TM 5-3805-260-24ELECTRICAL SYSTEMMost of the testing of the electrical system can bedone on the engine. The wiring insulation must be ingood condition, the wire and cable connections cleanand tight and the battery fully charged. If on the enginetest shows a defect in a component remove thecomponent for more testing.BATTERYTools Needed:5P300 Electrical Tester.9S1990 or 1P7400 Battery Charger Tester.5P957 or 5P3414 Coolant and Battery Tester.The battery circuit is an electrical load on thecharging unit. The load is variable because of thecondition of the charge in the battery. Damage to thecharging unit will result, if the connections (eitherpositive or negative) between the battery and chargingunit are broken while the charging unit is charging. Thisis because the battery load is lost and there is anincrease in charging voltage. High voltage will damage,not only the charging unit but also the regulator and otherelectrical components.9S1990 BATTERY CHARGER TESTERCAUTIONNever disconnect any charging unit circuitbattery circuit cable from battery when chargingunit is charging.Load test a battery that does not hold a charge whenin use. To do this, put a resistance, across batterymain connections (terminals). For a 6 volt battery, put aresistance of two times the ampere/hour rating of thebattery. For a 12 volt battery, puta resistance of three times the ampere/ hour rating. Letthe resistance remove the charge (discharge battery) for15 seconds. Immediately test the battery voltage. A 6volt battery in good condition test 4.5 volts; a 12 voltbattery in good condition will test 9 volts.CHARGING SYSTEMTools Needed:5P300 Electrical Tester.The condition of charge in the battery at each regularinspection will show if the charging system is operatingcorrectly. An adjustment is necessary when the batteryis always in a low condition of charge or a large amountof water is needed (one ounce per cell per week or every50 service hours)Test the charging units and voltage regulators on theengine, when possible, using wiring and componentsthat are a permanent part of the system. Off the engine(bench) testing will give an operational test of thecharging unit and voltage regulator. This testing will givean indication of needed repair. Final testing will giveproof that the units are repaired to their original operatingcondition.Before starting on the engine testing, the chargingsystem and battery must be checked. See the followingSteps.1.Battery must be at least 75% (1.240 Sp. Gr.) fullcharged and held tightly in place. The batteryholder must not put too much stress on thebattery.2.Cables between the battery, starter and engineground must be the correct size. Wires andcables must be free of corrosion and have cablesupport clamps to prevent stress on batteryconnections (terminals).3.Leads, junctions, switches and panelinstruments that have direct relation to thecharging circuit must give proper circuit control.4.Inspect the drive components for the chargingunit to be sure they are free of grease and oiland are able to drive the load of the chargingunit.2-76
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