just one function. i.e the braided wire to help conduct RF to ground and the stranded wire to provide a path to ground as the alternator needs to get electrons from somewhere.

I've looked at WJ8I site too. and noted he prefers to connect the neg lead near the battery but run through a bit of the body. ( which does create a slight resistance over direct connection) to help with ground loops by providing a common path to ground.

K8ERV
04-25-2011, 05:41 PM
Check the loaded voltage at the battery. I have done a lot of testing of car batteries since I noticed my camper voltage dropping a lot with a little load. I find that batteries stabilize at 12.6 some time after charging, but it drops a lot with just a few amps of load.

So unless you are charging it may be normal (tho not good) for the actual battery voltage to drop to well under 12 with a 12amp load.

TOM K8ERV Montrose Colo

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