MEP802a - Suspected Voltage Regulator/Quad Windings Issue

[OldWoodsDiesel]

First of all - to all of you here who have served our country - thank you sincerely.
Second - i'm a new member, but have been reading many of the useful posts on here the last couple of years as i've worked on minor things on my generator, so thank you for that as well.

As of last night, i encountered what i'd consider a non-minor issue. The short of it is:
unit was running for about 30 hours straight during a power outage with zero problems.
i shut it down to install a circuit breaker in-line with output (see unit history below for more info on this)
started it back up again (with new breaker in off (open) position but output voltage won't come up (240V 1Ph setting) - first time this has ever happened
Shut it down and consult my uncle who worked on these things for years for the coast guard

Observe field flash relay, then eventually manually flash exciter circuit to no avail
check voltages on regulator terminals and get the following:
Quad: 3.3vac 0.0vdc running, 300ohms off
Excite: 1.5vdc running
120v sense: 6vac running
Voltage adjust knob: 2.5kohm

Oh and my unit does have the quad fuse, BUT only yesterday did I notice that the previous owner had put both terminals on the same side of the fuse, thereby rendering it useless and the windings unprotected - wish I had noticed that sooner!

From my readings on here it seems that either my voltage regulator is shot and/or my quad windings are cooked. Hopefully no damage to the exiciter field or main windings, but I plan to test all those connectoins individually.

Advice from my uncle is to test function without the regulator: first unlook one of the quad wires and fire the engine up. See if voltage on the quad wires comes up to ~60vac (as I've read it should be on this forum). Then separately, remove exciter wires from regulator and apply 6VDC (via latern battery or similar) and main monitor output voltage. Obviously, it won't be regulated, useful voltage, but if it comes up to ~200+ volts, at least it’s a good indicator the exciter windings and main windings are OK.

Anything other than this expected behavior would lead to pulling the cover off the end of the generator head and physically inspecting diodes, etc.

Any other thoughts anyone might care to share?

If the regulator and/or quad windings test as suspect, it seems going with @kloppk's regulator replacement option is a relatively cheap hopeful solution. Any dissension?



______________end of current issue - read below if you want to donate the next 5 mins of your life only_______________________

Now for the back story on the unit in case anyone is interested:
Bought it in '13 for $400 with ~4000 hrs on the unit. Its an 07 Fermont unit, reset by letterkenny depot in 2010 and back from Jalalabad (at least so says the sheets taped to the outside). Definitely saw some service and rebuilds/repairs in its day, but motor looked good via internet auction images (no excessive rust on manifold, etc). All gauges were present and all wiring looked nominal. Only things missing were batteries and alternator. Obviously farmed for parts, so I took a gamble that I could bring it back to live.

Found the alternator and pulley online for $400 total (now an $800 generator), changed, fluids, installed $150 worth of batteries (now a $950 generator) and fired her up for the first time. Much to my pleasant surprise, she roared to life and put out clean power on whatever output I set her to. Used her about half a dozen times during power outages (we are deep in the easter portion of Penn's Woods and lose power regularly).

Fast forward 3 uncanny years with no outages more than a few hours. During these years, I kept her in a shed with a Noco charger on the batteries so ensure she started when needed (had dead batteries after one extended storage period and didn’t want to go through the rigomarole of charging batteries with my truck again). Anyway, I finally build a proper shed for her to live in next to the house permanantly - with aux fuel line from my 1100 gallon heating oil storage tanks - and the power goes out a few weeks later. I happy fire her up, check that ll gauges are nominal and go inside. All is well for a few hours, but then the power turns off. The output circuit interrupter had tripped - and ammeter is bounding all over the place. Take off the 3 controls side panels and find a MASSIVE mouse brothel. Cleaned it out, checked and cleaned connections for days and days, but all to no avail. By the by, I'm pretty convinced my trickle charger on the batteries in the shed made a perfect little winter time heater for these more annoying of God's creatures.

Anyway, I troubleshot that for a while more (only thing I didn’t check was the shunt resistors themselves), but after convincing myself that there was no actual short or internal overload present, eventually gave up when the next power outage came along and took power directly from the hot side of the circuit interrupter relay. Monitored everything closely with an ammeter and both the generator and house were happy for about a weeks worth of cumulative outages

Fast forward another couple weeks to the present and I decide to get a little safer by putting a 25A 240V slow-blow circuit breaker right after the voltage reconnection switch. For 50 bucks I figured the extra safety of not burning up the generator or my house should a short occur between the unit and my breaker box was worth it.

Well, she never recovered from that install - though immediately after the failed startup, I removed the breaker with no change. I can't see how the breaker is the problem, but rather figure that 30 hr run was the last few hours that some component had in it, and the breaker addition is just coincidence.

