Gen. set not producing 240v

[MstrCarpenter]

Looking for some advice and knowledge on how duel voltage generators change "full output" from 120v to 240v. I'm attempting to troubleshoot a Mitsubishi MGE6700, I need 240v output. A quick history; over a year ago I had to bypass the circuit breaker simply because the "handles" (for lack of a better term) were broken off during transit. I only moved the wires from the "load" side to the same terminal as the "line" side of the 240v breaker. The gen set did its job that day, and for many other jobs as well. I replaced the breakers today, and cannot get 240v output. It is unknown how long the 240v was out. I double checked the wiring by comparing it to another (same make and model); no errors there. The part that's got me stumped is I read 120v (+or-) across each of the hots and neutral, but nothing across both hots. There is a switch (dpdt) that's supposed to change the voltage. There's one 20a-20v duplex, one 30a-120v twist-loc, and one 30a-240v twist-loc on the front panel. I cannot understand why all of the receptacles are inter-, and cross- connected the way they are. I also don't understand why both "hots" pass thru a small ceramic ring attached to a P.C. board that may be the voltage regulator. The second unit has an intermittent problem of losing power, almost like lack of full fuel flow, but does function properly otherwise. I'll have to deal with that soon too.

 If it helps, I found a wiring diagram here http://www.mitsubishi-generators.com/pdf...0-6700.pdf

[EricU]

That's a complicated circuit, mego pretty quickly.

looks like there are two 120v windings, mc1 and mc2.  The ceramic thing is probably "I/D"  -- current to ??  Looks like it drives a solenoid. No doubt it's a sensor, don't think it affects anything unless it doesn't work.

My brain slipped a few gears when I try to figure out the switch.  Looks like in one position it gives you 120, at least on one of the receptacles.

[blackhat]

The wiring diagram shows a 3 pole switch, not a 2 pole.  Disconnect the wiring from that switch and check that each pole is switching as it should.  Carefully reconnect the switch and then check to see if you have 240v at the line side of the 2 pole circuit breaker when the switch is in the 240 position.

[EricU]

I was going to say that the problem is probably at the switch, one way or another.  I would suggest checking 1,2,3, then 4,5,6, then 7, 8, 9 so you don't have 9 wires all disconnected at once.

[blackhat]

8
.

[blackhat]

Check the brushes as well.

[EricU]

8
.

I count 9 unless some are shorted in a way that doesn't involve a wire.  Like 4 and 9

I'm just getting over the headache I got trying to trace the circuit around that switch.  Going through the sensor really makes a mess out of it. It seems to me that one way the two windings should be parallel (or disconnected), and the other way in series, but I just don't see it.

[TDKPE]

The part that's got me stumped is I read 120v (+or-) across each of the hots and neutral, but nothing across both hots. There is a switch (dpdt) that's supposed to change the voltage.

Check each of the two hots to ground.  Is there 120V there?

There is a switch (dpdt) that's supposed to change the voltage. There's one 20a-20v duplex, one 30a-120v twist-loc, and one 30a-240v twist-loc on the front panel. I cannot understand why all of the receptacles are inter-, and cross- connected the way they are. 

Because there are two windings in the generator, and the triple-pole, double-throw (TPDT or 3PDT) selector switch changes them from parallel to series connection so you can get full power at 120V (windings in parallel) or full power at 240V (windings in series, the default state in the schematic).  In series, the 120V receptacles only get power from one of the two windings, hence the 'half-power' capability at 120V.

I also don't understand why both "hots" pass thru a small ceramic ring attached to a P.C. board that may be the voltage regulator.

That looks like an inductive coil.  Both winding 'hots' pass through this, which activates the idle relay to bring the engine back to speed.

[Roly]

Check each of the two hots to ground.  Is there 120V there?


Because there are two windings in the generator, and the triple-pole, double-throw (TPDT or 3PDT) selector switch changes them from parallel to series connection so you can get full power at 120V (windings in parallel) or full power at 240V (windings in series, the default state in the schematic).  In series, the 120V receptacles only get power from one of the two windings, hence the 'half-power' capability at 120V.



That looks like an inductive coil.  At 120V, both winding 'hots' pass through this, which seems to activate a relay, but I haven't chased it to whatever relay that may be.  At 240V, both leads through the coil are at opposite polarity, so they cancel magnetically, and the relay (or whatever the controller is controlling) does not activate.

Are you testing for 240 v at the twist lock receptacle ? Not just across the two 120v outlet hots .   Roly

[MstrCarpenter]

I'm having a hard time following that switch too. It's even tougher following the actual wires. I can see how why I read 120v at each of the hots on the 240v recp. ; when the switch is down, X and Y are connected. What I can't understand is why it appears that the windings are wired in series, or why regardless of the switch location, I can't find 240v anywhere. I've have noticed that the small ceramic ring is part of the idle control; that part of the system appears to work on 120v load.

I stepped away before I pressed "POST".
Tom, Thanks! now I also get why there's no voltage across the two hots on the 240v twist loc. So in that case, Is it (or it is) possible that the second winding is not generating any power?

Roly, I have checked everywhere for 240v, with the switch in both positions. I did get about 90v on one lead to neutral; not sure where the switch was then, but the same happened on the "working" gen-set.