Tag Archives: destruction

Moving Ground

I did some rethinking on the power circuit for my two-way radio in the car. I had read multiple sources that connecting the 12V and Ground wires directly to the battery was the best way to minimize engine noise in the radio, so I went with that guidance and wired things directly to the battery terminals.

As it turns out, my assumption was half correct. The incorrect half could have set me up for disaster. According to an article written by W8JI, a situation could happen where — as a worst-case scenario — my radio is destroyed.

In the case that the radio is grounded directly to the battery, there are two connections coming from the negative post. One is a copper strap that goes from the battery post to somewhere nearby on the chassis body. The other connection is the ground lead to the radio.

So, if the chassis ground strap becomes loose, corroded, or disconnected, then everything in the car that’s powered will try to ground through the only battery connection left: the radio. This will result in instant destruction of its circuit traces and will damage the cable assembly until something either opens, melts, or catches fire.

The correct method for grounding the radio is to bolt the ground lead to a convenient place on the car body as close to the battery ground strap as possible. That way, if the strap breaks, the entire car loses its grounding.

I also learned that modern cars have sensors in the battery cable assemblies that measure how much current is being drawn from the battery. This signal goes to the ECU so it can command the alternator to produce more current. If the radio ground is connected directly to the post, it is upstream from this sensor and the ECU gets an incorrect measurement of current draw from the battery. Putting the radio downstream from this fixes that problem.

Foreground: battery ground post with current sensor. Background: new position of radio ground lead (blue) next to engine ground strap.

With these facts in mind, I made an adjustment to the circuit. I pulled the radio ground connector from the battery post and moved it down to a bolt that holds the ECU bracket. This bolt is mere inches away from the ground lead that goes to the engine block, so I know the connection is solid.

As an aside, I also see some guidance that I should take the fuse out of the ground lead circuit, but I’m not so sure about that. I’ll have to think more on it to figure out what will happen if the ground fuse blows. Will the radio have a floating ground? Will it continue to ground through the ground strap I’ve lashed to the radio body? Will I blow a circuit trace between the radio ground lead and the board’s internal connection to the radio body? I’m not sure.

More improvements to follow.