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Onan Generators

Onan 7.5 JB 3CR/2442T Added to the Fleet


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  #11  
Old 03-11-2018, 09:59:06 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Ok, I understand. Does the the spec S data sheet indicate 120 volt, 64 amp output? If so, perhaps Onan made a mistake in stamping the units name plate.
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  #12  
Old 03-11-2018, 10:15:25 PM
MBB MBB is online now
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Here is the build sheet. Maybe this will answer your questions.
Sometimes Onan will have advanced to the next Spec Letter but no notation in this case.
Attached Files
File Type: pdf 75JB3CR2442S.pdf (29.2 KB, 37 views)
File Type: pdf 219JB-7.pdf (171.1 KB, 27 views)
File Type: pdf 611-0806.pdf (222.0 KB, 20 views)
File Type: pdf Control Parts 179.pdf (60.3 KB, 19 views)

Last edited by MBB; 03-11-2018 at 10:58:44 PM.
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  #13  
Old 03-11-2018, 11:13:17 PM
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Ok Leon take the attached .pdf follow the Model 75JB3CR2442T note it gives you the wiring diagram and the exciter wiring diagram and the control number #179 use the attachments and it will show you all the info your looking for.
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File Type: pdf 75JB3CR2442T.pdf (67.3 KB, 29 views)
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Old 03-12-2018, 08:08:03 AM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Thank you MBB...


-Bob
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Old 03-17-2018, 03:11:47 PM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Happy St. Partick’s Day!!
Took a drive to Massachusetts today and picked up the 7.5 JB. Had a few surprises when I got there. The owner did not have the air cleaner assembly. Appreantly he had rented the house for the last 10 years while he served in the military and his tenants were less that honorable in various areas.
Seems more than a few items came up missing when he moved back in.
His wife convinced him to sell the Onan and get a “New” better unit. I decided not to get into that debate!

It does look like it has some mice damage in the control box and as the pictures indicated the over crank protection has been removed.
Here are a few more pictures and one with a question concerning 2 relays in the control box.

The unit turns over but will need work before it is ready to start.
The seller is a 30 year retired Army member and was very helpful and a genuinely nice guy.

I need to locate an air cleaner assembly as well as the gaseous conversion parts. It does appear to have the tri-fuel carb on it.

-Bob
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Old 03-17-2018, 03:22:28 PM
JoeE. JoeE. is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Those relays are part of the starting system to kick out the starter after the engine gets up to speed. I see the previous owner has a different starter solenoid mounted on the back of the control box, and the original is still inside the control box. The one on the outside is not the right type, fyi.

I'd venture a guess that they've wired around the two relays and another cutout switch because they had trouble with it one day and couldn't figure out how it all worked, so they just did what they could to make the engine run.
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Old 03-17-2018, 03:56:24 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

The upper relay in your first picture is the start-disconnect relay and the other (lower) pictured relay is the ignition start relay. The former is of open construction and can malfunction due to dirty contacts associated with its' open construction. The latter is the ignition start relay and is of closed construction. See page 47 in 967-320. Note your JB parts key is 4,5 when referring to the control group picture in the owners manual.

Looks like the previous owner did some rewiring and deviated from the original design as shown in 967-320.

There is no low oil pressure sensor thus no emergency relay in your model. Very simple design!
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  #18  
Old 03-17-2018, 04:12:03 PM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Thank you Leon....
Do I remember correctly that you have a JB with the Magneciter end on it?
Anything I should pay particular attention to prior to starting this unit up?

-Bob
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Old 03-17-2018, 04:50:13 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Yes. In your first picture in post 15, make sure the generator output power lead T2 is grounded to the chassis. Presumably the output is wired for 3-wire 120/240 volts. That would make T2 and T3 the neutral and they should be tied to the chassis. I suspect that is what is showing in that control box picture, upper right corner.

This is necessary because your model has auto field flashing on startup. There should be a wire from the starter side of the start relay which is located inside the control box BUT in your pictures, looks like the previous owner installed one outside on the back of the control box. If he did not connect the exciter field flashing wire from terminal 35 to the starter side of that start relay, not auto field flashing will occur. However, that is not important at this point as long as the generator voltage builds up.

It is important to make sure the previous owner hooked up that field flashing wire to the "load side" of the start relay and not the battery side of that relay. Yup can trace that wire back from "terminal 35" on the wiring diagram via the terminal strip in the C box and then to the load (starter) side of that external (if used) start relay.

Last edited by Leon N.; 03-17-2018 at 05:04:55 PM. Reason: A clarification
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  #20  
Old 03-17-2018, 07:21:01 PM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB 3CR/2442T Added to the Fleet

Thank you Leon...
I will look there to see what I have to work with. I need to ask JohnnyC how he is able to clean up all those crappy looking parts and make them look and work like new.
I will need to pull out the 2 relays from the control box and clean/verify and replace if needed. Looks like some wiring will need to pe replaced too.

-Bob
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