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Onan Generators

Building a "Mount" for the Onan Power Plant


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  #41  
Old 10-25-2017, 02:47:34 PM
JoeE. JoeE. is offline
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Default Diode photo

I hate when I forget something in a post and have to make another reply....

Photo closeup of the offending diode. See how nice the end of that pin looks?

That dark spot makes me think that pin is hollow, like the tube on an ink pen...

Like I said... hopefully it was just vibrational stress and not an electrical related failure

I'm off to go check on the availability of a replacement diode!
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  #42  
Old 10-25-2017, 04:53:01 PM
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Default Diode....

Okay, after a little digging in his parts bins I come up with one with the right polarity in the right stud size.

I also grabbed the broken diode and soldered a wire back onto the remaining portion of the pin sticking out...
He says it'll still work like that, so I'm going to try the brand new one and see if it works then I might try the old one too who knows...
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  #43  
Old 10-25-2017, 05:03:43 PM
Leon N. Leon N. is offline
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Default Re: Diode photo

You may luck out. Sounds like you have a defective diode. You mention vibration? There should be no vibration of any consequence. One test I would recommend WRT vibration. If your plant is tied down correctly, you should be able to take your hand and literally rock it slightly laterally WRT the shaft centerline. If you have excessive (?) vibration, maybe the engine fan is out of round, for example, a broken fin on the flywheel.

WRT that diode I found was able to locate it in a couple of document. On that schematic you mentioned, 625A631, it is shown as diode "v" connected to terminal 35. There are two more of the same labeled y & z. All three of these diodes are listed as item 5 and described as rectifier, field positive. They are also shown by an Onan part number, 305P239 on page 45 of 967-320 of 967-320, the JB PL.

If I recall from previous discussions and Stak information, these are beefy diodes. I'll bet they have a rather high PIV and forward current capability. Maybe some one can cross reference the Onan part number 309P239 to the numbers you mentioned, that is 80015 and 7242. Good luck.
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  #44  
Old 10-25-2017, 05:39:48 PM
gnucklehead gnucklehead is offline
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Default Re: Building a "mount" for the Onan Power Plant

Leon beat me to it, but I see the Diode marked V for the POS field.

EDIT: The broken diode appears to be an addition to the V diode

Last edited by gnucklehead; 10-25-2017 at 08:19:03 PM.
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  #45  
Old 10-25-2017, 06:08:27 PM
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Default Replaced with new diode...

.... And still nothing... It had the same polarity and same size and same everything, he said it should work... So I'm going to put the old one back in and try that.
It didn't have any battery charge or AC output...
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  #46  
Old 10-25-2017, 06:15:06 PM
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Default Maybe it's something on this assembly?

There are five of the stud type diodes on that assembly and four of the other kind.... the black cartridge type.... with leads out of each end.
I'm not sure if I read anybody say to check those toroid coil contraptions on there... The two big ones in the small one?
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  #47  
Old 10-25-2017, 06:19:25 PM
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Default Re: Building a "mount" for the Onan Power Plant

Where do you test for power to the Magnaciter tested for at?
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  #48  
Old 10-25-2017, 07:26:36 PM
gnucklehead gnucklehead is offline
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Default Re: Building a "mount" for the Onan Power Plant

Hmm.. There appears to be five stud-mounted diodes in addition to the broken one? I'm thinking the broken diode is a half-azzed modification that shouldn't be there. The "V" flashing diode that should be connected to terminal 35 is mounted to a flange with two other diodes.
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  #49  
Old 10-25-2017, 07:27:57 PM
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Default Re: Building a "mount" for the Onan Power Plant

I just refurbished my Mageciter (04SX1N3B) and replaced all the stud rectifiers. 20 amp, 400 PIV, available at (possibly) your local electronics store. On mine, 3 positive, 3 negative. The "v", "y" "z", and "w", "x" reference the individual rectifiers from the schematic to the wiring diagram. When I got mine, the packaging had "anode to case" and "cathode to case" markings. Also, the "direction" is printed directly on the rectifier. Connecting the battery incorrectly would also fry the charging diode in the control box, mounted on the heat sink. Use the same rating for that one, as well. BUT, use the supplied insulating materials - the heat sink is bolted to the control box (battery negative/ground). Not insulating this rectifier will let the magic smoke out. zuhnc
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  #50  
Old 10-25-2017, 07:33:35 PM
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Default Re: Building a "mount" for the Onan Power Plant

One cannot assume all stud type diodes are electrically the same. Take a look at the references I mentioned. The Magneciter or more specifically the exciter is powered from the stator leads E1 & E2. If the exciter is working correctly, you should measure a DC voltage ranging from a low value to a max value at full load of 40 VDC across the slip rings F1 & F2. That DC voltage provides the revolving magnetic field that excites the stator so the two stator windings that provide the 4-wire T1-T4 with T2 tied to the chassis before you crank the starter. When you crank the starter, and only during cranking 12 volts positive is provide via terminal 35 on the exciter through that diode to the rotor slip rings, F1 & F2 to temporarily flash the rotors revolving field thus enabling the stator to produce AC voltage and off you go.
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  #51  
Old 10-25-2017, 08:33:32 PM
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Default Re: Building a "mount" for the Onan Power Plant

