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Ex-Military Spec 6JB compression issue

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Old 03-14-2017, 05:39:13 AM
MadGutts MadGutts is offline
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Default Re: Ex-Military Spec 6JB compression issue

Ok so wound engine speed back up, but at 50 cycles im getting well over 300V!!! so in the manual it says to to adjust the resister by sliding the outer "connector" up or down...
So looking on the alternator -i took the end cover off i can see the windings and a variable resister (if thats the correct term, but there is also another one on the side of the alternator at the front near the engine on the side by the exhaust... so which is the one i am supposed to adjust?

Also whilst i had the generator running, with the cover on, there was smoke comming from the alternator "exhaust" which is what me remove the end cover... the top and bottom coils were very hot and the smoke was coming from them! after i let them cool, i checked the resistance and they seem ok - not short circuit so im hoping it was only down to the over voltage of the set...

Many thanks for you help guys.
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Old 03-14-2017, 08:07:12 AM
Wayne 440 Wayne 440 is offline
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Default Re: Ex-Military Spec 6JB compression issue

The resistor under the end bell is the one for AC Voltage, the one in the generator cooling outlet is for the battery charging rate.
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Old 03-14-2017, 09:11:20 AM
PopsGarage PopsGarage is offline
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Default Re: Ex-Military Spec 6JB compression issue

sounds like the magnaciter is changing to a magnasmoker . dont run it I'am sure someone smarter than I can guide you in the right direction for testing.
Where is Leon when you need him?
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Old 03-14-2017, 10:37:43 AM
Leon N. Leon N. is offline
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Default Re: Ex-Military Spec 6JB compression issue

Oh No! Over heating the mag amp toroid's "could" be caused by operating the magneciter at too low a speed/frequency. Onan does make a 50 Hz magneciter/1500 RPM machines. Are you sure your JB was meant for 50 Hz? Please take a close up picture of the JB name plate so that we can confirm you have indeed a 50 Hz machine.

Also, provide your complete model and serial number and that way a Stak member can hopefully find the original Onan factory build sheet. That will indeed confirm what you have.
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Old 03-14-2017, 10:49:31 AM
Jim Rankin Jim Rankin is offline
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Default Re: Ex-Military Spec 6JB compression issue

See the magneciter checkout pages in the Magneciter theory post in the FAQ section at the top of this Onan board. Page three of posts has the tables of symptoms and tests to diagnose. A number of them are high voltage problems.
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