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Author Topic: Generator vibration and torque pulses  (Read 22092 times)

jens

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Generator vibration and torque pulses
« on: September 27, 2007, 01:32:26 AM »
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« Last Edit: December 26, 2009, 09:05:54 AM by jens »

hotater

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Re: Generator vibration and torque pulses
« Reply #1 on: September 27, 2007, 01:40:50 AM »
WHOA there Jens---  The engine and the generator have to be  ONE piece.

Different strokes for different folks when it comes to mounting.  I like concrete and some like donuts.  That's fine, but the donuts should be supporting a frame that hold the engine and generator head totally rigid between themselves.  Otherwise the belt is sure to fail VERY shortly.
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

hotater

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Re: Generator vibration and torque pulses
« Reply #2 on: September 27, 2007, 02:25:45 AM »
Jens---

For a 20/2 engine I would think the lightest 'substantial frame' your could build would be 4" x 1/4" wall, box steel with round schedule 40 pipe bracing every foot.

I think the perfect 'portable unit' is an eight inch channel iron frame with the engine and genhead mounted to I-beam rails running lengthwise.   Sit the whole works on a half inch rubber mat and then pour the whole frame full of concrete.
  My next one will be exactly that.
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

hotater

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Re: Generator vibration and torque pulses
« Reply #3 on: September 27, 2007, 03:27:11 PM »
Jens--

Why not pry up the whole arrangement and put it on blocks to take the donuts completely out of the equation?  Put a block in the middle, right under the engine.....

I'd be willing to bet your frame is too light and suffering from 'checkerboard flex'.  That happens when too many squares make up a structure without diagonal bracing.  One of the easiest ways to get this bracings is by using round pipe as cross members.

I think you have an engine that wants to jump up and down and you mounted it on a springboard.    :o
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Eco Diesel

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Re: Generator vibration and torque pulses
« Reply #4 on: September 27, 2007, 07:22:50 PM »
Jens
That Marathon generator spun as smooth as is possible before leaving the shop. They are spun up and load tested extensively at the factory before going out the door. Marathon should even have a record of the vibration analasis. It is my inclination to start questioning your home made pulleys balance, runout and or groove pitch as you were having problems with belt alignment and belt jumping/climbing right from the start. These serpintine drives are from my experience and my customers experience to be very easy to align and ultra smooth running. The amount of vibration you are talking about is going to do major damage to both the alternator and engines bearings. I would seriously try a different pulley and see how things run. As you are no longer running a tensioner the belt tension is now unforgiving and any osolation or runout will result in a major pulsation between the engine and alternator. I would also mount that engine on something as heavy or heavier than the engine and alternator combined such as concrete without dampeners. From the looks of your frame it is probably heavy enough to be sitting dirrectly on concrete but not beefy enough to be suspended at each end by dampeners. I don't think I would mount mine on dampeners at each end and it's made out of 6"x 6" 1/4" wall tubing. I will send you out a 7.325 pulley for 650 rpm at no charge just so you can try it and compare. No worries if it doesn't make a difference or you don't want it later I will pick it up next time I am on the Island. Let me know.

Troy

xyzer

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Re: Generator vibration and torque pulses
« Reply #5 on: September 27, 2007, 09:36:20 PM »
Jens,
Do you have a link to a picture of your frame configuration somwhere? They are worth a thousans words!
Dave
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hotater

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Re: Generator vibration and torque pulses
« Reply #6 on: September 27, 2007, 09:45:27 PM »
Jens---

How are you going to balance the flywheels without taking the piston and rod out to weigh them??  They have counterweights cast in and will be WAY 'out of balance' without the engine hooked to them.

Consider this---the engine might be about as good as it's going to get....take it off the trampoline and see how good it really is.  You might have built in a problem without knowing it.
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Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

hotater

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Re: Generator vibration and torque pulses
« Reply #7 on: September 27, 2007, 10:07:35 PM »
I keep forgetting some people have extra cylinders!!

