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Voltage swings

I searched the forum and cannot find a suitable answer so here goes.  I noticed last summer while traveling in August (HOT).  Gen running going down the road.  Both roof AC's running to keep cool.  After a few hours I get a fault light on the inverter control panel and voltage is varying quite a bit.  By this I mean the volt needle on the inverter control panel is waving back and forth like one of those solar powered sunflower toys.  The movement of the needle is constant.  The voltage varies between 110 and 120ish volts.  I shut off AC's power down gen for a few minutes...by then the dash air has lost the battle and we begin to glow.  Restart everything and all is well...for awhile.  The process repeats every few hours.  I have seen similar events on shore power when consuming "too much" power.  (Both roof airs, oven on etc.)  I can only assume it is temperature related, maybe the temp of a componant?  Probably a lousy connection somewhere, but where to start?  Sorry if this is in another thread that I could not find. 
Mike and Mari
'98  36 270 WTFE
Build #5272
Club #17504

Re: Voltage swings

Reply #1 –
Our coach had bad fuel lines and the resulting vacuum leaks caused fuel starvation. 
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Voltage swings

Reply #2 –
Mike,

Does the problem also occur when you are just running one A/C unit, or only when both units are running?

The generators on Foretravel coaches are generously sized - normally, running both air conditioners won't overload them.  To function properly, the generator (electrical section) must be powered at a constant rpm by the engine.  So, first place I would check is the engine.  How long has it been since serviced?  Air cleaner fairly fresh?  As noted by Bob, any interruption in fuel flow (dirty fuel filter, leaks in fuel line) could cause erratic engine rpm, and erratic generator output.  There is a mechanical governor on the engine that maintains a constant rpm - perhaps something there not right?

If the engine is running smoothly, rpm is not fluctuating...then you will need to look at the electrical side.  Voltage regulator?  Wiring connections (power and ground)?  The generator output passes through the ATS before going to your electrical panel - does the ATS seem to switch back and forth from shore power to generator properly?

The voltage on our coach (when running generator) will sometimes fluctuate with varying loads, but never to the point of causing a power interruption.  This condition seems to come and go, and I've never determined what causes it.  So, when you do find the root of your problem, I will be interested in the solution.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Voltage swings

Reply #3 –
When my generator showed these symptoms, I replaced the generator voltage regulator.  Problem solved.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Voltage swings

Reply #4 –
I would start at the simplest, least expensive possibility. Clean and snug all connections first. Then, if that didn't correct the problem proceed to check the generating source and the controls for malfunction.
Nitehawk,  Demolition Lady, & our NEW master, Zippy the speeding BB cat.
1989 Grand Villa 36' ORED
Oshkosh chassis, 8.2 DD V8
2006 Saturn Vue AWD

Re: Voltage swings

Reply #5 –
If this is happening only when running the gen set then the first thing I would check is verify the engine rpm is constant. If it also happens on shore power? Then start your checks on the electrical side, first common point being the transfer switch.

The rythmic motion of the volt meter sure sounds like a generator governor issue.
Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Voltage swings

Reply #6 –
Mike,
If you are running the generator going down the road for air conditioning, why is the inverter on?
What does the coach (generator) AC voltage do when the inverter AC voltage starts to move around? Can you look at both voltages or are you looking at the coach AC (generator or shore power) voltage only ? Also what does the coach voltage look like when this problem happens while on shore power?
You say you have the same problem on generator or shore power, so that would lead me toward the inverter IF you are looking at inverter voltage.

John Duld
1995 U320C SE 40'

Re: Voltage swings

Reply #7 –
If the generator is running, whether the inverter or inverter/charger is on or off makes no difference.

The inverter merely "passes through" voltage from the generator (and activates the charger function of the inverter/charger as well).

Same on shore power-- when the inverter or inverter/charger "sees" 120 VAC from any source, it merely passes through that power-- it does NOT invert.

And as to the comment about "is generator RPM steady":  Absolutely, this is true for fixed RPM (generally 1,800 RPM) generators, but is NOT true for those with newer variable speed (speed based on load) inverters.  Again, very different animals.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Voltage swings

Reply #8 –
I would look first to the voltage regulator.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Voltage swings

Reply #9 –
Quote from: wolfe10 link=msg=264106

And as to the comment about "is generator RPM steady":  Absolutely, this is true for fixed RPM (generally 1,800 RPM) generators, but is NOT true for those with newer variable speed (speed based on load) inverters.  Again, very different animals.

If he has a 98 U270 ? The original generator would be a fixed RPM generator correct?

Fluxuating rpm could be caused by a fuel supply problem, governor problem or voltage regulator problem to name a few.
Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Voltage swings

Reply #10 –
Yes the volts pass through. I'm just one of those guys that if I'm not using it I turn it off. Guess it really doesn't matter.
He says he also has the problem on shore power. I wonder is that with the generator still running or shut down?
I don't remember if the generator or shore power has priority. If shore power has priority then that would eliminate the generator voltage regulator. If the generator has priority then would look toward the regulator.
However he could have more than one thing wrong.You can live with something until it becomes more obvious when more goes wrong. Then diagnosis is more difficult.  These voltage regulators do become erratic as they age.
I think this trouble shooting boils down to does he have this problem on two different power sources or not.
John Duld
1995 U320C SE 40'

Re: Voltage swings

Reply #11 –
Quote from: John Duld –

I think this trouble shooting boils down to does he have this problem on two different power sources or not.

Totally agree.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Voltage swings

Reply #12 –
Thank you for all of the replies.

1).  Gen runs smoothly with no RPM flux and gets regular service
2).  Chuck it does seem to switch between shore and gen as it should...shore power has priority.
3).  John it is the coach AC meter that fluctuates the inverter voltage is steady I think.  That is to say I have not noticed it moving around.
4).  I have seen the voltage less than steady on shore power as well.  Not as bad as on gen and I cannot remember getting the fault light on the inverter control panel unless I start the big motor while plugged in.  That will throw the fault light almost every time.  Probably a seperate issue.
Mike and Mari
'98  36 270 WTFE
Build #5272
Club #17504

Re: Voltage swings

Reply #13 –
Mike,
As others have said, sounds like the generator regulator could be the problem.
Like other operators have solved this problem with a new regulator hopefully it will help you.
Some of them cost more than others. Hope you have the less expensive one.
JD
John Duld
1995 U320C SE 40'

Re: Voltage swings

Reply #14 –
Mike,
  I had a bad battery isolator that was giving me a fault on the inverter panel when the engine was running. Not sure that matches your symptoms exactly.

Mark
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Mark and Tanya
Milton , Florida
US Navy Veteran (DV)
1999 U270 Special 40' CAI , 2015 Jeep Wrangler Sahara

Re: Voltage swings

Reply #15 –
I am having a similar presentation on the Powerwatch needle.  No wag on shorepower.  Checking the digital readout with genset shows a variation of a few volts.  117 - 121.  The needle however was bouncing continuously from 110 or so to around 118.  However, there is no bouncing with genset except when the AC is running.  One or both.  No alarms or error messages on either the Progressive readout or on the digital.

George and Steph
1997 U270 36 Build 5081 "Honu"
1180w Solar 400A lithium all Victron house system
Motorcade 17670, SKP 128300, FMCA F459019
73 VW Camper, 79 VW Camper, 2363 Sunline, and an Arctic Fox 25P