Rotational mass.

[Ratman]

Hello, I'm brand new to the forum and new to the idea of CHP, but I'm very keen to get started.
I have a friend who is way ahead of me and I'm gleening as much information from him as I can. One thing he tells me is the importance of rotational mass and advises me to wait for an ex Start 'o' matic CS as they have heavier flywheels. I intend to fit a heavy pulley to the generator.
So! how important is rotational mass? I understand the theory of it but does it really matter if the lights dim for a second or two when you switch the kettle on. 
Many thanks for reading and I look forward to your replies. 
Rob

[oliver90owner]

Rob,

First, welcome to the forum.

If the lights dim appreciably all the time you boil the kettle, you are overloaded.  A couple of seconds at the start is just governor reaction time.  This is not flicker, which can be a problem with lighter flywheels.

The problem of flicker is caused by the small, but rapid increases in rotational speed every time the engine fires and then as it slows before the next power stroke, ready to do it again.  At around 600 rpm there are only 300 power strokes a minute or only 5 per second.  We see by producing an image on the retina around 10 times a second so at this low frequency of speed variation it can become noticeable (and annoying).  Obviously, the more stored flywheel energy you have the less the speed variation between power strokes (due to the 'square' relationship between rotational speed and energy stored in a flywheel system.

The engineers at Lister thought it was important enough to put on the heavy engine flywheels for electricity generating sets and extra mass on the generator pulley as well.  It fixed the problem.  Things have not changed much over the last 50 years or so.  One thing that may well alter things is a good AVR (Automatic Voltage Regulator) controlling the excitation of the generator.  Possibly (or probably) end of problem.  The extra weight up to a certain limit is good if care is given to how it is done..

However if you are using a cheapo generator hanging weight on it's shaft may not be a good idea.  It may not have a big enough bearing(s) and the bearing(s) fitted as original may be sub-standard to say the least!  An outboard bearing may be required for longevity. 

Same with the engine, where TRBs may be set up wrong, or sub-standard, or damaged at assembly (hammering in flywheel gib keys?).  You must not simply hang more weight outboard of the existing flywheels without considering the possible effects on longevity.  The heavier duty Lister CD and CE engines had double plain bearings supporting their flywheels/crank.  TRBs are not supported over as long an effective bearing length as a plain sleeve bearing.

Lots of things to consider.  Only do it if you need to is my advice.

Regards, RAB

[Ratman]

Rab,
thanks for your excellent reply, now I understand the need for heavy flywheels, I'd just assumed it was to even out the speed when an additional load to the generator was applied.
Although I am a life long car mechanic I’d never taken the power strokes into the equation and obviously a slow speed engine exaggerates the problem.
Looks like I’m going to have to wait for a Start ‘O’ Matic engine to come along, or as you suggest use an AVR.
I intend to use one of those Chinese ST generators and the supplier has heavy cast iron pulleys for them, are the bearings in these generators up to the job, or will I have to use an additional outboard bearing.
Rob.

[oliver90owner]

Rob,

As soon as you say 'Chinese', alarm bells ring for me.  Not saying they are no good, just that the flavour of threads on this, and other boards leads me to be wary of the quality.  But there again, they are cheap.

The Lister gennys were well over designed, or just well designed for purpose and longevity.  The extra weight on the generator perhaps had something to do with the self-start as well as flicker suppression....don't know though for sure.

I would look carefully at the size of the bearings, particularly the drive end, and the radial loading you will be putting on it.  I reckon an outboard bearing is not a bad idea with these machines as long as the engineering is simple enough.

I am down south of the county, btw.

Regards, RAB

[Ratman]

Rab,
a fellow Yellow Belly, that's nice to know.
I've done a bit of research on these Chinese generators and the bearings they use are a very common one and very cheap to source a British replacement. As for the quallity of the windings etc I recon it's a case of try one and hope for the best.
I've just missed a CS on evilbay, got out bid in the last few seconds, not too bothered as it was a six spoke flywheel one.
Thanks again for your help.
Rob

PS: Do you attend shows and rallys with your Oliver.

[Stan]

Rob....standard lister 6/1 flywheels weigh in at about 143 lbs each.  The SOM (or electric) flywheels have a 3" x 4" solid rim, a 1" solid plate center with 2 oval holes and 1 smaller round hole and weigh in at 275 lbs each.  Quite a difference.

