Onan generator voltage too high and low

[falconman]

Yes I agree that our two issues may not be of the same cause. My voltage/ frequency readings are taken after the ATS via the Aladdin system monitor. I have checked and tightened all the connections. I did install a new ATS some time ago so that caused some concern. I have not been able to check the voltages at the generator since they are intermittent and have not returned over the last several times using the generator. I plan to continue my troubleshooting. As far as the OP's issue, with all the discussion about the ATS, I never saw where the generator had been isolated from the rest of the coach to try and determine the source. I might have missed that but I would have thought that would have been the first step, perhaps it was.

[shiggs68]

How this problem got off on the ATS is beyond me. Too confusing the read thru all the mis-stated or incorrect posts.

First, often the normal Neutral to Ground bonding does not always hold true from a generator. The generated voltage is not referenced to ground like a shore power distribution system. With that said, the different voltages to ground have no meaning other than to say Neutral and Ground are not bonded.

The fundamental problem is the differences between the two L1 and L2 readings to Neutral. This clearly indicates a voltage regulator problem internal to the generator. Load or no load, these voltages are monitored and regulated to be a consistent 120vac.

That problem should be focused on first then determine if there are any other problems after the regulator is repaired.


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[ShapeShifter]

Originally Posted by falconman

My voltage/ frequency readings are taken after the ATS via the Aladdin system monitor. I have checked and tightened all the connections. I did install a new ATS some time ago so that caused some concern.

While a bad connection in a transfer switch can cause some voltage variations, there is no failure mode of the transfer switch or wiring that can cause frequency variations. If you are seeing such frequency variations, there can only be one cause: the generator itself. (There is one other possibility in that the test instrument making the measurement is failing and the power is actually good but not being reported properly.)

Originally Posted by shiggs68

The fundamental problem is the differences between the two L1 and L2 readings to Neutral. This clearly indicates a voltage regulator problem internal to the generator. Load or no load, these voltages are monitored and regulated to be a consistent 120vac.

I agree with everything you are saying in your post, and agree that a voltage problem will often be in the generator. The OP's 10 KW generator is a true split phase 240 volt generator where the two hot leads are opposite polarity with each other compared to the neutral. As with any split phase supply, an open neutral can cause one hot voltage to be too high, and the other to be too low by the same amount. This is what the OP is reporting and what I think is the case.

If he were reporting both lines being high or low, or the errors were not equal and opposite, or if he had a smaller generator (which isn't true split phase and has both hots of the same polarity) then I would strongly suspect the generator.

I agree that the voltages right at the generator should be measured. But in this case, I'd be willing to bet a beer by the campfire that the voltages will be proper when measured right at the generator. While it hasn't been reported, I'm sure that the expensive diagnostics performed by Cummins Crosspoint did that test early in the procedure before determining that the problem was in the transfer switch (which I'm sure is a bad neutral relay contact.)

[shiggs68]

I agree to a point. Without understanding how the split windings and exciter windings are designed, it is impossible to assume the failure mode.

With that said, the correct troubleshooting is to start at the generator with a meter and work towards the load.


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[TQ60]

A bad ground to neutral may not cause this but a good connection helps...

Some state they do not understand so some basics.

Normal 50 amp system is 240 vac.

With 2 120 vac circuits in series so to speak.

Imagine a 2 cell flash light with 2 batteries now place a connection in the middle.

You have battery 1 and battery 2.

Now imagine adding 3 light bulbs in parallel to just one battery, connect to top of one battery and that connection in the middle.

All 3 same brightness.

Now add a single bulb to the OPPOSITE battery and it will be same brightness as the other 3 but being one instead of 3 the current is different but it is same voltage and brightness.

The light bulbs are connected in series across the 2 batteries in series and the wire in the middle carries the current of 2 of the 3 bulbs on one battery and the current from the single bulb flows through one of the 3 others.

That center wire carries the current that is NOT THE SAME on both legs.

Now if you cut the above wire from the center then the 3 bulbs will go dim and the single bright as the 2 sets are not the same and the voltage across each will be different.

The wire connected in between the batteries performed the same function as the white neutral wire.

Back to your mh.

The TOTAL voltage is correct at 240.

Each side measures different to the neutral wire so the current flows through each side is different but the neutral is not carrying the out of balance current.

There is a problem with the neutral between the source and the distribution panel.

Either a loose connection inside the generator or poor connection somewhere between the genny and the panel buss.

