Generator Died

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Woody

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My trusty Onan 7000 watt genset gave up the ghost on me yesterday. When I went to start it it turned over a few times and then just started rapidly clicking.
A friend of mine who is a fairly experienced RV mechanic came over this morning and we started trying to find out what was wrong, after having to buy a set of torx sockets, which I didn't have.
Finally got the cover off of the box that contains the circuit board, starter button, and solenoid and pulled the solenoid, thinking this was the culpret. Took the solenoid to the local auto store and they checked it out and pronounced it OK.
We then applied the hot lead of a 50 amp battery charger directly to the starter side of the solenoid and all we got was a slow groaning from the starter.
My friend says this means the starter is shot and will have to be replaced or rebuilt. We are going to pull the starter tomorrow but this will necessitate dropping the entire generator down to get at it.

Does anyone have any ideas or further tests I can do to make sure this is the problem ??

Woody
 

Gary RV_Wizard

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Before you go to all that work, you might pull the spark plugs and see if the starter can spin the engine with essentially no load on it.  That is, if you can get at the Onan's plugs...

Did the solenoid gives a series of clicks when you pushed the start button or just one click each time you pushed the start button?  Multiple clicks tells me the solenoid isn't engaging, usually low voltage/bad conection to the solenoid. A single click says the solenoid engaged but the starter didn't turn, wich suggests a bad starter or insufficient voltage to the starter terminal (from the solenoid).

I would also be sure that 50A charger had enough oomph to actually turn a starter . Battery chargers don't always deliver a lot of amps when faced with a big load - they tend to just feed whatever current the target (expected to be a battery) will easily accept. Chargers intended to double as an emergency boost have a separate switch for that purpose, which feeds full current (though at a reduced duty cycle).  Can you jump another battery straight to the starter? ANd make sure the charger/booster ground connection is good too.
 

Woody

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The charger had a separate switch for the 50 amp boost, the meter indicated it was putting out the full 50 amps. Suerely that would have been enough to turn the starter, if it was OK. When the button is pushed the clicks are continuous but when we used the boost the starter just hummed.
I've been having intermittent problems for quite a while where the starter would turn but then disengage prematurely and I would have to hold the button down again. The auto store was positive that the solenoid was good.

Woody
 

Karl

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Woody,

If your genset is like mine, you don't have to remove it to replace the starter. It's not easy, but it can be done. Did mine a few years back. You'll need a ratchet set with 4" or 6" extension, a u-joint, patience, and a good supply of swear words ;D If you need help with the latter, PM me and I'll see what I can come up with.
 

John From Detroit

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Woody said:
The charger had a separate switch for the 50 amp boost, the meter indicated it was putting out the full 50 amps. Suerely that would have been enough to turn the starter, if it was OK. When the button is pushed the clicks are continuous but when we used the boost the starter just hummed.
I've been having intermittent problems for quite a while where the starter would turn but then disengage prematurely and I would have to hold the button down again. The auto store was positive that the solenoid was good.

Woody

I do now know what the Onan starters take  but 100 amps or more is not at all uncommon in small car engines.

Before jerking out the starter take a jump battery (one with at least a 750 amp peak rating, I'd like a thousand) and hook it up to the positive post at the generator,  If it now starts, Great.

Next step requires you stop the engine, now using an extension lead hook your voltmeter up, Positive to the battery (Whichever battery starts the generator, On my rig that is the HOUSE battery, Hook right to the battery post.

The negative lead goes to the positive (Battery positive) lead on the generator.  now crank it and observe voltage,  Report the reading (Even if it's zero)  NOTE: A Zero reading is perfect and indicates no problem at all)
 

Woody

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Karl said:
Woody,

If your genset is like mine, you don't have to remove it to replace the starter. It's not easy, but it can be done. Did mine a few years back. You'll need a ratchet set with 4" or 6" extension, a u-joint, patience, and a good supply of swear words ;D If you need help with the latter, PM me and I'll see what I can come up with.

Karl,

My generator on the Pace sits in a little cubbyhole just big enough for it. It is supported by a steal tray that is bolted to both sides of the opening. There are a couple of holes in the try but nothing that looks large enough to drop the starter through. It's 94 outside today and we are staying in. When it gets cooler later on this week (supposed to be in 90's til Friday) I will take a look at it.
Isn't there a way to hook the voltmeter up to the solenoid and see how much juice is coming to it ?? We tried but got really wierd readings.

