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Onan Generators

Building a "Mount" for the Onan Power Plant


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  #71  
Old 11-06-2017, 12:45:45 PM
JoeE. JoeE. is offline
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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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Jim McIntyre Jim McIntyre is offline
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Default Re: Building a "mount" for the Onan Power Plant

Quote:
Originally Posted by JoeE. View Post
...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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  #73  
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
Leon N. Leon N. is online now
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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
Leon N. Leon N. is online now
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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
Carteret Carteret is offline
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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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  #79  
Old 11-06-2017, 08:35:41 PM
Leon N. Leon N. is online now
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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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  #80  
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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