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Onan Generator Power Output Quality

threejeeps

Registered
I am wondering if anyone has some information (quantitative, pictorial, or even anecdotal) regarding the quality of the power for BF, BFA, NG, and CCK generators.

Some specific questions come to mind:
1) How 'good' is the sine wave compared to grid?
2) When properly set up, what is the worst case frequency drift when large loads (e.g. > 80% rated gen capacity) come on?
3) generally speaking, what models have 'good' looking sine waves? Which ones don't?

I could see some quantitative values for #1 and #3, such as, at a given frequency, deviation of the generator waveform from a grid sine wave is no more than 1 volt across the entire cycle. etc.

I have looked in a few onan repair/service manuals and have not seen this type of information...then again, they may have used a measure that I am not familar with.
Any inisght is appreciated...

-J
 

Wayne 440

Registered
You probably will not find quantitative information floating around on the 'net for free, if at all. I imagine that very few people bother to quantify deviation from the "perfect" sine wave, because for most applications it really doesn't matter very much. The typical waveform from utility power is sometimes pretty far from ideal.

That said here is my take based on a few years of genset experience

(1) unless you look at it on an o'scope, you won't know the difference -.i.e. lights, refrigerators, computers and other stuff work just fine.

(2) if the load is really only 80%, not much - maybe 4-5hz short term. But a motor which pulls 80% of rated when running draws a lot more VA than that to start. That can result in significant Hz and V sags.

(3) everything I have ever used or owned that said "Onan" on it made a decent waveform.
 

len k

Subscriber
Last Subscription Date
12/12/2018
Onans are a very good gen and I think they are better than many other gens out there. I own a 7NHM (Emerald design). I don't have specifics , but here are some things to think about till others respond.

***Waveform:
I suspect the shape of voltage sinewaves, under a steady state load, of Onan's are pretty good compared to other modern 3600rpm China junk out there. I called another manufaturer and was told it had ~15-18% THD with spikes at sinewave peak, scrappy. And with all the electronic (non-linear) loads in your house these days even utility power doesn't have a clean voltage sinewave, (it's flat topped a bit). It just adds a 3-rd harmonic. But I don't think electronics will care much about that.

***Base 60Hz Frequency vs transient loads:
Electrical hz ouput is proportional to engine rpm. Suddenly adding a significant load (80%) on gen will breifly reduce hz(rpm) untill governer can respond, open throttle, engine inhales the higher fuel mix, and the next power stroke ignites. In the meantime the energy stored in the flywheel is consumed to drive the electrical load and rpm drops.
A similar thing happens when suddenly removing a significant load ( load dump), rpm/hz increases till gov responds and excess rpm energy in flywheel is consumed.

With steady state load, many Onans with a mechanical governer run ~61-62HZ no load and ~58-59 HZ at full load. The droop in hz is ~2-3HZ, The Onan Marquis 5BGM, 7NHM have an electronic gov and is advertized to be +- 0 HZ, ( at steady state load.)

I suspect most loads may not care much about this frequency variation. But some electronic loads may. I know people have trouble with some battery bank inverter/chargers. I guess they are too sensitive and shut down with breif gen frequency or voltage fluctuations. Also a person with even a 7.5kw JB Onan gen (it has a large rotating mass, flywheel effect) had problems with fancy German furances and dishwashers. Although it may have been a voltage or ground/neutral bond issue.


***Voltage:
I don't think any of the gens you mentioned have electronic voltage regulators. So voltage is proportional to rpm. High rpm gives high voltage. Normally gov workes well. But on load dump you will have a brief higher voltage as load is removed and rpm rises briefly. How high, I don't know. Good enough for basic loads like incandecent lights and motors.

I think the real issue with "quality" of SINE wave is some cheap battery inverters put out SQUARE waves or crummy "sine" waves. And transformers and motor will heat up on square waves. Square waves have a great deal of energy in the higher frequency harmonics, that ends up as energy losses (heat) in the iron motor laminations.
 

