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Author Topic: tell me about the "brushless" heads  (Read 1856 times)

mikenash

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Re: tell me about the "brushless" heads
« Reply #15 on: October 09, 2018, 06:04:27 AM »
Perhaps we could add a psuedo electronics and AVR section to this forum?

 In pre electronic times, like 200 years ago when I was a boy, voltage regulation was done passively, and did work rather well. I remember the old Westinghouse, Vickers, Markon stuff that wouldnt know what a transistor or SCR was, yet they ran well and maintained pretty good regulation and certainly didnt flicker.

Easier than messing  with heavy flywheels, try this.
Magnetic amplifiers were common back then, although they were not recognised as such at the time.
Its easy to make one.
take a common isolation transformer.
Short circuit the output terminals, or the input, it wont matter.
The other two unshorted terminals are connected in series with the generator load , ie the IT live goes to the live of the generator, the neutral to the lights/house.
What this does is place a current sensitive variable  inductance in series with the output generator current, the current increases as the voltage increases on each mains cycle, therefore filtering occurs on a cycle by cycle basis , much more accurate and quicker than can be achieved by varying exciter current alone.
 A transformer "reflects"  the impedance from the primary into the secondary, therefore with light loads, the transformer will have a higher series AC impedance than with heavy loads ,this is dependent on your particular  core saturation curve, reluctance and other boring stuff
Given the random nature of your transformer and generator combo, this may  work well or provide no change at all., but is just minutes to try.
 Ideally, custom inductors are required, but luck can happen with commonly available items.
I am assuming those with the nounce to be messing with this stuff also know to be safe.
To have this work well, a low value high current wire wound type adjustable resistance load should replace the transformer short, and then adjusted for best performance. These will commonly  be in around the 5 to 25 ohm range allowing the core saturation level to be adjusted
This method  can remove all high frequency flicker and tidy up shitty waveforms. when set up correctly
The transformer VA rating needs to be at least equal to the average generator load, err on the heavy side, if unsure, watch the temperature rise, warm is ok..

Mr Starfire, you are still alive.  Excellent.  I had wondered . . .

I have one of those Markon heads and am hoping for great things for it when it gets to the top of the list

Cheers

glort

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Re: tell me about the "brushless" heads
« Reply #16 on: October 09, 2018, 07:41:41 AM »


Mr Starfire, you are still alive.  Excellent.  I had wondered . . .

I have one of those Markon heads and am hoping for great things for it when it gets to the top of the list

Cheers

Well we hope he's still alive but did you even bother to read the date on that post you quoted??   ::)

BruceM

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Re: tell me about the "brushless" heads
« Reply #17 on: October 09, 2018, 12:32:56 PM »
I'd also like to add that shorting a winding on a transformer turns it into a very small value inductor- on the order of say 10 microhenries, with some resistance dependent on winding resistance, say 0.1 to 0.5 ohm.  This inductance is too small to have any effect on a 50/60 Hz waveform. The resistance will not help as Listerflicker is not a load related phenomina. This will NOT help with Listerflicker, Starfire was mistaken.

Listerflicker is caused by the variation in speed of the engine during compression stroke and power stroke; it results in voltage and frequency drop during the former and rise during the latter.  A fast responding AVR with plenty of source power can partially compensate the voltage change, but can't do a thing about the frequency variation.

I'm quite familiar with the effects of shorting of a winding per Starfire's suggestion since this is required in my 2 transformer, 5 step sine inverter.  This uses the two transformer's secondary windings in series per the old Trace SW series inverter.  Without shorting the primary, the huge inductance of the transformer secondary (half a Henry) will just filter the secondary output of the other transformer secondary, effectively eating it. 


38ac

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Re: tell me about the "brushless" heads
« Reply #18 on: October 09, 2018, 02:37:02 PM »
I am as electrically illiterate as they come but it is hard for me to imagine an electrical control  fix for what Bruce accurately described, the exact cause for "lister flicker".  If somebody were to have the instruments and knowledge to graph all four cycles in degrees of rotation and rim speed in FPS  I think the results would astonish most users and experimenters. Also remember that all this  is happening 5.4 times per second at 650 engine RPM.  I see it very distinctly in a mechanical ways when I drive equipment with a CS type via a 25' flat belt and watch the belt whip.  Maybe I will think to take a video next time i have one belted up and under a good loading, it is quite eye opening.

In an electrical installation I would think that the ultimate low tech fix for the situation  would be to charge batteries with the engine and run a good inverter?? ,, but I am getting into an area that I have zero experience and close to zero knowledge.

The engine on my  1115 /15KW standby set  operates a tick over 1900 RPM  so the cyclic  variations are much less and happening much faster than a CS type but the flicker still is bothersome for me. Funny thing is my wife doesn't even notice it.
Collector and horder of about anything diesel

Johndoh

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Re: tell me about the "brushless" heads
« Reply #19 on: October 09, 2018, 03:09:14 PM »
I have used  fluorescent lights off my yanmar I didn't notice any flicker. Do they flicker on a generator (i dont have great eyesight)
It is better to light a candle than to curse the darkness

BruceM

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Re: tell me about the "brushless" heads
« Reply #20 on: October 09, 2018, 06:42:08 PM »
Fluorescent light power supplies vary greatly.  Many of the newer designs are switching power supplies with a 100KHz high voltage square wave output.  On better designs, the output voltage is regulated which will eliminate listerflicker, on simple cheap one's it's not.

glort

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Re: tell me about the "brushless" heads
« Reply #21 on: October 09, 2018, 10:57:41 PM »

Would seem to me that heavier/ Doubling the flywheel mass should help. The greater the inertia in the reciprocating mass, the more resistant to speed change it should be. There is a term for it, Reactive power I think?  It's the gennys resistance to voltage drop when you dump a big load on the output.
With plenty of reactive power it will pull through and not give a big dip in output.

