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Building a "Mount" for the Onan Power Plant


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  #61  
Old 10-26-2017, 05:51:10 PM
Leon N. Leon N. is offline
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Default Re: Building a "mount" for the Onan Power Plant

Right hand rule--hmm, a little bit of knowledge can be a dangerous thing. You got to be crazy to try staring your JB with the battery polarity reversed. I hope no one trys that.

JoeE should check his factory build sheet. It may list the wiring diagram. Back in 1970, Onan sent me the correct owners manual for my JB which was built to spec P. Throughout the manual, there are several places where they refer to the factory build to spec. In some places the manual says, "prior to spec P" in other places it says " to spec F" and in other places it says, "beginning spec P". That terminology can be found in many Onan documents.
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Old 10-26-2017, 07:56:10 PM
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Default Re: Building a "mount" for the Onan Power Plant

My error. I do have two of the part #8, labeled "w" and "x", but I DO NOT have the part #8 that is connected between "ground" and terminal # 35. This appears to be the correct diagram for my Magneciter, as mine was (before refurbishing) conspicuously labeled "O4SX1N3B", with the exception of the aforementioned rectifier. My unit does not appear to suffer any issues without it. But, I will most likely install it. zuhnc
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  #63  
Old 10-27-2017, 10:08:39 AM
JoeE. JoeE. is offline
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Thinking out loud, if something was going to burn up because of the reversed polarity, you'd think it would do it immediately upon starting.

But, the thing sat there and ran for probably a good 60 seconds til I realized the problem and remedied it... and worked normally afterwards.

My question now... does AC production out of the generator depend on DC voltage supplied by the charging system?

Does it need constant excitation, or does it "self excite after it starts producing AC.. .and the DC produced only get used to charge the battery?

It looks like a lot of trouble disconnecting the leads from those exciter coils and figuring out which ones to test for continuity.
Disconnecting the individual diodes to check them for "open" or "short" won't be too bad, but that bridge rectifier... not sure about that.

Anyway, the cold weather gives me a good excuse to ignore it for a while
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  #64  
Old 10-27-2017, 10:19:37 AM
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Default Re: Building a "mount" for the Onan Power Plant

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... My question now... does AC production out of the generator depend on DC voltage supplied by the charging system?

I'm no magniciter expert, but I'm pretty sure the answer is generally no, with the possible exception of the need to flash the generator. The flash circuit would depend on the DC side of the system. Otherwise, the AC side is probably independent.
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Old 10-27-2017, 11:14:47 AM
Leon N. Leon N. is offline
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Default Re: Building a "mount" for the Onan Power Plant

Jim I think your answer for his version of the magneciter is 100 % correct. Thank you.

If his generator is producing 120/240 VAC but not charging then he has probably a failed 1/2 wave diode rectifier and/or a burnt out stator charging winding. Just trace the circuit on the control wiring diagram such as 611C805. Not much to it. That charging diode is located inside the control box. The resistor limiting charge current is located in the generator hot air exhaust. Didn't he say that resistor glowed red hot? Wow! Maybe that is what failed.
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Old 10-27-2017, 01:14:23 PM
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Default Re: Building a "mount" for the Onan Power Plant

There is no AC being produced.

The charge limiting resistor in the hot air exhaust tests good... 2 ohms resistance.

The charging diode in the control box tests good, also, I didn't remove it, just tested in insitu. I disconnected the wiring on terminals 7 and 8, I believe it was, and performed the test on those two wires... shows continuity one way, not the other. To me, that's good.

As far as the charging winding, I clamped one test lead to the terminal on the top of the charge current limiting resistor in the hot air exhaust and touched the other lead to the terminal it comes from up in the control box, and it has continuity.
Without the diagram right here in front of me, I can't tell you exactly where that was, but I followed the wire on the diagram and probed a few points up in the control box where it showed it went...

If I think of more that I checked, I'll come back and add that later.
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Old 10-27-2017, 02:30:45 PM
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Default Re: Building a "mount" for the Onan Power Plant

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Originally Posted by Jim McIntyre View Post
The flash circuit would depend on the DC side of the system. Otherwise, the AC side is probably independent.
So, all the AC side needs is a "flash", and it starts producing. AC has no polarity, so really, if the flash is just an instantaneous jolt of DC, how does it actually matter which way the flash circuit is powered?
I know it does, cause the manual says so, but it makes me curious!
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Old 10-27-2017, 05:15:48 PM
Leon N. Leon N. is offline
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Default Re: Building a "mount" for the Onan Power Plant

JoeE you raise some very interesting questions. The general answer to your question is No it does not matter. However, looking at and tracing the current path of the wrongly applied battery voltage, between E2 & terminal 35 could result in diode failures.

