Forum Discussion

swp5767's avatar
swp5767
Explorer
Aug 06, 2013

Generator putting out too much power

Hello all! I have an Onan 4.9BFA 4000w gas generator. There is a plug on the cable the way it was sold to me. The PO used this for a race car trailer to power one AC unit and some lights. He said he had no issues.. I would have to say the lights must have been really bright.

Here are some pics of what I have..

Below is the reading while its running.


Here is where the other end of the wire is.



Here is the schematic of the model I have.



What im not sure is, is it hooked up correctly? I tried testing different points on that termimal block and I either got 0 volts or 148 volts. Nothing in between.

Any advice would be helpful.
  • This is what did the trick. I removed tention from this spring till the voltage came down to 120VAC. With a hefty load on the unit, the power stays steady.



    Thanks for all the help!!
  • SWP, get an Onan service manual (can be ordered online from Onan if nobody's got one). Read up on how your model regulated frequency & voltage, and make sure you adjust with the right screw.

    Jim, "What you are experiencing is not a problem. It is an undocumented feature. Thank you for calling Microsoft."
  • copeland343 wrote:
    If meter is correct you will need to slow rpms down a little. Using the speed adjustment screw maybe a 1/16 of a turn.


    There is only one screw to adjust, but when I back it out some, it does not make contact anymore nor does the RPM lower anymore.. I can physically push it till the screw makes contact again and the RPM is lower, but as soon as I let go, it goes back into place.

    There must be more to that setting.. I don't see any kind of voltage regulator on this unit.
  • enblethen wrote:
    Have you checked the frequency?
    Some change voltage and frequecncy as RPMs increase.


    The voltage does lower when the RPM's lower. The one thing I cant test is the engine RPM. So I can get it down to 120 range, but the engine seems to be running too slow.
  • If meter is correct you will need to slow rpms down a little. Using the speed adjustment screw maybe a 1/16 of a turn.
  • After some more reading, these older Onans regulate power by engine RPM.
  • I noticed the voltage on the Onan I had was high when there was not a load on it. The load lowered the RPM slightly.
  • Not to ask the obvious but have you verified the meter on a known voltage source.
  • Have you checked the frequency?
    Some change voltage and frequecncy as RPMs increase.