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G8MNY  > TECHNI   05.10.21 10:00l 271 Lines 13184 Bytes #999 (0) @ WW
BID : 48701_GB7CIP
Read: GUEST
Subj: Petrol Generators for /P SSB 2
Path: PI8DRE<PI8CDR<DB0RES<ON0AR<GB7CIP
Sent: 211005/0743Z @:GB7CIP.#32.GBR.EURO #:48701 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                      (Updated Jul 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Part 2

LOAD COMPENSATION
In the simple bob weight RPM control engine system, better load voltage
regulation can be obtained with some additional load current feedback (feed
forward) control.
This can easily be applied, by adding a small solenoid (e.g. from an old VCR)
rewound with a few turns of suitably insulated & thick enamelled copper wire,
that takes the 230V full load current. It is then mounted firmly on the engine
or alternator & linked up to aid the speed setting spring. Even though the DC
solenoid is now operating on 50Hz the pull is quite adequate if it has a fully
wound bobbin.                        __
                      CRANKCASE BOB ³()³AXLE
                     WEIGHT GOVERNOR³  ³
            __ AXLE                 ³  ³ SPRING  ___ SPEED
CARBURETTOR³()³             holes in³ :³-/\/\/\-[___[SCREW      ÚÄÄÄÄÄÄÄÄ¿
  THROTTLE ³  ³       adjustment arm³ :³======================²²³SOLENOID³
      ARM  ³__³=====================³__³        BOOST____\      ÀÄÄÄÄÂÄÂÄÙ
         GAS--->    LINKAGE       <--- REVS     PULL     / Alternator³ ³Load
                                                             Neutral   Neutral
N.B. The solenoid pull is proportional to:-
     1/ the load current squared,
     2/ the number of turns,
     3/ the location of the movable iron slug,
     4/ the solenoid size.

Fine load compensation adjustment is best done by varying the length of the
solenoid linkage (piece of coat hanger wire?)

I have done this modification to several generators now, & here is results of a
1.3kW rated (1.5kW peak) Honda generator to make it produce a steady 240V (UK).

LOAD   BEFORE MOD  AFTER MOD    IMPROVEMENT
WATTS    VOLTS       VOLTS      VOLTS   %
   0      250         250          0    0
 100      240         240          0    0
 500      230         238          8   3.5
1000      220         242         22   10
1500      200         240         40   20

With this modification the throttle is opened much earlier than before "when a
load is applied", rather than when the engine has slowed down. So as soon as
the load comes on, you hear the engine immediately "throttle up" under load, &
heavy loads maintaining the voltage much closer to that of real mains! This
means not only is the static regulation much better, but also the dynamic
regulation as well, as there is not the usual hang time while the RPM drops
before the throttle is opened.

Although this modification improves the peak load ability, the mean engine
rating should be kept the same, as the cooling, bearing ware etc. are
unaltered. e.g. don't plug in that 2kW heater!

LOADS TO WATCH
Switch mode PSUs loads are more immune to voltage variation, but actually
exhibit a negative impedance load to the generator, so they can be the cause of
voltage hunting, as the generator control loop fights the varying current to
voltage load. But normally there are no problems, & they are very efficient for
/P use, if there are no QRM problems! Over voltage surge protectors are
normally part of SMPSUs & may cause fuses to blow etc. if you seriously over
voltage them!

Another load hazard worth mentioning are small kettles (350W) that use half
wave rectification (e.g. 115V 180W heater misused on 230V with a diode by the
makers!)
e.g.
     ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄLÄÄÄÄÄÄÄo/oÄÄÄ´>ÃÄÄ¿
    ( 5R lead or  240V AC  on off     80R
    (   winding   +15V DC              ³  3A 50% of time 
     ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄNÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ  = 360W

On small magnetic devices like an isolation transformers or a generator the DC
current will saturate the core (lock up) & reduce the inductance by many times,
resulting in dramatic loss of output power or possible damage. Even on a long
resistive lead on real mains, the resultant Mains + DC can damage other kit
(transformers fuses especially torroidal).

Constant voltage transformers (CVTs) that are tuned to 50Hz generally are not
very useful on generators feeds, as the supply frequency is not that accurate,
but they will protect against overvoltage & poor sine wave at a 10% power cost.

