Generators and Motors
[Home] - [HELP] - [Forums] - [Library] - [Photo Gallery] - [Groups] - [Classified Ads] - [Subscribe] - [Links] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Vintage Electrical Equipment > Generators & Motors General Discussion > Onan Generators
Forgot Password? Join Us!

Notices

Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 7.5 JB-18R/2731AA Followed me home!


this thread has 39 replies and has been viewed 1554 times

Reply
 
Thread Tools Display Modes
  #21  
Old 08-14-2017, 11:22:32 AM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

I'm guessing intermittent voltage reg board.

Try monitoring voltage while moving or tapping voltage pot on voltage regulator board, then try tapping all around the whole board. The pots like to get dirty/intermittent contacts when old, and sometimes the solder joints have issues.

If you have the optional external voltage adjust pot check that the terminals don't have corrosion or are loose. That external pot loads the regulator circuit and if you lose the connection to it then voltage can jump. Also check that jumpers are clean and not loose on V1, V2, V3, and common V4 board terminals. They also load the regulator to adjust the voltage setpoint.

---------------
Also check terminals at genhead. My female spade terminal at F1/F2 broke when I removed it, metal was brittle. Onan had similar problems on their NH gens. I also have a JB spec AA

Last edited by len k; 08-14-2017 at 12:49:59 PM.
Reply With Quote
The Following 2 Users Say Thank You to len k For This Post:
Sponsored Links
  #22  
Old 08-14-2017, 01:49:35 PM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Thanks Len..
I will try that hopefully before the weekend and post my results.
I have attached a picture of the monitoring panel, when the voltage was behaving!
Attached Thumbnails
Click image for larger version

Name:	IMG_3798.jpg
Views:	55
Size:	81.7 KB
ID:	288594  
Reply With Quote
  #23  
Old 08-19-2017, 03:56:08 PM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Ok...today I started troubleshooting the YD regulator board using the information from Len. Took off the covers, traced the wiring from the 300-1006(D) board back through the housing down to the generator head. Everything looked good. All the connections were tight and generally clean and free from corrosion. I removed each spade lug from TB1 and reseated them. Started the unit and had the same results, 91 to 95 volts. Started to gently rap on the circuit board and the adjustment pots. No visible change in output voltage. Stopped and restarted the generator 3 or 4 times as I poked and prodded. No change. On the 5th restart, magically I had 122 volts on each leg.
I did notice that someone in the past had left a pair of the wires from the generator head tied together with a wire nut and a short pigtail. The other end of the pigtail has nothing connected to it, it is capped off with a wire nut. I tried to locate wire numbers on these 2 wires but failed to see any.
Not sure what these two wires do or if they might be contributing to the erratic output.
Any suggestions?

I have located a supplier, (Flight Systems), for a new regulator board at the price of about $225 plus shipping. Would hate to spend that amount of money if it is not necessary.

Will poke a bit more tomorrow..time to save a beer from its captivity in a plain brown bottle!

Cheers!
-Bob
Reply With Quote
  #24  
Old 08-19-2017, 08:23:24 PM
BigBlockChev's Avatar
BigBlockChev BigBlockChev is offline
Subscriber
 
Join Date: Jan 2007
Location: Coquitlam, BC, Canada
Posts: 1,767
Thanks: 309
Thanked 1,277 Times in 753 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Did you check the wires under the metal cover over the generator head, the F1 and F2 wires there are known to fail sometimes. Do the two maretted wires make any difference when they are separated? Cheers Dan
__________________
It's always something simple.
One test is worth a thousand guesses.
If some is good and more is better then too much is just enough
Reply With Quote
  #25  
Old 08-19-2017, 09:08:23 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

On my JB the female spade terminals to F1/F2 genhead terminal at genhead were brittle and broke when I tried to pinch them tighter. I hear NH gens have same brittle terminal problem.