Quote:
Originally Posted by zuhnc View Post
I just refurbished my Mageciter (04SX1N3B) and replaced all the stud rectifiers. 20 amp, 400 PIV, available at (possibly) your local electronics store. On mine, 3 positive, 3 negative. The "v", "y" "z", and "w", "x" reference the individual rectifiers from the schematic to the wiring diagram. When I got mine, the packaging had "anode to case" and "cathode to case" markings. Also, the "direction" is printed directly on the rectifier. Connecting the battery incorrectly would also fry the charging diode in the control box, mounted on the heat sink. Use the same rating for that one, as well. BUT, use the supplied insulating materials - the heat sink is bolted to the control box (battery negative/ground). Not insulating this rectifier will let the magic smoke out. zuhnc
Does yours have this diode with E2 on the stud? Is it insulated from the chassis? These are pretty slick regulators, really interesting the way it works

https://www.smokstak.com/forum/attac...7&d=1508902333
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  #52  
Old 10-25-2017, 10:05:29 PM
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Default Re: Building a "mount" for the Onan Power Plant

Per the schematic, "E2" (AC input to Magneciter and same as T2, AC output to load, must be grounded) is connected only to the "pigtails" of rectifiers labeled "y" and "x", one positive and one negative, as well as terminal "E1" on the "bridge rectifier" (the 4 individual small diodes), in addition to one end of the voltage control resistor. My unit does NOT have item number "8" on the schematic. It seems to work well without it. And, I do not know the purpose of rectifier "8". It may be similar to the free-wheeling diode mounted on some relays to bypass or reduce transient voltages caused by the relay (read - field flash circuit) when the start disconnect circuit operates. None of the rectifiers on the Magneciter assembly is insulated from its copper mounting plate. The plates act as a heat sink. The document "Onan Magneciter Service- SECTION 4. REVOLVING FIELD GENERATORS.pdf" is available on the twinslan site, I believe. That document has all the relevant information, schematics and wiring diagrams for the Magneciter. zuhnc
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  #53  
Old 10-25-2017, 10:33:06 PM
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Default Re: Building a "mount" for the Onan Power Plant

I would think you should have item no. 8. It is described as "Rectifier - Field negative and consists of two diodes, w & X.

Keep in mind there are different wiring diagrams depending upon your particular JB and factory build to spec letter. Here we are talking about the 04SX1N3B exciter which contains automatic field flashing which was introduced with factory build spec P.
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  #54  
Old 10-26-2017, 05:21:32 AM
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Question Re: Building a "mount" for the Onan Power Plant

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Originally Posted by nothingbutdarts View Post
I'm still trying to get my head wrapped around the fact the starter worked OK with the fact the battery was hooked up backwards?
Same here.

It's a DC motor, correct?
Wouldn't it run in reverse?
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Old 10-26-2017, 07:28:01 AM
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Default Re: Building a "mount" for the Onan Power Plant

No it would not run in reverse unless one changed the direction of the DC current flowing in either the armature or the field but not both. Usually just switch the two field pole wires to reverse the current flowing in the field relative to the armature winding. The starters are DC series wound motors as opposed to shunt wound motors. There are also compound wound DC motors but that is another story.
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Old 10-26-2017, 09:57:45 AM
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Default Re: Building a "mount" for the Onan Power Plant

DC motors with permanent magnets will reverse direction with polarity, because the field doesn't change poles..

The broken diode and chassis connections don't show up on DWG 625A631 (nor the parts list), but it does show up on the drawing on page 4-14 in the pdf as another type #8 anode stud. Page 4-7 has a biig caution statement about negative-ground battery and grounded alternator T2 requirements for the auto flash to work (and avoid damage). Lots of info on resistance measurements and testing. You'll need to look at the controls for any semiconductors that might have been zapped.

http://www.twinslan.net/~n0nas/manua...GENERATORS.pdf
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Old 10-26-2017, 11:38:45 AM
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Default Re: Building a "mount" for the Onan Power Plant

OK then, which one of you two want to do a video of reversing you battery cables on the battery and crank the generator????

Last edited by nothingbutdarts; 10-26-2017 at 12:24:21 PM.
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  #58  
Old 10-26-2017, 11:42:19 AM
Leon N. Leon N. is offline
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Default Re: Building a "mount" for the Onan Power Plant

gnucklehead one must be very careful to use the correct wiring diagram for the specific magnectier being discussed. The thread author is referring to 625A631 and that diagram DOES show type #8 there as "v" with its anode connected to terminal 35. The diagram on page 4-14 is a "typical" magneciter diagram for a particular class of static exciters. It may be a later version or an update to 625A631. The thread author needs to confirm.

What you say about PM dc motors is true but those PM designs are generally for low torque applications.
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Old 10-26-2017, 05:14:32 PM
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Default

I'm not claiming that I'm using the right schematic, I'm just going by what the model of the machine listed at the top of the pages as far as the control wiring diagram is concerned.
I'm pretty confident on the Exciter page because it is listed as 04SX1N3B Exciter wiring diagram
The Machine model number is 7.5 JB - 3CR/8389T.
None of the diagrams in the manual I have printed off go past spec P, so I can't guarantee any of the stuff I'm looking at is actually aimed towards my model of machine.
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Old 10-26-2017, 05:27:00 PM
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Default Re: Building a "mount" for the Onan Power Plant

PM motors are why most people think that reversing polarity reverses rotation direction, definitely doesn't apply here You managed to write down in one short sentence, what would take me a couple of rambling paragraphs to explain Darts, I'll find an old starter motor without magnets and try it.. google right-hand rule for magnetic forces, might help explain.

Maybe the entire "typical" diagram doesn't apply, but it sure looks like it does for the autoflash section (terminal 35 to the POS field) - fairly confident that the Joe's broken diode does not appear on drawing 625A631.This diode (anode stud mounted to the chassis) and the V diode both have a connection to terminal 35.
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