From looking at the picture....trampoline.   I'd sit three 4x4s under it and crank it up to see where you are.  The engine is in a perfect place to set up a spring action in the middle, in my opinion.
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

xyzer

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Re: Generator vibration and torque pulses
« Reply #8 on: September 27, 2007, 10:09:14 PM »
Jens,
That is right...us 6/1ers and 12/2ers are external type guys. I would go get some modeling clay and do the mr x method and see if you can calm it down. The dampers should be fairly stiff. I can move my 6/1 maybe an 1/8" using my body weight. That heavy of a setup would need some real stiff ones!
Dave
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listeroidsusa1

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Re: Generator vibration and torque pulses
« Reply #9 on: September 28, 2007, 02:49:24 AM »
I've had good results with conveyor belting. It has tire cord embedded in it so it is very strong, but still cushions it a bit. I use contact cement to glue it to the bottom of my frame rails and with the weight of the engine it has held up very well. You don't need much, I use 3/8" belting, just enough to eliminate the hard frame from the hard floor. (otherwise it can "bounce" on the hard floor when it fires) It works pretty good for me. I'd use 3 pads on each side to allow the engine/generator to "adapt" to the profile of the floor. It usually works even better after it has taken a "set" after a few days. When I first installed my engine it had a tendency to pound against the anchors in the concrete and it was hard to keep the anchor bolts tight. With the conveyor belting under the frame I haven't had to tighten my hold down bolts in the past 4 years. The engine doesn't shake either!

rcavictim

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Re: Generator vibration and torque pulses
« Reply #10 on: October 01, 2007, 11:22:41 AM »
Jebs,

That package looks nice.  The matrathon alternator looks very `expensive`.  I really like the exhaust manifold you made which I see acts also as a bit of an expansion chamber.  Nice work!  As for the white paint?  My suggestion is to take all the glamor photos of the finished plant now before you start using it!   ;D  The white does look nice though.

From the picture it is obvious to me that you have created a flex situation the way the generator is mounted which will offer little resistance to the pulley and opposite end of the alternator to nod up and down like a see-saw given the right mechanical excitation.

I would suggest that you make some end caps for the big box rails of the base and fill them with wet cement (regular sidewalk mix of gravel and sand which will cure into a heavy solid reinforcement).  That will take a LOT of flex out of these main beams.  If you have some rebar handy you could put that in there too.  You will have to demount the hardware so as to have the rails vertical to do this.  Use the rebar as a tamper to get the air pockets out as you fill, then just leave it in there.  Cap the second end once the cement cures.

Those four small box tubings of the mount scheme for the Marathon head could benefit from being stuffed with a portland cement/ sand mix (no room for stones here) and a chunk of heavy rebar permanantly inserted within their length.

If you insert some large diameter round steel pipe (also filled with cement) as cross beams between the rails and up touching immediately below each of the engine mount box tubes, stitch welding them to those engine mount box rails and welding also at the ends to the main frame rails,  that will help.  In cunjunction with that you should also fill the two engine mount cross box tubes with cement.  The result of this combo reinforcement will go a long way towards restricting the rotational vibration around the crankshaft which you are now seeing (top of engine swinging towards and away from the alternator.

Once you have done the mods I suggest your nice looking frame will look almost identical to how it looks now and will weigh twice or more as much.  Placing the whole thing on a 3/4 inch thick rubber agricultural mat on a concrete floor may be all you need.
« Last Edit: October 01, 2007, 11:42:20 AM by rcavictim »
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mobile_bob

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Re: Generator vibration and torque pulses
« Reply #11 on: October 01, 2007, 08:45:01 PM »
Jens:

i have been hesitant to reply to this thread, but seeing how there has been some debate on the issue i would like to suggest the following

the rubber mounts on the engine end are "not" in the right position, they need to be moved outward substantially
and widened as well substantially.

optimally you want those mounts to be centered so that the center of the mounts are in line with a vector line formed by line from  the center of each piston
through the center of of each crankcase mounting bolt and down to a terminus that is within the center of each rubber mount.