I have a 7.5JB-3CR/2442AA ( 120/240 single phase gen). When I disconnected the reg and attach a car bat (12.7VDC) to genhead field terminals F1/F2 I get ~ 140 VAC out the 120 leads. Being 3 phase you should read the manual but I suspect you will get that voltage too.On mine the field is ~ 12 ohms. F1 at the genhead wants to be positive WRT F2, otherwise excitation will fight the small magnet in it.

I almost wonder if one of your 6 rotating diodes is intermittent, but I know little about how much voltage drops when they are open.
Reply With Quote
The Following User Says Thank You to len k For This Post:
  #26  
Old 08-19-2017, 10:20:35 PM
Wheel1943 Wheel1943 is offline
Subscriber
 
Join Date: Jan 2014
Location: Tioga, Pennsylvania
Posts: 77
Thanks: 57
Thanked 74 Times in 22 Posts
Smile Re: Onan 7.5 JB-18R/2731AA Followed me home!

If you decide that you do need a regulator board, you can always go the Elcheapo route with a SX460 board for 19.99 with free shipping. I just done my second conversion to a JC yesterday, and it works very well. See Jim McIntrye's thread--SX460 Voltage regulator on old generators. He's got a great writeup on this conversion. I just ordered another 460 board this evening to put on the shelf. In your case maybe it is indeed just a loose or corroded connection.
Attached Thumbnails
Click image for larger version

Name:	tech.michigan.PNG
Views:	26
Size:	64.4 KB
ID:	289036  
Reply With Quote
The Following 2 Users Say Thank You to Wheel1943 For This Post:
  #27  
Old 08-20-2017, 11:26:26 AM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Interesting idea about one of the 6 diodes being intermittent. I will have to look deeper into that.
Reply With Quote
  #28  
Old 08-20-2017, 11:51:25 AM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Rather than dig into the rotor right away, easier to first do this test .

As a test I'ld supply the field with battery excitation, that way if you still have the problem you will know it's not the regulator

Last edited by len k; 08-20-2017 at 12:18:32 PM.
Reply With Quote
  #29  
Old 08-21-2017, 08:03:28 AM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Hi Len
Yes indeed I am planning on doing the test you mentioned. I was just speculating on the possibility of the diode issue and digging into how they work and all. I absolutely agree it is better to test and know what you are up against then to throw parts at something.

For clarity sake, if I understand your testing method, I can remove the F1 and F2 connections from the regulator board and substitute +12 volts DC on the F1 wire to the genset and the -12 volts DC to the F2 wire. In effect bypassing the output of the regulator board. (Akin to full fielding the regulator in the old Delcotron alternators on GM cars and trucks) This should give me a stable, albeit higher then normal, output voltage at the genset.

Correct?

-Bob
Reply With Quote
  #30  
Old 08-21-2017, 09:19:48 AM
nothingbutdarts nothingbutdarts is offline
Sponsor
 
Join Date: Apr 2014
Location: Bailey, Colorado, USA
Posts: 2,049
Thanks: 4,550
Thanked 899 Times in 608 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

I believe you have it down pat! Hopefully it will make good A/C that way and you can eliminate the stator and rotor!
Reply With Quote
  #31  
Old 08-21-2017, 02:17:54 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

EICBob.... that's my idea.....replacing AC voltage reg output with a battery. Common test. But I'ld read the service manual, some other threads I've read talk about 12 and 3 or 6 volts making full 120V with 3 phase gens. I have not fully read the service manual. I suppose you could start low and see what you get, then work your way up to 12VDC.

Guess onan made a few versions, maybe the lower ecitation voltages were magnaciters ???
Reply With Quote
The Following User Says Thank You to len k For This Post:
  #32  
Old 08-26-2017, 02:26:55 PM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Len
Here is what we found out while testing the regulator board today.
Disconnecting F1 and F2, supplied 5 volts DC at F1 and F2, resulted in 120 volt AC at both lines. Increasing field voltage to 10.5 volts resulted in 160 volts at L1 and L2. Seems like the generator is working fine.
Reconnected regulator board, measured 2.5 volts at F1 and F2, resulting in 90 volts at the output of line 1 and 2.
REALLY rapped the board, and the voltage jumped to 145 volts, and could not reduce below 130 volts.
Looks like I need a voltage regulator.

