[ARC5] Question...

Sun Nov 1 13:26:26 EST 2020

Hi,

We have mentioned the "flywheel effect" to help with sudden load 
changes. The prime mover (engine) needs a good surplus of power to 
quickly respond to sudden load increases. Training and experience 
generating electricity aboard Navy ships.

73,

Bill  KU8H

bark less - wag more

On 11/1/20 1:18 PM, Scott Johnson wrote:
> The biggest problem with toy generators is they have poor speed regulation,
> and typically poor voltage regulation and droop compensation.  Inverters
> cure some of these ills, but I doubt the SMPS in the computers cares all
> that much about harmonic content, rather is is probably more sensitive to
> voltage droop and variation.
> Some very small gensets use a Lundall or "claw pole" generator, much like an
> automotive alternator.  The machine intentionally produce a squared off
> waveform, which , in the case of the alternator, is advantageous since it is
> more efficient to rectify.
> Most small gensets are two pole machines running at 3600 RPM (60 Hz), with
> very little rotating mass to help short term speed variations, So as Ben
> said they spend more time below 60 Hz than above.  The inverter addresses
> most all of the problems, IF it is sophisticated enough to have a proper
> high rate PWM output (many are not).  I recently had experience with a
> Capstone 1 MW inverter derived turbine generation system, and the power it
> produces has lower harmonic content that the grid to which it was connected.
> I can see that very soon, most likely all small gensets will be inverter
> sets, they are rapidly improving.  I look forward to replacing my 10 kVA MEP
> generator when a decent one is available.
> 
> 
> Scott V. Johnson W7SVJ
> 5111 E. Sharon Dr.
> Scottsdale, AZ 85254-3636
> H (602) 953-5779
> C (480) 550-2358
> scottjohnson1 at cox.net
> scott.johnson at ieee.org
> 
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> On Behalf
> Of Ben Hall
> Sent: Sunday, November 1, 2020 8:57 AM
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Question...
> 
> Hi Ken,
> 
> First things first - put the genset on the scope and see if you've got a
> problem.  There are a lot of people out there who like to scream "all
> generators are dirty, they are going to screw up your computers" who have no
> idea what they are talking about.  (and generally are in the business of
> selling filters and whatnot)
> 
> I've been inside a lot of gensets, fixed more than I can count, and have
> learned a lot.
> 
> It's likely that your genset, being 7500 watts, is NOT an inverter genset
> known for being extremely dirty.  Most generators of that size have a
> standard generator head where 3,600 RPM of mechanical rotation is converted
> to 120 VAC 60 Hz AC without any trick circuitry.
> 
> (when you run it, does it run at a stead speed regardless of the load?
> Or does the speed change as you plug things into it?  The former is not
> going to be an inverter unless it has some sort of "smart idle"
> circuitry, and the later is definitely an inverter type)
> 
> Theoretically, these non-inverter generators should generate a sine wave due
> to the mechanical motion being converted directly into AC without any
> inverter trickery.
> 
> However, in practice, theory doesn't match reality.  Your generator is
> likely single cylinder...and a four-stroke single cylinder at that...so for
> three our of every four strokes, the rotational speed is slowing down...and
> during the power stroke, it's speeding back up.
> 
> So what you get, is not a pure sine wave...but it's not going to be horribly
> dirty, either.  Those military gensets are likely multi-cylinder, powered by
> a mil-spec engine like a 2A016, 4A032, or whatever multi-cylinder diesels
> they are using these days...making the RPM much more steady...plus they are
> going to have good output filters on them.
> 
> I'd put the scope on it (carefully, of course) and see what you've got both
> at no-load and whatever load you can put on it before doing anything...
> 
> Now to the "screw up your computer" thing...modern computer power supplies
> are multi-voltage, 100 (Japan) to 240 VAC (Europe) input, 50 to
> 60 Hz input, and the first thing they do with the incoming AC is rectify it
> to DC and filter it...  Very hard to kill these.
> 
> Thanks much and 73,
> ben
> 
>> I have a "small emergency generator", 7500 watts, brand new. > >  From my
> reading, I find that the output waveform is very "dirty"
> as it > is some sort of "stepped" square-wave. I have not yet looked at the
>> wave-form with an oscilloscope, but I am not expecting it to be very
> pretty.
> 
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