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B&S 15.5hp OHV Engine Won't Run Lights or Charge Battery???


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05-18-08, 06:23 AM   #1  
B&S 15.5hp OHV Engine Won't Run Lights or Charge Battery???

I have a Craftsman riding lawn mower (model #917.256531) with a Briggs & Stratton OHV 15.5hp engine (model 28N707 type 0173-01). The headlights aren't working and the battery seems to need charged everytime I start the engine.

I was going to rewire the headlights directly to the battery with switch & fuse, as per this thread I posted in the electrical forum on how to wire it up...
http://forum.doityourself.com/showthread.php?t=345634

But it appears from the responses in the above mentioned thread there is an underlying issue that needs resolved (low voltage magneto went bad). Can anyone confirm this from the symptoms I provided above, and suggest a remedy (and where this magneto is located)?

The high voltage magneto that goes directly to the spark plug is easy to locate, but the low voltage one is giving me problems as the repair manual for this engine has alot to be desired.

All help is appreciated...and thanks in advance!
Tom

 
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05-19-08, 01:00 AM   #2  
You are correct, there is an underlying issue. The charging stator is underneathe the flywheel. It has 2 wires coming out from it right next to the starter. There should be 13.5 or more volts from the red wire here with the engine running at full speed. If there is not, the stator needs to be replaced. This should correct the charging and light issues. The white wire produces AC current solely for the lights when the engine is running.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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05-19-08, 02:56 AM   #3  
Thanks Cheese!

Yesterday, I got the lights working for a very short period of time, but I haven't been able to get them to work since.

Since I got the riding mower, near the engine there have been two wires (red & black) that had been sheared off and nowhere could I find where they needed reattached. Having seen a picture of the magneto and associated red and black wires to the harness, then knowing where the magneto is located, I looked even closer and found red & black wires coming from under the flywheel that had also been sheared off, but so much so it was hard to splice wires back onto them. So I spliced the wires back together, started the engine, turned the ignition switch to the position to turn on the lights and they turned on...but only for a few seconds. Ugh!

So I started the engine, disconnected the negative to the battery, then disconnected the harness to the low voltage magneto and the engine died. Then I started the engine again, left the battery all connected and disconnected the low voltage magneto wire harness but the engine still ran. During both tests, I used my meter and tested the hot from the low voltage magneto harness and it was giving *at least* 12V DC current during both tests. I'm not sure what this means other than the magneto is apparently now is giving power...but the lights still don't work, and I'm not sure if the battery is being charged. But the ammeter on the dashboard works now, if that is any consolation.

After the lights didn't work anymore, I didn't think yesterday to pull the lighting wire from the ignition switch, then check to see if current is being sent from it. I did re-check the wire splices from the magento and they seem to be good.

Results from the the positive 12V DC current test show the low voltage magneto is working, so do you think something else farted out when the lights quit working?

Thanks in advance!
Tom

 
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05-19-08, 11:49 PM   #4  
We need to get the terminology striaght so that I know what parts you're talking about. I think you're referring to the alternator or stator as the low voltage magneto, and the armature coil as the high voltage magneto, correct?

You will have 12 volts at the stator with the battery connected and the harness connected to it. Again, you should have at least 13.5 volts at the red wire coming from under the flywheel with the engine running at full throttle. This should be at the connector after the diode. If your wires are cut that close to the engine, then the diode is not on it. The test must be made at the diode, not the wire under the flywheel. This must be DC volts. 12 volts is not enough and leads me to think you are reading battery voltage, since there is battery voltage on the harness at that connection point.

The black wire right next to the red wire is the lighting circuit. It comes from a seperate winding on the stator that also produces AC voltage, but has no diode to convert it to DC. This wire should have AC voltage on it with the engine running.

Test these wires without the harness connected and engine running at full throttle.


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05-20-08, 04:16 AM   #5  
You are correct regarding what I'm referring to, cheese.

I tested both wires for AC and DC last night and they are both giving current. I believe the red wire was giving about 14 volts DC and close to 30v AC...I think Heck, I wish I would've writen down all the numbers because now after sleeping on them I can't remember them exactly. I certainly was getting current.

Somehow the lights kicked on without me doing anything, and stayed on for quite some time. While on, I tried wiggling every wire connection between the lights and coil but could not get the lights to turn off (trying to mimic an loose wire). But wouldn't you know it, as soon as I thought everything was working well I put the seat switch back together and the lights farted out soon afterward of turning the the engine on. I don't think it is the seat switch, but something is giving out. And while out, I again wiggled all wire connections but could not get the lights to turn back on.

From what I've determined, the coil is working, and I believe the diode exists inline just before the wire harness on the red wire as there is something shrinkwrapped to the wire at that location. But the battery has seemingly allowed the engine to start up without jumping now. Is this good to run it without the diode? btw, the flywheel armature/stator is about $45 for my engine, so it's a good thing the diode is there.

Tonight when I get home from work I'm going to re-test the wires and write the data down, dagnabbit.


Last edited by Buddur; 05-20-08 at 05:08 AM.
 
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05-20-08, 07:12 PM   #6  
Posted By: cheese Test these wires without the harness connected and engine running at full throttle.
I got 16.5 volts DC from the red wire, and 14.5 volts AC from the black wire from the disconnected stator wire harness, and yes there is a diode on the red wire.

So I connect the stator wire harness back up, disconnect the lighting wire harness where it detaches so you can remove the tractor hood, and test that harness for power. I read 14 volts AC from it. So I figured the issue had to be downstream of that harness on the wires to the lights.

When I connected the lighting wire harness back up I had power to the lights. I found a loose connection at the other half of that hood lighting harness, and I think I fixed the problem.

So actually, to get the lights working there were 2 problems, the stator wiring AND that lighting wire harness. Now the ammeter on the dashboard works, and I'll bet (if I knew how to test for this) the battery is getting charged now.

This quest to repair this riding lawn mower has been so satisfying to me. Thanks cheese for taking the time to comment and assist me, I've learned alot from this.

Tom

 
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05-20-08, 09:57 PM   #7  
Sounds like you've got this whipped! If the ammeter is moving toward the positive side with the engine running, then the battery is recieving current...so it is now charging as well. Glad you got it fixed!


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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