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Onan Tech Star 35G Saavy?


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  #41  
Old 01-06-2018, 02:21:10 PM
JT240Z JT240Z is offline
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Default Re: Onan Tech Star 35G Saavy?

As I understand it, the only real advantage to a 3600 RPM generator is frequency stability. Load changes that can cause minor variations in engine speed have less effect on a 3600 unit than an 1800 unit. Surprised that nobody developed mid-sized generators using motorcycle engines (air or water cooled) Seems higher RPMs would be a very little problem for them since they're designed to operate at a constant higher RPM.

Last edited by JT240Z; 01-06-2018 at 02:32:19 PM.
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  #42  
Old 01-06-2018, 03:46:49 PM
Leon N. Leon N. is offline
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Default Re: Onan Tech Star 35G Saavy?

Re the comment: ]minor variations in engine speed have less effect on a 3600 unit than an 1800 unit}

The Onan frequency spec is 5%. 5% of 3600 is greater than 5% of 1800. Hmm. This problem is, however, over come with the introduction of a different type governor.

Operating at 3600 usually puts the engines performance higher up on the speed/brake horsepower curve. This enables one to build a smaller light weight engine.
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  #43  
Old 01-06-2018, 04:26:41 PM
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Default Re: Onan Tech Star 35G Saavy?

My thinking along with immediate lack of FULL lubrication is that a stone cold mass (engine) is now revved to 3600 rpm and none of the parts have expanded to WORKING tolerances such as cylinder heads to block and pistons to cylinder bore. I think that's why UPS had so many head gasket failures on the L634. The guys started them right up cold and left the building hammering the throttle.

Not to start a war about wear as such but I tend to agree with Leon N. and the Onan statement.
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  #44  
Old 01-06-2018, 04:31:53 PM
Birken Vogt Birken Vogt is offline
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Default Re: Onan Tech Star 35G Saavy?

In practice I have always seen if it is a 2.0 liter engine then it is good for 20 kW electric.

If you spin it twice as fast you get twice the power so now it is a 40 kW engine.

Of course manufacturers frequently use engines a bit larger than they need because of cost considerations so a 2.3 engine at 3600 making only 35 kW is not unusual.

But how much difference in cost would there have been between a Ford 2.3 and a Ford 240/300 when manufactured is what makes me scratch my head.
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  #45  
Old 01-06-2018, 05:02:14 PM
JT240Z JT240Z is offline
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Default Re: Onan Tech Star 35G Saavy?

Quote:
Originally Posted by Leon N. View Post
Re the comment: ]minor variations in engine speed have less effect on a 3600 unit than an 1800 unit}

The Onan frequency spec is 5%. 5% of 3600 is greater than 5% of 1800. Hmm. This problem is, however, over come with the introduction of a different type governor.

Operating at 3600 usually puts the engines performance higher up on the speed/brake horsepower curve. This enables one to build a smaller light weight engine.
Isn't the spec 5% of line frequency. Example being, +- 3hz for a 60hz system? A 3600 RPM unit would have to have an RPM variation twice as much as an 1800 RPM system to have the same line frequency variation.
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  #46  
Old 01-06-2018, 05:12:52 PM
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Default Re: Onan Tech Star 35G Saavy?

True, the same speed variation with half the number of poles (2 vs 4) would equal 1/2 as much frequency variation. Since stored energy varies as the square of speed, the 1/2 speed machine needs 4 times as much rotating mass to achieve the same stability. Everything is a trade off.

I agree that the six cylinder engine wouldn't cost that much more to make than the four. The 1/2 speed generator would need approximately twice as much material to make, but the total manufacturing cost again probably wouldn't be that much more either. There's no question which one I'd choose.
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Old 01-06-2018, 05:51:26 PM
Leon N. Leon N. is offline
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Default Re: Onan Tech Star 35G Saavy?

I cannot comment on the performance of the 2-pole, 3600 RPM generators. However, with regard to the 4-pole 1800 RPM Onan generators, the 5 % figure is based upon the flyball governor's ability to hold the RPM within design limits which translate into a 5% droop from NL to FL. The spec is not 5 % of line frequency, it just so happens that is what the engine govenor's performance translates into.

Now, if, because I do not know, the 3600 RPM, 2-pole machines employ the same type of governor then the droop would be twice as much as I see it.

I understand the newer 3600 generators employ what is called a synchronous governor or something along that line most likely not a flyball type governor as used on the 1800 RPM machines. Maybe someone else can explain.
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Old 01-07-2018, 09:01:44 AM
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Default Re: Onan Tech Star 35G Saavy?

OK

the newer generators are using electronic governors.

yes I have one of those "G" brand but a contractor model V twin
[relay controls for the engine "potted" electronics for VR & gov.]
It has idle control and after a brief burst at 3600 warms up at a lower speed.
[while I unwind the cable] then turn off the idle control and apply the load.

If I knew then [2006] what I know now I would have spent the money otherwise
so far it is still OK; while my late friend who purchased the NG fed home unit,
did not fair as well [quit and widow sold it rather than repair/maintain it] smart.

it is part how well the engine is designed for a speed, AND,
what margin is left of that capacity for longevity.

the alleged 17.5 KW continuous rating of my gasoline fed model
I only load to a maximum continuous 50A x 240 V = 12000 watts
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  #49  
Old 01-07-2018, 10:57:27 AM
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Default Re: Onan Tech Star 35G Saavy?