Leon N.

Registered
Interesting that you ask. I do have a dated 4 page Onan Tech bulletin T-023 from August 1964 entitled: Problems of Television Set Operation On Generating Plants. I could make it available if interested. It does discuss asynchronous operation of generators "and" input waveform distortion which could disrupt the TV vertical synchronization if the TV power supply does not remove all ripple.

It also discusses the Onan generators with a static exciter (Magneciter) which includes a magnetic amplifier voltage regulator that have a notch in the generating plant output waveform. It doesn't say very much but cautions the user would you believe to use a brand or model of TV that is not susceptible to these effects.

I realize you did not include the Magneciter models in your inquiry, but I will say I have seen no detrimental effects in my home powered from a Magneciter.

If interested, send me a private email with your mailing address and I will send you a copy. I do not have a pdf version.

Leon
 

len k

Subscriber
Last Subscription Date
12/12/2018
I notice alot of the modern tv's I disassemble for parts have switching power supplies. I haven't really looked too closely to see if a 60HZ line runs eleswhere for the TV circuits , but I don't think it did. So I would guess modern TV's are relatively immune to minor variations in 60Hz even at load dump. BUT they may NOT be immune from accompaning high voltage.
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
This topic seems to come up often. "Power quality' has to be considered in view of the intended load. Whatcha got that you're worried about?

With the CCK sets, the biggest concern I have, based on what I see on mine, is the overshoot when a large load is suddenly removed. It was substantial - the 120V popped up to about 160, as I recall.

Over in this thread, I showed the JB output waveform was about as good as utility mains power...

http://www.smokstak.com/forum/showthread.php?t=111420

Then there was this thread, that raised more questions than were answered...

http://www.smokstak.com/forum/showthread.php?t=116568&highlight=sine+wave
 

len k

Subscriber
Last Subscription Date
12/12/2018
WOW 160V !!!! Thats 226V peak.
I knew voltage would rise on load dump, but I didn't know it would rise that much.

That could kill a line recritifer section cap in a switching power supply. I just looked at some old VCR and TV switching supply in my parts bin. Cap's only rated for 180 to 200VDC. (and you will be applying 226V to it)

I guess that's why Onan made a sales ad highlighting the RV Emerald Series (NHE, NHM....) with electronic volatge regulators with CAPPED voltage output. The J series Onans also have a magneciter or an electronic regulator , I'm just not familiar with them.
 

Isaac-1

Registered
Last Subscription Date
01/12/2014
The problem with any generator with a voltage regultor is the fact they may perform just fine until some component of the voltage regulator fails then the voltage may spike or swing wildly.
 

len k

Subscriber
Last Subscription Date
12/12/2018
Well a voltage regulator is a step in the right direction. Having a hi voltage only when it fails vs everytime a AC or water heater cycles off. I gave some thought to a hi voltage disconnect relay to minimize duration of any hi voltages on regulator failure.
 

Leon N.

Registered
Re this discussion about voltage overshoot. Happiness is having a Onan Magneciter equipped alternator. The Magneciter equipped generators voltage dip and overshoot is less than 12% on application or removal of rated continuous load in one step!! And with minimal electronics, just a diode bridge you can't beat it! Unfortunately it was too expensive, in my opinion to continue in production.
Leon
 

len k

Subscriber
Last Subscription Date
12/12/2018
Magneciter (magnetic amplifier)..... didn't know it's specs. 12%, that nice performance!! Pretty bullet proof too. Now I know why everyone likes them. It's 3 wound coils make it pricey. All wound components are expensive to produce, too bad.