The SOM generator, (not always made by Lister) also has a smaller flywheel type pulley on it, not sure how much it weighs but by the look of it it's about 75 lbs.  You have to be careful of putting too much weight on the generator flywheel though, you'll get the dreaded chirp.  The belt wont' be able to keep up with the torque.  Just ask Jens.
Stan

[ronmar]

If you can source one, I would highly reccomend using a micro "V" automotive serpentine belt pully on the generator head.  IMO, they transfer the torque far more smoothly than a set of "V" belts would and there are no belt matching/balance issues like you find with multiple "V" belts.  I am really impressed with how mine spins the generator head.  If you havn't already, I would highly reccomend a trip here www.utterpower.com . George has a lot of cool information on his website.   
As oliver90 mentioned, an AVR will really take the edge off of the flicker produced by a slow speed single.  But it will make the frequency excursions with load changes a little more severe.  With the AVR holding the voltage steady with a load change, say when a well pump kicks on, makes the ramp up of the mechanical load applied back to the engine very steep.  With a non AVR ST head, the voltage drops a little as the load is applied so the mechanical load ramps up a littl slower on the engine.  With the AVR on mine, the exhaust really huffs black smoke with a large load change.  The transition without the AVR is much nicer IMO. A little voltage change with load changes is also nothing to worry about.

As for flicker, one thing I have notied is that it dosn't really effect compact florescent bulbs.  I can still slightly detect it, but I really have to look for it.  Setting in my living room watching TV, the only real way I notice that I am on generator power is I can barely detect the thump thump thump of the engine running out in the shed.  Flicker on an incandescent bulb jumps right out at you.

Excellent advice has been given on added weight.  If you can, hold out for a SOM engine with those heavy flywheels.  If you can't, I think you will find that it works pretty well even with the lighter wheels, Mine does.

Good Luck with your project.   

[Ratman]

Thanks for the most valuable information I've received from you all on this one, I’m pleased I’ve joined this forum, some very knowledgeable people on here. 
I do intend to use a micro vee belt, one of the few modern things that actually have a use.
I take it that ‘flicker’ is mainly evident with normal light bulbs, do those low energy things work ok, I don’t really like the light they give off but if it helps with the problem of flicker, I may have to use them.
Rob

[cujet]

The 6/1 and ST combo produces massive flicker with compact fluorescent bulbs. Especially during very high loads. I noticed this yesterday on Bob Gross's 6/1. We loaded it up to "full rack" and the flicker was severe. However, at low loads it was not bad at all. I think voltage has something to do with this too.

I made a minor attempt at reducing flicker by installing extra large/extra heavy flywheels on my 20/2. I also installed a very heavy generator head flywheel. It makes some flicker and I find it annoying. It does not compare well to grid power in any way. The voltage, frequency and sine wave shape are all over the map. Worse than that, my belt chirps on every power stroke, no matter how tight I make it.

I have come to the following conclusions:

1) There are much better generator heads than the ST. Get a quality 4 pole modern gen head.
2) Doubling the inertia of the engine's flywheels seems to be necessary.
3) Higher RPM is your friend with regard to flicker and AC power quality.

[t19]

I ran a 6/1 with a 3ST head.... no flicker noticed and I have CFBs

I now have a 10/1 with a  7 ST and still no flicker noticed

[ronmar]

My 6/1-ST5 produces much better light with CFL's than regular incandescents.  Like I said before, I really have to look to see flicker in the compact florescents.  Regular florescents such as I have in my garage show it more than the CFL's ...  The production quality does vary on the ST heads, and some require a little mor TLC than others.  Improperly bedded brushes could cause voltage variations and cyclic noise/flicker.

As for frequency being all over the place, that is purely a function of your engine governor stability. RPM IS frequency...  Since these heads are typically harmonically excited, voltage is also dependent on RPM, so if your freq is varying due to RPM changes, then so will your voltage. 

Cujet, What size head are you running on your 20/2 that chirps?

Ron

[cujet]

My setup is a GTC 20/2 with a ST-15 head and a single 8 rib belt. The generator pulley is 70 pounds and has 2 different belt ratio's.

Take a look here for a pic.

http://www.cujet.com/html/other_projects.html

[cujet]

1)  The production quality does vary on the ST heads, and some require a little mor TLC than others.  
2) frequency being all over the place, that is purely a function of your engine governor stability. 

First, my point was simply that ST heads have a really crummy siine wave output. They do not use any form of skewed stator or other modern design criteria. Therefore they produce lower quality power than a quality modern generator head.

Second, Listeroid governors have very poor RPM control. This is by design. Many of us have made attempts at improvement. Still, when compared to a typical small diesel genset, the Listeroid frequency is all over the place. Mine varies from 63HZ no load to 57 full load. Not good.

By way of comparison, Bob Gross has an Onan marine diesel genset. From no load to high load there is only a half a HZ swing. And response is instant and the sine wave output is proper.

[mobile_bob]

just curious

how many folks set their gensets up with the belt slack side on top vs slack side on the bottom?

engineering text dictates slack on top as being the preferred manner of design.

just wondered if this had any correlation with reported belt chirping?

bob g

[MacGyver]

just curious

how many folks set their gensets up with the belt slack side on top vs slack side on the bottom?

engineering text dictates slack on top as being the preferred manner of design.

just wondered if this had any correlation with reported belt chirping?

bob g

Mine has the slack on top. (generator to the right of the engine) No chirp.
I believe Tom's has the slack on top also.