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Hank F.
Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 15008
Experience:  RV tech since the beginning of the millenium.
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I have an onan 7000 rv generator that starts,runs,produces no electric

Customer Question

i have an onan 7000 rv generator that starts,runs,produces no electric inside coach.from ground to power breakers i have 40 volts going through them.
Submitted: 2 years ago.
Category: RV
Expert:  Robert replied 2 years ago.
Hi my name is Robert...

What is the year, make and model of the RV? When you are connected to shore power do you have AC power?

Does your generator automatically transfer power into the RV or do you have to plug a cord in?

Robert
Customer: replied 2 years ago.

1999 Allegro Bus

Yes, when we are hooked to shore power we have correct power in the RV. The generator automatically transfers power into the RV.

Expert:  Robert replied 2 years ago.
OK

You should have an Automatic Transfer Switch (ATS) the ATS will detect the incoming power source and switch between shore and generator power. I would see what the AC voltage is going in and out of the ATS if you have good voltage going in and low voltage going out it is the issue. IF you have low voltage going into the ATS then it is going to be a problem with the generator. The ATS can be located in a few areas, sometimes it is next to the shore cord and other times it can be inside, the shore and generator cable will lead right to it.... Robert
Customer: replied 2 years ago.

the voltage from shore power to the ATS is correct. The voltage from the generator to ATS is 0 from neutral to either hot. The voltage from hot to hot is 57 volts.

Expert:  Robert replied 2 years ago.
OK

Then you are looking at an internal issue with the generator. It could be a number of items... There is another expert on this site that has more knowledge on these Onans then I do when it comes to troubleshooting internal components, if you like I can put your question back up and he might be able to assist you more. My goal is for you to be satisfied..... Robert
Customer: replied 2 years ago.

Thank you Robert. Yes please send this question to the other expert.

Expert:  Robert replied 2 years ago.
No problem.

Hopefully he will have a look at your issue....

Robert
Expert:  Hank F. replied 2 years ago.

Hello!
My name is ***** ***** I am going to assist you with this.

What is the full model number of the genset, exactly as it is written on the data label?

.

Customer: replied 2 years ago.
Model number. 7.0NMH-FA/26105H
Customer: replied 2 years ago.

I cannot see your answer.

Expert:  Hank F. replied 2 years ago.

I hadn't had a chance to respond to you yet. I work 2 jobs and help on Just Answer in the evenings.

I need you to do a few tests for me, and let me know all the results. We should get to the bottom of this pretty quickly.

1. Connect a frequency meter to the output of the genset, and start it up. What frequency reading do you get?

2.

Find the voltage regulator mounted to the base pan of the set, directly behind the control box. It is the aluminum box about 3" square with the 12 wires coming out of it. The connector is actually inside the control box. Remove the control panel.

Unplug the connector. Set your meter to ohms. Testing on the harness side of the plug, not the voltage regulator itself, ohm across pins J4-9 and J4-10. It should read 20-30 ohms.

Next, we need to check the brushes and slip rings. Remove the air cleaner. Directly behind the air cleaner is the end bell of the generator. In the middle of the end bell is a small plastic rectangular cover. Use a flat tip screwdriver to pry the cover out and expose the brush block.

The brush block will have 2 round holes in it with a single uninsulated wire going through. This is the brush lead. Use a small probe or piece of small diameter stiff wire and push the probe through the hole until it touches the brush. Mark the probe where it is flush with the brush block. Remove the probe and measure from the mark to the end of the wire. If it is more than 1", the brushes are worn out and must be replaced. Remove the 2 screws securing the brush block, turning each screw 3-4 times each. The brush block must come out straight, as it is made of ceramic and is very fragile. Be careful not to drop the screws down into the end bell. They are very difficult to retrieve. Use the wires to help pull the brush block out. Inspect the ends of the brushes. They should be smooth and not cracked or chipped. They should be worn into an even arch pattern. They should slide freely into and out of the brush block. If they stick or bind, clean the brush block with electrical contact cleaner. Inspect the slip rings. They are the 2 bands that the brushes ride on. They are made of copper and should be as shiny as a new penny. They should be smooth and have no pits or scratches. If they are dirty, you can clean them by removing the spark plug wires and grounding them out. (You do not want the engine to start when cleaning them). Attach a piece of scotch brite to the end of a small stick. Press the scotch brite against the rings and crank the set. Do not crank for more than 15 seconds without stopping for a minute or two to let the starter cool. When the rings are clean, ohm across them. They should read 20-30 ohms. If not, the rotor is bad and must be replaced. If it is good, reinstall the brush block.

Reconnect the 12-pin connector at the voltage regulator. Set your meter to VDC and connect the black probe to a good ground. Insert the red probe into the back of the plug at wire J4-7 and press the start button. It should read at least 10V. Insert the red probe into the back of the plug at wire J4-9 and press start. It should read at least 12V and climb as you hold start. Insert the red probe into the plug at wire J4-10 and press start. This voltage can vary from 1.5 - 20 volts, as long as there is voltage showing.

What are the results of these tests?

3.

Remove the wires from the brushes, paying attention to which wire goes to which brush. Insulate the wires so they can not touch ground.

Make up 2 jumper wires that will attach to the brush terminals, and install a 5A fuse in one of the jumpers.

Connect the fused jumper to the positive (right hand) brush, and to the battery post of the starter solenoid.

Connect the other jumper to the negative (left hand) brush, but do not connect the loose end at this time.

Set your meter to VAC, and connect the negative lead to a good ground. Connect the positive lead to the back of the circuit breaker.

Press and hold ‘Start’. While holding ‘Start’, connect the loose end of the second jumper to a good ground. There may be a large spark when you connect it, but the spark will not hurt you.

With both jumpers connected, check the output voltage. It should be between 30 and 50 VAC.

How much voltage is there?

.

Customer: replied 2 years ago.

I will do these tests in the morning. Thank you

Expert:  Hank F. replied 2 years ago.

Ok

.

Expert:  Hank F. replied 2 years ago.

Have you done these tests yet?

.

Customer: replied 2 years ago.
I don't have a frequency meter. I did try to test the ohms across those specific pins. There are numbers molded into the connector plug that I used. The generator was not running and there were no ohms registered. Should the generator have been running?
Expert:  Hank F. replied 2 years ago.

We really need to know what the frequency is - it will tell us a lot.

The numbers should not be on the plug. The numbers are stenciled on the wires themselves.

Do not have the unit running when doing the resistance checks.

.