Forum Discussion

KendallP's avatar
KendallP
Explorer
Apr 29, 2014

Onan 4.0 BFA - Hot Rodded! But...

OK. "Hot Rodded" might be just a wee bit of an exaggeration, but...

I'm pretty proud of my tuning job... regardless of the lack of any real skill required.

So I began to notice the old '86 Onan, even after a complete tune-up, would not hold voltage well with much of a load. In fact... as I recall, I believe my first indication may have been a high charging voltage from the old Magnetek 6300.

I got a hold of the service manual and went through the steps, i.e. first the idle, then the main mixture screws. Problem still there.

So the remaining, most likely candidate was the governor spring. If almost 30 years old... then... yeah. Might be a bit worn. But all the digging in my pockets yielded no fruit. And patience is for wimps and smart people. My family needed to go camping, darnit!

Now many of you know that this old Onan relies on RPMs to determine voltages and frequencies. Not ideal. Just ask Ol' Mex to weigh in on that. You might be in for an earful.

The manual calls for adjusting the governor for an idle voltage of 127 and frequency of 61 with the engine warm. Tolerances are basically 5% on either side of 60 hz, i.e. 57-63 hz with a maximum, no-load voltage of 132 and a minimum, full-load voltage of 108. When it comes to my A/C pump... I don't like that 108 figure one bit.

Now there's an adjustment for the spring. But I figured that would only raise the idle voltage. A weak spring can't really be adjusted away. Unless...

It occurred to me that the spring attachment location on the governor arm is adjustable. So why not use a little, basic physics, i.e. leverage! Worth a try, right?

Long story short... with a little trial and error... using my Kill-a Watt as a guide... with a warm engine... and PRACTICALLY REGARDLESS OF LOAD... I was able to garner... get this...

~128V (verified with another meter)
59.9-60.1 hz
Power Factor - 1

My A/C pump never had it so good. And the Magnetek appears to be very happy, as well.

Now sure... I'm guessing my sine wave is not smooth as a baby's behind. But this is definitely good enough for the girls I go with!

With one exception...

A bit of a surprise...

Under a heavy load, i.e. A/C and 1500W electric heater (my method for exercising 'er,) the voltage actually CLIMBS into the 132 mark. The frequency remains near 60.

So...

I know the manual states that 132V is the upper tolerance... and, to a degree, I generally like more voltage than less, but...

What do you guys think of this voltage?

Gramps (Mex.) I'm expecting you to weigh in, here.
  • JiminDenver's avatar
    JiminDenver
    Explorer II
    Apr 29, 2014
    hey I have some left over nitro-methanol from my RC days, some of it 25% nitro. I'm sure it would perk the old generator right up. In fact I bet it would get a 3100i to run my AC....once.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 29, 2014
    Uhhhhh....

    Would you settle for nitroglycerin, sub-lingual? Turbo? Turbot?

    Chrome header, yeah last time that happened the bumper left my forehead bleeding.
  • KendallP's avatar
    KendallP
    Explorer
    Apr 29, 2014
    smkettner wrote:
    I thought I was going to read about chrome headers and nitro-methane fuel injection.... sheesh

    Heh heh heh. Made ya' look. Suhhhcker. :)
  • time2roll's avatar
    time2roll
    Nomad
    Apr 29, 2014
    So make the initial setting 3 volts lower.

    I thought I was going to read about chrome headers and nitro-methane fuel injection.... sheesh
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 29, 2014
    Yeah I know, reality is a bummer. Try as I might to avoid it, things-as-they-are is a real monkey on my back.
  • KendallP's avatar
    KendallP
    Explorer
    Apr 29, 2014
    MEXICOWANDERER wrote:
    Where did I see a downloadable Onan factory service manual?

    This is the one I used. I printed the pertinent pages to pdf. The governor is on pg. 23.

    And yeah... I said in the beginning that you had an opinion on the old Onans. And I recall that sweet mod you had made.

    Now how many parades of mine are going to try and rain on today, Gramps??? :)

    No, I appreciate your advice, as always.

    I'm comfortable with the tuning method I've employed. She reacts very well and adjusts quicker than ever to various loads. In fact, she's never run so well.

    My main question for you was in regard to the peak voltage. Murphy requires I adjust it down now... since you recommended it. Otherwise I'll have no one to blame but myself if I fry something. And I like to reserve my right to blame something or someone... else.

    Thanks!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 29, 2014
    My recommendation is to get your hands on a factory manual. Chris Bryant is right on the mark about many of the older Onans. Onan was famous for building machines so complex with coils, chokes and transformers, it boggles the mind. The governor does more than "control" engine speed. It averages out load surge requirements and then complicates things even further with speed "response time".

    Servicing an Onan, is like painting a by-the-numbers picture. "Start here, go to there, if this does this, try that, but if that causes ....."

    I purchased a permanent Woodward Electronic Governor to follow me into the grave. It maintains 60.0 Hz until the motor cannot sustain speed due to overload.

    I loved coupling the older Onan's with the BW Magnaek 775-2 ferroresonant charger. "How Can I Charge My Batteries Faster?" In went a matchbook cover shim thus raising the engine speed to 63 Hz. And voltage resonance to 14.5

    The older GM Delco 20Kw railroad reefer generators were similar. A manual is essential to get to where you want to be.

    Personally? I do not like voltages above 127.

    With 132 volts you risk voltage peak-to-peak values in excess of many components inherent in electronic systems. Your peak to peak voltage now must be in the 170's. Couple that with an induction motor switching on and off and that makes my skin crawl. We used to laugh and label the Onan waveform pant-angular.

    Where did I see a downloadable Onan factory service manual?
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Apr 29, 2014
    I seem to recall that there is a voltage adjustment on some of those- involves changing a transformer tap.
  • KendallP's avatar
    KendallP
    Explorer
    Apr 29, 2014
    JiminDenver wrote:
    I guess the questions are did the generator do it before and what is the effect of the high voltage on the various devices you run? I usually don't feel good pushing the limits, especially with older equipment.

    Only the second question. The generator definitely didn't do this before I adjusted the governor. My concern is in regard to the effects of 132V on various components.

    But as I mentioned above, this higher voltage only occurs in rare cases. So if components can handle 132V for a few minutes, on a very rare occasion... then I'm probably good to go because I'm thrilled with the way it acts with more typical loads.

    But if I'm told I should absolutely not allow 132V, ever... then I will readjust the governor spring down a hair. I'm sure I will lose my perfect performance at typical loads, though. AND it's a bit of a PITA to try and get it just right. We're talking almost microns of movement in either direction here... almost. Might be a millimeter.
  • KendallP's avatar
    KendallP
    Explorer
    Apr 29, 2014
    j-d wrote:
    Seems odd to me that the hZ at a higher voltage is lower than at a lower voltage.

    Ah, but I didn't say that. I'm going off of memory a bit, but I had stated that voltage was up, but frequency still "remains near 60." It's a hair over, but not by much. I doubt even 61. Definitely nowhere near 63, though.

    Yes, with the book saying that 132V and 63 hz are at the top of the tolerances... one would ASSume that 132V should get you around 63V. But it doesn't. That's a little odd, yes. But I'm not going to stress about it. I think I'm good on cycles.

    The concern is more in regard to anything hard-wired or plugged in to a 132V circuit.

    However, bear in mind that this voltage only occurs when I'm running 'er at somewhere near 3300W or so. This will very rarely happen in everyday camping. At most it could happen when we're running the A/C and then flip on the microwave. But how long is that going to last?

    First off, we almost never use the microwave. Secondly, if we did, it wouldn't be for long. And afterward the voltage would drop right back down to around 128.

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