Inductive loads like rotators & iron ballasted fluorescent lamps, are good if
they are fully Power factor (PF of 0.9 = partly) corrected with a large AC
capacitor.

Typically a 30W rotator transformer
needs a 0.47uF @ 300V AC & a 20W         L ÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄ¿
fluorescent lamp needs 100VA                     test C³      )º INDUCTIVE
correction that is 5uF @ 300V AC.      MAINS          ===     )º LOAD
Having them fully corrected (PF=1)            AC AMP   ³      )º
helps with other peak pulse loads, as    N ÄÄ Meter ÄÄÄÁÄÄÄÄÄÙ
the sine wave shape is maintained!

The exact amount of C needed to tune the load can be measured if you have a
bank of suitable caps to try out. Use an AC Ammeter in series with the N wire
to the load & try out various Cs in series/parallel until you find the value
needed for minimum current. Warning mains is dangerous & caps stay charged!

The actual gain for a fully corrected load is small & may not actually be worth
the trouble. Using mains filters & PF correction caps can degrade mains
intercoms!

RMS & SINE WAVES?
As mentioned earlier the alternator design is responsible for making a good
sine wave, but heavy electronic rectified loads also cause problems as the
alternator will only produce an approximation to a sine wave with resistive
loads.

A typical linear & electronic equipment usually draws next to no current over
most of the AC cycle except at the crest of the wave when the diodes in these
PSUs charge up large capacitors. The resulting pulse current can be very high,
say 10A peak for only a 100W 400mA RMS computer load!

On real mains, the impedance is normally
only an ohm or two, with little reactance.     ÚÄÄÄÄÄÄ10êÄÄ¿
But a small generator is quite different     º(  XL=       ³
a 500W generator may have around 10ê         º(  15ê      LOAD
resistive + 15ê inductive reactance.           ³           ³
So a high current pulse on the crest of      ~240V         ³
generated output will just clip the            ÀÄÄÄÄÄÄÄÄÄÄÄÙ
output to a square wave.

With magnetic feedback control on the generator, the true RMS power may stay
the same, but real mains is normally 240V (230V EU) & peaks to 340V & your
electronic equipment needs that peak voltage to work properly, & not some
clipped 240V square wave that has the same RMS voltage!

340v PK_³   __                         ³          GENERATOR WITH
240v____³  /  \ Sine Wave        ?? PKÄ´ ,--ÄÄ,  RECTIFIED LOAD
RMS     ³ ³    ³  MAINS                ³ ³    ³
     0vÄ´³- - - ³- - - ³            0vÄ´³- - - ³- - - ³
        ³        ³    ³           254v_³        ³    ³
        ³         \__/            RMS  ³        `ÄÄ--'

So to partly remedy this, some over voltage is desirable, say 253V, the mains
maximum. But at this voltage resistive loads like lamps & valve heaters will
have reduced life, but the HT or PSU headroom will be a little more like
normal!

ACOUSTIC NOISE
There are 4 main sources of noise in any engine..

1/ Engine air intake, a pulsed suck at 50Hz on 2 strokes & 25Hz on 4 strokes.
2/ Engine mechanical noise, bearings, big ends, 4 stroke valve gear, couplings.
3/ Cooling air rush, through Engine & Alternator, higher pitch fan blade noise.
4/ Engine exhaust noise, both from the silencer output & from silencer walls.

1 & 4 change quite a bit with load, with higher frequency components at low
loads to loud predominately lower pitched note under heavy load. Other noises
are often mainly rattles of loose parts.

With their higher compression & very explosive combustion, Diesels are always
noisy (Typically 20dB worse than Petrol), often from the clanking movement in
heavily worn highly stressed parts.

The restriction on gasses to & from the engine degrade performance, which is
why you do not see mufflers & silencers on racing cars or aircraft.

Commercial industrial generators never used to have much more that small "tin
can" as an exhaust silencer, & an oil bath air filter housing designed for
cleaning, but no muffing action was normal. But since more awareness of the
dangers of noise at the work place etc. modern generators are much quieter.

