Quick overview (the why and the how, in plain terms)
- Purpose: The charging system keeps the battery charged and supplies electrical power while the engine runs. If it fails you get a drained battery, dim lights, slow starter, or electrical chaos.
- Alternator vs. original TE‑20 generator: The TE‑20 originally used a dynamo/generator and a separate mechanical regulator. Many owners later convert to a modern alternator. An alternator is more reliable and produces usable current across a wider RPM range. Before you start, confirm whether your tractor currently has a generator (dynamo) or an alternator and whether the system is 6V or 12V and positive or negative ground.
- Basic theory (analogy): An alternator is like a bicycle dynamo or a water pump. The engine spins the alternator rotor (the impeller). The rotor creates a rotating magnetic field. Stator windings “catch” that changing magnetic field and produce AC, which the rectifier (diode pack) turns into DC. The regulator controls field current so output voltage stays roughly constant regardless of engine RPM or electrical load.

Components (what each piece does)
- Pulley: driven by the engine belt; turns the rotor.
- Rotor (field): electromagnet on the shaft. Field current makes the magnet.
- Stator: fixed stationary coils around the rotor that generate AC when the rotor’s magnetic field moves.
- Rectifier (diode pack): converts the stator’s AC into DC that the battery and electrical system use.
- Voltage regulator: controls current to the rotor to keep voltage in range.
- Brushes & slip rings (some alternators / generator setups): deliver current to the rotor. Brushes wear.
- Bearings: support the spinning shaft; wear causes noise or wobble.
- Fan(s) & housing: cool the alternator.
- Wiring, main output lug, sense wire, ground.
- Battery, fusible link/fuse, ignition/on switch: system-level parts that interact with the alternator.

What can go wrong (symptoms and causes)
- No charge / low voltage: broken belt, bad diodes, failed regulator, open stator winding, no field current (open rotor), corroded connections, blown fusible link.
- Intermittent charging: bad brushes, failing bearings, loose wires, slipping belt, worn slip rings.
- Overcharging: defective regulator.
- Noise / whining / growling: worn bearings or loose pulley.
- Smoke / burning smell: shorted diode or heavy overload.
- Battery drains while engine off: alternator diodes leaking (reverse leakage).

Tools and parts you’ll need
- Tools: basic hand tools (wrenches, sockets), screwdrivers, pliers, multimeter (volts/ohms/diode), wire brush, sandpaper, contact cleaner, feeler gauge, torque wrench (helpful), small puller for pulley (sometimes), soft-faced hammer, bench vice (optional), drill and driver for bench spin test (or rotor dynamo test setup).
- Parts to have on hand: replacement brushes, rectifier/diode pack, voltage regulator (or new alternator if converting), bearings if needed, gaskets/fasteners, belt, fusible link or main fuse, electrical connectors. Rebuild kits for your alternator/generator are common.

Safety and prep
- Disconnect the battery negative terminal first (confirm ground polarity first). Work on a cool engine.
- Label wires before removing. Photograph wiring for reassembly.
- Wear eye protection and gloves.
- Avoid shorting battery terminals with metal tools.

Diagnosis before removal (do these tests first)
1. Measure battery voltage, engine off. Healthy battery: ~12.6V (12V system) or ~6.3V (6V system). If very low, charge battery first — testing on a dead battery is misleading.
2. Start engine. Measure battery voltage. Alternator charging target:
- 12V system: ~13.6–14.6 V at normal operating RPM.
- 6V system: ~7.2–7.6 V at normal RPM.
If voltage is below these ranges, charging is insufficient. If above, regulator may be bad.
3. Check belt tension and condition.
4. With engine running, wiggle wires and listen for changes — intermittent charge often shows up quickly.
5. Diode test: with multimeter diode test, check rectifier diodes (if accessible). In-circuit testing can be noisy; pulling the connector gives better results.
6. Measure resistance of stator windings and rotor field (consult expected values if available). An open or short to ground is a failure.

Removal (typical steps on a TE‑20 — adapt to your tractor)
- Disconnect battery negative.
- Remove belt(s). Loosen alternator/generator mounting bolts and move it out of the way; remove main output and field wires after noting positions.
- Label and remove connectors, regulator linkages if separate.
- Remove alternator/generator from its bracket.
Note: TE‑20 specifics vary by model and any conversion. Keep fasteners and spacers in order.