I traced all 12 wires off the generator set, and I believe it is currently wired 3 phase parallel wye.
Here is the current wiring on my generator set: T4 T5 T6 T10 T11 T12 are tied together at the neutral post.
T3 and T9 are capped.
T2 and T8 are tied together on L2
T1 and T7 are tied together on L1

What would be my best bet for rewiring to single phase 220 VAC?

- Bob
Reply With Quote
  #33  
Old 08-26-2017, 02:42:05 PM
nothingbutdarts nothingbutdarts is offline
Sponsor
 
Join Date: Apr 2014
Location: Bailey, Colorado, USA
Posts: 2,049
Thanks: 4,550
Thanked 899 Times in 608 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Quote:
Originally Posted by EICBob View Post
I traced all 12 wires off the generator set, and I believe it is currently wired 3 phase parallel wye.
Here is the current wiring on my generator set: T4 T5 T6 T10 T11 T12 are tied together at the neutral post.
T3 and T9 are capped.
T2 and T8 are tied together on L2
T1 and T7 are tied together on L1
Yes, your capped leads T3 & T9 would be L3 in the three phase output you are currently wired for.

For 120/240 output:

T2, T4, T7 and T12 are LO
T1 & T6 are L1
T8 & T10 are L2
T9 & T11 are tied together and capped. Same with T3 & T5, also tied together and capped off.

Last edited by nothingbutdarts; 08-27-2017 at 12:50:49 AM. Reason: added info.
Reply With Quote
  #34  
Old 08-26-2017, 03:06:09 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Quote:
Originally Posted by EICBob View Post
Disconnecting F1 and F2, supplied 5 volts DC at F1 and F2, resulted in 120 volt AC at both lines. Increasing field voltage to 10.5 volts resulted in 160 volts at L1 and L2. Seems like the generator is working fine.
Long as it's steady , I guess those voltages are ok, you have to read manual to see if field excitation voltage different for 3 VS 1 phase gens. My single phase JB made ~140VAC out the 120 lines with car bat ~ 12.6 VDC to F1/F2.....But 3 phase gens might have different field coils. My field coils ( F1/F2) were 11.5 ohms.

Quote:
Originally Posted by EICBob View Post
Reconnected regulator board, measured 2.5 volts at F1 and F2, resulting in 90 volts at the output of line 1 and 2.
REALLY rapped the board, and the voltage jumped to 145 volts, and could not reduce below 130 volts.
Sounds like my bad board, hit it and things change. You might try checking that jumper from pin 1 to 3 on board has a good connection. Without good connection the voltage pot won't be able to reduce voltage. Others say these boards have bad solder joints. Could try running gen and move the voltage pot, if voltage jumps around could replace the pot if your handy with a soldering iron. ( same for stability pot)

Flight systems sells good replacement boards at better prices than Onan. Could put in a SX460 voltage reg if price is an issue ~ $30.
Reply With Quote
  #35  
Old 08-26-2017, 07:24:08 PM
Jim McIntyre's Avatar
Jim McIntyre Jim McIntyre is offline
Subscriber
 
Join Date: Nov 2004
Location: Mooresville, Indiana, USA
Posts: 3,807
Thanks: 614
Thanked 2,004 Times in 1,179 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Quote:
Originally Posted by len k View Post
...Could put in a SX460 voltage reg if price is an issue ~ $30....
Yep - here you go:

https://www.smokstak.com/forum/showthread.php?t=139868
Reply With Quote
  #36  
Old 08-27-2017, 06:46:36 PM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Hi Len
I did some more tinkering on the regulator today, the resistance across F1 and F2 is 12.5 ohms. According to the YD manual, 900-0184, page 12, the resistance should be 12.2 +/- 10%. Looks good
I took the regulator board out, while doing that the F2 male terminal on the board came loose! Hmmm??
Looking closely at the back side I noticed some scuff/chaffing marks on a few traces. Am guessing wires fron the output pigtail caused that. I touched up the traces with my soldering iron and re-soldered the F2 male terminal back on to the board. Put the voltage regulator back in and started the gen set...voltage was at 127 VAC at L1 and L2. (Correct for the current 3 phase configuration).
Not totally convinced I have solved the issue but am feeling a little better!
Will post more as I continue making this JB a reliable unit again.
I also changed the oil and filter while I was at it!

