Radio Wiring

[miniyazz]

Hi all,

I'm planning on installing a 5W CB radio (UH5060) in my Pajero NX and I'm wondering about the wiring for this and hoping to get some input.

My best options seem to be either: a direct (fused) permanent live to the main battery (allowing radio comms with the engine/other accessories off) with a fused earth back to the main battery - probably the easiest option in terms of routing wires since the antenna wire will also have to make its way through the firewall - or the same thing, but instead wired to my auxiliary battery which is in the boot.

The latter option has the advantages of no chance of draining the main battery, and possibly a cleaner power signal due to fewer accessories being powered? (Probably the only thing whilst driving at least will be a fridge, and it is charged via a DC-DC charger).

Does anyone have any thoughts on the above, and also on what gauge wire I should be looking at running? Given its a 5W transmitter which I think should draw most of the power, I can't see it needing a cable rated for more than about an amp, and so I should be fine with something like 20AWG. Is there any particular benefit to using large gauge cables for CB radios?

Thanks

[basil]

I think the 5watts will draw around 2 amps, so base your wire gauge on that.
Seeing your running a dc to dc charger, your voltage supply shouldn't be an issue as generally radios will accept down to 12.5 volts without problems.

Cheers,

[miniyazz]

Thanks; do you know if there is likely to be an audio quality difference between the two methods? Or if e.g. a ground loop isolater is likely to be of more use if the issue arises?

[basil]

There should be no difference what so ever in audio quality.
That is determined within the radio and unless you are getting alternator whine through the radio, which can generally be eliminated by installing a ferrite bead in the power cables as close to the radio as possible.
This occurs in petrol vehicles much more than diesels.
Don't worry too much as I have never experienced it yet with uhf radio frequencies, only on amateur hf frequencies.

Cheers,

[miniyazz]

There should be no difference what so ever in audio quality.
That is determined within the radio and unless you are getting alternator whine through the radio, which can generally be eliminated by installing a ferrite bead in the power cables as close to the radio as possible.
This occurs in petrol vehicles much more than diesels.
Don't worry too much as I have never experienced it yet with uhf radio frequencies, only on amateur hf frequencies.

Cheers,

Thanks. In that case I might as well earth it direct to the chassis then, instead of fused directly back to the battery negative?

[Keithyv]

Absolutely no reason to put a fuse in the -ve feed.
Just earth the radio chassis and / or earth wire to the chassis.

[miniyazz]

Absolutely no reason to put a fuse in the -ve feed.
Just earth the radio chassis and / or earth wire to the chassis.

That is not correct, if you wire anything (except for a fully isolated piece of equipment) back to the negative on a battery terminal, you have to fuse it otherwise if your main chassis link to the battery becomes corroded and ceases to conduct, and there is a pathway via your direct earth link (e.g. via bolting it to something connecting to the chassis, everything earthing to the chassis will earth via your tiny cable with a high chance of an electrical fire.

See here: https://www.w8ji.com/negative_lead_to_battery.htm

Anyhow, I shall wire to chassis and if I run into issues I can worry about it then.

Thanks all

[koshari]

That is not correct, if you wire anything (except for a fully isolated piece of equipment) back to the negative on a battery terminal, you have to fuse it otherwise if your main chassis link to the battery becomes corroded and ceases to conduct, and there is a pathway via your direct earth link (e.g. via bolting it to something connecting to the chassis, everything earthing to the chassis will earth via your tiny cable with a high chance of an electrical fire.

See here: https://www.w8ji.com/negative_lead_to_battery.htm

Anyhow, I shall wire to chassis and if I run into issues I can worry about it then.

Thanks all

read a little more carefully, Keithy said there is no need to place a fuse in the -VE feed.

[Kingbrown]

read a little more carefully, Keithy said there is no need to place a fuse in the -VE feed.

In theory (and technically) miniyazz has a point in the desirability of fusing any additional connection that's directly onto the battery's negative terminal (unless other precautions are taken, such as ensuring that the connected equipment doesn't also have another path to earth).

But what is the combined probability/likelihood of the following ?

a) Losing the main connection between the negative of your battery and the vehicle body/chassis,
AND
b) Installing an earthed piece of equipment
AND
c) A lightweight connection from that earthed equipment to the negative of the battery.
AND
d) Current being carried by the lightweight connection exceeding it's capacity (eg charge current, starter current, accessories current etc etc).

[Keithyv]

I think the whole point is why would you even run a dedicated earth wire to a battery anyway?

All that theory about IF the main earth gets corroded etc. etc. is a moot point.
You don't need to run a dedicated earth, therefore you can't put a fuse in it and therefore there will be no problems.
IF there is an earth problem at the battery then everything will stop working.

I do agree, however, that IF you wired an earth directly to the -ve terminal and IF there was an issue that affected the main earth but not that individual earth run you COULD have excess current through that single earth.

[miniyazz]

In theory (and technically) miniyazz has a point in the desirability of fusing any additional connection that's directly onto the battery's negative terminal (unless other precautions are taken, such as ensuring that the connected equipment doesn't also have another path to earth).

But what is the combined probability/likelihood of the following ?

a) Losing the main connection between the negative of your battery and the vehicle body/chassis,
AND
b) Installing an earthed piece of equipment
AND
c) A lightweight connection from that earthed equipment to the negative of the battery.
AND
d) Current being carried by the lightweight connection exceeding it's capacity (eg charge current, starter current, accessories current etc etc).

While c & d are quite plausible (who runs a radio earth at a gauge large enough to cope with alternator load for example?) I agree a and b combined are a bit of a stretch. I don't know what the chances are of equipment being earthed but I suppose a loose chassis-earth bolt due to e.g. corrugations over time would be a valid possibility.

The moral of the story is, as Keithyv said, always earth to chassis, and you won't have problems