Why do I need a new Generator - Part II

[mstailey]

I wanted to start a new thread to stay on point.

Ok, here is the deal;
The electrical goodies I spoke of are in a box on top of the unit that houses a printed circut board, diodes and such. Wires from that box run to yet another box where the high tension wires a hooked to a block then run to a circut breaker panel. It's what is in that box that is causing the problem, or so I'm told.

To review the problem, after a few moments of running the voltage meter on the panel starts swinging rapidly between 109..121 VAC. This was confirmed by me with a volt meter testing at the leads on the gen set. RPM was verified 3 times with repeteable results which was 1801..1803 rpms. The throttle (governor?) does not hunt while there is an electrical load. To test this I engerized the engine pad heaters, for example and the engine has a momentary drop in rpms but recovers quickly. Again engine does not hunt. Coinciding with the voltage swing my 110v lights flicker at the same pace as the swinging needle on the panel meter.

I had mentioned of putting 5k so far into this gen set. After a review of the invoices last night its more like $6,132.47, to be exact.

The total dollar amount was done in 2 stages:
1st - $1,783.46 which included:
Gen survey
Oil change with filter
Fuel filter change
Valve adjustment
Belt guard
Repair broken bolt for fresh water cooling pump pulley

The gen set then ran for only 4 hours - just died and would not restart.

2nd - $4,349.01 which included:
Travel time for mechanic
rebuild 2 injectors
rebuild injector pump
replace engine shutdown solonid
replace glow plug

Now it's hard to publicly admit when one has been taken for a ride but it would appear that I'm the passenger in this case. Coupled with the fact that I've got this much money invested so far to keep from being a total fool, I should finish it and get it operational. My thoughts are what choice do I have?

I've been in MI for a 1.5 years (moved from LI) and still getting the lay of the land as far as service companies. The company that did the work has an excellent reputation but I'm starting to feel they are not as sharp on the back-end (Scrods definition) mechanical / electrical.

After the original thread I had to come clean with myself and figured out the reason for asking this group about replacing the gen set with an inverter was my way of not facing the fact that I've not done a real good job on this gen set. In other words mad at myself for not shopping this around or bringing it to the attention of this fourm and it's nicked me pretty hard.

So that being said, I'm going to try to make this set work. Bill (Trojan), thanks for the phone number and I'll call you later today.

To the rest of the group, thanks for taking time and giving your input.

 

[yachtsmanbill]

On my 6.5 gas unit - 1800 rpm ONAN MCCK-- a few rpm change has a direct effect on FREQUENCY which has a direct effect on VOLTAGE. Do you have a FREQ meter on your panel? If you can get that to stabilize your volts will follow suit. If you want to sell it I mite be interested. I am in Chicago and my 58 Hatt needs a generator. ws

 

[Genesis]

I HIGHLY doubt that's the control box per-se. Sounds like a bad connection or a bad rotor field coil (the latter is pretty bad as a rebuild on the generator end is expensive enough, in my mind anyway, to scrap the unit)

 

[Avenger]

Do you have a FREQ meter on your panel? If you can get that to stabilize your volts will follow suit.

Mike has established that it's running at 1801 - 1803. I promise that if that's true, his frequency is stable. If voltage is wavering and frequency is not, it's an electrical problem. You're right, voltage will vary if frequency changes. But that's not what's happening here. So his mechanic may not be completely off the mark.

 

[jim rosenthal]

Mike, avoid beating yourself up. No one calls a repair outfit with the intention of ordering a lousy job and shafting themselves. (it does happen, unfortunately). Another way to look at this is that you've hopefully done the big stuff on the engine part of the set, anyway. The problem is, as you say, it is easier to find guys to work on the engine end than the generator end.

I think I would, if in your shoes, shop for the absolute best deal I could on a new set (which I still think doesn't have to be 7.5Kw) and then see what I could get for the old set for parts. It is not worthless. Or- buy a similar set for parts, and rebuild what you have. But- I think you would enjoy the peace of mind that goes with new stuff and a warranty.

