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Pulled my portable generator out of the garage cause I wanted to juice my camper for a little spring cleaning and some modifications, and after I installed a extra outlet, I plugged in a tester and checked for anything wrong, it read there was a reverse polarity (swap between hot+neutral), went back and double checked and nothing was wrong, so I kept checking around and I round that the generator was pumping out the power with the reversed polarity.

Its doing that because the magnetic fields swapped inside the generator, right? And the way to "reset" the polairty is to connect some kind of power source and short the system out for 4-5 seconds so the fields can change back right? I remember I did it on something a long time ago, but I really forgot how I did it. I think I used 12v DC current from a car battery, or mabye it was a cut up extension cord on household current, I really dont remember which one I used to set things straight. I scoured google and didnt really get a straight answer on that, so it brought me here.

I'm like you, I have a vague memory of a procedure called "flashing the field." Pretty sure it involved 12 VDC. I don't remember much more than that, but I think it was for a condition where the generator had no output at all rather than a polarity swap.

Nonetheless, I doubt that is your problem. With 120 AC, the only thing which makes the Neutral a Neutral is the fact that it is connected to earth ground at the source. The polarity shifts 60 times a second anyway.

If you haven't already, I'd check it directly at the generator. Have you ever checked the camper before? I'd bet it has been that way for a while. If it is consistently backwards throughout the camper, I'd switch it at the generator or the supply cord to the camper or leave it be. Most devices aren't going to care. It will cause problems with ground fault protective devices though.

[This got a little wordy]

The key to correctly answering your Q is knowing what this generator is supposed to be doing.

Is it a typical household generator? One that you use for powering typical household appliances and tools? If so, it will generate 120v or 120/240v AC. It might have a 12v battery charging outlet too.

Or is it something special, and generates 12v only? If so, it's probably vintage.

All modern portable generators are really alternators, just as in the automotive realm, generators were replaced by alternators by 1973 (AFAIK, VW was the last holdout using a generator, in about 1972). That portable household generators are called generators is confusing.

Generators have a segmented armature (rotor). They can produce DC or AC voltage, depending on how they are constructed. Alternators have slip rings, or in the case of portable generators, often are brushless.

If you have a "generator" that is supposed to be powering the camper's 120v stuff, and if it's constructed in the last 30 years, it's an alternator. The only alternators that ever required "flashing the field" were made a long time ago, and AFAIK they would produce the correct AC polarity regardless of how the field was flashed.

That behind us, "flashing the field" was a very common operation back in the day, and in the automotive realm a procedure typically used in two situations:

• Replacing the generator with a rebuilt unit;
• The vehicle had sat for a very long time with a dead battery or no battery.

Old automotive generators depended upon the unit having residual magnetism after it had been in use. On a lot of generators, it would not make any voltage without residual magnetism, or it could produce a reversed polarity because the residual magnetism was too weak. "Flashing the field" for automotive generators involved briefly full-fielding (applying full battery voltage to the field coil) the generator very briefly, to reestablish the residual magnetism, and in the process also make certain that the residual magnetism itself is the correct polarity. If the field was flashed reversed, the generator could (not would, but could) generate reverse polarity current. More commonly, a generator that had not been flashed upon installation just wouldn't produce any current at all.

Automotive alternators never needed to have their field flashed. They do not depend upon residual magnetism for output polarity nor for priming; they are externally primed (which is why an alternator will not produce current to a completely dead battery; some voltage must be present before an alternator will come online.

Some old gensets did require flashing their field, as a design flaw. Onan mentions situations where its old generators must have their field flashed, and some military spec gensets actually have a field flash pushbutton to do it manually without extra know-how. Later versions added a small permanent magnet to the armature to avoid this mess.

Back to your situation: In household wiring, the terms "hot" and "neutral" are arbitrary terms. The AC power generated does not inherently have a hot and neutral property; it is only in reference to ground (whatever that is) that one lead or another can be said to be "hot".

Neutral and Ground must be at zero potential in reference to each other.

When facing the 120v outlet on the generator (or anywhere), if it's a modern polarized outlet, the taller blade hole should be "neutral", the shorter blade hole "hot", and the round hole ground. Let me use Google to go find a nice picture of an outlet. . . ah, here's one:



NB: this is the female socket we are looking at. If you look at the male plug, such as a cord end, the tall and short blades will be swapped side to side. This is important!

Neutral and Ground must be at zero potential in reference to each other.
If you measure any voltage at the socket above 0.01v, the socket is miswired. If you do your measurement somewhere else, it may be normal to see a slight voltage difference, but the Neutral an Ground wires are bonded, per code, either in the generator or in household wiring at the breaker box.

So, Kassim, where are you sticking your probes and what are you measuring?

I was doing a simple test with the receptacle tester, the one with the three lights on it. I originally plugged it in through the camper and discovered it was backwards, then i plugged it straight into the generator to confirm it. It does make alot of sense though, I got shocked with the breaker off, which would happen if the neutral became hot.

I found the generators owners manual on coleman's website-
Owners Manual
On page 7 it shows a diagram and the procedure for exciting the generator, Im just gonna try juicing it in the other direction with a car battery and see what happens.

Ill try conducting other tests when I get back out to the generator (not at my house)

kassim503 wrote:I was doing a simple test with the receptacle tester, the one with the three lights on it. I originally plugged it in through the camper and discovered it was backwards, then i plugged it straight into the generator to confirm it. It does make alot of sense though, I got shocked with the breaker off, which would happen if the neutral became hot.

Those LED testers are quite handy. I have three of them scattered around

I found the generators owners manual on coleman's website-
Owners Manual
On page 7 it shows a diagram and the procedure for exciting the generator . . .

