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G8MNY  > TECHNI   04.10.21 09:20l 214 Lines 10043 Bytes #999 (0) @ WW
BID : 48612_GB7CIP
Subj: NORTHERN 650W 2 Stroke Genny
Sent: 211004/0710Z @:GB7CIP.#32.GBR.EURO #:48612 [Caterham Surrey GBR]

By G8MNY                                       (Updated Sep 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I bought this very clean & hardly used non working 63cc one at a junk sale, &
"it worked OK last year" I was told! It seems identical to the Wolf, Pro User &
KINGAVON versions.

On looking into the non-running, there was no intake "suck". This is a 2 stroke
with an angled engine & the carburettor ported into the crank case with a reed
valve, rather than an upright engine with bottom edge of piston valve intake.

Oil Measuring
  Filler Cap                       Handle 
        ===                              ===  
       /~~~~Tank~~~~~\                 /~~~~~~Tank~~~~~~~\
      -----------------               ---------------------
 Mains|              DC|~~~~~~~~~~~~~~~~|On/off
      |(0)=      _-~\Silencer        |MAINS   choke []|
 ChokeTap Start\\\\\\Plg                       ===== |\ 
      |Ŀpull~\\Cyl\               ޳-----------------| |Pull
  Air |Carb,\/~~~\\_-~     Alternatorݳ       Air       ||Start
 Box &|      ( )                 ޳      Filter     | |
Filter\ \___/ /                  _________________|/
       """         """                   """           """
Checking the ignition, there was a weak spark OK, & there was compression, so I
tried putting petrol/ether spray into the crankcase through the reed intake
valve, but the engine still did not fire. So I put took the silencer off
(needed painting anyway) & put spray through the exhaust port, this did give a
bang on turning over, so the ignition & timing was OK.

The fault was eventually found to be a popped out crankshaft bearing air seal
rubber, between the engine & the alternator. This may have happened if there
had been a back fire in the crankcase, or just a lot of compression. There was
non of the usual spring circlip in a groove to hold it in place in this design!

      __        __ & RIGHT ANGLE
      Ŀ     SEAL CLAMPS
Web  Tap    Tap  Web
    hole><hole            >  Air tight Oil Seal
        (o)(o)                (o)  Ball race bearing

To get to the fault, I needed to split the alternator off the engine (3 outer
bolts) & remove silencer & gently levering off the end casing. A long bolt
through the alternator shaft holds it on to the tapered crankshaft, this was
the first problem & a smart tap the socket set freed this OK. Then on the lose
bolt a sharp tap with a hammer to free the crankshaft off the alternator rotor.
Now was the problem of fixing the hardly worn air seal back in place so it
would not spin. Initially I used instant gasket sealant, but eventually I added
2 right angle metal pieces, held in by drilled & tapped screws in the available
cast lugs around the bearing, these lock the seal in place.

But this failed a year later with the captured seal managing to get half way
out. I managed to find a new tight fitting seal & a circlip to hold it in
place just in cast it started to rotate & loosen as the old one did.

Also I noticed the Alternator Fan was loose, this removes about 100W of heat, &
blows it over the exhaust, but it was able to free wheel! I used 2 part glue
(resin & hardener) to fixed that OK, & re-fixed the 2 locating lugs etc.

             Long Bolt
      Bearing  [~~]
  l    ݱ    l  FAN
__u_ _ ݱ _ _u__
     ۱ݱCOIL &

Not having the handbook etc. I have reverse engineered the diagram...

  12V           240V AC                   STOP
Charging          Ŀ                 o\__
+   -           E    __              bn    bk
3A Bridge       N   L  ///             ------------
Rectifier                            |Electronic|Ŀor
       (155V)                      | Ignition |       
7A    15u 450V   2.3A                |  Module  |   0.22k2
Trip  ĴĿ     Trip                ------------   ()))))ͻ
  gn   ye                                     =====     
 gn  ye    bk rd             rd/wh bn  bk      Coil   EHT
__ __ _ _ __ _ __ _ _ _ _ _ _ _ _  _ _ _ _ _  _ _ _ _ lead
                         |    34|(   )|                
 .3 3.2   6.8  ROTOR  | Timing|(   )|           Plug 
 ()) ((()  (((() (((() | Pickup   > <5k
  ====  ====    =====  ===== | & Magneto 730  __    __
                       Ĵ>Ĵ |                 ///    ///
  A L T E R N A T O R  R |     C R A N K C A S E