Stupid simple to check as you already know how to measure it in the first post.

You need to measure at the generator connections.

Sorry for long note and batteries not best example but should be close enough for demonstration.

[nothermark]

Originally Posted by shiggs68

I agree to a point. Without understanding how the split windings and exciter windings are designed, it is impossible to assume the failure mode.

With that said, the correct troubleshooting is to start at the generator with a meter and work towards the load.


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That works. Better yet shut off all power and start with an resistance check from the neutral on the generator to the transfer switch. It sounds like the neutral may be open or the ground in the transfer switch is not there.

FWIW the voltage of floating connections is a combination of loads on the hot legs dividing power and whatever stray coupling is going on. The less load the more coupling comes into play. I would not try to figure out a circuit like that. It's too big a can of worms. The difference between safety ground and neutral is enough to know they are not connected so fix that and see if there are more problems. The place to fix it is at the transfer switch generator connections. That is per code. If that does not fix it look at the neutral and grounds between the generator and transfer switch and the connection through the transfer switch. They have to switch the neutral through the transfer switch or they cannot ground the generator side without messing up the ground to neutral when on shore power. At this point it can be a bad neutral on the genset, a bad ground to the genset, or a bad transfer switch. I cannot tell and do not recall if he really fixed it yet. ;-) Based on Cummins telling him transfer switch I could assume the saw a difference on either side of the switch so assumed a bad connection through it.

[jdwky]

OK now I'm REALLY frustrated... After getting the "diagnosis" from Cummins Onan, I ordered a new transfer switch. Installed it today........ SAME PROBLEM. It's not the transfer switch.

Must be somewhere between generator and ATS.

To the folks who wanted confirmation I tested at the generator, yes, with the wires disconnected from the genny, it gives normal readings.

I traced the wires best I could, but they are hidden well along the center beam of the coach. I will post some pics in the next post, please let me know if you see anything fishy. I opened the junction box that is abeam the genny, no signs of corrosion or water inside and everything was tight.

Here's the fishy part, I received a slight electrical shock as I was tightening the screws on the junction box via my screwdriver. Faint, but noticeable (I've taken direct 120v hits before, those were jolting). I've also felt a faint shock when touching metal on the 50amp cord reel while finagling around in the basement working on the ATS. Seems somewhere there is a loose wire.... I was hooked up to shore power at the time.

To reiterate though, nothing changed on the motorhome before this problem occurred. We were dry camping with generator running fine for ~18 out of the previous 24 hours.

Please, any ideas, before I drive this rig into the river??

[jdwky]

Junction box 2 feet from genny.

Disconnected wires from AC posts.

AC posts on top of genny give good readings when Unhooked.


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2013 Wrangler JKU toad
2006 Vans RV-9A

[nothermark]

Have you figured out where the ground to neutral connection is made? It should be around the transfer switch. With the power off have you checked for continuity between neutral and safety ground on the generator side of the transfer switch? These should be connected together somewhere in that chain. It sounds like you have an open somewhere in there. At this point I would not rule out the idea that the factory forgot to do it.

I would also check the chassis connection to the generator assuming there is a braid grounding jumper to provide a ground path around any vibration isolators.

[jdwky]

If factory forgot to do it, would it have worked for three years with no problem? Just doesn't make sense to me. I will attach some pics of the transfer switch, maybe you can point out where the safety to neutral ground is for me. I really don't know.

Shore power in is top left, genset top right.


2012 Entegra Aspire
2013 Wrangler JKU toad
2006 Vans RV-9A

[dpinvidic]

You have proven that the genny is good by measuring at that point.

Have you actually worked your way down stream with a volt meter taking the same measurements.
The power starts at the genny -> transfer switch -> inverter -> breaker panel -> wall plugs.

And you may have a EMS system in line also.
You should measure the input and output side of each of these devices.
Since it worked from the factory, it is likely a poor connection, or a broken/damaged neutral/grnd wire.
I did not read every post, but if you still have a problem, I don't think you did this.

Regards,

Dan

[ShapeShifter]

Originally Posted by jdwky

Must be somewhere between generator and ATS.

I agree, if it were after the transfer switch, it would happen on shore power as well. While it's possible that the new transfer switch also has a fault (or the wires were connected improperly) I think that's really stretching it. I'd dismiss the transfer switch until all other possibilities are eliminated.