Bench inspection and repair (step-by-step)
1. External clean: blow out dust, spray contact cleaner, brush off corrosion.
2. Remove pulley and fan as needed (note any spacers). Use a puller if stuck.
3. Open the alternator/generator:
- Alternator: remove rear cover bolts, separate housing halves carefully (beware of gasket/seal).
- Generator/dynamo: remove end caps to access commutator and brushes.
4. Inspect bearings: check for smooth spin and side play. Replace if rough or loose.
5. Inspect brushes and slip rings/commutator:
- Brushes should be spring-loaded with adequate length. If worn to near base length, replace.
- Clean slip rings/commutator with fine sandpaper or commutator stone. Remove glazing or grooves gently.
- Ensure brush holders aren’t bent and springs exert pressure.
6. Inspect rotor/field winding and stator:
- Check rotor windings for continuity (low ohms) and that they aren’t shorted to ground.
- Check stator for continuity and no shorts to the housing (high resistance to ground).
- Burned, discolored, or brittle windings usually mean rewind or replacement.
7. Test diodes (alternator):
- Remove diode pack if needed.
- Diodes should conduct one way only. Replace diode pack if any diode fails.
8. Check regulator:
- If external, bench-test or swap with a known-good regulator. Internal regulators on alternators usually require replacement as a module.
9. Replace worn parts:
- Install new brushes, bearings, diode pack, regulator as needed. Use correct replacements.
10. Reassemble, ensuring seals and gaskets are correct and no foreign objects are inside.

Bench test after rebuild
- For alternator: clamp the body, rotate the rotor with a drill at moderate speed. With rotor unpowered, measure stator AC (should read AC voltage on three-phase leads if possible). Apply field current (connect rotor slip rings to a small 12V supply through a resistor per instructions) and measure DC output at the main output stud — you should see charging voltage rising with applied field. Use diode test and multimeter to confirm DC output.
- For a generator: similar test with field applied, check output at commutator under rotation.
- If you’re unfamiliar with bench powering the rotor, many shops can bench-test alternators cheaply.

Reinstallation on tractor
1. Mount alternator/generator and align pulley and belt. Set belt tension per good practice — not too tight (bearing damage) and not too loose (slip).
2. Reconnect all wires: main output to battery via fusible link or fuse, sense wire to battery/ignition as originally wired, field/ignition lead as appropriate.
3. Reconnect battery (negative last).
4. Start engine, measure voltage at battery. Expect target voltage ranges above. If charging ok, check under load (turn lights on) and re-check voltage.
5. Ensure regulator settings are correct if adjustable (some old regulators have a small set screw).

Common troubleshooting tips and gotchas
- No charge but rotor has continuity: check ignition/field supply. Often a single wire or a cut wire at the ignition switch or generator cutout is the problem.
- Replacing diodes but still no output: check stator and field windings.
- Intermittent charge that cures with tapping alternator: usually brushes or bearings — replace brushes and inspect slip rings.
- Overcharging after replacement: swap regulator or check sense wiring; a sense wire on the alternator must be connected to battery post or correct point.
- Always replace the fusible link if it has blown: a blown link indicates a serious short; find cause.
- Grounding: on older tractors with positive ground, doing a 12V negative-ground alternator swap needs system ground conversion — change battery cable routing and ensure all wiring is correct. If you convert polarity, change starter motor, ignition coil, and check other components for compatibility.

Alternator conversion notes (if you opt to replace the original generator)
- Many TE‑20 owners fit a modern small-alternator + regulator and adapter bracket. Advantages: reliable charging at idle, lighter maintenance.
- Wiring: you will run an output wire from the alternator through a fuse to the battery positive. You will also add an ignition/stator field warning lamp lead or sense as the regulator requires.
- Ground: ensure system polarity matches the alternator. If existing tractor is positive ground and alternator is negative-ground, you must convert the entire electrical system or source an alternator configured for positive ground.
- Mounting: adapter brackets exist; make sure alignment and belt routing are correct.

When to replace instead of repair
- Stator or rotor windings badly burnt or shorted — replacement or professional rewind recommended.
- Diode pack integrated into housing and gearbox damage — replacement alternator can be cheaper and faster.
- Severe bearing or housing damage — consider new/reman alternator.

Final quick checks after repair
- Belt properly tensioned and aligned.
- All electrical connections clean and tight; no paint or corrosion at terminals.
- Main fuse or fusible link installed and correct rating.
- Voltage under load stable in normal range.
- No unusual noises or heating on alternator surface.

Concise troubleshooting checklist you can use on the tractor
1. Check battery voltage engine off.
2. Start engine, recheck voltage.
3. If low: check belt, connections, fuses.
4. Wiggle wires with engine running — watch voltage to find intermittent.
5. If still bad, remove alternator/generator and bench-test diodes/field/stator/brushes.
6. Replace brushes/diodes/regulator/bearings as required, re-test, reinstall.

That’s the full beginner‑friendly roadmap: how it works, what fails, how to test, what to replace, bench‑repair steps, and what to check when reinstalling. Follow the safety items, label everything, and if any rotor/stator looks burned or you’re unsure of winding tests, a local auto-electric shop can bench-test or rewind cheaply compared with risking a mistaken rebuild.
rteeqp73

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