IA Renewal Seminar 2014

IA Renewal Seminar 2014

Introductions Introductions Scott Durham President, Co-Owner Overview of FAA / EASA Certified Repair Station Instrument & Accessory Overhaul Location: McClellan CA (Sacramento)

Topic Starter Generator Brush Check and Change

Agenda Starter Generators The Basic Generator Identifying Generator Types Advantages/Make-up of Shunt & Series Generators Typical Brush Types Standard Brush Life Performing Visual Inspection Commutator Appearance Performing Electrical Checks Performing Bearing Checks Brush Length Indicators Brush Change? Brush Lead Formation Brush Run In Factory Recommendations Shaft Alignment

Starter Generators Many makes, models, sizes and manufacturers. Various current ratings, 150, 200, 250, 300, 400 up to 600 amps. Two most common types Shunt Generator Series Generator All made up of the same basic parts

Basic Starter Generator Armature Stator Drive end bell Anti Drive end bell Shaft Assy Fan Fan Cover Bearings Brushes Terminal block

Starter Generator Shunt vs Series Series winding Three large terminals and two small terminals Shunt winding Two large terminals and two small terminals

Series Starter Incorporates Shunt Field, interpole and compensating windings Additional start winding connected with the armature and terminal C on the terminal block. C=Start B=Generator E=Ground Terminal C serves as the input for the start power source.

Shunt Starter Incorporates Shunt Field, interpole and compensating windings Does not have an additional start winding. Terminal B serves as the input for the start power source and after the generator has started becomes the generator output. B=Start/Generator E=Ground

Starter Generator Shunt vs Series Series generator advantages Maximum Starting Torque Maximum No-load Speed Shunt generator advantages Higher mid-range High speed starting torque C=Start B=Generator E=Ground B=Start/Generator E=Ground

What is a Carbon Brush? A carbon block used to transmit current between a stationary and moving parts of a generator or electric motor.

Typical Brush Types Carbon Graphite Particle Flake Electrographitic Typically Cored Non-Cored Electrographitic Long Life

Brush Filming Brush performance is dependent on a mico-thin Oxide film which develops on the surface of the commutator during operation. The Oxide formation relies on the presence of water vapor and oxygen or on the introduction of lubricating additives in the brush.

Standard Brush Life Brush and Commutator wear is a function of electrical load, environmental condition and brush grade. Standard Brush Life is Approximately 500 Hours Long Life Brushes can be the exception to this and are designed to operate the full TBO under normal conditions. Long Life Brush aka XL Series, Millennium, Diamond Range Note from the manufacturer: (Brush) Performance is subject to aircraft operation methods: short flights vs. long flights. Short flights with high number of starts degrades the brushes quickly and reduces TBO time.

Standard Brush Life During field operations, individual brush wear rates may vary significantly. Selectivity The tendency for a higher percentage of total current flow to travel through one brush. Heavy loads. Cored brushes Significant variations in spring tension Periodic brush inspection is required between overhauls Goodrich Corp recommends that a brush check is performed every 250 hours if not specified by the Airframe manufacturer or Operators field service experience.

Visual Inspection Remove Access Covers. Remove carbon and copper dust using compressed air. Starting at the shaft (Drive) end, working your way toward the fan (Anti-drive) end. Visually inspect for damage to components (Fan, Brush rigging, Shaft, Main Terminals, etc.)

Visual Inspection Visually inspect commutator appearance. Note: Generators using cored brushes will cause commutator grooving. While this is a normal occurrence, it is recommended that the commutator be resurfaced prior to performing a brush change. If damage is found, it is recommended that the unit be returned to a qualified repair station for service.

Acceptable Commutator Appearance TSO 750 HRS Commutator film dark, even and Shiny Brush face smooth and glossy.

Acceptable Commutator Appearance (Cored Brush) TSO 600 HRS Commutator grooved Commutator film dark and shiny Brush face smooth and glossy.

Poor Commutator Appearance TSO 490 HRS Commutator uneven, rough Brush face uneven and pitted

Electrical Checks Check the Insulation Resistance between Positive terminal B and the frame using an Ohmmeter. Resistance measurement should be 10K Ohms or greater. If the Resistance measurement is less than 10K Ohms, clean the generator with compressed air again and retest. Note: if the generator does not pass the electrical resistance check, it should not receive a brush change. It is recommended that the unit be returned to a qualified repair station for service.

Bearing Check Stand unit vertically on shaft and secure from tipping Mark Brushes and Holders To ensure brushes can be returned to the original holder if removed. Lift and secure or Remove Brushes Rotate unit slowly in direction of normal rotation Normal rotation can be found on the unit I.D. plate. Direction of rotation is interpreted with the shaft facing you however in most cases is counter clockwise. The bearings should rotate relatively smooth and should not sound dry. Note: Some bearings use a high temp lubricant which may make a good bearing feel rough. If damage is found, it is recommended that the unit be returned to a qualified repair station for service.

Brush Wear Full Length Approximately 50% Worn 100% Worn

Brush Change? Things to consider when deciding to do an in field brush change: Is the general condition good? Is my commutator appearance good? Is my insulation resistance acceptable? Are my bearings smooth?

Brush Change Consumables Brushes! Isopropyl Alcohol 180 grit sandpaper or Garnet Paper Masking Tape Q-Tips or Lint Free Cloth

Brush Change Remove and discard brushes Clean the commutator with Isopropyl Alcohol Cut 180 grit sandpaper or Garnet Paper slightly wider than the brush contact area and 1 longer than the circumference of the commutator Tape the leading (narrow) edge of the sandpaper with Masking Tape. Trim the edges of the tape at a slight angle.

