Grounding mobile radios

[dixie729]

I've always grounded my radios to the battery post. On my installs and we also did it for the unfitting company I use to work for.
I've seen on a couple of post here not to. But I didn't see why not to.
Why would you not want to ground it directly to the battery?
Steve, maybe you can shed some light on this.

Kevin.

Sent from my XT1097

 

[Thunderknight]

If the vehicle (factory) ground strap from the battery to the engine block fails, the radio acts as the negative side for the whole vehicle. The radio might not like seeing all the current of the starter motor!

 

[SteveC0625]

I've always grounded my radios to the battery post. On my installs and we also did it for the unfitting company I use to work for.
I've seen on a couple of post here not to. But I didn't see why not to.
Why would you not want to ground it directly to the battery?
Steve, maybe you can shed some light on this.

As an installer of commercial and public safety radios, I follow the manufacturer's guidelines. And, as Thunderknight pointed out, you don't want the radio carrying the current load of the starter electrical system should there be a failure of some kind.

Here are the Motorola install manuals for the Commercial and Professional series of radios:

https://drive.google.com/file/d/0B3k529wkRVv1ZFJCOWNSZXpBS0k/view?usp=sharing

https://drive.google.com/file/d/0B3k529wkRVv1ZE5QVnIwUGJTQVE/view?usp=sharing

They both call for vehicle chassis grounding not the negative terminal of the battery. Other Motorola product line install manuals call for the same. There's also no mention of fusing the ground side of the power cable. I know there's lots of debate about this in the ham world, but you won't hear much (if any) talk about it from the pro installers and upfitters who do this work on a regular and frequent basis. We have to deal with multiple systems, not just a radio or two, in a vehicle. Grounding and eliminating interference are very important to us so following each manufacturer's instructions for installation of each device is critical to the finished results.

 

[gewecke]

I've always grounded my radios to the battery post. On my installs and we also did it for the unfitting company I use to work for.
I've seen on a couple of post here not to. But I didn't see why not to.
Why would you not want to ground it directly to the battery?
Steve, maybe you can shed some light on this.

Kevin.

Sent from my XT1097

. Ground it to the frame, Always. :wink: 73, n9zas

 

[prcguy]

If the main battery ground connection fails, current could flow through the radio negative lead to the radio chassis then through the coax shield to the grounded antenna mount. If this happens you would know right away due to lights dimming, etc when you try to start the vehicle.

If you continued to crank the starter it would eventually heat the radio ground lead, internal connection inside the radio and the coax shield and possibly melt insulation. I think the likelihood of a main battery ground cable failing in a modern vehicle is close to the probability of the vehicle getting hit by lightning.

Otherwise you should always run the radio ground lead right to the battery to provide the least amount of voltage drop and the least amount of noise pickup. I've done a lot of very high power radio installs and there is noticeably less voltage drop grounding right to the battery vs to the vehicle body or chassis and usually less noise pickup. For an HF installation you should also run a very short ground strap from the radio chassis to the closest vehicle ground point provide a better RF ground and reduce the chance of RF on the radio chassis and mic cable due to antenna problems.
prcguy

QUOTE=Thunderknight;2525113]If the vehicle (factory) ground strap from the battery to the engine block fails, the radio acts as the negative side for the whole vehicle. The radio might not like seeing all the current of the starter motor![/QUOTE]

 

[n0nhp]

If your radio is noisier when connected to chassis ground than it is connected to battery ground, the ground straps and cable is failing. Fix them. Should you choose to ground to the battery terminal, fuse the ground lead the same as the power lead.
Again, an ex-pro installer, I can't get under dashboards the way I used to!

Bruce

 

[mmckenna]

This isn't a "one size fits all" sort of thing, and I'd worry about any installer that claims it is.

I was always taught that negative should always go to the negative terminal on the battery, however I discovered that it isn't always the case. I've run across installs on identical factory new vehicles that didn't work well with the negative at the battery. It had lots of alternator whine on TX. Moving the negative lead to the body fixed the issue on all these vehicles.