Here's the fishy part, I received a slight electrical shock as I was tightening the screws on the junction box via my screwdriver. Faint, but noticeable (I've taken direct 120v hits before, those were jolting). I've also felt a faint shock when touching metal on the 50amp cord reel while finagling around in the basement working on the ATS. Seems somewhere there is a loose wire.... I was hooked up to shore power at the time.

This is quite possibly an artifact of the problem you are trying to track down. It generally points to a grounding problem. I'd solve the major problem first, as fixing that might fix your mild hot skin problem.

Please, any ideas, before I drive this rig into the river??

Hold your breath as you go in?

Originally Posted by jdwky

Attachment 100070
Junction box 2 feet from genny.

It looks like there has been water collecting in there for a while, and then evaporating. You might want to get a new cover plate gasket before buttoning things up? It looks like a standard weatherproof junction box, any home center should have a replacement (but you might not be able to get just the gasket without also getting a new cover plate.)

Since water obviously got in there, it might be a good idea to open up all of those wire connections and make sure they are clean. Clean them up (and replace wire nuts?) if they aren't.

Attachment 100071
Disconnected wires from AC posts.

Those connections (especially the neutral) look rather dirty and oxidized. It's possible that's the problem right there? I'd clip off the exposed ends of all of those wires, and strip back to bright shiny copper.

Attachment 100072
AC posts on top of genny give good readings when Unhooked.

If the wires look that dirty/oxidized, it's probably worth cleaning inside those connections as well. If you have a tiny wire brush to get in there, it may help. It may also help to remove the wires going into the other side of that junction block and see how dirty those are: clean that side up as well.

Originally Posted by jdwky

If factory forgot to do it, would it have worked for three years with no problem? Just doesn't make sense to me.

I agree. Lack of ground/neutral bonding could cause the tingle you felt, but I simply don't see it causing the voltages that you are seeing relative to neutral.

Clean up those connections and connect everything back up, and then test it. If you're still getting the bad voltages, try this: (some of the steps may seem redundant and you might be tempted to go for broke and do the full end-to-end test first, but I have all the steps in there, and in that order, to make sure the test setup is working before getting too far into it.)

1. Shut down all AC power sources (generator, inverter, shore power)
2. Plug a long three prong extension cord into an inside outlet
3. Using a meter in resistance (continuity check) mode, measure between the neutral of the extension cord (wide flat slot) and the neutral wire at the transfer switch (the one that goes to the breaker pane, looks like either terminal 4/T2.) There should be continuity - low resistance. (If there wasn't, you would also have problems on shore power, so a lack of continuity shows a problem with the outlet/cord/meter you are using.)
4. Now, measure between the neutral of the extension cord and the generator neutral at the transfer switch (Terminal 3/L2 on the right hand contactor?) If there is continuity, then the transfer switch is normally in the generator position, and you can skip to step 5. If there is no continuity, then the transfer switch is normally in the shore power position: if this is the case:
   • TEMPORARILY put a jumper on the neutral line across the contactor (3/L2 to 4/T2)
   • DO NOT attempt to run the generator or plug into shore power with this jumper in place!
   • Repeat the measurement, verify that there is continuity between the extension cord neutral and terminal 4/T2
5. Measure between the neutral of the extension cord and the TB2-3 terminal of the generator terminal block. There should be continuity. If there is, then you don't have an open neutral and it's time to think of new ideas.
6. Assuming there is no continuity to the generator terminal block, open up the connections in that junction box that's 2 feet from the generator. Is there continuity to there?
   • If not, there is a break in that wire from the junction box to the transfer switch, try to trace the wire and see if there are any more junction boxes.
   • If there is continuity to there, measure for continuity between that junction box and the TB2-3 generator block terminal. No continuity means a break in that wire, continuity means that something went wrong along the way: connect everything up and start over.

If you put in a jumper in step 4, REMOVE THE JUMPER before trying to restore ANY power source!

Basically, the long extension cord is giving you an easy way to connect to one end of the neutral path: the probe from the meter should be able to be stuck in the blade socket of the extension cord and stay there. You can then drag the extension cord to the various other places where you are making measurements, and you know that one side of the meter is already in place. You're just tracing the neutral wire back to the generator, looking for the place where you lose continuity. Once that happens, you know the problem is somewhere between that point and the last place where you had the continuity. Look for additional splices or breaks between those two points - each time you find one measure up to that point, and you will be able to tell if the break is before or after that splice.

It's a basic divide and conquer strategy.

Good luck!

