voltage of your bike battery likely isn’t something you
need to lie awake worrying about but as they say, “A little
knowledge is a dangerous thing.” Ah, maybe that’s
not the best cliche? (VBG)
So what is the practical difference between
a 12 volt battery and a 6 volt battery? If they are of the same
physical size then they likely contain about the same amount
of electrolyte and have the same surface area of plate material
so we can expect that each will store the same amount of electrical
So let’s look at “What if”:
What if I put a 12 volt battery into
my bike in place of the 6 volt battery it is supposed to have?
OK what will happen is that the 12 volts of electrical pressure
will be twice as much electrical pressure as the circuits were
designed to operate under. Very basic electrical theory will
indicate that twice as much pressure will cause twice as much
electricity (electrons, amperes, amps.) to flow. This will be
bad news because the circuits/components which do the job of
producing heat will now produce twice as much heat as was intended.
Components such as light bulbs will be very bright for maybe
a second or so and then will burn out. Relays, ignition oils
and the like, may last for some time but will also fail due
to too much heat being produced. Electronic components such
as transistors, integrated circuits and the like will fail,
maybe instantly, maybe faster.
This brings us to a very important bit
of electrical and electronics theory. It is important to recognize
that all electrical and electronic components, wires and so
on, are composed of smoke. That’s right, they are made
of smoke. The main difference between electrical components
like headlight bulbs, starter motors, handle bar heaters and
electronic components such as transistors and ignition modules
is that electrical components tend to contain a lot of smoke
while electronic components contain very little smoke.
Here is where the theory becomes practical:
If you let too much smoke out of a component, it will stop working.
Electrical components like starter motors contain a lot of smoke
so you can let a lot out before they quit working but ignition
modules contain only tiny amounts of smoke so almost any smoke
lost will see them fail.
I challenge anyone to show how this theory
does not apply in the real world.
Wires contain a lot of smoke, the bigger
the wire, the more smoke.
Much of what we do in service or repair
is to replace something which has had too much smoke let out
or to ensure that we install something so that no smoke will
Now, back to putting the 12 volt battery
into my 6 volt bike….What will not happen is that the
battery will be charged. Why? It takes more than 12 volts to
completely charge a 12 volt battery. Remember in the last article?
Each cell of a lead acid battery has a bit more than 2.1 volts
so a fully charged 12 volt battery is actually a 12.8 volt battery
and we will measure up to 13.2 or 13.4 volts across a 12 volt
battery which has just been taken off the charger or just been
in the bike. Typical 12 volt charging systems will apply 14.2
to 14.8 volts across the battery which ensures a full charge
and a quick recharge. The numbers for a 6-volt system will be
about ½ of those for a 12 volt. The 12 volt battery would
function somewhat if it were dead when put into the 6 volt bike
and the bike’s charging system allowed to charge it but
the result would be a weak six volt battery which would soon
fail due to sulphation (more on these terms later). In short
we wouldn’t do this.
Have you noticed that your cage’s
and bike’s lights become brighter when the engine is running?
Why? When the engine is off, the charging system is not in operation
so the most voltage available to power the lights is 12.8 volts
and this will fall as the battery provides power. When the engine
is started, the charging system operates and the system voltage
rises. In some applications the charging system can operate
at full output when at idle speed but most require that the
engine be at a higher speed. Watch your tach as you gradually
speed up the engine to see at what speed your charging system
is reaching high output. You cannot expect a low battery to
recharge much below this engine speed as a rule of thumb. As
I said earlier, more voltage (pressure) means more electricity
flowing so more work is done. There is a limit to the benefit
of higher voltage since we don’t want to fry things so
this is where the voltage regulator acts to limit maximum voltage.
to the batteries… So what happens if I put a 6 volt battery
into my 12 volt bike? Also a bad idea! Think of too little pressure
causing too little flow so too little work being done. The lights
will be very dim, the starter will not turn the engine fast
enough for it to start (likely) and regardless, the ignition
system will not produce a strong enough spark to fire the fuel
(if the ignition is common to the battery system) so no go.
In a later article we can explore some additional problems which
will result from low battery capacity. If we succeed in starting
the engine such as by bump starting a KLR, the charging system
will begin to operate and one result will be over charging of
the battery which will boil dry and be ruined.
Next time: charging and recharging the