This is a brushless alternator with the excitation of the rotor magnetically
charged up each half cycle from circulating 90 out of phase currents from the
exciting 15uF capacitor. The rotor winding has a diode across (& back emf R) it
to maintain the current, half a cycle after the kick. Excitation only starts at
high enough RPM (2000RPM) to overcome the diode voltage drop loss, with the
weak residual magnetic rotor field. This system is more reliable than the brush
type, but it does produce a kink in the load winding waveform & there is no
opportunity for voltage control other than engine RPM.

As I did not have the special DC plug & lead, I made a plug (- |) from 2 brass
strips, poked these into socket & through cardboard, to form the plug's mould
base, & fitted a cardboard tube. Made the lot into a good mould, & with the
petrol tank removed up end the generator to get the socket level, spay oil /
grease into the socket holes & refit the plug strips & mould.
   _       Mix up resin & hardener with some fiber glass to add strength
 Ŀ  for the plug base. pour in & tamp down. When set remove the new
   plug, cut off the cardboard mould, Grind & file off the resin
          lump into the wanted shape, Solder on the new lead to the brass
          strips noting +/- & tape the lot up in rubber amalgamating tape,
  _       this finishes the plug.

Although there is a 7A trip (12A to activate!) before the bridge, the rectifier
is only made from 4x 3A diodes in the connector box with no heat sink! To
improve on this, I cleaned off all the painted copper track, & flowed a thick
layer of solder all over it to act as a heat spreader. And I also doubled up on
the diodes, putting 4 more on the copper side of the PCB. Note the current trip
does not prevent blowing the diodes on wrong battery polarity! So a 13A fuse in
the charging lead will help that!

In practice though on a good battery the charging current is only 3-4A, but
enough to boost a flat car battery (@ 10A ?) in a few mins so you can crank the
car over.

1/ To reduce the VHF/UHF ignition noise, I have added a loose coax braid over
the lead earthed at the plug screened cap.

            ________       Added loose Coax Braid
     Metal -================================----- EHT Lead To
     Cover |n|-================================ Magneto coil
suppressor ݳ~|~~~
 plug cover 
        _  ~~~
            ~u~Spark Plug

2/ To improve the voltage regulation, I applied my current solenoid feed
forward modification. This was easily done, 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 4A full load current (neutral).
Mounted is with a single large screw, firmly on the engine webbing, by the
speed setting adjuster. (Tap/Make hole in webbing) The solenoid piston is
linked up to aid the speed setting spring as the load comes on. The length of
the thick link wire is critical so that the piston only just goes fully home at
full throttle, & if less compensation is needed the wire can be bent slightly
to adjust the effect (Mount the petrol tank via a pipe elsewhere for testing).
                      SPRING      ___ SPEED
                 o,/\/\/\.[___[ADJUSTOR SCREW
                 o  Link Wire   Ŀ
                     BOOST__\    Alternator
                      PULL  /      bk bk  Load
                               Neutral Neutral
                 Throttle link

N.B. Solenoid pull is proportional to:-
     1/ the Mains load current squared,
     2/ the number of turns on solenoid coil,
     3/ the location of the movable iron piston slug.

With this modification a good 230V @ 750W peak is available under resistive
lamp load tests from this small generator.

Although 2 stokes are not the best engine for efficiency etc. & fuel oil mix is
needed, their simplicity & reliability if maintained (clean carburettor &
muffler) it does give a simple lightweight power source. The noise of this one
changes from poor putting misfires on no load, to a steady 50Hz hum on higher

N.B. if the engine is difficult to start, "ether spray" in the air inlet does

So a lot of work was needed, but now I have good genny in the end for /P work.

See my TECH buls "Regulating 12V Generator Output", "Cheaper Generators" &
"Petrol Generators for /P SSB"

Y Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP

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