Techtip2

SAVVA – Technical tip - No 2

Battery Care

One often hears collectors saying that they are converting their cars from 6 to12 volts -
mainly because of starting problems. Sometimes it’s a worth while improvement, but may we suggest,
before making the change, you first make a few simple checks to see if you can save yourself a lot of hard work.
Older cars were designed to work on 6 volt systems and with their low compression engines they did a very good job,
even in the coldest conditions. One justification for changing over to 12 volts is for those who do a lot of night
driving – by changing over to 12 volts and fitting a higher output generator (or alternator) one can step up the
wattage of the driving lamps (bulbs) to modern standards and add to the safety of night driving. Of course,
one can also fit a higher output 6 volt generator, but they are difficult to find.

If the old engine doesn’t turn over in a nice friendly fashion start checking items like timing, wiring,
compression etc – mainly wiring. A simple check is to connect a voltmeter to the starter motor terminal and see
what voltage it cranks at. Another test is to crank the engine and check the voltage at the coil. A year or two
ago a club member purchased a 1938 eight cylinder Packard that throughout its entire life this car had a
reputation of being a bad starter – especially when hot. The new owner, quite rightly, refused to accept
the fact that Packard ever produced a car that had starting problems. After a preliminary investigation of
battery condition, earthing, wire size etc. a simple check showed that the voltage at the coil was only 4.0 volts.
The problem turned out to be a serious volt drop in the wiring circuit due mainly to a faulty ignition switch and
a fuse holder of dubious quality. When a temporary piece of wire was connected directly between the battery and
the coil - it started first turn. A replacement ignition switch and fuse holder ended years of suffering.

Bad connections are not only the prerogative of older cars, recently, a more modern 12volt sports car
cranked over freely but took a long time to fire up. Everything appeared to be in excellent condition but it
was found the voltage dropped to 9 volts at the coil. Only by an examination of the wiring was the problem
identified – the bolt holding the earth strap from the battery to the chassis had rusted badly causing a
very poor connection. In this case the problem was difficult to locate as the connection was under the back
seat in the most inaccessible position imaginable. A new earth strap was fitted and the problem was solved.

·ncidentally, always check the thickness of the battery cables on six volt systems. So often they
have been replaced with modern ones from local spares shops and these are designed for 12 volt systems.
Using these thinner cables the 6 volt starter will turn over quite happily – but expect a drastic voltage
drop at the coil. If thicker cables are difficult to find one can always use welding cables, or, in an emergency
double up the thinner ones.

So there you have it, before changing over to 12 volts, check a few points first, otherwise you may
simply make the 6 volt problem a 12 volt problem.