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Frequently Asked Generator Questions

Jim Rankin

The real zig-zag single phase reconnection!

Found this on the ACMOC forum a couple days ago and realized that this is the zig-zag connection. Different from the dog leg which I had been calling zig-zag. Neat thing is this one doesn't require a 12 lead set, a 9/10 lead Y connected set can do single phase with this one.


Jim Rankin

Re: The real zig-zag single phase reconnection!

Note about the zig-zag connection shown below..............Most common 10 lead generators are 480 volt capable and connecting one in the zig-zag as shown will produce 240/480 single phase, not what you need for your house!

Instead, connect the generator leads in the low voltage 3 phase configuration (parallel Y) and use 2 lines and the neutral with the voltage set to 127/220 or so.

Jim Rankin

CATERPILLAR generator set model/serial number code

A "neighbor" of mine here in Alabama sent me this information on Caterpillar generators. I have one without the generator and engine serial number tags (completely corroded away from a long time spent on a radio station along the gulf coast) and the only designation I could find was the generator code stamped in the steel casing of the generator near the lifting anchor point on top.
Generator Serial Number
The engine serial number is stamped on the engine
information plate and on a plate on the left side of the
block toward the rear. The generator serial number is
stamped on the generator nameplate and on the right
side of the generator frame forward of the terminal box.
Requests for information and orders for parts should be
accompanied by the engine and generator serial numbers.
1. The group of numbers before the letters indicates
generator frame size. The letter T may appear before
the first group of numbers. This indicates a
"tropicalized" generator, that has been dipped in
epoxy to prevent moisture entrapment in
2. The letter T is the symbol for Caterpillar Statically
Regulated Controlled Rectifier generators. The
letter B is the symbol for Caterpillar Statically
Regulated Brushless Excited generators.
3. The next letter indicates the voltage rating of the
generator as follows:
115-230 volts 60Hz
125-250 volts-Single Phase . . .. . ...... . 60Hz
H 230-460 volts . . . . . . . . . . . . . . . . . . . . . 60 Hz or
125-216 volts . . . . . . . . . . . . . . . . . . . . . 60 Hz or
200-400 volts . . . . . . . . . . . . . . . . . . . . . . . 50 Hz
287-575 volts ..... .. ... ... ... . .... 60 Hz or
230-460 volts . . . . . . . . . . . . . . . . . . . . . . . 50 Hz
2400 volts 60Hz
SR 4
120-240 volts . . . . . . . . . . . . . . . . . . . . . 60 Hz or
125-250 volts-Single Phase . . . . . ... . ... 60Hz
208-416 volts . . . . . . . . . . . . . . . . . . . . . . . 60 Hz
240-480 volts . . . . . . . . . . . . . . . . . . . . . 60 Hz or
200-400 volts . . . . . . . . . . . . . . . . . . . . . . . 50 Hz
300-600 volts . . . . . . . . . . . . . . . . . . . . . 60 Hz or
240-480 volts . . . . . . . . . . . . . . . . . . . . . . . 50 Hz

Serial No. follows

T 50 TH 1013

Note, this does not give you information directly on the electrical capacity of the generator end, however, the frame size should narrow it down considerably.

These are the codes for the SRCR brush type
115-125/230-250 volt single phase and 3 phase 60 hz (appears to be wound either as single phase or 3 phase, but could be 3 phase reconnectable to single)
120-125/208-216 volt 3 phase reconnectable to
230-250/416-460 volt 3 phase 60 hz
200/400 3 phase 50 hz
287/575 3 phase 60 hz
230/460 3 phase 50 hz
2400 3 phase 60

SR4 brushless
L same as above
S 208/416 60 hz 3 phase
H 240/480 60 hz or 200/400 50 hz 3 phase
G 300/600 60 hz or 240/480 50 hz 3 phase

Hope no one else has one without the data plate with all the amperages, phase and volt as well as reconnect information. :eek:


How does a magnetic pickup sensor work I am looking for a MPU sensor to buy near Pune? How is the RB Electronics manufacturer?

Kimbra Dean

Last Subscription Date
A magnetic pickup is a very simple device. It consists only of a small bar magnet with a coil of wire around it. The end of the pickup is positioned very near a gear or a pulser wheel with teeth shaped similar to gear teeth. As the teeth pass the end of the magnet, the magnetic flux in the coil varies causing an AC voltage to be produced by the coil. The output voltage is fairly low, ranging from less than 1 volt to a few volts. The output voltage drops off very fast as the the gap between the pickup and the gear teeth is increased.


