Gen. set not producing 240v

[TDKPE]

If you follow the top lead from MC1 (black), down through the coil, then up to the twist-lock REC1 terminal "X". "Y" then goes to the other twist-lock, but also tee's off through the switch at 8 to 9, and on to the white back to MC2. Blue and Red from MC1 and MC2 respectively are connected to each other via the switch at 6 and 5. That's the center tap of the two winding generator. I've traced it as Blue being the neutral of MC1 and Red being the 'hot' of MC2.

That's all with the voltage switch remaining in the default position as shown on the schematic. And in that position, REC1 gets its 'hot' from MC1 (black), and neutral also from MC1 via the Blue lead. But that's just one of the two windings, so it's only good for half-power when running in 240V mode.

I've corrected my previous post, as I had the polarity through the induction coil backwards in 240V mode.

Edit: Also, the 120V twist-lock REC2 gets its power only from the other winding, MC2, when in 240V mode, but from both windings when in 120V mode, like the duplex REC1. So you can still get full power from REC1 and REC2 combined when in 240V mode, but you'd have to split the load between them, and I don't know why you'd bother. Plus, if using the duplex in 120V mode, you don't have to be concerned about evenly spitting the load, as it all goes through both windings together.

[EricU]

in general the windings are independent and have 120 v across them when the generator is running.  This voltage is floating until it's hooked into the wiring.  If you hook the high side of one to the low side of the other, you get 240v.  If you hook high side to high side, low side to low side, you get 120v.  It's always possible that the connection of high side to low side is lifted somehow.  Bad connection, no connection, bad switch, etc. To me, this sounds like your problem, the connection putting the windings in series is not happening somehow.

A lot of people have problems understanding floating voltages.  I find that I have to explain it to Ph.D.s and grad students pretty often, because laboratory power supplies have floating voltages until you tie them into a known voltage, usually ground

[blackhat]

A bad brush could keep one winding from producing any power.

[TDKPE]

A lot of people have problems understanding floating voltages.  I find that I have to explain it to Ph.D.s and grad students pretty often, because laboratory power supplies have floating voltages until you tie them into a known voltage, usually ground

One of my pet peeves.  Goes along with the 'need' to ground a portable generator 'for safety', especially one that's not connected to a grounded distribution system.  

A bad brush could keep one winding from producing any power.

Good point, and in that case, one of the two receptacles should not be working when in 240V mode, either REC1 or REC2.

[MstrCarpenter]

All of you deserve a giant Thank-you! for helping out with this. I've learned a lot here since last night. Following that wiring diagram is tough; I was tempted to print it out and trace the circuits with colored markers. I was informed today that they don't frequently need 240v, so they're not sure how long it's been out. They do need close to the full 30a @120v almost every time they use it, and yes, they do have some cords with 120/240 twist-locs but only use one hot and neutral. (Sometimes only the Owner's electrician can open the panel so we have them install a four wire 240v twist-loc and take what we need from there.) I personally make up all the cord caps, and no one will mess with them; but if they fit together without bending or cutting the prongs, it's fair game to them.

I'll check all the connections again and test each field for power when the "full Load switch" is in the 240v position. Tom, from what you said, I can understand why Blackhat said that one of the 120v receptacles would be dead if one winding wasn't producing power. You also said something about the loads on the two windings being even. I have no doubt that this was ever a concern with the workers using the equipment. Could it be a major reason one of the fields died?

I'll report what I find, and how I fixed it so others can appreciate how this forum's members really strive to help everyone. Thanks again.

B.T.W. That second gen-set needed a pilot to manually pump the gas pedal to keep it running today. One of them has to be back in service fast or three men won't be able to work without the hassle of renting one.

[Roly]

All of you deserve a giant Thank-you! for helping out with this. I've learned a lot here since last night. Following that wiring diagram is tough; I was tempted to print it out and trace the circuits with colored markers. I was informed today that they don't frequently need 240v, so they're not sure how long it's been out. They do need close to the full 30a @120v almost every time they use it, and yes, they do have some cords with 120/240 twist-locs but only use one hot and neutral. (Sometimes only the Owner's electrician can open the panel so we have them install a four wire 240v twist-loc and take what we need from there.) I personally make up all the cord caps, and no one will mess with them; but if they fit together without bending or cutting the prongs, it's fair game to them.

