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Ground questions

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MB

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Ok, I know this has been talked about before in these forums, but I would like to get more opinions.

Which way should you ground a radio/scanner/2-way radio for vehicle instalation:

1. Run ground cable to nearest chassis ground with no fuse.
2. Run ground cable to nearest chassis ground with fuse.
3. Run ground directly to battery ground terminal with no fuse.
4. Run ground directly to battery ground terminal with fuse.

Most directions say to use #1.
I have seen some saying to use #4.

Will you get less vehicle noise from #4?

Whis way is the right way?
 
N

N_Jay

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MB said:
Ok, I know this has been talked about before in these forums, but I would like to get more opinions.

Which way should you ground a radio/scanner/2-way radio for vehicle instalation:

1. Run ground cable to nearest chassis ground with no fuse.
2. Run ground cable to nearest chassis ground with fuse.
3. Run ground directly to battery ground terminal with no fuse.
4. Run ground directly to battery ground terminal with fuse.

Most directions say to use #1.
I have seen some saying to use #4.

Will you get less vehicle noise from #4?

Whis way is the right way?
#1 is right
#4 is only if #1 causes problems
 

jim202

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There have been a number of know it alls that keep saying to put a fuse in the negative return line of radios to prevent damage if the vehicle looses the battery to ground connection. This is the heavy wire going from the battery to the frame and or engine.

I have been in the two way radio service field now for close to 40 years. I have never seen any comercial radio damaged by this cause. Generally if the battery ground is starting to go bad, you will be having starter problems long before the high current can pass through the radio ground wire or the coax shield.

The best I can say it is an old wife's tale. All the large trucks, fire trucks, front end loaders and the like I have ever worked on have never had a radio damaged from a poor battery ground cable. I will say that it is best to disconnect the radio if your trying to jump start the engine with an external battery though.

Putting a fuse in the ground wire just adds to the cost. adds additional resistance to that wire and makes for another place for a bad connection.

Do as you please. Listen to who you want.

Jim



MB said:
How would #1 cause problems?

So, is it OK to fuse the ground?
 
N

N_Jay

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jim202 said:
There have been a number of know it alls that keep saying to put a fuse in the negative return line of radios to prevent damage if the vehicle looses the battery to ground connection. This is the heavy wire going from the battery to the frame and or engine.

I have been in the two way radio service field now for close to 40 years. I have never seen any comercial radio damaged by this cause. Generally if the battery ground is starting to go bad, you will be having starter problems long before the high current can pass through the radio ground wire or the coax shield.

The best I can say it is an old wife's tale. All the large trucks, fire trucks, front end loaders and the like I have ever worked on have never had a radio damaged from a poor battery ground cable. I will say that it is best to disconnect the radio if your trying to jump start the engine with an external battery though.

Putting a fuse in the ground wire just adds to the cost. adds additional resistance to that wire and makes for another place for a bad connection.

Do as you please. Listen to who you want.

Jim
There have been MANY cases where a bad ground has cause either radio damage or a fire.
Go ask Motorola about the ambulances that burnt up in the mid 80's.

Closest ground only causes problems where the vehicle has other ground problems.
Then you use the battery AND always fuse it.
 

tspainiv

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The instructions that came with my Icom 208h tells you to ground to the NEG terminal and fuse it. The power harness that comes with it has a fuse in both the power and ground wires.....
 

MB

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tspainiv said:
The instructions that came with my Icom 208h tells you to ground to the NEG terminal and fuse it. The power harness that comes with it has a fuse in both the power and ground wires.....
My ICOM IC-F521 instructions say the same..
 

mastr

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N_Jay said:
#1 is right
#4 is only if #1 causes problems
Exactly right. I have worked on some of those ambulance radios that got toasted when they passed the starter current to ground via various avenues that were never intended to carry 250A. The "instructions" are written to the lowest common denominator, to show "John Doe" how to make his new radio work. Experience and a comprehensive understanding of the subject at hand are far better resources in this case. If you must run a negative to the battery, always use a fuse of comparable size to the "hot "lead. 99 percent of the time an unfused lead to the nearest substantial chassis ground will work.

Most new ham gear includes a fused negative lead to prevent the "E350 meltdown" potential in the hands of an in-experienced installer, the fuse is technically only needed if the negative goes to the battery.
 
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MB

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Right now I have my radio wired as per the directions. Fused ground wire to battery (#4).