My generator runs, but won't generate

Down the same lines as "My engine cranks, but will not start", a generator that is spinning has just a few simple reasons why there is no output.

Refer to prior notes on generator parts... the rotor and stator being the mechanical reference of windings... rotor is turning, the stator is stationary, ONE of the two is a magnetic field, the other, is the output windings.

There is no RULE that says the field must rotate, or the field must be stationary- generators are built both ways, and they're built a variety of ways, for a variety of reasons, but in ALL cases, the reality is that you need a magnetic field, and you need output windings, and one must mechanically cross the other... revolve around it, in order for your generator to produce output.

That being said, there are VERY FEW reasons why a perfectly running generating plant will refuse to generate output.

The first, is that some protective device, some piece of switchgear, some breaker, etc., is not closed. This is the most obvious reason why you'd have no output, and the easist to diagnose without asking anyone, so always check this FIRST.

The second, is that the generator has no EXCITATION.

Which leads to the question... WHAT is EXCITATION?
Excitation is current flow which generates the FIELD. Without excitation, there is no magnetic field for the output windings to spin within, or around. Remeber- two sets of coils- one is the field, the other is the output... one is spinning, the other stationary. Without excitation current, there is no magnetic field, thus, no output.

Where does excitation come from? In most generators, it is developed by a specific winding in the generator, and it's Direct Current.

Remember back in 5th grade science class, when you made an electromagnet by wrapping wire around a nail? If your class was adept, the next step, was to make TWO, and then drive them into a dowel rod, put pins in the ends, set it in a pair of V blocks, with a horseshoe magnet around it, then apply voltage to the windings, and watch it move from N to S. Then you made a COMMUTATOR, so it'd connect, then flip polarity over and over again, henceforth, a MOTOR.

Generator is the same thing, but backwards... spin the shaft, and electricity comes OUT of the wires. The FIELD is the horseshoe magnet.

Now in a generator, the field isn't a permanent magnet... because the faster you spin a generator with permanent magnet, the HIGHER THE VOLTAGE coming out. In some alternators (motorcycles and outboard motors), they use this, but not in big AC or DC generating plants... because the FIELD STRENGTH determines output voltage under a given load. As the load increases, a little more field excitation keeps the voltage from sagging... and under a very light load, backing off the excitation current keeps the voltage from overshooting. To make it a little more complicated, the engine, when loaded, will slow down a smidgen, and then the governor SENSES that it's a smidgen on the low side, so it opens the throttle to 'pick up' a bit. Well, when the speed of the rotor/stator relationship becomes lower, output voltage drops. When it goes faster, it rises... so having an excited field gives lots of regulation flexibility to keep tighter output.

Where were we? Oh... my generator runs, but doesn't generate.

The MOST COMMON problem that I've found on old generators, is NO EXCITATION. Of course, it could be something obvious, like mouse turds stuck in the brushholders. Sometimes it's the fact that the exciter's DC power is coming from an AC winding rectified by something that's not rectifying. Particularly the case in one prior to the late '60's, they'll have SELENIUM rectifiers... looks like a bread-slicer on a long bolt, with four wires comin' to it... two are AC from the exciter's windings, the other two are DC going to the main generator field. Selenium rectifiers are cool, in that they were the early technology for solid-state diodes. They're NOT cool, in the fact that they got rather hot (hence, the big heat sinks), and also the fact that as they aged, they tended not to do it gracefully. They go kaput, and often, not all at once, but rather, in pieces. They start falling apart internally.

Did I mention that... no, I didn't. When you look at a generator, you're looking at more than just a generator. You're looking at an ALTERNATOR (creates your output AC) and an EXCITER (which generates field current for the ALTERNATOR). Sometimes, they're really, really, really easy to spot- If you look at a massive generator (like a 5-cylinder Fairbanks-Morse in an old municipal powerplant), and there's a belt-pully off the hind end, driving what looks like a big electric motor... THAT is the Exciter. If you're looking at a smaller plant, you'll see a fat part (the main alternator) and at the end, a smaller part (the exciter). Frequently, that smaller part has a cover held on by a couple small bolts or screws, when you lift it off, you'll see brushes in there, and mebbie a centrifugal switch or two, and some wires that go to the control box marked F1 and F2... and on SOME generators, you'll just see the main alternator section, because the excitation WINDING is integrated into the main alternator somehow.