[jdwky]

Originally Posted by ShapeShifter

I agree, if it were after the transfer switch, it would happen on shore power as well. While it's possible that the new transfer switch also has a fault (or the wires were connected improperly) I think that's really stretching it. I'd dismiss the transfer switch until all other possibilities are eliminated.


This is quite possibly an artifact of the problem you are trying to track down. It generally points to a grounding problem. I'd solve the major problem first, as fixing that might fix your mild hot skin problem.


Hold your breath as you go in?


It looks like there has been water collecting in there for a while, and then evaporating. You might want to get a new cover plate gasket before buttoning things up? It looks like a standard weatherproof junction box, any home center should have a replacement (but you might not be able to get just the gasket without also getting a new cover plate.)

Since water obviously got in there, it might be a good idea to open up all of those wire connections and make sure they are clean. Clean them up (and replace wire nuts?) if they aren't.


Those connections (especially the neutral) look rather dirty and oxidized. It's possible that's the problem right there? I'd clip off the exposed ends of all of those wires, and strip back to bright shiny copper.


If the wires look that dirty/oxidized, it's probably worth cleaning inside those connections as well. If you have a tiny wire brush to get in there, it may help. It may also help to remove the wires going into the other side of that junction block and see how dirty those are: clean that side up as well.


I agree. Lack of ground/neutral bonding could cause the tingle you felt, but I simply don't see it causing the voltages that you are seeing relative to neutral.

Clean up those connections and connect everything back up, and then test it. If you're still getting the bad voltages, try this: (some of the steps may seem redundant and you might be tempted to go for broke and do the full end-to-end test first, but I have all the steps in there, and in that order, to make sure the test setup is working before getting too far into it.)

1. Shut down all AC power sources (generator, inverter, shore power)
2. Plug a long three prong extension cord into an inside outlet
3. Using a meter in resistance (continuity check) mode, measure between the neutral of the extension cord (wide flat slot) and the neutral wire at the transfer switch (the one that goes to the breaker pane, looks like either terminal 4/T2.) There should be continuity - low resistance. (If there wasn't, you would also have problems on shore power, so a lack of continuity shows a problem with the outlet/cord/meter you are using.)
4. Now, measure between the neutral of the extension cord and the generator neutral at the transfer switch (Terminal 3/L2 on the right hand contactor?) If there is continuity, then the transfer switch is normally in the generator position, and you can skip to step 5. If there is no continuity, then the transfer switch is normally in the shore power position: if this is the case:
   • TEMPORARILY put a jumper on the neutral line across the contactor (3/L2 to 4/T2)
   • DO NOT attempt to run the generator or plug into shore power with this jumper in place!
   • Repeat the measurement, verify that there is continuity between the extension cord neutral and terminal 4/T2
5. Measure between the neutral of the extension cord and the TB2-3 terminal of the generator terminal block. There should be continuity. If there is, then you don't have an open neutral and it's time to think of new ideas.
6. Assuming there is no continuity to the generator terminal block, open up the connections in that junction box that's 2 feet from the generator. Is there continuity to there?
   • If not, there is a break in that wire from the junction box to the transfer switch, try to trace the wire and see if there are any more junction boxes.
   • If there is continuity to there, measure for continuity between that junction box and the TB2-3 generator block terminal. No continuity means a break in that wire, continuity means that something went wrong along the way: connect everything up and start over.

If you put in a jumper in step 4, REMOVE THE JUMPER before trying to restore ANY power source!

Basically, the long extension cord is giving you an easy way to connect to one end of the neutral path: the probe from the meter should be able to be stuck in the blade socket of the extension cord and stay there. You can then drag the extension cord to the various other places where you are making measurements, and you know that one side of the meter is already in place. You're just tracing the neutral wire back to the generator, looking for the place where you lose continuity. Once that happens, you know the problem is somewhere between that point and the last place where you had the continuity. Look for additional splices or breaks between those two points - each time you find one measure up to that point, and you will be able to tell if the break is before or after that splice.

It's a basic divide and conquer strategy.

Good luck!

Good stuff right here! Will work on this tonight, thanks!

[shiggs68]

Based on the picture of your transfer switch, it appears that the bonding between neutral (white) and safety ground (copper) is accomplished by the light gauge Brown wire going from the ground buss (left side) to the White wire on the right contractor.

It looks like there is a small gauge lug under that White wire.

I'd say, remove all power and remove those to verify. There may be a bad crimp there.


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