ST-15 flicker reduction with flywheel (question)

[cujet]

My 20/2 'roid drives a 23.3 inch flywheel at 850RPM (de-rated from 1000RPM). The ST-15 generator head has a very cool "Mike Montieth" heavy pulley. That pulley can accept a "bolt on" flywheel to reduce flicker.

So my question is this: How much flywheel do I need on the ST head to significantly reduce flicker? I believe Mike said he can make me a 16 inch flywheel that's 2 inches thick as that's the size that fits my application.

If you look carefully, you will see that the pulley also has a smaller diameter that allows me to run the engine at 600RPM for lower output and lower fuel consumption.

[piperpilot3tk]

Chris, I don't know how much mass it would take to do the trick, or if it will even completely eliminate the flicker, however I think the large bearings of the ST-15 will support more of a shaft load than you are probably able to fit to it.  So if it were me I would go big or go home 

[ronmar]

The problem you are going to start running into is the transmission of energy from the flywheel to the generator.  That added mass will also increase the generator head's reluctance to increase in RPM during the power stroke.  At some point, the belt is going to be unable to deal with the load being applied during the power stroke.

I have thought about experimenting with flicker points, but just havn't got around to doing it.  Some older single cylinder gensets used these to switch a little added resistance into the field circuit during the power stroke, to "take the edge off" of the output voltage during the acceleration of the power stroke.  It should be pretty easy to drive a set of contacts off of the cam on a single.  A twin would be a little trickier as both ends of the cam are used, but I think a delay circuit could be used in conjunction with the intake tappets to provide a more level voltage output... 

[Tom]

IIRC a SOM has a 150 lb weight on the gen head. Perhaps Mike could make you a set of nesting flywheel plates that weigh around 50 lbs ea so that you could add and remove weight to determine the optimum weight.

[38ac]

You may also want to consider smoothing out the power pulses with added weight to the crankshaft. On the originals Lister used both. As Ronmar said at some point adding weight to the gen head shaft is going to be a strain on the drive belt. I have a twin myself. The original thought was having two cylinders the flicker problem would be much less, duh! And I knew about the uneven firing too. I believe that the twins are actualy worse than the singles all other things being equal. Good luck!

[dieselgman]

I don't know if Lister ever sanctioned it but I have seen multiple flywheels (3 and 4) installed on CS models before. That should stabilize things a bit once it is up to speed, maybe. Not sure how much improvement that might make. Has anyone out there tried this out?

dieselgman

[Horsepoor]

Chris,

I have an extra, non spoked, flywheel free to a good home if you want to try it. It is in good shape and left over when I added the PowerAna electric start kit. Do you want to try it?

Incidentally, wow, great photo, what a chick magnet....

[toydiesel01]

I have been toying with the idear of adding a small cap to the gens out put to help take the edge off.
Will this work?

[ronmar]

I have been toying with the idear of adding a small cap to the gens out put to help take the edge off.
Will this work?

No!

It would work to stabelize a DC voltage, but not an AC one...

[piperpilot3tk]

Horsepoor, if Chris does not want that extra flywheel I would LOVE to have it. 

[bschwartz]

   "....It would work to stabelize a DC voltage, but not an AC one..."

But isn't it a fluctuating DC in the Z winding that then causes the poor AC?
If so, could the capacitor be put in line (actually parallel I think) with the Z?

[Tom]

Brett, he's changed to an AVR that runs on a 120v ac leg. That completely eliminates the z winding from the system. The only issues left should be mechanical.

[bschwartz]

The AVRs I got from Tom still used the Z winding, but the AVR regulated the output.
What model AVR does Tom sell that eliminates the Z winding all together? 

[Startomatic]

i attached a Kubota 5hp donor flywheel that i had. with the engine running at 630 rpm, the additional flywheel on the ST5 eliminate the flicker totally.

however, the belting now "kick.kick.kick" on every firing stroke. i guess i have to live with it.

my Vbelt is on un-groove flywheel on the engine end.



the grey pulley was the original drive for the radiator fan. was now thinking to piggy ride a automotive alternator with it to charge battery.

[ronmar]

  "....It would work to stabelize a DC voltage, but not an AC one..."

But isn't it a fluctuating DC in the Z winding that then causes the poor AC?
If so, could the capacitor be put in line (actually parallel I think) with the Z?

The Z winding generates the energy used by the field. it is AC, and goes thru a diode rectifier to make unfiiltered DC to be fed back into the field.  The Z winding generates energy based on 2 factors.  Generator load, and generator RPM, so the voltage output is partially RPM dependent.  The RPM fluctuations of a single cylinder4 stroke engine(acceleration during power stroke, and deceleration during other 3 cycles) is what causes the flicker.

Caps added to the field diode output, will filter the rough half wave rectified DC into a flatter DC voltage, which will clean up the AC output waveform.  It will also increase the voltage output a little, but will have no significant effect on flicker, because the source(z winding) is still varying with the RPM pulses...

The only ways to get rid of flicker are to:
1.  Reduce or stop the RPM fluctuations, by adding cylinders, switching to a gas turbine or hydro as a prime mover.  Adding flywheel mass will reduce but not eliminate the pulses from a single.
2.  Add an AVR that will monitor the output and modulate the field input to electrically stabelize the voltage output and help tame the flicker.(most common modern solution)
3.  Add a cam and contacts to switch resistance in and out of the field circuit in conjunction with the power stroke to modulate the field input in conjunction with the power stroke to help
     tame flicker.(old school solution used by Onan and I suppose others)
4.  Use the generator output to make DC and either charge batteries or directly feed DC to an inverter, and use the flicker free inverter power.(Honda's solution used on EU series inverter/generators)