JD LT133 Shunt Relay

Lewisk5 · Sep 16, 2011

I just got a John Deere LT133 that has some electrical problems. I have them mostly figured out except for the shunt relay. This is the relay that is connected to both input wires of the voltage regulator. It is powered off of the ignition switch and grounded with a diode. When the relay is not powered it shorts the stator to itself thus not charging the battery. What is the purpose of shorting the stator to itself? I would think that his would damage the stator. It has partially melted the 4 pin connector connecting the tractor to the engine.

Shaun

t1 · Sep 16, 2011

The shunt relay shorts the stator, causing an increased current draw from the magnetic field and causes the engine to stop quicker.

I copied the explanation fro mthe JD Service manual below

The shunt circuit is used to cause the engine to stop
faster when the engine is shut off. When the key switch
is in the RUN position and the PTO is off and the brake
is on, or the operator is on the seat, the shunt relay is
energized and opens the contacts that connect one
phase of the alternator to ground. This reduces the
load on the alternator to 2-3amps for recharging the
battery and 3-5 amps for illuminating the headlights.
When the ignition is grounded to shut the engine off,
(See “IGNITION & SHUTOFF CIRCUIT OPERATION–
LT133/LT155”.) the shunt relay is deenergized. This
allows contact across the normally closed set of
contacts, grounding the alternator. This places a load
on the alternator, which in turn places a load on the
engine. Since the engine ignition system has been
turned off, the engine has no power to turn the extra
load. The result is that the engine stops spinning faster.

Lewisk5 · Sep 18, 2011

That makes since. I wondered why it would have shorted itself. Thanks for the help.

JD LT133 Shunt Relay

Lewisk5

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t1

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