Old slower running 4 stroke generators with 4 poles (1500 RPM) seem much
quieter with their 12Hz exhaust pulse, but they are often VERY heavy for their
rating, as a much larger flywheel has to store energy for 7 load half cycles
before the next compression & then explosion.

                                      108 dBA @ 5M
Noise screens can            _  In___Ex
work very well in      Four | | ³Genny³  HEAT
the open, here is      Hay  |_| ³_____³  SIDE
a good example.        Bail | |_ _ _ _
                       Wall |_|_ _|_ _|

                            78dBA @ 5M
SAFETY
Exhaust gases, these are dangerous & engines should never be run for any time
in an enclosed area! E.g. no more than 1 min in a garage !

Earthing, needed for safety to reduce the chance of shock, but floating
generator supplies are generally much safer from this point of view than the
normal N & L mains. This is because it is almost impossible to get a
significant shock current to earth from either power line.
 _________                         __________
³GENERATOR³=======================³ RADIO TX ³  \³/
³ CHASSIS ³        FLOATING       ³  & AERIAL³ÄÄÄÙ
³& SOCKETS³_       240V AC         ~~~~~~~~~_³_
 ~~~~~~~~~_³_     (typically)              EARTH
 EARTH STAKE      ( 2x 120V )              STAKE
                  (off earth)

With actual balanced supplies 120-0-120V where the 0V is hard grounded
(e.g. 110V building site transformer) there is still a shock hazard, but much
reduced. But the current from either side of feed needs fusing, or you could do
welding to earth with it!

I always use an earth stake to provide some static protection at least. I use a
large galvanised T section one with an eyelet for the security chain too.

Some generators warn you not to use both DC & AC outputs at the same time. This
may not be due to a loading or regulation problems, but due to safety! This is
because the DC output winding is often part of the 230VAC load winding, & that
can put DC onto the AC output or bypass some of the safety trip features, as
well as MAKING THE 230V NON FLOATING & therefore more hazardous!

If you intend to use both at once do at least use a ELCB/RDC mains trip plug!

Generators are also HEAVY, especially if fully fuelled. Accidentally dropping
one on your foot is unlikely to brake the generator, but your foot is something
else? Backs to are a human weak spot, so get help/lift correctly!

Another problem is bad weather (typical contest Wx). Some generators suck in
large amounts of damp cooling air for the alternator. So insulation breakdown
of the windings will eventually happen if high levels of moisture are always
around! So during maintenance the odd spay off light oil/damp start plastic
sprays (not on the slip rings!) may prevent this!

Under rainy field day conditions try an awning or an old gazebo to take the
worst of the Wx off the generator.

The risk of FIRE is always present, whether from a damaged carburettor pipe, or
spilling petrol on to a hot exhaust. When generators are ready to run or
running, a good fire extinguisher (power/gas type, NOT WATER!) placed nearby &
not too close is essential.

Some generators have small tanks & others have quite large "safari" tanks.
Obviously the small tanks are safer from the fire point of view with less fuel
to "go up", but filling up more often soon negates this safety advantage.

Spilt Diesel Oil is also a fire hazard if there is any wickering material like
dry grass, straw or even dry soil around & a flame source.

Obviously don't let people smoke near the generators or fuel tanks. If you
allow public on the site, then sign the fact. In still air Petrol vapour hangs
around & a dropped hot fag end can start a fire at least 20m away!

One point from Ralph G7IED, was a report of an exploding generator harming
nearby people with shrapnel. This is very rare & might be related to over
revving, bits that could fly out of an engine are the conrod & the flywheel,
most other bits do not have enough energy, so flying bits from a working engine
with it covers on is very rare.

SECURITY
Generators & full petrol cans, laying about in a field are a magnet to some
types of people. One advantage of using a large earth stake with a welded
eyelet is it can be used to chain & padlock up generators. Even chaining 2
generators together may make then too heavy to move.

A local club has lost a large running generator 50M away, they went to see why
the power had stopped, only to see a pickup truck driving off with it out of
the field gate!

I have never lost a generator to thieves so far, but I have lost full 5 gallon
Gerry cans, so I now lock them up as well!

The end.


See also buls on "Cheaper Generators", "Regulating 12V Generator Output" &
"Madusa SIP 2300 Generator Repair" 


Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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