Is their any benefit in changing it to a short non fused wire to chassis ground (#1)?

Or should I just leave it like it is?

I noticed that with the way I have it now, every now and then I will get noise / open squelch on a couple different frequencies. Should their be less noise if is connected directly to the battery? Or is it the positive wire that the noise comes from?
 

KC4ZEX

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The noise you are hearing could be anything from anywhere that is intermittently coming in on the specific freq. Unless its an alternator whine or spark plug poping or something like windshield motor or elec window motor noise caused by your vehicle their is not much you can do about it except turn the squelch knob a little tighter.
 

mastr

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MB said:
Right now I have my radio wired as per the directions. Fused ground wire to battery (#4).

Is their any benefit in changing it to a short non fused wire to chassis ground (#1)?...
In all probability, you will not find a measurable difference given the radio you have. A 208h doesn't draw enough power on TX to have significant voltage drop issues.

W
 

MB

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mastr said:
In all probability, you will not find a measurable difference given the radio you have. A 208h doesn't draw enough power on TX to have significant voltage drop issues.

W
I don't have a 208h, that was a different poster. I have a 50 watt IC-F521 VHF-HI radio.
 

mastr

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The same goes for your unit. Unless you are running 100w TX or more, the minor voltage drop induced by a fuse and the extra lead length won't matter much.
 

jim202

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I would be willing to bet that any problems with the ambulance grounding systems that you indicate have toasted radios also had some indicating signs that a problem was developing. More than likely, the engine didn't crank over very well and the operator put the dual battery switch into the dual mode to overcome the problem.

Again I go back to my original statement, that a properly maintained electrical system will never cook a radio that is grounded directly to the vehicle frame.

The Jap track radios that include a fuse in the negative wire do it for those people that don't ever look under the hood until the engine won't start.

I too have worked on a large number of ambulace radios. Never in my 40 years of doing the radio service work have they ever cooked a radio. A few words to the garage that does the service work takes care of the problems. All you need is to look at the cables when the oil is changed. Saves a bunch of road calls for an engine that won't start or quit working. Saves the ambulance people a bunch of money in the long run.

Jim



mastr said:
The same goes for your unit. Unless you are running 100w TX or more, the minor voltage drop induced by a fuse and the extra lead length won't matter much.
 

Al42

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mastr said:
The same goes for your unit. Unless you are running 100w TX or more, the minor voltage drop induced by a fuse and the extra lead length won't matter much.
A 50 watt radio probably draws between 6 and 10 amps on transmit. If there's only 1/2 ohm between the chassis "ground" point and the negative battery terminal, that's 3-5 volts drop. It wouldn't actually happen, because at 10 volts the radio wouldn't be putting out anything near 50 watts. The radio lead and fuse/fuse holder combo is included in the design by the manufacturer, so it's not going to cause a voltage drop - the voltage drop is designed in.

The original question, however, was the difference in noise performance between a battery ground and a chassis ground. Since a) the battery is a big dead short for noise, and b) the chassis may be loaded with noise currents going every which way, battery ground is a much more noise free connection. Since there's no reason not to connect to the battery, that's always the connection of choice.
 

mastr

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Jim 202- If you have never seen an E350 melt down, you have really missed out on a sight. A number of ambulance owners/builders in the early 80's found out why that fuse is needed, when they ran the negative to the BATTERY TERMINAL instead of a good chassis ground, as you recommend. I always use a fuse in the negative lead if a customer insists that it go to the battery (-) terminal. Since I know battery cables can and do fail, I prefer to use a resource that is under my control (a fuse in the negative lead), to negate the possibility of radio damage due to an issue that is not under my control (overall condition/integrity of the battery to frame cable(s) and the associated connections).

If the engine won't crank, it isn't my problem. OTOH, if the engine won't crank and white smoke simultaneously boils out of the radio, it is my issue to deal with. I greatly prefer replacing a fuse to telling an electrically ignorant station commander that his finger-tight ground cable fried a new CDM, Astro Spectra or Orion.

Obviously, a fuse is not required in the negative lead if it goes to chassis ground directly, as a battery ground cable failure would only result in a "no power" situation as far as the radio is concerned.

