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Possible new toy Onan 7.5 JB


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  #131  
Old 02-26-2017, 12:30:01 AM
JohnnyC JohnnyC is offline
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Default Re: Possible new toy Onan 7.5 JB

Before ripping it all apart and making adjustments, please recondition the pitted points and re-gap if needed. If they are pitted, the points condenser could be bad and caused sparking and eroded the points contacts over time. What you can do is ensure that there is good continuity when the points are closed. When checking, make sure one of the leads to the points is disconnected otherwise your reading may not be accurate. There are other ways to check the points too.

Spark plug wires may some resistance unless you have solid core wires which I doubt.

JohnnyC
New Jersey

Last edited by JohnnyC; 02-26-2017 at 09:32:47 AM.
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  #132  
Old 02-26-2017, 09:22:39 AM
PopsGarage PopsGarage is offline
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Default Re: Possible new toy Onan 7.5 JB

Ed, I think Len or Leon could answer the question what size fuse, I can check my MDJB under full load tomorrow and let you know what AC current is at full load I would add 15or 20% to allow for surge current.

Bob
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  #133  
Old 02-26-2017, 09:36:35 AM
JohnnyC JohnnyC is offline
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Default Re: Possible new toy Onan 7.5 JB

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Originally Posted by squidtrap View Post
So- the flower show was great actually lots of hardscapes, not really many flowers, 1/2 ways to you JohnnyC, just over the bridge, 1st x on 287, Edison expo center. Lots of free food and wine,
--- snip ---
Ed, I know where you were at. That is about 55 minutes without traffic to my place. I used to travel everyday for 28 years to Piscataway (until the company outsourced all our jobs to Ukraine for cheap-azz IT labor). Piscataway is not too far away from Edison.

JohnnyC
New Jersey
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  #134  
Old 02-26-2017, 10:12:45 AM
squidtrap squidtrap is offline
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Default Re: Possible new toy Onan 7.5 JB

JohnnyC- will try and get pic of plate, all of a sudden its one thing after another. Now phone took a sh#t. I think things are happening because i want to play green!!!!!!!!!!!!!!! its 1 phase ONLY, also posted options few threads back. Surprised leon has not been around, our sets are almost identical. I need him and his expertise for a few days, its not to complicated, but i am stupid, cant see or hear, but smell like a bloodhound.

Yes i just need to get through the basics, going to try and play later, right now need to keep wife happy till noon.

Also need to check HATKO N/C and LOPKO N/O, both of them will kill spark. Also will check wires, super high resistance, one i believe was in the K
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  #135  
Old 02-26-2017, 10:25:54 AM
JohnnyC JohnnyC is offline
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Default Re: Possible new toy Onan 7.5 JB

Quote:
Originally Posted by squidtrap View Post
JohnnyC- will try and get pic of plate, all of a sudden its one thing after another. Now phone took a sh#t. I think things are happening because i want to play green!!!!!!!!!!!!!!! its 1 phase ONLY, also posted options few threads back. Surprised leon has not been around, our sets are almost identical. I need him and his expertise for a few days, its not to complicated, but i am stupid, cant see or hear, but smell like a bloodhound.

Yes i just need to get through the basics, going to try and play later, right now need to keep wife happy till noon.

Also need to check HATKO N/C and LOPKO N/O, both of them will kill spark. Also will check wires, super high resistance, one i believe was in the K
Take your time, no rush... You got the 7.5 JB home safely. 1 phase is all you need for the house. As for things taking a sh!t, it can't be as bad as Dave2500..... Soon after he got home with my ex-5.0 CCK his truck caught fire when the hood insulation fell onto the hot turbo...

My luck may run out today with my new 7.5 JB and the switch that came with it. As you may know, I will be playing with the switch today in my garage by hooking it up. Not knowing anything about it, by 4 pm my garage maybe a pile of ashes I will post pictures if this happens and if I survive.