I would think that extra flymass would help with the flicker but what I have read says it does not.  Can't understand why not?

BruceM

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Re: tell me about the "brushless" heads
« Reply #22 on: October 09, 2018, 11:10:15 PM »
Flywheel mass does greatly affect flicker and measurably so as I noted in my earlier post. Lister didn't put the extra mass on the SOM flywheels for sport, and the generator/charger/starter had a great deal of rotating mass as well.  This got the flicker level down as much as my custom AVR does with the lighter flywheels.

For totally flicker free, as 38ac and others have suggested, generating DC for an inverter is the way to go.  If you'd like clean AC without EMI, make sure you add a 2 stage commercial filter. It won't affect your efficiency but it will clean up your power. 



38ac

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Re: tell me about the "brushless" heads
« Reply #23 on: October 10, 2018, 12:07:55 PM »
Yes, Lister added weight but not only to the flywheels but the generator shaft as well. Why both places? Because there are two reasons, not one for adding rotating weight  to a gen set.  The extra weight on the flywheels is primarily there to smooth out engine pulses while the flywheel weight on the generator is there to  smooth out loading variances, primarily motor loads would be my guess. Why both places when it all could be added at one place or the other? The answer is stress on the drive.  If all the weight was added to the generator shaft then all the reactive forces of that flywheel as pertaining to smoothing the engine have to be transmitted through the drive belt(s)  If weight is needed to start heavy motor loads and it is added to the engine crankshaft you have the same situation in reverse, the drive must transfer it. Of course there is going to be some back and forth to which mass is doing what under varying  conditions but it remains that if the primary reason for adding flywheel mass is to smooth out power pulses that weight should go on the engine crankshaft. But if the primary reason is to help the set pick up high loadings such as motors starting across the lines then that weight should be added to the generator shaft.

  A good friend of mine got a lesson in this when he built up an extremely nice set from a 17HP Ruston Hornsby Mark CR diesel and a large capacity head. Knowing that flicker was going to be a huge issue with that 400 RPM prime mover he added a massive flywheel to the generator shaft. It didnt fix his flicker problem because you couldn't keep that belt form slipping and chirping each pulse no matter how tight it was,  his "fix" was placed on the wrong shaft.
« Last Edit: October 10, 2018, 12:10:01 PM by 38ac »
Collector and horder of about anything diesel

ajaffa1

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Re: tell me about the "brushless" heads
« Reply #24 on: October 10, 2018, 12:36:04 PM »
+1 38ac. The mass needs to be on the primary mover to reduce pulses from diesel detonation/ compression stroke and etc. The mass needs to be on the generator head to reduce brown out due to sudden/excessive  loads. However you do this there is going to be belt slip which will eventually lead to wear and belt failure.

Some people have tried using flexible rubber couplings, rather than belt drive, with limited success.

Bob

glort

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Re: tell me about the "brushless" heads
« Reply #25 on: October 10, 2018, 12:57:26 PM »

Very good heads up Butch.  Makes perfect sense... when a smart person explains it.

Bob your Mention of belt wear got me thinking. it would seem to me that adding all this extra weight to the engine or genny shafts is also going to cause greater loadings and therefor wear. One could of course eliminate that by the use of a jackshaft arrangement to take the extra weight load but that's more work an expense.

Despite the average 10% inefficiency of an inverter and extra cost of that, I'm thinking where the flicker is a problem, it could be a very worthwhile alternative for Lighting.  As circuits have to be split anyway, in an off grid application one could wire all the lighting from the inverter or just go low voltage from the start which is probably easier than ever now with all the LED's around.  One could either put a car alt on the engine or just have the AC head supplying power which went to a charger to top up batteries and run the lights or inverter off that.

The big Advantage I see to teh inverter system with a small battery bank is you would have lighting or some power when the engine wasn't running.
 Could watch TV, run the fridge, or have lights for if you needed to get up at night and didn't want to start an engine for 10 min of lighting.
Easy to run an additional car alt with the AC alt. I have 2 car alts on my lister driven by a serpentine belt with a tensioner in the middle.  That was done with an inverter setup in mind. Enough power directly from the alts to run a 2 KW inverter without eating into the battery charge and to bring the batteries up as quick as possible when they were discharged.

Easier for me to source inverters and do wiring than find suitable flywheels and set up lay shafts and bearings but others may have easier access and better mechanical abilities.

BruceM

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Re: tell me about the "brushless" heads
« Reply #26 on: October 10, 2018, 01:21:44 PM »
Inverter-generators are a marvelous product, the only thing missing with all commercially available inverters today is cleaning up the high frequency EMI such that it would be suitable to wrap, unshielded, around the sleeping and living areas of pregnant women and children, and anyone else with any chronic health problems or a family history of same. (Everyone.)