I think alot of the J- series gens (JB, JC......) had magniciters . At least those with a spec # less than ~ AA !?!?
 

threejeeps

Registered
thanks for all the replies...lots of stuff to consider. I'll try to fill in gaps/issues that were brought up:
1. Regulation depends on sensitivity of the load - right - In three ways: voltage amplititude, frequency, and power factor. Basically what I want is they best I can get with mods applicable to BFA. (Not concerned about cost at this point, just need to understand what is out there).
2. TV issues: I grew up repairing TVs in my dads TV shop..from 1960s to late 1990s. Depending on the design of tv, the vertical sync was triggered off line frequency-60 frames/sec. Some receivers more sensitive than others. Newer sets do it digitally with precise oscillator. Would I power my 40" LCD tv with it? Only if I had to, but want to make sure I've got the power cleaned up as well as possible. Most loads I would have would be unaffected by frequency variation, but more suceptable to voltage variation.
3. Yea, aware of the cheap 'square wave' inverters.. and the harmonics in the square wave and the problems they cause. I just wanted to make sure the BFA was close to sine wave produced by power company (and I know power company is not exactly ideal but damn close). I know output is a sine wave, just wondering about deviation...I may do some experiments on my own. The information you have would be useful.
4. Voltage Regulation - yes, basic speed regulation proportional to voltage regulation. Thats OK, sorta...So brings up question:
Are there any onan or 3rd party VRs retrofits for BGA? Given lag in govenor based systems, field control seems like only alternative, given the basic design of the BGA. Seems like a pretty neat lil project to design one if none exists...

Much thanks to all those that have responded...I do believe I am infected with the green itch...lol

4.
 

len k

Subscriber
Last Subscription Date
12/12/2018
voltage regulation for TV ....... Could look into a APC Smart UPS type unit to add to gen output for your $$$ TV's+ electronics. They are supposed to regulate utility voltage in addition to being a UPS for utility failures. Don't know the specs on them, make sure you get one with sine output, some are squarish ouput.

The Onan emerald series (NHD, NHE, NHM, .... and lower power brothers BGE,BGM...) and newer models already have a electronic regulator from the factory.
 

threejeeps

Registered
voltage regulation for TV ....... Could look into a APC Smart UPS type unit to add to gen output for your $$$ TV's+ electronics. They are supposed to regulate utility voltage in addition to being a UPS for utility failures. Don't know the specs on them, make sure you get one with sine output, some are squarish ouput.
thanks, makes sense...I am not a fan of sine wave or modified sine wave inverters (althought some modified SWI are fairly good). Because I understand how the waves are produced and the harmonic content can be bad for other devices, I stay away from them. Smart UPS is a good approach to be used locally...thanks again.
J
 

len k

Subscriber
Last Subscription Date
12/12/2018
I think someone said the APC smartUPS will regulate utility voltage even without it's batteries hooked up.
 

threejeeps

Registered
thanks, makes sense...I am not a fan of sine wave or modified sine wave inverters (althought some modified SWI are fairly good). Because I understand how the waves are produced and the harmonic content can be bad for other devices, I stay away from them. Smart UPS is a good approach to be used locally...thanks again.
J
Whoops, that should be 'square wave or modified sine wave inverters'... apologies
 

MachinistRich

Registered
I work on generators for tv and movie production that have a serious amount of electronics for the sole purpose or regulating the engine throttle which is what maintains the frequency. Engine rpm and frequency are directly related. A really good voltage regulator will not fluctuate and there are also numerous controls available that will drop the generator off line for conditions of under/over frequency and under/over voltage. The entertainment industry spends big money on their equipment and I have not heard of any electronics being damaged due to any of the generators I have ever been called out to repair or service. Hz and volts only fluctuate by tenths of a point on these units and other than the controls the engines and generator ends are rather ordinary.
 

Leon N.

Registered
What MachinerRich says about the electronic speed and frequency controls in the modern day generators is accurate. However, from an overall reliability and endurance aspect, the stuff that is on the market today, especially in the small standby power plants can't hold a candle to the Onan J-Line prime movers of the past. Any one who is mechanically inclined and takes a look at the two designs I think will come away with the same conclusion.
Leon
 
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