JLG sky trak mmv Service Manual page 582

Electrical System
The Battery
When a charged 12V automotive battery is allowed to
stand without a load, its terminal voltage is measured to
be about 12.6V at room temperature. (Standard lead acid
type automotive battery.) To charge the battery, a 14V
source is applied across its terminals, and current is al-
lowed to flow into the battery.
The amount of charge current that a battery will accept is
determined by the state-of-charge of the battery and its
capacity. At 14V, the battery will only take the amount of
current required, or is capable of receiving, to charge it.
(The battery will still draw current after charging fully,
however, this is relatively small compared to the charging
current.) With this in mind, it is seen that a larger alterna-
tor will not charge a battery faster than a smaller one, pro-
viding the battery charging requirements and load
requirements do not exceed the output limits of the alter-
nator.
Given the proper charging voltage, the battery will deter-
mine the amount of current that it requires for charge.
If the battery is "low" (discharged), the charge current will
be high. 50 amps or more is not uncommon to charge a
low battery such as a Group 27. Heavy charging may be
in the 100 to 200-amp range for 4D or 8D types. As the
charge is replenished, the charge current decreases to a
few amps or less for a fully charged battery.
Alternator Output Current
Equalizer
Input
Current
Equalizer
Alternator
24 Volts
* - Current required for battery balancing
10.102
"B" Battery
12 Volts
"A" Battery
Charging
1
Current
12 Volt
Load
"A" Battery
12 Volts
MM4490
If the charge voltage changes across a battery, so will the
current flow into the battery. Increasing the voltage will
cause the current to rise and vice versa. This can lead to
overcharging or undercharging conditions of the battery,
and a reduction of battery life. Because of this, it is very
important to keep the system voltage regulated at the op-
timum level.
Some charging systems today are equipped with temper-
ature sensing voltage regulators, which adjust the charge
voltage automatically. This does not present a problem to
the equalizer, as the output to input voltage is a fixed ra-
tio, i.e. = half. The equalizer will maintain proper battery
balancing (1) under all voltage conditions.
b. Battery Equalizer Maintenance
Very little maintenance is required for the equalizer (2).
Generally, keep the fins clean so that the unit will cool as
it should. Do not allow oil, dirt, etc. to build up on the sur-
faces, as it acts like insulation, inhibiting the cooling abil-
ity of the fins. Keep material from clogging the space
between the fins, blocking the flow of air.
Periodically check the connections. Clean as required.
Connection problem symptoms are:
• Hot wire or connection(s)
• Discolored stud, nuts, fuse cover, or insulation
• Low or no output
Heat is a telltale sign of bad connections. Look for discol-
oring of studs, nuts, fuse cover, or insulation from exces-
sive heat.
The best way to check a connection is by measuring the
voltage across the connection. The higher the reading,
the worse the connection. A "good" wire connection
should drop less than about 0.025V (25mV) when about
100 amps is flowing through the connection.
Before measuring the equalizer connections, start the en-
gine and turn ON heavy 12V loads. This will make poor
connections easier to find.
For the fuse connections, a voltage reading of 0.025V
(25mV) or less is good when the equalizer output current
is about 75A.
Measure from the equalizer stud (3) to wire terminal (4)
with a digital voltmeter. When the drop approaches 0.05V
(50mV) or more, the connection should be cleaned and
re-torqued.
Note: From the factory, the fuse connections will mea-
sure about 17mV @ Output current = 75 amps.
Model MMV Rev. 12-04