 

[TedZ]

Trouble shooting the gen end is not difficult if you have a manual. That should be done. If the gen end is bad, get a new generator. After you're done taking the gen end off to get it out. take the rest out and sell it for parts. I doubt the gen end is bad, however as they are very robust by today's standards.

Folks that knew anything about the relay logic control panel are retired or pushing up daisies. The service folks used to carry a complete unit with them and send the bad ones to Onan for shop rebuilds with the proper test equipment. A friend of mine had a generator service guy replace a whole control unit for $150 plus labor. He buys them used and swaps them out. I'll try to get his name but there are lots of bad MDJE's around with ok control panels.

The question is, is it the control panel? Probably not, but you may have to eliminate it if the diodes are all ok, and the serviceable items and connections on the back of the gen end are ok. IMHO that is where the problem is. Read how this generator regulates voltage and check the items sequentially. Of the nine leads that go from the control panel to the gen end, something as simple as a wire chafe will cause your symptoms. Forget the frequency. The generator is running the right speed...that's all you need to know there.

The manual has a trouble shooting area and your problem is described. Check it out.

Good luck.

Ted

Ted

 

[Jaxfishgyd]

This is all useful info. I have a 9.0 kw on my boat and have had 3 different mechanics work on it over the years.

All did a good job and I was not overbilled.

BUT.......

The one question I asked all of them before they left was "Is the rpm's and voltage what they are supposed to be."

All 3 checked it out (I watched all 3 do it so believed them) and said "yes, it's running at 1800 prm and 120 VAC coming out"

My question to all of them (and now you guys), then WHY do our electric clocks "gain" 20 mins a day when I run the genset but run properly on shore power???

The genset was running with a load when all 3 did their checking....

 

[Genesis]

Because they're not running right on frequency!

 

[Pascal]

yep, you've been a very good passenger.. geesh... what do they charge up there, $300 an hour ?

if the engine side is now working well and if the generator itself is good, is there a way to convert the regulation to a more modern system ?

this may sound crazy, but if all alternator work the same then couldn't you regulate the output with an electronic regulator ? ny norpro 18 uses a Marathon Electric regulator, little electronic box (I have a spare, $100+).

maybe if they contact them with the alternator specifics they can recommend a voltage regulator that would work with your alternator

http://www.marathonelectric.com/generators/Parts_Svc/avr_conn.asp

and if the alternator is shot, it could be replaced... after all, the engine doens't care what alternator it's connected to, the vice versa. as long as it gets 1800 rpm...

 

[Jaxfishgyd]

Naw, it's actually very cheap up here compared to when I lived in Ft Lauderdale and W.Palm Beach.
The 3 times I had the genset worked on was other things which were fixed right and the first time. I did have them check for rpm and voltage but DIDN'T ask about frequency.... (I kinda figured that to be the case after reading all the replies earlier in this thread!!!)
Pascal, have been playing A LOT with google earth, know Biscayne Bay so where is your marina at? Think Ang said South of Rickenbacker but see several in that area.
I can see my boat very well when I zoom in on it up here !
One of the main differences between Jacksonville and Miami is you must know and speak spanish down there, I have to learn redneck up here.......

 

[Pascal]

charlie,

go to www.sandbarhopper.com and download the Biscayne Bay KMZ file... it includes a bunch of marinas, anchorages, pictures, etc... Dinner Key is shown, my boat is on the northside of the southernmost pier, 2nd from last

it's good to check frequency, i bought a Shurite Line monitor, it plugs in any outlet and displays either freq or volts. a must have on any genset equip'd boat

 

[Genesis]

FYI frequency is adjusted by the engine's RPMs. If its exactly 1800RPM you will have exactly 60Hz. VOLTAGE is adjusted by the electronics box via how much energy is put into the (rotating) field coils. The drive current for the electronics is picked up from the unit and rectified, then regulated to provide the appropriate voltage (for most TTL type electronics, this is +5V) The voltage regulator circuit is in most units very simple and analog; problems usually come from the diodes being damaged or bad connections. Some newer units use microprocessor controls, but not many - there's little argument for doing it that way other than enabling fancy communication and panel options.

Thus, frequency is adjusted at the engine governor - not normally at the electronics, unless you have an electronically-governed engine, which is rare. There is usually a locknut to loosen and a bolt to turn to adjust this.