W
 

mastr

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Al42 said:
A 50 watt radio probably draws between 6 and 10 amps on transmit. If there's only 1/2 ohm between the chassis "ground" point and the negative battery terminal, that's 3-5 volts drop. It wouldn't actually happen, because at 10 volts the radio wouldn't be putting out anything near 50 watts. The radio lead and fuse/fuse holder combo is included in the design by the manufacturer, so it's not going to cause a voltage drop - the voltage drop is designed in.

The original question, however, was the difference in noise performance between a battery ground and a chassis ground. Since a) the battery is a big dead short for noise, and b) the chassis may be loaded with noise currents going every which way, battery ground is a much more noise free connection. Since there's no reason not to connect to the battery, that's always the connection of choice.
We shall have to "agree to disagree" here. It is my contention that there would be little difference 99 percent of the time at that power level. I use a very simple method to determine where my "ground" lead will go, since a fuse is only needed with a (-) battery terminal connection. If the (-) lead fuse is supplied, route both wires to battery, as you are going there anyway and two wires are no more trouble. If the (-) lead has no fuse go to chassis ground. Address the "noise" issue only when it is apparent.

W
 

MB

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Al42 said:
A 50 watt radio probably draws between 6 and 10 amps on transmit. If there's only 1/2 ohm between the chassis "ground" point and the negative battery terminal, that's 3-5 volts drop. It wouldn't actually happen, because at 10 volts the radio wouldn't be putting out anything near 50 watts. The radio lead and fuse/fuse holder combo is included in the design by the manufacturer, so it's not going to cause a voltage drop - the voltage drop is designed in.

The original question, however, was the difference in noise performance between a battery ground and a chassis ground. Since a) the battery is a big dead short for noise, and b) the chassis may be loaded with noise currents going every which way, battery ground is a much more noise free connection. Since there's no reason not to connect to the battery, that's always the connection of choice.
Thanks Al42! That is what I thought, but I just needed someone to confirm it.

My original question that strated this whole thread is finally answered! Thanks for clearing this up for me.
 

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Al42 said:
A 50 watt radio probably draws between 6 and 10 amps on transmit. If there's only 1/2 ohm between the chassis "ground" point and the negative battery terminal, that's 3-5 volts drop. It wouldn't actually happen, because at 10 volts the radio wouldn't be putting out anything near 50 watts. The radio lead and fuse/fuse holder combo is included in the design by the manufacturer, so it's not going to cause a voltage drop - the voltage drop is designed in.

The original question, however, was the difference in noise performance between a battery ground and a chassis ground. Since a) the battery is a big dead short for noise, and b) the chassis may be loaded with noise currents going every which way, battery ground is a much more noise free connection. Since there's no reason not to connect to the battery, that's always the connection of choice.
What a subject we have here! Tastes great - less filling.

1) If you have "only" 1/2 ohm between ground and battery then you have a different problem altogether. You should have no more than a few tenths (yes the difference between .5 and .1 or .2 doesn't seem like much but it is at these low voltages). The voltage drop should be under a volt at 10 amps (or any amps for that matter), probably in the range of .5 to .7 volts or else you need to check the connections and/or use bigger wire. And yes, the radio probably wouldn't work with 10 or 11 volts. Some don't even like 12 or less.

2) As for noise pickup - it is not 100% best to use ground-to-battery connections. I have seen them actually pick up more noise. I had a jeep once that did that. I'm guessing it is the antenna effect of the leads running next to other electrical wiring and around the engine compartment or ground loops from the radio to the chassis to the battery and back to the radio.

Conclusion: Go to the battery with both leads and FUSE THEM. If you hear lots of noise, especially on transmit, try grounding to the car body with a short lead.

Let us know how it works out!
 

Al42

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gcgrotz said:
What a subject we have here! Tastes great - less filling.

1) If you have "only" 1/2 ohm between ground and battery then you have a different problem altogether.
We're not talking about grounding to the engine block at the point at which the battery cable connects. "Ground" in the passenger compartment, especially in some installations, is made to the vehicle frame, the inner fender wall, a cross-member under the dash - anywhere there's a piece of metal and the receiver comes to life when power is turned on. I've seen 10 ohms and more between the ground point and actual ground.
You should have no more than a few tenths
Yes, I agree, should have. The battery terminal normally has, at most, a milliohm or two resistance to the battery post - some grounds aren't very good.

Conclusion: Go to the battery with both leads and FUSE THEM. If you hear lots of noise, especially on transmit, try grounding to the car body with a short lead.
Agreed.
 
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