Woody
 

Karl

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Woody,
BUMMER! At least I had some room to work in :'(

Isn't there a way to hook the voltmeter up to the solenoid and see how much juice is coming to it ??
Not without a high-current DC ammeter. You could come close, however, by applying Ohm's Law. Disconnect the positive (+)  lead of the battery - whichever one is used to start the genset. With your meter set to ohms, read from ground to the output side of the solenoid. That will be the resistance of the starter. Now set the meter to DC volts, reconnect the battery positive cable, and measure the voltage from the input side of the solenoid to ground. That's the voltage available to the starter. Now plug these two readings into the calculation I=E/R. Let's say you read .15 ohms and 12.3 volts. The equation would be I=12.3/.15 which equals 82 amperes. That's what the starter will draw. To make sure the solenoid is not defective, disconnect BOTH of the large wires connected to it making sure they don't touch anything metal, and with your meter set to Ohms again, push the 'Start' button for the genset and read the resistance between the two large posts that you removed the cables from. It should read 0.0 ohms. Anything above that would indicate dirty or corroded contacts. Reconnect the cables. If you have any doubts about it, use a battery jumper cable and connect one end of the red cable to one of the large terminals and touch the other end of the red cable to the second large terminal. There will probably be some sparking, but you're bypassing the solenoid and the starter motor should crank the genset over. If not, you've got a bad starter, or the genset is partially or completely frozen up, possibly due to a lubrication problem. Check the oil level, color, and smell. It shouldn't be black or have a burned smell.
 

Gary RV_Wizard

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The charger had a separate switch for the 50 amp boost, the meter indicated it was putting out the full 50 amps. Suerely that would have been enough to turn the starter, if it was OK.

Maybe, but only maybe Woody.  There is a tremendous initial current draw as the starter motor tries to overcome the inertia and compression of the engine.  It's similar to the starting load on an a/c copressor, where the initial, momentary current draw is 3-4x what it takes once things gets moving.  The charger is intended as a booster for a weak battery, not the sole power source for a high amp device. 
 

Woody

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No, the solenoid is separate from the starter, like the older model Fords used to be. It's virtually impossible to check across the solenoid while it is attached to the genset. Its bolted to the sidewall of the box it is in with no way to get to the rear ear. Removing it is another chore as their is almost no slack in the battery cable. The nuts for the mounting bolts are welded to the bracket on the solenoid and it has to be removed by unscrewing the torx bolts from outside, then the wires from the circuit board have to be removed and the solenoid twisted as much as possible so that you can fit an open end wrench in and work the nut on the cable loose about 1/3 turn at a time.
Some design engineer should have had parts of his anatomy removed for designing this thing.
I may try to take a couple of pics so you guys can see what I am dealing with.

Woody
 

John From Detroit

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Karl said:
John,

Maybe I'm just a little brain dead after all this heat we've been having, but I don't understand what the second part of your test procedure will show. Please explain.

Karl, it's measuring the voltage drop in the lines as the starter motor draws current.  Ideally there should be none, in practice there will always be some,  a few tenths of a volt is nothing to get upset about, a few volts is, which is why I said post results back here, if there is, oh, say 5 volts drop in the line, then it's time to go connection by connection to see where all the voltage drop is.

And then clean and polish when it's found
 

chaajoad

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I can't add anything useful but I have to say - some of you guys truly know your stuff. Ohm's law? Impressive. And all the suggestions - I'd like to have any of you as a neighbor. Wow!
 

Karl

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John,
The negative lead goes to the positive (Battery positive) lead on the generator.
This is my point of confusion. I think you meant to say "the negative lead goes to the positive (Battery positive) lead on the STARTER."

Let me add a warning: If you do that, make sure you remove the test lead BEFORE releasing the starter button. If you don't, you'll send one heck of a high voltage inductive spike through your meter, possibly damaging it.
 

Woody

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I have to postpone doing anything out there for the next few days. Temp outside right now at 1:30PM is 96 actual and 105 heat index. I have some lung problems and I can't even take a breath out there. Thank God for AC.

Woody
 

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