May 1977
CONTINUOUSLY CONNECTED VOLTMETER INSTRUMENT PANEL
GAGE AND DEAD BATTERIES
1. An EIR has been received on the CCE-IHC 20 Ton Dump Truck, Paystar F5070, which attributes dead battery
conditions to the truck manufacturer's commercial practice of connecting the voltmeter to a "hot" terminal thus providing a
continuous operating gage with no means of shutoff. The gage operation is not wired through the ignition switch.
2. With the voltmeter alone discharging the 4-battery pack on the CCE-IHC D mp Truck, the fully charged batteries
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would be dead in a 9 1/2 month time period. The voltmeter current consumption pulls about six hundredths of an ampere-
hour from the 416 ampere-hours of the battery pack. It is apparent that the voltmeter is not the immediate cause of the
batteries going dead.
3. Regardless of the vehicle, the major cause of batteries going dead is the combination of electrical leakage across the
top of dirty batteries and insufficient vehicle alternator charge and operating time. The publications of the battery and
truck manufacturers (for commercial users) and of TMs and PS Magazine (for Army users) tell the story on cleaning,
servicing and charging of batteries.
4. The reason that the truck manufacturer wires the voltmeter directly to a "hot" battery terminal with no disconnect is to
insure that the voltmeter's correct reading is available to the driver before the engine start is attempted. By reading the
voltmeter immediately upon getting into the truck, the driver is able to check the condition of his batteries without any
external charge or discharge causing reading errors. The various makes and models of voltmeters all have a dampening
fluid in them to prevent needle vibration. As a result, it takes time for the voltmeter needle to move up from the off
indication to the battery condition. Turning the ignition switch to the " on" position could cause enough of a battery
discharge to reflect low battery charge state reading. Reading the voltmeter after operation also creates an error,
because the alternator, during charging, puts a surface charge on the battery plates. Readings after operation make the
batteries look to be in good condition even though they may need attention..
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