Note that most mechanical governors have a bit of "droop", and thus if you set the frequency to be spot-on under load you will note that its a bit off on the high side when the generator is unloaded. This is normal. I generally set the frequency to be spot-on when under the genset's typical operating load, and accept that it will be off a couple of Hz when either very heavily or very lightly loaded.

 

[Trojan]

Charlie I think I might have led you astray the other day. WE are dealing with AC generating not DC. The only thing that can cause that kind of voltage swing is a bad field connection. There is no reason for diodes in your unit. Your unit must have brushes. They did not have brush less generators 25 years ago. I don't know of any brush less generators. The worst case is a bad field winding. I don't believe what the mechanics are telling you. Put a ohm meter across the output of the generator and turn the generator by hand real slow and watch the meter. Make sure all the power is off and the motor will not start. Also open any breakers at the generator. Watch for the meter swings. The meter will show you where the voltage loss is. If there is a voltage regulator and I doubt. Then you might have to go on the back side of it to get a good reading. It's has got to be the armature connections. Voltage is controlled by the field windings........I must have been still asleep when you called. That is what happens when you get old. Senior moments.

BILL

 

[TedZ]

We need to get straightened out here.

As respectfully as i can say it, if one doesn't think there are diodes or some form of rectfication in an AC generator, you simply don't understand the way they work.

You must supply DC to the alternator's (generator's) revolving fields or you don't get AC output or any output for that matter. The way you magnetize the fields is with DC, period. Regulating the DC current (field strength) is the way you regulate the AC output. If you blow a diode, your regulation goes south. IF YOU DON'T BELIEVE THAT, I CAN'T HELP YOU and you will never fix your generator!!

Just follow my previous post or read the trouble shooting section of the manual. It is not that hard,

Ted

 

[Trojan]

You are correct for the most part. I was not referring to the diodes for the stater DC voltage. In any event I don't believe a bad diode will cause the rapid voltage swings that he is having. But maybe. I'm not there to see what he has. He could have SCRs controlling the voltage in the fields using a voltage chip. But this is a 25 year old generator. Without seeing the circuit everyone is just guessing. He needs to look at the board in his unit to determine what he has. How do you get the DC voltage to the rotating stater. BRUSHES. Through the commutator. Diodes don't control voltage they only rectify it. Unless you are using the inverse threshold voltage as a trigger drive and a zener diode does not count. I do know how a generator works. I just don't know what type unit he has and neither does he yet. That is what we are trying to find out. He has no manuals or schematics on his unit. He said he was going to look at his unit.



BILL

 

[TedZ]

Lots of manuals on eBay but they are free at:

http://www.gbwoodies.com/OwnersManuals/DorryManuals/OnanOperator/index.htm

Download it and print it out. No big deal.

Ted

 

[Trojan]

Charlie according to the web sight that Ted has given for a MDJE you have 4 brushes that contact a collector ring. I think I would start there. There are also 4 diodes and a resister combo for voltage control. There are 2 positive and 2 negative diodes used in the field. There does not appear to be a circuit board but it looks more like a mounting board. Something you could easily service. I don't know where this assembly is located though. Because of the rapid voltage swing. I would check the brushes first and then move to the field diodes. I think you have lost one of the field voltages.



BILL

 

[TedZ]

Hi again,

Those are all located at the outboard end of the generator, i.e. farthest from the engine. The whole assembly comes off and is easy to work on. Could easily be a brush ir a corroded collector ring. Check the diodes while they are in your hands. They should all ring out with the same parameters and they won't in all likelihood. Replace the ones off spec. If you have a meter just measure the resistance with the leads on in one way and then reverse them and write down the numbers. Not a complete test, but not bad.

To state the obvious just in case, it is important, even with such a robust generator end, to disconnect the load (rotary switch) before you start and STOP the generator. Most important when stopping.

Good luck. Fix this thing so we can forget about this thread!! :--)

Ted

 

[Trojan]

Ted, that is where I though they were but was not sure. I hope I never have the same problem. The water muffler for the generator is right there. I hope we have given him enough information to get it fixed.


BILL