[ARC5] Question...

Sun Nov 1 16:05:42 EST 2020

    Mechanical AC generators don't always generate sine wave outputs even under constant speed and ideal conditions.  It depends on the geometry of the laminates in the stator and rotor.
    The classical description of an AC generator involves a homogeneous field in an air gap and no laminated cores.
     We had a situation many years ago when we were upgrading the electronics in high voltage terminal of our Van Der Graff accelerator from vacuum tube to solid state electronics. There were a number of Glassman power supplies controlled remotely in the HV terminal (top of the accelerator). The whole accelerator was contained in a very tall pressurized vessel at around 15 atmospheres.  Making it difficult to get to during operation. It takes says to depressurize remove the many ton vessel and close it up and repressurize it.
   We would every so often blow one of these expensive power supplies and have to replace it. The output power MOSFET would short out. The company that did the upgrade could not figure it out. So we dug into it and found the problem.
   The rectified supply voltage was in the Glassman power supplies was way to high.
    Since you can't just run a power cord across 7MV they were powered by a 400Hz generator drive by the large belt that transfers charge from the bottom to the top. The output of the generator was sinusoidal thru most of the cycle but there was a bump on the top and bottom of each cycle about 30% greater than it should have been. This generator originally powered filaments and choke input filters.  But now with all these new Glassman Power supplies had capacitor input filters.
  We install a buck transformer in series with the Glassman power supplies and that solved the problem.
An AC power source may provide the correct RMS Voltage or Peak Voltage and even both at the same time and still not be close to being a sine wave.

    Say, when are they going to advertise realistic voltages for "Stun Guns"?

73
Bill WA4LAV
________________________________
From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on behalf of Dennis Monticelli <dennis.monticelli at gmail.com>
Sent: Sunday, November 1, 2020 3:17 PM
To: Bill Cromwell <wrcromwell at gmail.com>
Cc: ARC-5 Maillist <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Question...

CAUTION: External Sender

The solid state inverters are indeed the future.  They cure all the major ills, save space, weight, and maintain good efficiency over wide load variations as people have noted.   And they don't have to generate RFI to do their job, though unfortunately many do, leaving the mess for the user to clean up.

Dennis AE6C

On Sun, Nov 1, 2020 at 10:27 AM Bill Cromwell <wrcromwell at gmail.com<mailto:wrcromwell at gmail.com>> wrote:
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<mailto:scottjohnson1 at cox.net>
> scott.johnson at ieee.org<mailto:scott.johnson at ieee.org>
>
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net<mailto:arc5-bounces at mailman.qth.net> <arc5-bounces at mailman.qth.net<mailto: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<mailto: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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