JohnnyC
New Jersey
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  #136  
Old 02-26-2017, 10:43:06 AM
Leon N. Leon N. is offline
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Default Re: Possible new toy Onan 7.5 JB

I would not recommend fusing the exciter. It does not take much to keep the JB running at 1800 RPM. It either is going start with a wide open throttle and come up to speed right away or it is not going to run at all. The plug wires should be solid core copper. I am not familiar with the diesel JB characteristics, but from what I read, it requires a bit more. TLC or it could chug away at reduced RPM when one injector fails. That is bad news for the Magneciter if continued for any length of time. One would think such a user would notice the lights dimming and shut it down.
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  #137  
Old 02-26-2017, 12:29:16 PM
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Onan Dan Onan Dan is offline
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Default Re: Possible new toy Onan 7.5 JB

Ed your question on the Centrifugal set of points they remain open when engine is not running the point setting for those is 0.020" they are called Starter Disconnect Breaker points They are closed by a centrifugal mechanism when the engine reaches approx. 900 rpm therefore the starter is disconnected. service manual for JB&JC Gensets 967-0120 Page 5-7 fiqure 5-8 Breaker points just clean points set and check gap. same for the breaker points I do believe the gap on those is 0.020 also. onan dan
model and serial number?
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  #138  
Old 02-26-2017, 01:57:58 PM
len k len k is offline
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Default Re: Possible new toy Onan 7.5 JB

Centrifugal set of points..... Gap is likely set right, just dirty points. I would first just drag some sand paper thru the points. Maybe 220 then 320. I'ld use a good grade of silicon-carbide grit like 3M black grit sand paper for car body work.(grit doesn't fall off)

Plug wires being different ohms...... Carbon wires can have several thousand ohms in a foot or two. Maybe 8-10k in 3ft.
If they are both carbon and if there is that much difference between them then possibly the steel wire pushed in at ends is rusted. I push in a thin paper clip ground to a tip as replacement. I've fixed a lot of car wires. I've even pushed the new steel wire right thru the silicone boot when boot is glued to the wire, worked well.

Good to have tight silicone boots on the wires, it tends to seal and keep condensation from shorting out voltage on porcine of plugs and coil on humid mornings.

If engine runs slow I'ld completely disconnect magnaciter to protect it till you get engine running close to 1800.

Last edited by len k; 02-26-2017 at 02:12:32 PM.
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  #139  
Old 02-26-2017, 02:06:03 PM
Vanman Vanman is offline
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Default Re: Possible new toy Onan 7.5 JB

Quote:
Originally Posted by Leon N. View Post
I would not recommend fusing the exciter.
Why not, Leon? A fuse has no effect on the circuit in which it is placed until the circuit is overloaded. If it blows, the generator is simply no longer excited and harmlessly freewheels. Keep a spare or two on hand.

If it blows it means that it saved your Magneciter voltage regulator and field winding.

But if the field winding develops a short between turns, the regulator may well keep the lights on bright until something else smokes, such as the Magneciter. Unless it is properly protected with a fuse.

And if the speed drops down some- for any number of foreseeable reasons- it'll also keep the voltage up. Until something smokes. Unless it is properly protected with a fuse.

To me it's no different than running an unattended engine without at least a low oil shut down.

The ONLY argument I can see against Protecting the regulator and field would be the case of a Concourse machine.
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  #140  
Old 02-26-2017, 02:16:35 PM
len k len k is offline
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Default Re: Possible new toy Onan 7.5 JB

I don't believe in crossing my fingers and hoping, I like to control things. Although you can shut down engine if rpm is low ......IF you happen to be standing next to it when that happens

I'ld fuse the $$$$$$$$ magnaciter. Problem is finding the right amp/time curve for the fuse/breaker. Would need to do some tests to find normal magnaciter current draw VS time for different loads and load transients. If you undersize the fuse worst that can happen is your in the dark for a few minutes till you replace fuse

I believe I heard Onan did fuse the rotor winding with a breaker on later specs, but that won't save the magnaciter coils from overheating on low hz

Other option is to put a one-shot thermal fuse on each magnaciter coil, wire it in series with 120 supply to magnaciter.
Have to tape a thermocouple wire to coils to determine normal operating temp on hottest day of year and worst case thermal load on magnaciter coils. Check temp on downwind side of coils (hot side)

Last edited by len k; 02-26-2017 at 02:50:19 PM.
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