| |
G8MNY > TECH 26.12.05 17:57l 112 Lines 5428 Bytes #999 (0) @ WW
BID : 10455_GB7CIP
Read: DL1LCA GUEST OE7FMI
Subj: Petrol Generators for /P SSB 3/4
Path: DB0FHN<DB0MRW<DB0WUE<DK0WUE<DB0RES<ON0AR<GB7CIP
Sent: 051226/1008Z @:GB7CIP.#32.GBR.EU #:10455 [Caterham] $:10455_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Oct 05)
VOLTAGE REGULATION
ENGINE RPM
This is normally 3,000 RPM for 50Hz 3600 RPM for 60Hz. The speed is generally
stabilised by a spinning bob weight governor that moves out weights under
centripedal force to close the carburettors' throttle, against a speed setting
spring that opens it. The basic problem with this feedback arrangement, is that
the throttle cannot be opened, unless the RPM drops, often by as much as 10%
(eg 50Hz down to 45Hz) for full load, with a resulting frequency & voltage
drop.
For many items the correct voltage is necessary for the correct & safe
operation. Over voltage is generally damaging, under voltage can cause many
different type of effect, from frequency drift to Tx distortion, to computer
brown-outs that can damage your HDD.
Some generators use overall voltage control, affecting the throttle directly,
and/or feedback that varies the rotor excitation level.
LOAD COMPENSATION
In the simple bob weight RPM control method, better load voltage regulation can
be obtained with some additional load current feedback (feed-forward).
This can easily be applied, by adding a small solenoid (eg. from an old VCR)
rewound with a few turns of suitably insulated & thick enamelled copper wire,
that takes the load current. It is then mounted firmly on the engine/alternator
& linked up to aid the speed setting spring. Even though the DC solenoid is on
50Hz the pull is quite adequate if it has a fully wound bobbin.
__
CRANKCASE BOB ³()³
WEIGHT GOVERNOR³ ³ SPRING ___SPEED
CARBURETTOR__ holes in³ :³-/\/\/\-[___SCREW ÚÄÄÄÄÄÄÄÄ¿
THROTTLE ³()³ adjustment arm³ :³=======================²³SOLENOID³
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 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.
I have done this modification to several generators now, & here is results of a
1.3KW rated (1.5KW peak) generator to make it produce a steady 240V...
LOAD BEFORE MOD AFTER MOD IMPROVEMENT
WATTS VOLTS VOLTS VOLTS %
0 250 250 0 0
100 240 240 0 0
500 230 238 8 3.3
1000 220 242 22 9.2
1500 200 240 40 16.7
With this modification the throttle is opened much earlier when a load is
applied. As soon as the load comes on, you hear the engine rev 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.
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 control loop fights the varying current-voltage load. But
normally there are no problems, and they are very efficient for /P use, if
there are no QRM problems. Overvoltage 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 (eg 115V 180W heater misused on 230V with a diode!). On
small magnetic devices like isolation transformers & generators the DC current
will saturate the core (lock up) & reduce the inductance by many times,
resulting in dramatic loss of O/P power or possible damage. Even on a long
resistive lead on real mains with one, can damage other kit (transformers) with
the DC produced!
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.
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 needs a 0.47uF @ 300V AC & a 20W fluorescent
lamp needs 100VA correction that is 5uF @ 300v AC. Having them fully corrected
(PF=1) helps with other peak pulse loads, as the sine wave shape is maintained!
L ÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄ¿
test C³ )º INDUCTIVE
MAINS === )º LOAD
AC AMP ³ )º
N ÄÄ Meter ÄÄÄÁÄÄÄÄÄÙ
The exact amount of C needed can be measured if you have a bank of suitable
caps to try out. Use a 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 gains for fully corrected loads are small & may not actually be
worth the trouble!
N.B. mains filters & PF correction caps can degrade mains intercoms!
Part 4 has RMS Sine Waves, Safety, & Security
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