I am not an expert on the exciter but strictly from an understanding of how it works and looking at diagram 625A631 I would venture to say the following in regard to your questions.

The revolving field is powered by a DC current with F1 being positive and F2 being negative. Onan says on the 7.5 JB spec sheet that the exciter puts out 40 volts @ 400 watts with a transient response of 1400 watts.

So here you come and impose a negative voltage on terminal 35 WRT E2. Maybe this mistake destroyed one or more diodes in the dc series circuit involving the rotor F1-F2. Just trace the possible paths through positively biased diodes and the toroid's from E2 back to terminal 35 which was mistakenly the battery negative side..

I do not think any damage was done to the rotor. Even if the rotor was magnetized in the wrong polarity, it still would generate an AC voltage across the three stator windings. The problem may be that one or more of those rectifier diodes that are in series with the rotor F1-F2 circuit my be blown and thus no AC voltage may be developed. Not sure. If you could some how measure the DC voltage across F1 - F2 that may tell you something.

So what is the current status of your magneciter? Does it work?
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Old 11-06-2017, 01:17:02 AM
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Ok, an update... nothing positive, but nothing negative, to report

I checked the two different stator windings today... they have continuity, not shorted or open.

Again, I checked the battery charge winding... it shows continuity.

So, I disconnected the exciter from the generator housing. Made some labels and attached them to relieve me from straining my eyes to see the dim label attached to the terminal strip on the exciter where the wiring loom connects.

MAN... I really don't want to disconnect all these things to check those 3 "reactors" (torroid coils?) continuity and diode "health" ... all those varnished connections... nuts on diodes.. everything is varnished. There are 3 resistors.. 2 large and one small, on the thing.. those will be easy.

I'm having trouble trying to translate what I'm seeing on the schematic to where terminals are where on the exciter.... like "G1" and "G2"... which "control reactor" is A and which one is B... little details like that make it difficult to know exactly where to start.
I figure doing the process of elimination by checking the resistors out.. eliminating them, maybe I can slowly figure out which things are which and where their wires terminate...

I'm guessing it's probably a rectifier... but I want to eliminate all the irreplaceable items first.. those "gate reactors" and the "control reactors".

Didn't I read in another thread that there is an item available to do away with this exciter? I read the thread, but can't remember the exact language.. didn't want to get my hopes all up..
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Old 11-06-2017, 10:57:41 AM
Leon N. Leon N. is offline
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Default Re: Building a "mount" for the Onan Power Plant

Why not take a closer look at the schematic portion of your wiring diagram, 625A631 and trace the current path from E2 back to E1 since you inadvertently reversed the 12 volt battery leads and made the chassis ground the positive side of the battery. Note, T2 and E2 should always be connected to the chassis. Not sure but you may have blown one or more diodes in the exciter. I would suspect that is the case before checking the resistors unless one of the resistors shows evidence of over heating.

I would use a high resistance ohm meter and first without disconnecting any of the diodes, see if you can measure a front-to-back ratio of at least 100 to 1 in resistance. maybe you cannot not due to circuit connections but maybe you can.

I would start with diode # "y" and diode # "w" and see what you get from the forward resistance vs the back resistance by reversing your meter leads.

If all this looks and sounds reasonable, maybe you burnt open one of the DC control windings in toroid A or B or even the control reactor. To check for that, you would have to disconnect some of the connections to those toroid's.

Before I would do the later, I would follow the trouble shooting listed in Section 4 entitled the Revolving Field Generators.
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Old 11-06-2017, 12:45:45 PM
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Default Re: Building a "mount" for the Onan Power Plant

The major problem is in identifying the individual components by trying to decipher the schematic.
Testing will be the easy part, figuring out what is what and which connection is which, from the diagram, is the hard part.
Like I said, which is gate reactor A and which is B... It's not hard to figure out which one is control reactor....
Something else....I'm going to have to run to the hardware store and buy some new wire label assortments so I can identify these wires as I remove them ....so they get put back where they came from... The ones I have are probably 20 years old and the adhesive on the back of the strip is lacking.
E2 and E1 and 35 are not readily identifiable on the insulation covering the wire... F1 and F2 are.
When I came in the shop this morning, all those labels that I made and applied to the wire we're laying on the floor scattered out... The adhesive let loose and they all came off the wire... All except the letter 1 for the E1...
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  #72  
Old 11-06-2017, 01:04:59 PM
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Default Re: Building a "mount" for the Onan Power Plant

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...which is gate reactor A and which is B?...
'B' has a connection to F2 of the field. 'A' doesn't.
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Old 11-06-2017, 01:06:28 PM
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Default Re: Building a "mount" for the Onan Power Plant

