MJM 2019 Two Stage Starter

TWO STAGE STARTER MOTOR

Matthew Munson 2019

▪ Better understand a two stage (soft start) starter ▪ Precautions

Modern diesel engines use a two stage (soft start) gear reduction starter for the following reasons:

▪ Increased starting torque in a smaller starter package ▪ Reduced wear on ring gear and starter pinion ▪ Ease of service due to smaller size and weight ▪ Heavy duty roller clutch drives withstand shock load ▪ Most have over crank protection (OCP) built in ▪ Most have index able front housing for better clearance

An older style, direct drive large starter draws @ 50-100 amps of current initially, compared to @200-300 amps for a modern two stage gear reduction type.

This requires a separate Magnetic (Mag) switch to handle the high amp load in addition to the starter solenoid.

▪ If replacing a direct drive starter motor with a two stage gear reduction motor, a Magnetic switch must be installed or damage to the trucks starter electrical circuit may occur.

Tooth Abutment - is when the starter pinion contacts the face of the ring gear but does not engage the ring gear. This will be heard as a single clunk noise with no cranking of the engine. If this occurs, return ignition switch to the ON position and try to start the truck again, typically tooth abutment will not occur two times in a row due to the small amount of pinion rotation needed to engage ring gear.

Battery Voltage – Due to the high amp demand of the 2 stage starter it is important that the batteries remain fully charged at all times. Low voltage can slow the 1st stage (pushing pinion into ring gear) and can arc/weld the contacts in the main solenoid causing the starter to stay engaged.

Ignition 50 Key Mag Switch 30

BA Ignition key is start position closes contacts in Mag switch, enabling current to flow to starter solenoid

The solenoid current is high enough to produce a slow rotation of the electric motor, while the drive moves forward and the plunger completes its race front view side view © 2019 SPARTAN MOTORS, INC. | PROPRIETARY AND CONFIDENTIAL 9 SOFT START, STAGE TWO (CRANKING)

Once the pinion is engaged and the plunger closes the solenoid contacts, the main current is established and the starter cranks the engine at full power

50 IK HELPER RELAY 30

Two stage starter motors should be operated for no more than 30 seconds at a time with a minimum cooling time of 2 minutes between cranking. The large amount of current drawn by the starter motor can cause damage to the starter motor, batteries, battery cables and connections.

To minimize the chances of damaging a starter due to excessive heat, some starters utilize a over crank protection (OCP)switch. This normally closed switch senses when temperatures reach unsafe levels, switch opens and shuts down the crank signal from the ignition switch for several minutes.

▪ Never bypass (jump) a starter by using a screwdriver or similar tool to short across start and battery post at solenoid. This will bypass the soft start and apply full amperage to a spinning drive pinion. The result will be a broken starter and or ring gear.

▪ Never hit a starter with a blunt object to “unstick” it. This can result in broken field magnets inside the starter.