Brush Change With abrasive side out, insert the taped end of the sandpaper into the brush access port. Secure tape to commutator using a hook tool

Brush Change Rotate armature or housing in direction of normal rotation to wind the sandpaper into the unit Carefully install the new brush set Note: Do not secure brush lead to holder at this time. With all brushes installed, rotate shaft or housing in direction of normal rotation Make 2-3 complete rotations.

Brush Change Remove one brush as a sample Note: The sanded portion of the brush will appear dark and uniform in comparison to an unseated brush. Sanded Un-sanded A Coarsely seated brush has 100% of the contact surface sanded Continue this procedure until all brushes are coarsely seated

Brush Change Once seated, raise each brush spring and move the brushes about half-way out of the holders. Gently place the spring against the side of the brush to hold it away from the commutator. Grasp the trailing edge of the sandpaper through a brush access port and slowly pull the sandpaper out of the unit and detach the masking tape.

Brush Change Carefully blow out the carbon residue using compressed air. Remove residue that may have been left by the masking tape using Isopropyl Alcohol. Carefully lower the brushes and attach the brush lead terminal to the respective holder. Tighten the brush screw to the required torque in the AMM. Note: make sure terminal does not twist when tightening the brush screw.

Brush Lead Formation Proper brush lead formation is important. If the brushes cannot freely travel through the holder, the brush may (hang up) lose contact with the commutator causing the generator to fail. There is no one way to form all brush leads. If performing a brush change, it is recommended that you call a qualified Repair Station for proper lead formation. Note: A repair station will need to know the PN of the unit and brush being installed.

Improper Brush Lead Routing TSO 490 HRS Brush leads hanging up on holder Commutator pitted. Armature shorted Proper brush lead placement is important when doing 100hr checks. This will help eliminate shortened unit life. Brush leads should be routed to follow brush wear.

Brush Run In Brush Run In is important Brushes that are not run in can damage the brush surface and cause commutator failure during start or generator mode. There are two methods for brush run in. Drive stand Motorizing Drive stand process is preferred however, requires equipment generally not found in the hangar.

Brush Run In Motorizing Equipment Required: 28 Volt Power source DC Power Supply Battery Inverter 28 Volt Contactor Switch Single Pole, Single Throw Resistor 5 Ohm, 100 watt fixed» OR Variable (Ohmite RKS16RE) Cradle ( V Block) Tachometer

Brush Run In Mount and secure the generator in the V Block with the terminal block facing up. Make all electrical connections B+ to Contactor E- to Neg Power Source A to Resistor and Contactor Contactor/Switch to Positive Power Source

Brush Run In Close switch and energize the circuit. If the unit rotates opposite direction of normal rotation, check for incorrect lead connections. Adjust the power source to obtain 50-75% of the maximum speed Speed range can be found on the ID Plate A Variable Resistor can be used in place of R1 if an adjustable DC Power source is not available. This will control the field and allow for speed adjustment. R1

Brush Run In Motorize the unit until the brushes are fine seated. A minimum of 75% in the Axial direction and 100% in the rotational direction recommended A properly seated brush will have a smooth/semi-gloss surface.

Factory Recommendations Excerpt from Skurka SL # 225 AL-2 RECOMMENDED OVERHAUL PERIOD Unless established otherwise in the aircraft operator s own Airworthiness Limitations or Operating Specifications, the recommended overhaul period for SAI starter-generators is 1,000 hours with a minimum of 1 brush change prior. (500 Hr Standard Brush Life) AL-3 FIELD SERVICING LIMITS Recommended field service on starter-generator units is limited to brush inspection only. All other repair and/or overhaul activity should be carried out by an authorized repair station. Except for brush inspections, aircraft airworthiness is accomplished through removal and replacement of the starter-generator. AL-4 START CYCLES After every start cycle, the starter-generator as well as the engine should have the opportunity to cool off. The minimum cooling times are stated below: 30 seconds ON 1 minute OFF

Factory Recommendations Goodrich Corp Reference Document 23700 MM CAUTION-THE MAINTENANCE AND REPAIR PROCEDURES PERFORMED BY LINE MAINTENANCE PERSONNEL ARE RESTRICTED TO THOSE PROCEDURES FOUND IN THIS MANUAL. MAINTENANCE AND REPAIR PROCEDURES THAT ARE NOT PART OF THIS MANUAL MUST BE PERFORMED BY AN AUTHORIZED REPAIR STATION Brush Life: Typical acceptable brush life varies from 400 to over 1500 hours, even up to 2000 for some applications, depending on the aircraft Installation, operation and cooling conditions.

Shaft Alignment Shaft Mis-Alignment causes Vibration Shaft failure Oil leaks Avoid expensive failures by aligning your drive shaft prior to installation

Summary All Brushed DC Starter Generators are basically the same. Two basic types of windings, Shunt and Series. A good commutator will have a dark even shiny film. A good brush face will have a smooth glossy surface. Commutators that are rough and pitted should be serviced. Course and fine brush seating is important. Proper brush lead routing is important to avoid shortened life. Three things to consider before brush change. 1. Commutator appearance, 2. Bearings, 3. Insulation resistance. Shaft mis-alignment can cause failure, vibration and oil leaks. If damage is found, it is recommended that the unit be returned to a qualified repair station for service

Questions? Questions? Comments?

Contacts Scott Durham (Starter Generators etc) 916-434-5194 Office 916-671-991 Cell scottd@freedomaeroservice.com Kevin Sherman (Instruments etc) 916-434-5194 Office 916-474-0324 Cell kevins@freedomaeroservice.com www.freedomaeroservice.com