I would have bet money that no generator built within the last 30 years required field flash, but I see I would have lost that bet . . .

Im just gonna try juicing it in the other direction with a car battery and see what happens.

Won't change a thing. Voltage (shown by your lit LED on your tester) from Neutral to Ground is a wiring fault, period. You have a miswired receptacle on your generator. Sue Coleman, it's the American Way. Be sure you can prove you are injured and emotionally scarred for life -- that's easy, but now you also have to prove the generator has something to do with that

Ill try conducting other tests when I get back out to the generator (not at my house)

If you have one, try using a DMM set to AC scale and put probes in the Ground socket and the taller blade. If you have any voltage more than, say, 0.1v (I bet you have a lot more than that, to light the LED), get Coleman to buy you a new generator

asavage wrote:

Im just gonna try juicing it in the other direction with a car battery and see what happens.

Won't change a thing.

Oh well. Either I give up at this point and pretend the whole thing never happened, or ill reverse the wires on the whole setup and do it right. 'Cause the circuit breaker wont trip if there is a short with the reversed polarity, and the wiring in this beast is shoddy at best. It was re-wired by a baffoon around '78 or so, wired it right, just didnt use no wire clamps at junction boxes, and used solid wiring for stationary environments instead of the multi strand that should of been used in this mobile situation.

asavage wrote: If you have one, try using a DMM set to AC scale and put probes in the Ground socket and the taller blade. If you have any voltage more than, say, 0.1v (I bet you have a lot more than that, to light the LED), get Coleman to buy you a new generator

I can bet current between the neutral and ground is gonna be 120v. If this generator isnt as old so that the warranty expired, I would probably send it back and get a nice shiny new one. Too bad I didnt notice earlier, bad luck on my part. But now I have to make sure that I wire it up so that the two circuit breakers on the generator are also functional in case of shorts.

kassim503 wrote:If this generator isnt as old so that the warranty expired, I would probably send it back and get a nice shiny new one.

If it's miswired, they'll fix or replace it even out of warranty, because it's a hazard no matter how old it is and they won't want the legal liability. Problem is only if you can't show that it hasn't been tampered with.

Too bad I didnt notice earlier, bad luck on my part. But now I have to make sure that I wire it up so that the two circuit breakers on the generator are also functional in case of shorts.

If you want it fixed right, open up the genset's panel and reverse Hot and Neutral yourself. It's generally quite easy to do.

But flashing it won't help, it's already making power and you can't change the polarity of an AC device, because it doesn't have any: the "Hot" is only "Hot" relative to Ground, and "Ground" is whatever leg of the AC that is bonded (wired) to "Ground" in the generator. Single-phase is not rocket science. Move two wires, retest, done.

asavage wrote: If you want it fixed right, open up the genset's panel and reverse Hot and Neutral yourself. It's generally quite easy to do.

I know that would be the smartest thing to do, but the only way to open up the panel is to remove the gas tank and heat shield, so its really just a case of me being lazy. 4 bolts to swap the wires at the generator head, or 12 to do the panel method, I guess its all gonna depend on how much daylight is left by the time I head on over there tonight.

Took the whole unit apart- determined both the hot and neutral leads and traced the wires up, really didn't find any problem with the design. The only thing I found was that there was a connector between the outlet panel and the generator head, and it could be easily reversed, so that there would be a hot/neutral swap. It is able to be plugged in upside down and right side up, don't ask why they could of designed one with a tab to make it idiot proof, cause I have no clue why either. My belief is that it was simply plugged in backwards from the factory, and I plugged it all in right and put it back together.

Plugged my handy tester in, it read a hot/ ground reversal, I dont know why, Nothing seems to be grounding out, would it do that if the generator is not grounded to the earth or anything?
I tried to stick my VMM into a puddle of water and to the ground screw, it acted as a decent but not great ground and it didnt seem to be dishing out any energy. I even tried touching the ground and standing in that same puddle of water, taking care to not let the electricity cross through my heart. After all I dont feel like dying

I might try dragging another tester out there and see what happens, I mean I must have a million of them around. And try testing for electricity in the ground on the generator to a ground connection from a grounding pole





Also im noticing its putting out around 128-132 volts instead of the normal 115/125, are they supposed to be accurate down those levels? and if not, is it easy to fix?

Earlier, you'd said:

kassim503 wrote:I plugged in a tester and checked for anything wrong, it read there was a reverse polarity (swap between hot+neutral) . . .

Latest is:

kassim503 wrote:My belief is that it was simply plugged in backwards from the factory, and I plugged it all in right and put it back together.

Plugged my handy tester in, it read a hot/ ground reversal.

This is beginning to sound like your five-page overheating saga. You have misidentified some of the wiring. Those cube testers are very reliable. And measuring from a portable generator to the actual earth (like a puddle) is not going to work, you will be mislead. The term "Ground" in power distribution does not automatically have anything to do with dirt.

oh no, your right, this better be solved now. I dont have time to bs around anymore.

Isnt the ground just a 10 foot copper rod driven into the ground?

I really dont think its a hot/ground reversal, everything inside works when running the generator in its current state, and that would mean everything would have to be shorting out.

As far as the generator knows, ground is the outer case and framework. This in turn could be connected to a ground rod. If a generator is installed in a permanent fashion it would be.

If you check from the frame or engine block of the generator to the ground connector in the receptacle is there any voltage? How about from the Neutral in the receptacle to the frame? Hot to frame?

Neither the ground or neutral should show any voltage when referenced to the frame.

The hot should be nominally 120.