siliconchip.com.au Australia’s electronics magazine June 2019 67
because I had been “showing off” the
newly installed winch to the missus
the night before, and maybe I’d used up
more charge than I’d thought. I man-
aged to charge it up enough to start
it, but just to be sure, I bought a new
battery that morning and installed it.
The trip was a success, although it
was tough on the vehicle. Minor body
damage will remain forever as a re-
minder to never tackle that track again.
A few days later, when I tried to
start the car for the commute to work,
the new battery was again dead flat.
The battery was also quite warm to
the touch. The charger refused even
to try charging the new battery. Luck-
ily, I’d kept the old one, and it was on
charge. I put the old battery back in
and it started the car easily.
I thought that I’d simply been sold
a dud battery. When I took it to the
place I got it, they declared that it
had a shorted cell and replaced it for
me, although I didn’t put it in the car
straight away.
The very next morning when I at-
tempted to start the car, it was again
dead. The battery was again warm to
the touch. This time it had ejected a lot
of electrolyte into the engine bay too! I
now thought that the car might have a
massive “phantom load” that was ut-
terly discharging the battery overnight.
Over the years, I’ve added a cou-
ple of extra power feeds directly from
the battery terminals, including one
for radio equipment and one for the
new winch.
As the winch was the latest change
I had made, I suspected it might have
caused this problem. Just to be safe, I
disconnected everything that wasn’t
essential to running the car.
I removed the now-dead old bat-
tery and put the second new battery
in and drove to work – late and some-
what confused.
During my lunch break, I started
looking for this phantom load. I used
an ammeter to measure the current
flowing through the extra power wires
I’d installed with the vehicle switched
off, but couldn’t find any. I then con-
nected the ammeter between the posi-
tive terminal of the battery and the bat-
tery connector itself and got a reading
of about 35mA. That seemed normal.
So I was stumped. Two batteries
failed in the same way, yet I couldn’t
find any phantom loads. I spent the
next couple of days doing further
current and resistance measurements
while jiggling cables and connectors.
I also spent time checking the alter-
nator voltage regulation as maybe it
was overcharging batteries and caus-
ing damage. I was pretty puzzled all
as everything measured as being OK.
Maybe I’d just gotten unlucky twice,
but I started disconnecting the nega-
tive side of the battery terminal every
night just to be sure.
A week after all this began, I had
some spare time but was out of ideas,
so had another look under the bonnet. I
remembered that the last battery event
had spewed acid everywhere, so I de-
cided to hose out the engine bay. It got
a good wash, especially near the bat-
tery, where most of the acid was. Then
I heard the distinct sound of rapidly
boiling water, similar to frying.
This noise directed me to the fault
like a beacon. A single wire, part of a
larger wire loom, had been rubbingagainst the metal of the battery hold-
er, probably for years, and had finally
scraped through the insulation.
This wire is obviously connected
to the battery positive terminal and is
situated in such a way that the slight-
est bump or vibration could allow it
to short against the grounded frame,
or remove the short. So that’s why I
couldn’t find it earlier.
This would have driven me mad.
Being well hidden from view means
that I would never have seen the bare
wire if the sound hadn’t alerted me.
The repair was simple: some self-
amalgamating tape for the wire, and
an extra physical barrier material
wrapped around the entire wire loom.
Intermittent faults are the worst,
and are particularly soul-destroying
when it means you can’t trust some-
thing you need to use every day. This
time, I was lucky! SC