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Onan Generators

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


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  #31  
Old 08-21-2017, 02:17:54 PM
len k len k is online now
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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 ???
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  #32  
Old 08-26-2017, 02:26:55 PM
EICBob EICBob is offline
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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
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  #33  
Old 08-26-2017, 02:42:05 PM
nothingbutdarts nothingbutdarts is offline
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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.
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  #34  
Old 08-26-2017, 03:06:09 PM
len k len k is online now
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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.
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  #35  
Old 08-26-2017, 07:24:08 PM
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Jim McIntyre Jim McIntyre is offline
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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
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  #36  
Old 08-27-2017, 06:46:36 PM
EICBob EICBob is offline
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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
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  #37  
Old 08-27-2017, 08:56:17 PM
len k len k is online now
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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/
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  #38  
Old 09-05-2017, 10:48:42 AM
EICBob EICBob is offline
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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
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  #39  
Old 09-05-2017, 12:33:30 PM
len k len k is online now
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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.
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  #40  
Old 09-11-2017, 12:40:52 PM
EICBob EICBob is offline
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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
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