OK, there's my generator story. Thanks for reading if you made it this far. Looking forward to any wisdom you much more experienced folks may have to offer.

 

[kloppk]

When you start the set and hold S1 in the START position you ought to get ~120 VAC at the convenience outlet and see normal voltage on the sets AC voltmeter.
If you do that confirms the generator will put out power and the flashing function is working.

When a set is running normally and with no load on it you should see the following approximate voltages at the VR
Terminals 1 & 2 1.07 VAC
Terminals 3 & 4 120 VAC (AC voltage sense into the VR)
Terminals 5 & 6 5.0 VDC (DC voltage supplied by the VR to the gen head field windings)
Terminals 7 & 8 69.1 VAC (AC voltage from Quad winding to power the VR)

If you're not getting ~69 VAC from the Quad windings then then they may be toast as well as your VR.
Since the previous owner bypassed the fuse next to the VR I suspect that the VR got hit with a voltage spike, shorted out it's diode bridge which in turn caused the Quad winding in the gen head to burn out.
I suspect the previous owner kept blowing the fuse and got tired of replacing it so they jumped the fuse out.

Let me know if you need one of my VR's.

 

[OldWoodsDiesel]

Awesome. thanks for the quick response.

When you start the set and hold S1 in the START position you ought to get ~120 VAC at the convenience outlet and see normal voltage on the sets AC voltmeter.
If you do that confirms the generator will put out power and the flashing function is working.

i didn't probe the convenience outlet (or exposed main output wires), but the voltmeter on the unit definitely does not come up to nominal (240 or 120 pending settings) with the S1 held in start. I believe that was my uncle's logic in going at it with the 6V battery - remove the question of a potentially bad field flash circuit and test only the output capability of the main windings. if that test fails, big problems in the output or exciter windings may be the case. Will test as you suggest first, though.

When a set is running normally and with no load on it you should see the following approximate voltages at the VR
Terminals 1 & 2 1.07 VAC
Terminals 3 & 4 120 VAC (AC voltage sense into the VR)
Terminals 5 & 6 5.0 VDC (DC voltage supplied by the VR to the gen head field windings)
Terminals 7 & 8 69.1 VAC (AC voltage from Quad winding to power the VR)

If you're not getting ~69 VAC from the Quad windings then then they may be toast as well as your VR.
Since the previous owner bypassed the fuse next to the VR I suspect that the VR got hit with a voltage spike, shorted out it's diode bridge which in turn caused the Quad winding in the gen head to burn out.
I suspect the previous owner kept blowing the fuse and got tired of replacing it so they jumped the fuse out.

i agree, it does seem logical that may be what happened - i'm pissed at myself for not noticing that bogus fuse connection (or non-connection) before.

My biggest fear is that the mices (or their detritus) done got into the rotating assembly and caused damage to the main windings or exiciter windings - rendering the whole unit nearly worthless. Unfortunately (or maybe fortunately for my metal state), i'll be a away a few days and will have to look into all this when i get back.

Let me know if you need one of my VR's.

Will do - but i do have a question, out of curiosity - In having read about your VR design, clearly the benefit of not needing the quad windings to be functional is a huge help, but how does that work? voltage divider on the 120V sense circuit? no need to give away the secret sauce if you don't want, i'm just curious.

Thanks again.

 

[kloppk]

PM sent

 

[OldWoodsDiesel]

Ok - i've finally had a chance to run through some additional testing on this.

With the unit up and running and the quad leads disconnected from the VR, the quad output is only 5 VAC. As this number reportedly should be ~60VAC, I believe this means that the VR did kill he quad windings as suggested above.

Then with VR completely disconnected, i started the unit up and applied 6V to the exciter windings. With the unit output set at 240V/1Ph, I measured an output of 120VAC at the load terminals. With the unit set at 120V/1Ph, i measured an output of 60VAC at the load terminals. I can't see how a short or open in the main output windings would lead to exactly half of the rated out put under these conditions - i'd expect it to be an all or nothing thing. that said, my 6V supply to the exciter windings was just a 6V lantern battery and the voltage drew down from ~6.5V under no load to ~5.8V when connected to the exciter windings. My guess (again, no electrical engineer here) is that the current output from the battery was not sufficient to generate enough field in the exciter windings to get the output voltage up to where it should be. I.e. it is a very bad/dumb voltage regulator.

I'm tempted to go pick up another lantern battery and hook them up in parallel and see if the output voltage comes up farther. but then again, i think i'm confident enough that the voltage regulator is the cuplrit and i should just get a new one on order before the power goes out again!

Any additional thoughts/feedback are much apprecaiated.