We bought our motorhome used and not running!!! My husband is a great mechanic and got it running. He had to clean the fuel tank, put in a new fuel pump and it fired right up...we got lucky! The previous owner had fiddled with the Onan generator and we were given a box of parts he hadn't reinstalled. My husband rebuilt the engine and it runs great but puts out too much voltage. He contacted a company called Flight Systems and run a bunch of diagnostics to determine what was wrong. They sold us a new voltage regulator. He installed it but it got fried....so they sent us another one but generator is still putting out too much voltage. When we fire it up, it puts out about 200 volts and settles to 170. He hasn't connected to the motorhome until he gets this figured out. Any suggestions would be so appreciated!

Lots of hits on that on google. Perhaps it's running too fast.

"He hasn't connected to the motorhome until he gets this figured out."And be very sure it is fixed before you do.

Old man has the answer for the first thing to check.

thanks! I will let my husband know to check that

The motor would have to be screaming fast to put out that voltage

Onan Marquis 5500 put out too much voltage | Good Sam Community

SuzanneNS
Explorer
Jul 06, 2020
Thank you all! My husband is reviewing everything now. Hopefully we find a fix!!
MrWizard
Moderator
Jul 04, 2020
Here is a connection diagram for different voltages
The one in the Yellow box, is the one I think you need, 2 wire neutral grounded

Click For Full-Size Image.

Red box is... 2 wire neutral isolated aka floating like a portable generator

Click For Full-Size Image.
zigzagrv
Explorer
Jul 03, 2020
Might be comparing apples to oranges, but my Generac Guardian 5500 recently started acting up and was putting out 153 volts after driving through much rain. Removed cover to expose control board and found it was covered in a thick layer of dust and grime and was damp from the previous days rain. After cleaning the dust off, I sprayed the contacts and plug with electronic contact spray. That fixed the problem.

You said you replaced the control board, but did you clean the plug?

Also, after cleaning the control board, I discovered a tiny potentiometer which, according to the manual, is used to adjust the output voltage.
Kpackpackkelley
Explorer II
Jul 03, 2020
Need the full model number
MrWizard
Moderator
Jul 03, 2020
Get the model #
From the data plate on the onan
Download the service manual
All of these older generators are capable of putting out 230v, it depends on how the 4 output wires from the stator (out put windings) are connected,
At 200v , it is probably connected for 230 but running too slow to produce full voltage
Flight system control boards are the best there is
STBRetired
Explorer
Jul 03, 2020
The engine is supposed to be running at 1800 RPM. Look at the rating plate on the right side.
Dusty_R
Explorer
Jul 03, 2020
Check the RPM the engine is putting out and find out how many RPM it's rated at.
MEXICOWANDERER
Explorer
Jul 02, 2020
The motor would have to be screaming fast to put out that voltage
SuzanneNS
Explorer
Jul 02, 2020
thanks! I will let my husband know to check that
bgum
Explorer
Jul 02, 2020
Old man has the answer for the first thing to check.