I've installed many commercial radios from different vendors, and I've seen installation instructions go both ways. I've seen radios with fuses just on the positive and radios with fuses on both leads. I've installed 100 watt mobiles where the positive lead on the new factory power cable was 18 feet long and the negative lead was 3 feet long with a lug on the end.

The suggestion that the vehicle could ground all it's systems, starter, etc through the radio is a valid point, but you'd have to ignore a whole lot of issues with the vehicle for this to happen. Yeah, some customers are stupid enough to do that. Truth is that even if you run the negative lead to the battery, you can still have issues. If the radio chassis is grounded, as it is on a lot of installs, the juice will find a path.
If this was an issue, all vehicle grounds would go back to the battery, but they don't. Many auto stereos have a negative power lead and a ground, either through the chassis or through the antenna. I have yet to see this be an issue.

There is always going to be an argument about how individuals think this should be done. Truth is installers should be smart enough to trouble shoot issues like bad grounds and understand how these things work. When in doubt consult the install manual for the radio and check with vehicle manufacturer up-fitter guides.

Honestly, though, I can't see an issue with running negative back to the battery, but you can get noise from long unshielded power wiring. Grounding the radio chassis with a short dedicated ground braid to the vehicle body can solve a lot of issues.

 

[dixie729]

That's how I was taught too, ground to the battery. We never ran into any issues that I know of when I was an emergency vehicle installer.
I never put into consideration of the radio carrying all that load. Makes sense.
Thanks guys. I just wanted to throw that question out there for myself and some of the others to see.

Sent from my XT1097

 

[AI7PM]

On newer vehicles, if you ground to the battery, the vehicle systems management computer may not be able to do proper battery analysis. Grounding at the chassis where the pigtail ground comes from the battery and through the sensing loop prevents that.

 

[AK9R]

On newer vehicles, if you ground to the battery, the vehicle systems management computer may not be able to do proper battery analysis.

Very true. My 2011 Ford F-150 had no less than three current sensors on the ground wires going back to the battery. One of the computers used the data from those sensors to selectively de-energize various power feeds to keep an abnormally high current draw from completely discharging the battery.

 

[03msc]

On newer vehicles, if you ground to the battery, the vehicle systems management computer may not be able to do proper battery analysis. Grounding at the chassis where the pigtail ground comes from the battery and through the sensing loop prevents that.

This is my understanding, limited as it is, also. Of course, this is only the newer vehicles; the older ones this wouldn't apply to and the other issues may be more the reason for going to the grounding point instead of the negative terminal on the battery.

It can be confusing, though - seems anytime this is brought up there is a differing of opinions. If a vehicle is fairly new I think going to the grounding point is important for the battery management system to function properly.

 

[gungatim]

I just installed my Yaesu FT2900 in my new truck and went direct to the battery as it specifically says in the manual. Since both leads come from the factory with fuses, I don't see why it would be a problem. if the radio lead acted as ground through a failure wouldn't the fuse blow before doing any damage? in-line fuse holders are cheap and widely available at the parts store if the negative lead doesn't already have one.

 

[Project25_MASTR]

I just installed my Yaesu FT2900 in my new truck and went direct to the battery as it specifically says in the manual. Since both leads come from the factory with fuses, I don't see why it would be a problem. if the radio lead acted as ground through a failure wouldn't the fuse blow before doing any damage? in-line fuse holders are cheap and widely available at the parts store if the negative lead doesn't already have one.

Yes. But traditionally the negative lead was left unfused. As stated above, Motorola doesn't include a negative lead fuse and also cuts the ground lead to only 3ft from the radio.

I don't even have a ground lead on my Astro spectra in my pickup. I do, but it was short and just floats so it's not hooked up to anything. The tray is a chassis ground design…the bolts in the mount are grounded to the chassis.

Here's another thought. When you have a chassis ground system and a fused lead straight to the negative post, you actually have a ground loop. If you were to blow the negative fuse and your radio's chassis isn't grounded…the coax shield becomes the path to ground (assuming a dc grounded mount).


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