I'll check all the connections again and test each field for power when the "full Load switch" is in the 240v position. Tom, from what you said, I can understand why Blackhat said that one of the 120v receptacles would be dead if one winding wasn't producing power. You also said something about the loads on the two windings being even. I have no doubt that this was ever a concern with the workers using the equipment. Could it be a major reason one of the fields died?

I'll report what I find, and how I fixed it so others can appreciate how this forum's members really strive to help everyone. Thanks again.

B.T.W. That second gen-set needed a pilot to manually pump the gas pedal to keep it running today. One of them has to be back in service fast or three men won't be able to work without the hassle of renting one.

When your checking it, it apperars that there is a terminal block inside the control box where all the leads internal from the generator terminate.  Check between the black and blue leads (should be 120v ) the panel voltmeter shoud read the voltage between the red and white leads (should be 120v also). Normally the main power MC1 & MC 2 are wired directly and do not have brushes.  The exciter will have brushes but it looks as it just has one coil so it is working.   My guess would be the 120/240 switch is bad unless some one did some rewiring.    Roly

[MstrCarpenter]

When your checking it, it apperars that there is a terminal block inside the control box where all the leads internal from the generator terminate.  Check between the black and blue leads (should be 120v ) the panel voltmeter shoud read the voltage between the red and white leads (should be 120v also). Normally the main power MC1 & MC 2 are wired directly and do not have brushes.  The exciter will have brushes but it looks as it just has one coil so it is working.   My guess would be the 120/240 switch is bad unless some one did some rewiring.    Roly

So I said I'd report back; here's what I (finally) found. The switch checked out fine. I only had to remove a couple of leads to isolate it from the rest of the system. The only brushes I found are for the 12v charging circuit, they were fine too. MC2 (one of the primary windings) had both a short and an open circuit. The red wire had burned through (the open) and fused itself to the white wire way up behind the control panel, just outside the generator housing. That would explain why my tests didn't correspond with the wiring diagram. The fix was much easier than finding what needed to be fixed, and I did replace the mini-breakers. Note to self; bypassing a 30a breaker can cause problems, but I still don't understand 30a on 12 ga. THHN.

I could not get the second generator with the stalling problem to stall, but the owner kept trying anyway. I told him I was so good I could fix it just by looking at it!

Put new breakers in a third that had not been used in 2 years because I wasn't the one who bypassed them. The owner didn't trust the guy who did. The carb bowl was half full of sticky varnish goo that wouldn't break down with brake cleaner, and I didn't have carb cleaner. I can barely keep it idling with full choke. I'll clean the carb another day. Another note to self; That's not diesel in the blue fuel can, it's stale gas. Don't put it in the bobcat or back-hoe!

Thanks again to everyone that helped.

[EricU]

Good news you got it fixed.  I also have the capability to fix things by just showing up, although people often dont' seem very satisfied by that outcome.

As far as 30 amps through 12awg wire, I suspect that's considered a free air application, so higher currents are allowed.  I didn't find one for THHN, but some 12 awg wire can take more than that in free air depending on the temperature rating.  A single strand of TW in free air is rated to 30, and everything else will either take 35 or 40 amps. In any event, that's' not covered by the NEC, and the listing agencies can be somewhat lax depending on the manufacturer.

[TDKPE]

12 gauge copper THHN has 90C insulation, and a 30A rating (NEC Table 310.16). The NEC restricts it to 20A in an obelisk note for most common applications, especially those dealing with dwelling unit wiring and cable assemblies like NM (Romex). But not for all applications (like motor circuits). And the NEC is for building installations anyway. The NEC doesn't hold sway over equipment like generators anyway, and like your wall oven or vacuum cleaner with the puny internal wiring, it's tested and listed (hopefully) that way, and is perfectly fine for the intended application.