Re: Elecraft Digest, Vol 162, Issue 8

[Elecraft mailing list]

Hi.

I haven’t seen "Kent's instructions", but running the radio -ve power
lead direct to the battery when the radio also has a "Ground" at the
antenna, could result in the destruction of the radio and/or antenna
cable, if the battery ground strap to the vehicle frame goes bad.   
That is not so uncommon as you might think, even on modern vehicles.

Think about where the engine starter current (and alternator produced
charging current) ideally flows, and where it will try to go, if that
ground strap is at all compromised (usually by corrosion, but could be
less than well re-fitted after some maintenance work.)  Meanwhile, you
have provided another battery ground route via your prized radio, and
antenna cable.

The rig -ve lead to be safe, should go to the vehicle frame to prevent
such disaster, NOT directly to the battery -ve terminal.

I've seen a simple CB radio explode under those circumstances and burn
out the car interior.  (I was involved in helping put out that fire with
portable extinguishers that were available.)

I've also personally experience a vehicle electrical fire while driving
(not radio related) and it's not pleasant in any way!...

If you *Must* wire the radio -ve power lead direct to the vehicle
battery (a temporary install for Emcom etc) include a fuse in that -ve
lead, and also make sure that the ground path via the radio and antenna
etc, can take the fault current without damage before that fuse blows!

This is not an EMC/RFI problem, it is a fire safety issue.

Note too, that many modern vehicles incorporate a form of regenerative
braking using the alternator to provide more retardation when you lift
off the throttle at speed.   That can (does) raise the battery voltage
quite a bit, some not so modern (but expensive to repair/replace) radio
kit might object to that.

Also, for that very reason, the battery is rarely charged to more than
about 70% of it's ultimate capacity, to provide "space" for such regen'
braking action generated energy.

It is unlikely that current vehicle build principles are that different
between the US and UK (or rest of the world for that matter) in this
respect.

Stay safe.

73.

Dave G0WBX.




On 10/10/17 13:32, [hidden email] wrote:

> Subject: Re: [Elecraft] Mobile from 117 VAC
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> There's nothing like doing the job correct, and Kent's installations
> seem to indicate such.
>
> I've used my Tentec 599 Eagle in my 2005 GMC Somona with a Hustler array
> on the rear, power cables direct to the battery.? No issues any band 80
> - 6 meters.?? Same basic configuration and installation in the travel
> trailer.? It does however slightly "modulate" the interior LED bulbs on CW.
>
> 73
>
> Bob, K4TAX

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[Don Wilhelm]

All,

Dave is correct, but the point where the negative lead is connected
should be near the battery, not in the cabin where there may be
unexpected resistances because of adjoining body panels.

If you are diligent about bonding the various panels together, then you
can connect the radio negative almost anywhere, but still near the
battery is the best choice to assure a low resistance connection.

73,
Don W3FPR

On 10/10/2017 12:35 PM, Dave B via Elecraft wrote:

> The rig -ve lead to be safe, should go to the vehicle frame to prevent
> such disaster, NOT directly to the battery -ve terminal.
>
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