So where is this all going? Well, just like in a car alternator, if you're not getting excitation, you're NOT gonna get alternator output. That exciter needs a magnetic field to generate the DC that the ALTERNATOR needs in order to create AC output. The '5th member of the Beatles' (the late, great Billy Preston) said it right- Nothing from Nothing leaves Nothing- 'ya gotta have something.

When you spin the generator up, the EXCITER starts generating DC current to drive the main alternator by virtue of JUST A LITTLE magnetism that's IN the iron around it. We call it RESIDUAL magnetism- magnetism that exists because it's an electromagnetic gadget.

Back to 5th grade... you took the nail, stuck a magneto n the head, and touched it to a paperclip, and it picked up the clip. Removed the magnet, and the paperclip fell off. This is because the permanet magnet "SHARED" it's magnetic field to the nail. Next, you swiped the nail over the horseshoe magnet a half dozen times, then the nail became magnetic, all on it's own. You MAGNETIZED the nail.

Suffice to say, this is exactly what happens with the framework of a generator. When it's working, that magnetic field is 'magnetizing' the chassis of the generator in MANY places.

Remember that nail you magnetized? go back to the school, find your desk, open it up, and pull out that nail. Check-see if it'll still pick up that paperclip, I guarantee it won't. Why? Because you magnetized it over five decades ago, and it's sat in there, all by it's lonesome, waiting for you. The magnetic field you rubbed into it, gradually fell away... the residual magnetism is gone.

Here's another neat trick they DIDN'T teach you: Magnetize the nail, test it. Now, place it, give it three light whacks to drive it into the desktop (now you know why they didn't teach you...) Pull it out, and see if it'll pick up that clip.
It won't. By smacking it, you strained the metal, and destroyed the magnetism.

Your generator NEEDS residual magnetism... specifically, the EXCITER NEEDS it. If it has no residual magnetism, it WILL NOT generate field current.

You've no doubt heard of 'flashing' the field. What you're doing, is applying current from an outside source, to artificially create a magnetic field for the generator to 'kick itself' in the pants. To properly flash, you need to access the field wires, and connect to them SAFELY, while the machine is running and ready to accept a load.

If you're adept with electricals, good of eyesight, and careful with your fingers, it's not a difficult task to flash a field... and I'm good in all of the above (my eyes ain't what they were before I turned 45, but...) But I'll tell you the OTHER way, that you really can't mess up, and can't get hurt doing, and can't get wrong.

Go dig out that big permanent magnet that your dad bought out of the Edmund Scientific magazine back in '78... or take a chisel and knock the 40oz magnet off the back of the Jensen 6x9 you had in the back shelf of your Nova, and slap that sucker on the side of the Exciter.

Why? Because your generator has been ASLEEP for long enough to have forgotten it's residual magnetism. Slapping a magnet on the side gives it JUST A WEE BIT, and that's all it takes, to remind it that it's a GENERATOR.

Now, you might not see much power coming out at first, but do this: Put a 50-75w incandescent light bulb on it (not a CFL, not an LED). You'll get a little glow at first. Let it run a while, and eventually, you'll see it come up a little, and when it finally breaks out of it's amnesia, the light will wake right up.

But we're not done yet. Get a milkhouse heater... y'know, the kind with a big long resistive wire lookin' like an '80s toaster oven through it, and usually TWO load settings (like, 750 and 1400w). Plug that rascal in, set it to LOW, and flip the switch. If your incandecent bulb goes OUT, then shut the heater off, and let the lamp glow for a while longer. Eventually, it'll dim a bit, but the engine will grunt and the heater will glow. Now, walk to the refrigerator, open, and remove a cold beverage. Close fridge, open beverage, and enjoy the fact that gravity holds you in the lawn chair. Then take the dog for a walk. Empty the trashcans in the workshop. Surf the forums for a while. Come back, flip the heater to full-roar, and listen to the engine grunt. Let it be for another 15 minutes, then remove magnet. If it stays glowing, let it work for another half hour.

After that, it should start and generate fine... AS LONG AS YOU EXERCISE IT REGULARLY. Each time you bring it on line, with a load, you reinforce that residual magnetism. It builds it a little bit more, each time... but that means not just STARTING the machine, but PUTTING A LOAD on it.

Mount a couple incandescent lamps on the machine, for three reasons: 1) so you know it's generating... 2) so that it's always got a resistive load to help rebuild that residual, and 3) so that when the power's out, and you're starting it up, you can put the flashlight down and go fart with the transfer switch.