In need of Onan electrical end

Uh Oh
Do you have a model number? MDxxx ?? Serial and Spec number. This may take some research. I'm already in some rum (can you tell?) & may be tomorrow before I can get back.
You may have a transformer excited system. There used to be some air gap adjustments.
,rc

What is your hertz full loaded? Turn the RPM's up 25-50rpms and see where your voltage is at. It's entirely possible that your electrical end is going bad as well. But to me it definately sounds like RPM's. How many hours are on the generator? Your electrical end is over 20 years old, and they usually go anywhere from 2500hrs-4500hrs (electrical end) before needing to be rebuilt. If it's Westerbeke, Marine Gear in Ft. Laud (a Westerbeke dealer) does a good job with them.

Model MDKD S/N H 900341952. I understand the rum.. I do red wine to preserve the liver a few more years. Talk to you in the morning and thanks for your help
David

Still chugging on my Genset

Ralph,

Spent some hours yesterday on genset.

There is a test like you suggest in the book. First I am transformer regulated not electronic. On the flow chart for high or low output, there is a test to measure across S1 and S2. The result should be 60VAC plus or minus 5%. With and without a load. Mine reads 55VAC. That would be only a couple of volts out of spec. I then went on to check the input to the exciter on F1 and F2. I remember that P-46 told me that it should be 12VDC. It is the output of the bridge rectifier. Mine reads only 9.2VDC. It seems logical to me that if my exciter voltage is low then my gen output would be low as well. I pulled the bridge rectifier and measured it with three different meters on the diode or rectifier scales. Spec says (in the flow chart for testing the rectifier) 5-50 ohms and of course infinity in the other direction. All 4 rectifiers read less than an Ohm. I am going to look up the formula for bridge rectifiers and see if this makes sense. In other words what value of AC in equals what value of DC out. I’m not yet convinced the rectifier is bad. I will work on it a little later today.
Let me know what you think if you get a couple of minutes. Thanks Dave

Will do in the morning. Built the cable and found where to do it on the exciter. I will let you know if this reflashes the field and pumps up the voltage. Thanks for your continued interest. Hope your install goes smooth.

Bottom line for now

I have completed my work for now on my Onan 8KW. With a tremendous amount of help from Ralph and P46 here is my story.

I flashed the exciter field. That moved me from 107 to 112.
I changed the regulator rectifier and suppressor and that didnt do much but I feel better about it.
Before I tore the bell off the front to change out the main rectifiers I bought a new frequency meter and double checked that I was still at 60Hz. At almost full load I was dropping only a couple of tenths of a Hz to 59.8
I thought that I should run up the RPM to 61Hz to see what effect that had on my voltage. I moved from 112 to 117 and then down to 116 after a half hour load of 50A. I think I will run it this way for the summer unless anyone thinks running at 61 under load or 62 light load, will hurt anything. Thanks all. Dave and thanks for letting me slip in on this forum now back to P46

I believe the fuel injection pumps are usually set for plus or minus 3% hertz. so 58 t0 62 is reasonable operating range based on those numbers

running at 61 hertz shouldn't be enough to hurt anything at all and 116 volts is enough that it shouldn't either. It sounds like your electrical end might be needing a rebuild soon. What rpm's is th engine running at?

Yep, send pictures and rum. You started this mess and I think you o Dave & I some good stuff.
You Post kids are so cool and I enjoy every Post, post.

I'm going to find a way to find Dave and offer first round. P46, Well, May take a while more but the day is coming,,,,.

Look forward to great results and fine pics of your ER. Don't forget performance data of your new Genny.
,Ralph

The book says 1800 but I dont have a tach and I dont know how check it. Thanks for asking. I just touched the throttle screw to get the Hz up.

Do you have a laser tachometer? I bought a cheap digital one online to check the engine tachs against real RPM and it will easily do the gen too.

4 pole generator @ 1800 rpm = 60 htz. 61 htz = 1830 rpm. 62 htz = 1860 rpm. If the freq meter is good, your reflective tape tach should pick up the same rpm as above. Verifying my figures (magic number 30), 50 htz is 1500 rpm.
On a small crank pulley, don't make the foil tape to a large square. I still have use of my fathers strobe tach from the ice ages, still dead on when I can get it (Not sure it's in the will for me).
Hand held hold-on tachs have some small issues, usually folks are to chicken to hold it steady, on center or while the engine is screaming.

,rc

They make photo tachs that are pretty cheap these days.....I used one that someone had and it worked perfectly......and I think it was just over $100

Checking RPM

Thanks guy's for your input as always.

I will check harbor and online for a low cost digital tool. Ralph, I too have a vintage strobe but I thought I needed a spark to use it.

According to your formula I should be running just above 1830.
Dave

Naw, That's a gas timing light.
On this ole strobe tach you rotate a thumb wheel while the light is machine gun flashing and pointing at the crank pulley. When you see that same pulley position not moving, read your display on the box. Thats the rpm.

Or set the box to 1800, position the strobe light in front of the crank pulley, then adjust the gen-set till the crank pulley looks solid. You can get a sense of adjustment by watching the crank rotate left or right. When it's steady, your rite on.

It's an old clumsy setup. More duct tape than metal left for the box.

How about one for $32.00.


Neiko Professional Digital Laser Photo Non-Contact Tachometer (20713A) - Agrimart