Johson charging rectifier

[Macengine]

I have a 1980 Johnson Workhorse. A previous owner had it converted from hand to electric start. No charging gear was fitted. I have now obtained the correct charging coils to fit to the stator but I don't have a rectifier and in anyy case they are very expensive in Australia where I live. I am a retired Elect.technician and it was my intentlon to build a full wave bridge rectifier using diodes on suitable heat sink. I now understand that the Original equipment model uses 6 diodes. Normally 4 would be OK. can anyone advise me why they use 6 and does any know how the 6 are connected.?

 

[tallcanadian]

Re: Johson charging rectifier

what size motor you got there, macengine?

 

[Macengine]

Re: Johson charging rectifier

what size motor you got there, macengine?

Sorry I forgot to mention the HP, it is 40hp.

 

[Vic.S]

Re: Johson charging rectifier

No problem .

You have three wires from the stator coil assy you have bought, right.

The rectifier is the same as a three phase one.

This diagram should tell you all you need to know. (Ignore the top one that for wiring AC lights)

 

[Macengine]

Re: Johson charging rectifier

Thanks Vic S.--That looks OK. will try it out and will let you know how it works.

 

[Macengine]

Re: Johson charging rectifier

Hi all I made up the new diode bridge and mounted it, I am sure it will be O.K. This was the last job to finish after fitting a totally re-built powerhead.
Sadly the engine won't start; no spark! I have fitted and gapped new points and new plugs. magneto driver coil seems O.K. (reads 1.7 ohms on the 200 volt scale). flywheel magnets hold a big screwdriver in suspension. Ignition coils, primaries read 1.7 ohms (200 ohm scale) . Ignition coil secondaries measure 17.3 and 13.3 respectively (200K scale) Imention the scale as I am using a cheap Digitech Multimeter and it will not measure coil secondaries on the lower scales. Obviously one coil has shorted turns but I can't get a spark with either.
I would like to check the ac voltage output from the magneto coil but I have no idea what it should be, can anyone help? Also any other advice woul be appreciated.
This engine has not been used for 3 years and the ignition coils had only been fitted for 6 months and had about 8 hours running time. The engine seized, I let it cool squirted a bit of oil in the cylinders and it re-started. After 2 hours running it rattled like hell so I dismantled and a mate re-built the powerhead, hower the coils were O.K. at the time I dismantled it The coils are cylinder head mounted.
Sorry about the length of this diatribe but a lot of it seems relevant when diagnosing. We are nearly half way thro the 1st of Jan now in Australia so I reckon many people will be just stating to celebrate.. Have a great time and a safe, healthy and happy new year.---------Macengine

 

[F_R]

Re: Johson charging rectifier

Edit: Oops, wrong motor. Deleted

 

[James R]

Re: Johson charging rectifier

Dont find a 1980 40hp listed on BRP, however I can assume that you have a Power pack on this motor having plugs and sockets. Try cleaning the plug and socket pins to see if you can get your spark back. Your charging system is irelevant without a spark mate.

 

[Macengine]

Re: Johson charging rectifier

Thanks James R, actially the motor is not 1980 I think it was built around 1975 but this is an ex Australian Army motor and I was given the date when it was released (unused) by the army. I suspect it was built around 1975/6 and the serial number is 8127958. The ignition id contact breaker type with the points etc. under flywheel. The ignition coils are mounted on the cylinder head.
Sorry about the confusion (it had me fooled too.----Macengine

 

[hawkerjv]

Re: Johson charging rectifier

Hi,
Have you got spark yet?
Sounds like the low tension ignition system. This one uses two sets of points and condensers and one exciter coil under the flywheel one secondary coil for each cyl. It was a transision system between the old High tension system and the ones with module. Works good on my '75-25HP and '76-35HP.
Jim in Wisconsin

 

[Macengine]

Re: Johson charging rectifier

Thanks Hawkerjv, I think you are probably right as I have tried a number of ignition coils (these are the cylinder head mounted ones) , I have checked the leads and the points a hundred (it times it seems) and they all test OK. This leaves 3 possibilities 1- The driver coil. 2- The capacitors. 3. Weak magnet strength. The problem is that you need a special meter to read the value of the supply into the primary (ie. the magneto output) it is a peak voltage DVA meter. I am hoping to get a loan of one next week but in the meantime I will buy new capacitors and try again. Does any body know what a multimeter should read on a healthy engine ie. the voltage between the coil primary and ground? Or indeed will an ordinary multimeter show anything.Mine doesn't but then the engine is crook. Also what should the resistance of the driver coil be?
In the meantime I am fishing from my mate's boat but he is getting fed up with it as I am catching fish and he isn't.
Thanks again.--------------Macengine