What's the point of a brief burst at 3600? From what I know the only good thing about those "G" machines is their frequency control system. It seems to me tight frequency control is more important than voltage control. Kind a important to have closer reins on speed especially when spinning so fast as compared to the slower machines.

Could it be that burst at 3600 is a subtle assurance that the machine will require maintenance $ sooner rather than later. A ha, those G people are smart entrap endures taking advantage of the uniformed. Sorry, but, I'll keep my old Onan. You can bury it with me if you like.
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Old 01-07-2018, 11:26:08 AM
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Default Re: Onan Tech Star 35G Saavy?

We can talk all day long. About the good and bad of 3600rpm. But if you ever stood in a room. While a Tech Star came apart at speed. You would understand why I hate the things.
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Old 01-07-2018, 01:15:04 PM
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Default Re: Onan Tech Star 35G Saavy?

Always one of my favorites to watch...listen to that rod sound like a buzz saw against the internals just prior to grenading. Thats why its OSHA rule to not be in a dyno room while testing, and never a good idea to be along side an engine when load banking at full load. You may or may not get that "buzz saw" warning sound a couple seconds prior to the event.

https://youtu.be/ZfttA0mds-c
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Old 01-07-2018, 01:25:13 PM
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Default Re: Onan Tech Star 35G Saavy?

Eric. It is even more fun when a part. Goes between your legs. Just below a special part. Makes you sit in your truck. Saying a few prayers.
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Old 01-07-2018, 01:57:07 PM
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Default Re: Onan Tech Star 35G Saavy?

I don't stand along side any engine or fan, no matter what the RPM, any more than I can help it when running, loaded or not. And definitely never when starting, should the governor have a hard time getting control of it.

I've seen what can happen and I don't want to be there when it does.
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Old 01-07-2018, 02:06:05 PM
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Default Re: Onan Tech Star 35G Saavy?

Heck, when on a locomotive under full load, especially those 4400 hp, 16 cylinder GEs, and needing to walk between front and back, I would jog past the engine itself lol. And those were only blasting along at ~1050 rpm!

That model of engine was known for puking power assemblies. More like launching them. After busting through the adjacent door, and then bending the 1" solid steel handrail, they were known to fly along ways from the tracks, sometimes even into someone's house, via their roof!

Those are "old" now, curiously having been replaced with a V 12 of the same rating. So far as I know, the new ones don't have this problem.
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Old 01-07-2018, 02:38:56 PM
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Default Re: Onan Tech Star 35G Saavy?

What are you guys talkin about? Why would a GE locomotive engine fly apart if properly maintained? What would cause a diesel no less to fly apart?

I'll tell you something that makes me take notice around here especially in th Summer time. That is these inter city CNG fired busses with the engine in the back and that cooling fan screaming. I often wonder how fast it is spinning and is there a danger it could fly apart and hurt someone? They are very noisey.
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Old 01-07-2018, 02:58:32 PM
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Default Re: Onan Tech Star 35G Saavy?

Leon, those gas engines make a lot of heat, and given the engine location, ventilation isn't the greatest. I believe the bulk of the noise you hear on those is the fan, which if variable, is likely locked into direct drive on hot summer days for most of the time the engine is loaded... same as standing directly in front of a direct discharge radiator on a genset. (and possibly with an even higher fan hub drive ratio than a genset due to the poor ergonomics of rear engine compartments.)

As for the old diesels, my belief is that big iron will break in a big way, albeit a rare occurrence. Just the physics of large quantities of rotating mass. No different than a small engine failure, just much more dramatic due to said mass.
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Old 01-07-2018, 03:11:26 PM
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Default Re: Onan Tech Star 35G Saavy?

Leon, those engines were just known to fail in that way. Statistically rare, yes, but across thousands of units it's happened a number of times, and, as was stated, catastrophic.

Their air tanks have also been known to explode. Not as scary if you were up on the engine, but when on the ground I used to run past those too lol.

My point in the discussion of our fear of 3600 RPM engines was that I used to jog past those GEs, even though they were only running around 1000 RPM.
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Old 01-07-2018, 03:20:29 PM
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Default Re: Onan Tech Star 35G Saavy?

Quote:
Originally Posted by Leon N. View Post
What are you guys talkin about? Why would a GE locomotive engine fly apart if properly maintained? What would cause a diesel no less to fly apart?
Maybe it wasn't.

Or maybe it was designed too close to the edge , with little safty margin. We all know how managers push for cost when we know they shouldn't.
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Old 01-07-2018, 03:31:59 PM
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Default Re: Onan Tech Star 35G Saavy?

I had one of those Military 2A042 5kw 2 cylinder generators. It ran at 3600 rpm. It had tremendous electric motor starting power probably due to the mass turning so fast. I had it in a partially enclosed car port with a 16 gallon keg to feed it. It served me well but you couldn't be near it without ear protection. The bad part was the hydraulic lifters would not pump up some times and that poor thing would be running at speed with one or more of the lifters banging away.
The military manuals for it showed how to built a revetment with two layers of sand bags. Don't know if that was to quiet it down or to catch the shrapnel when it exploded.
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Old 01-07-2018, 03:45:21 PM
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Default Re: Onan Tech Star 35G Saavy?

Interesting. I have a question about those noisey radiator cooled fans. Is it true, if you spin such a fan to fast, it looses efficiency and will merely spin and not move much air? Is there an optimum speed for any fixed bladed fan?
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