GENERATOR - WCS Distributing, Inc.

3/2007GENERATORGeneratorsGenerator basicsYamakoyo generators employ a generator set with a brush-excited rotor that utilizes anAutomatic Voltage Regulator (AVR) for reliability and no need to flash the field coils.General rules• Add up the customer’s wattage demands and match them up with the right generator.We’ll briefly discuss physics of field coil power generation as a function of demand v.output. Under-powering tools can damage both the genset and the tool.Watt’s law states that P=VI, where P is watts, V is volts and I is amps. Thus, a 120 voltdevice that draws 7 amps requires 840 Watts of power. However, motors like thosefound in drills, compressors, pumps, etc. require up to five times the rated running loadto overcome inertia and get the rotor turning. So, the same motor that requires only 840watts to run can require up to 4200 watts of starting power.Some people assume that if you under-power a motor it will simply fail to run or that thebreaker will trip. However, the extra power required during startup only lasts for thirtymilliseconds or so, whereas the breaker takes up to a half-second to sense a problem.Imagine a garden hose rated at 300 PSI. Imagine what would happen if you subject it tovery brief shocks of five times that much. The hose might not burst right away butwhether it lasts for five or fifty occurrences, basic laws of physics tell us that sooner orlater it will. You wouldn’t think of selling a garden hose to use on a pressure washer.• Always ground the generator to earth.• Always set the breaker to the off position while starting the engine, and never leave atool turned on while switching the breaker on.• Never switch the breaker on and off while a tool is running. Where household breakersand some power tools can absorb voltage spikes, a genset will not be so forgiving.©KBN‐Yamakoyo www.kbnusa.com Page 1

3/2007GENERATORQuick check diagnostics.There are three main components to a generator: the engine, control panel, and thegenerator set (genset), which contains the rotor, brushes, AVR, and the stator. We applyvoltage to the rotor and as it turns inside the stator it induces alternating current.Problem diagnosis is the process of isolating components and testing them individually.The only special tool required to solve generator problems is an accurate multi-meter withalligator clip and probe-style tips.• Engine problems must be resolved before working on a genset. If the engine is notperforming to spec, you will run into problems identifying and repairing problems in thegenset. The correct RPM for our generators is 3600 RPM.• Don’t go in search of a complex answer when the problem may be a loose wire. Themachine in the photograph below will run but will not produce power. Can you see theproblem? Hint: look at the molex connector.©KBN‐Yamakoyo www.kbnusa.com Page 2

3/2007GENERATOR1) No voltage:1. First we must isolate the control panel from the generator set. Remove the 4 wiresthat go to the control panel. Note that the wires are color-coded and paired insidewhite fiber wraps, red with green, and yellow with blue. Each pair represents aStatorRotorBrush assemblyAutomatic VoltageRegulator (AVR)Terminal blockseparate coil. Leave all the other wires connected for this test.2. Start the machine and check for voltage at yellow and blue, and green and red,respectively.©KBN‐Yamakoyo www.kbnusa.com Page 3

3/2007GENERATOR3. If you do not have 120VAC at the terminals, there is a bad connection somewherein the control panel. Trace the wires with a continuity tester to find the fault. Start atthe leads that attach to the breaker and work from there.2) No voltage at coil terminals:1. Check for a broken carbon brush. Remove the brush holder and inspect the springsand carbon elements for chipping or loose wires. Inspect the slipper rings. If they’vegot some corrosion clean them with 0000 steel wool.2. Check the resistance at the stator. Disconnect all of the wires that go to the faceplateand tie them up out of the way before performing a continuity test. On the Q3.7Generators the resistance between red and green, and blue and yellow, respectivelyshould 0.6 Ohms +- 0.2 Ohms. On the Q8.7 series the value is 0.4 Ohms +- 0.2Ohms. If you have infinite resistance there is an open in the windings and you mustreplace the stator.3. At the rotor windings, use alligator clips to check at solder points instead of at theslip rings. You’ll need to remove the AVR to do this. Be careful not to ground yourtest leads on the aluminum case or you will get a false reading. The resistance valuesfor the stator are between 46 and 65 Ohms. If your reading is out of range, the rotoris bad and must be replaced.©KBN‐Yamakoyo www.kbnusa.com Page 4

3/2007GENERATOR4. If the resistance values are correct, check for voltage at the brushes. Remove theleads that go to the brushes and attach a DC voltmeter. Make sure that you observethe correct polarity. Start the machine and check to see that you have 6-14 VDC atthe brushes. If there is no voltage, the AVR is bad. (The reason we do not checkvoltage at the brushes first is because there are instances where the AVR is not theonly problem and we want to make a thorough diagnosis of all possible problems.)©KBN‐Yamakoyo www.kbnusa.com Page 5

3/2007GENERATORDisassembly instructions for Q3.7 generator.1. With the engine running shut off the gas valve and let it run until it stalls. This will useup the fuel in the float bowl and keep it from seeping into the air cleaner when you turnthe machine on its end in step 11.2. Remove the gas tank and set it in a secure location away from sparks or flame.3. Completely drain the oil.4. Remove the battery.5. Remove the muffler protector and the muffler. NOTE: You do not need to remove thesupport brace that is attached at the right hand foot of the genset mounting bracket.6. Remove the rear cover and disconnect all of the wires that go to the faceplate and tiethem up out of the way.7. Remove the AVR, brush assembly, and the screws that hold the terminal block onto thegenset housing.8. Some models have a square rectifier located in the rear of the genset instead of behindthe control panel. If your model is so equipped, detach the wires to go into the coils.9. With an air impact wrench, loosen the rotor bolt. If you do not have an air wrench, havea helper lock the flywheel with a strap or flywheel tool while you loosen the bolt. Rethreadthe bolt until it is about halfway in.10. Remove the four bolts that secure the stator mounting bracket to the rear enginehousing.11. Lay out some clean shop cloths and stand the generator on its end.12. Remove the shock absorber nuts from the underside of the rear lower cross member.Disengage the shock absorber studs from the cross member and lift the stator/coverassembly out with the shock absorbers still attached, as shown. NOTE: the stator isheavy so make sure you have a good grip on it. You may need to tap the stator gently onthe side with a rubber mallet to break it loose. If so, bend back the tabs on the sheetmetal cover and remove it, but be careful as the edges are very sharp. NOTE: Do notstrike any part of the stator with a metal hammer. Take care that the coil wires do not gethung up on the stator as you lift it out.©KBN‐Yamakoyo www.kbnusa.com Page 6

3/2007GENERATOR13. If you don’t have a rotor-removing tool, you need not go to the expense. Hold one endof an 18 inch length of 2x4 against the steel plates on the side of the rotor and sharplyrap on the other end of the 2x4 with a heavy hammer. Have a helper hold the machinesteady to keep it from creeping. Impact the rotor as close to the end (away from theengine) as you can while holding the wood in contact with only the steel plates. Graspthe rotor firmly and pull up on it with steady rocking motion. If it doesn’t come loose onthe first try, rotate it 180 degrees and try again. Generally, two or three sharp blows areall it takes.Assembly is the reverse of these steps.Final torque values are as follows:Rotor bolt 55 ft. lbs.Stator mounting bolts 17-20 ft. lbs. Tighten in two or three steps in a crosswise pattern.6mm screws 7 ft. lbs.Mounting stud nut 30 ft. lbs.©KBN‐Yamakoyo www.kbnusa.com Page 7