to illustrate, the left hand piston at top dead center, start a line at the center of that piston down through the centerline of the left crankcase mount bolt and continue down to the center of the rubber insulator.

where you have them now the torque action of the engine is transmitted mainly to the frame instead of into the mounts on the engine end.

i would expect that your movement at the generator shaft is quite high.

if you were to move those mounts under the engine as described, and add another crossmember with another set of mounts that coincide with
the other two vector lines from each piston  down thru the inside crankcase bolts (those closest to the genhead), you would transmit the vibration more directly into the mounts and not have them diverted into the frame, also
the torque action of the engine would be far better contained and not transmitted to the generator, resulting in less movement.

i don't know if this is clear or not.

bob g
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mobile_bob

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Re: Generator vibration and torque pulses
« Reply #12 on: October 01, 2007, 08:55:45 PM »
at the risk of starting another 6 month debate :)

properly engineered mounting systems do not need to be massive in weight, (generally)

typically massive mounting systems are used to mask other issues, or used because they are more expedient,
cheaper, easier to fabricate and install onsite, by folks that either cannot or are unwilling to engineer a mounting system.

(now that is probably going to piss off somebody, but that is not my intent)

rather it appears that there will always be folks that will try to mount these engines on other than a ton of concrete, so
there will always be a need for an understanding of how to do it correctly.

ignoring this fact will not make it go away, so maybe we need to at least try to incorporate some engineering into these
light mounting systems.

we all now know pretty well how to mount them with a ton or two of concrete, that is well proven and understood to
just plain work.

what is unclear and rears its head over and over again is how to engineer a steel frame with some form of isolation,
this i for one feel needs much more analysis and debate.

but what do i know,, i am just an arguementative son of a %$#@&

bob g
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ronmar

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Re: Generator vibration and torque pulses
« Reply #13 on: October 01, 2007, 10:19:53 PM »
typically massive mounting systems are used to mask other issues, or used because they are more expedient,
cheaper, easier to fabricate and install onsite, by folks that either cannot or are unwilling to engineer a mounting system.

(now that is probably going to piss off somebody, but that is not my intent)


Hey, I resemble the later part of that remark.:)  And I am Not pissed off at all.  Expediency is exactly why I went with a high mass mount structure, AFTER establishing a good state of balance and rigidity in the base frame.  It is well proven technology and quite affordable.  Thirtyfour 60# bags of concrete can be had for as low as $68 on sale.  Add a wood form, wheelbarrow, hoe, clean water(3QT per bag) and some sweat, and a 2000# base is well within most peoples abilities.  If you want to be lazy, rent a portable mixer for the afternoon.  In my case I already had a 1300# block that I sandwitched between my frame and a lower base plate that seems to be working well with my 6/1.  I said it before, re-inventing the wheel can be fun, but R&D is time consuming and costly and I prefered to use what spare time I had available for this project on developing affordable heat recovery.  

Jens if you search this forum for "resilient mount" or something such, you will find several pages of  ummm "Discussion" on the subject that took place a few months ago.  It includes I believe some math, theory and diagrams from both viewpoints.

Ron  
« Last Edit: October 02, 2007, 03:52:13 AM by ronmar »
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mike90045

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Re: Generator vibration and torque pulses
« Reply #14 on: October 02, 2007, 02:10:44 AM »
Ok, so much for that idea .... damn ... back to square 2 of trying to figure out how to reduce the overall frame vibration.
Any input on generator vibration from torque pulses - is there a need to worry about them? Should one install additional steel between the engine and generator besides the main frame to which they are both bolted ?
Jens

 If, your gen head is bouncing around, without a belt spinning it, I'd stick it on a good solid 1/2" plate of steel, with adjustment slots on the plate.   You don't want your expen$ive head frame to be torn apart because of resonances with the listeriod mounting frame.

 If you get your 20/2 balanced nicely, even having a plate under your gen head, can't hurt anything I could foresee.