-Bob
Reply With Quote
The Following User Says Thank You to EICBob For This Post:
  #37  
Old 08-27-2017, 08:56:17 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

On reg board check that terminals are not loose, in particular 1, 2, 3, 4, 5, 6, V1, V2, V3, V4(com). Looseness on these can cause high voltage.

Depending on your jumpers, and how you have things set up, not all of above will have wires/jumpers on board's male spade terminals.

Reg Schematic is in beginning of YD service manual 900-0184, it's in this link
http://www.twinslan.net/~n0nas/manuals/onan/
Reply With Quote
  #38  
Old 09-05-2017, 10:48:42 AM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Good Morning all
This weekend, I took out the regulator board, placed it in my Panavise, used a large magnifying light and touched up all the male tab connections on the board with the soldering iron. Did some more visual inspections on the remaining traces. Used a bit of scotch brite on the terminals themselves and placed the board back in.
I rewired the 12 leads to give me 120/240 single phase out to my distribution box and monitoring panel.
Crossed my fingers and fired the unit up.
121 VAC on each leg from a cold start!
Now on to some stress testing before I commit to saying this unit is ready for prime time!
Cheers!!

-Bob
Reply With Quote
  #39  
Old 09-05-2017, 12:33:30 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,312
Thanks: 371
Thanked 5,168 Times in 3,760 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Power it up and tap it all over to find any remaining intermittent. My reg output voltage goes on, off, and various midways while tapping. Not bad to test it hot and cold too, maybe 3 points: 10 deg F, room temp and 100. Only problem with cold is if it's fall or summer after you cool it in your freezer when you bring it out to run humidity will condense all over it. possibly shorting components, That's why they like to conformal coated the board, we made stuff for defense uses.

Last edited by len k; 09-05-2017 at 12:43:37 PM.
Reply With Quote
  #40  
Old 09-11-2017, 12:40:52 PM
EICBob EICBob is offline
Registered
 
Join Date: Jun 2017
Location: Turner, Maine
Posts: 30
Thanks: 27
Thanked 10 Times in 7 Posts
Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Hi Len
Did a little, emphasis on little, work on my JB this weekend. On a cold start, the voltages were stable at 121 per leg. Let the unit warm up for about 20 minutes. The voltages remained stable. I did a little tapping and turning of the regulator pot and so far so good. I need to get some time to do a load test and reconnect the unit to my 100lb propane tank.
I remounted the factory muffler vertically onto the exhaust manifold and removed the extra piping. Will invest in a vibration isolator for the exhaust after the generator building is constructed and the unit finds it resting place

Cheers
-Bob
Reply With Quote
The Following User Says Thank You to EICBob For This Post:
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

F o r u m Jump

Similar Threads Chosen at Random
Thread Thread Starter F o r u m Replies Last Post
Another Onan JC followed me home! b74eqcm Onan Generators 9 09-07-2014 01:16:56 PM
got my Onan 15 JC home Kpack Onan Generators 112 01-16-2014 09:17:53 PM
A new onan followed me home Gettysburg150 Onan Generators 7 11-18-2013 09:09:45 AM
Another Onan followed me home lijobi Onan Generators 7 09-09-2012 04:25:27 PM
Got my Onan home, how old? krawlr Onan Generators 12 07-14-2009 02:22:53 AM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 10:01:23 PM.

Smokstak and Enginads site search!


All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2016 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277