I have found the wires labeled G1 and G2 coming from the gate reactors where they attach to the bridge rectifier.
Another thing that's difficult is making out what the numbers are on the schematic itself... They don't reproduce well, making it hard to differentiate between a letter G and a letter C and a number 6... 😋
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Old 11-06-2017, 01:45:53 PM
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Default Re: Building a "mount" for the Onan Power Plant

This may sound easy but what I would do is use a continuity tester or ohm meter and start from a physically known point on the schematic and probe along following the wires. As for not being able to read the small diode numbers on the schematic portion of the wiring diagram, if you cannot see the small diode designations like. "v" or "w" let me know and maybe I can email you a blown up copy. Just need you emai address. Or, maybe I can attach it to this thread. What do you think?

Here is another way to trace out the exciter circuits. Referring to your wiring diagram, 625A631 please notice the 7-terminal strip on the diagram. I have attached a picture of mine. Notice the bottom terminal is not used, no wires attached to it - and that terminal strip is also shown on 625A631. So, for example, terminal 35 is the top terminal, E1 is the fourth terminal down from the top and E2 is the fifth terminal down on that terminal strip.
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Old 11-06-2017, 03:35:58 PM
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I print the schematic off the download I think I got from you already... on my nice laser scanner. It reproduces exactly what it sees on the screen... it's just the download isn't very crisp itself.

Anyhow, I took the result to work and used their copier to enlarge the exciter diagram 175%, and the other diagram next to it 200%.

That helps, but if I do still have trouble deducing some of the numbers/letters. Like I said, since they're not crisply scanned in the first place, it's hard to tell a 6 from a G from a C.

I can see the 4 diodes letters, alright. I'm just suffering through tracing wires from the torroids and figuring out their numbers.

I also searched and found the discussion about the Powertronics UVR500 and SE350 to replace the exciter.

I see that they are discontinued. So, is that the end of a workaround in case a persons' exciter is fried, or is their another source of equipment to replace them with?
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Old 11-06-2017, 03:57:27 PM
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Default Re: Building a "mount" for the Onan Power Plant

What are you tying to do anyways? Would not disconnect anything until reasonably sure a component is bad. That entire exciter may be conformal coated thus remaking good terminal contacts may require extra care.
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Old 11-06-2017, 07:19:29 PM
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Default Re: Building a "mount" for the Onan Power Plant

Yes, those wire markers have weak adhesive. Your fingers can’t have any oil on them.
The cloth wire markers work best. Most forgiving of typical working conditions.
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Old 11-06-2017, 08:12:36 PM
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Ok, brought the exciter home to my shop where I could put it up on the bench in good light and check things.

I realize that every wire and connection has the conformal coating...

Knowing that, each of the 4 wires from each gate reactor was disconnected from their respective terminals... G1/G2, C1/C2... then S1/S2... all showed continuity. I haven't checked their exact resistance, yet.. forgot to do that.

I checked the the negative side diodes, X and W... they're good. After supper, I'll go back out and do some more.

When I go back out, I'll figure out how to check the bridge rectifier and diodes V and Y.

I'll update this if I learn anything later tonight.
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Old 11-06-2017, 08:35:41 PM
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Default Re: Building a "mount" for the Onan Power Plant

If you think it would help you, I can send you a B & W copy of an Onan original document which explains in a semi technical sense terms how the Magneciter works. It includes wiring diagrams and explains how the various pieces that compose the exciter work together. Send me a PM with your email address and I will get it off to you.

I do not know why I continue to offer this, but if you want a full color copy of this 22 page marketing document in living Onan colors which includes with pictures the features of the J line machines specifically the JB gas and the JB diesel along with the Magneciter back end. Just send me a check for $20 and I will trek to the repro center to make a full size copy and mail it in a do not bend envelope.
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Old 11-06-2017, 11:21:11 PM
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Ok, I checked the resistance of the two Gate reactors and the single Control reactor.... with an accurate meter... all right on the money.

Item 2~ "damping resistor" .. ok @ 250 ohms....

Checked and Ok'd item 6 ~ "stabilizing resistor. 500 ohm.

Haven't checked "item 3~ voltage control resistor" yet... but, it looks fine, no sign of overheating.

It's getting down to the diodes V, Y and Z ... or the bridge rectifier. Those 3 diodes are on the copper heatsink that shows positive on the schematic.

I'm beginning to think it's not even this exciter.. that maybe something upstream... something up in the "control box"... but most all that is concerned with engine starting and running.

I won't be upset if it is, and I just jumped the gun on disassembling nearly the whole generator end.. at least this way I have a good idea how this is supposed to operate... and take away all the "black magic" surrounding how this thing is supposed to work, and what is delicate and what is rugged... as far as parts go.
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