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05/26/2007 11:43:30 AM · #1 |
Weird question, but I thought there might be someone here who could help me.
I have a John Deere L120 riding lawn mower that is great except for the fact that it no longer charges the battery while it is running. It has gotten to the point where if I start with a fully charged battery, by the time I finish mowing my lawn it will not start again unless I manually recharge the battery.
I am absolutely clueless at this type of thing, but I was hoping that someone might have an idea of what was wrong. The local shop can't take it in for several weeks, so I thought if I could get a place to start working on it, I might be able to tackle it myself. Any ideas?
Thanks! |
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05/26/2007 11:47:03 AM · #2 |
| Does it have the 3 cylinder diesel engine? If so, then there is a good chance that the alternator is faulty. Or, the battery is duff and won't take or hold a charge. Check the distilled water level in the battery. |
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05/26/2007 11:49:10 AM · #3 |
I don't think it's the battery because I swapped out the battery several times and kept getting the same results.
It's a gasoline engine, not diesel, and it has two spark-plugs, so does that mean it's a two-cylinder engine? Would it still have an alternator, though? (See, I really am clueless). |
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05/26/2007 11:49:15 AM · #4 |
It sounds like the alternator/generator needs replacing.
Does the battery hold a charge? I mean, if you charge it right after you mow, does it start the next time you mow?
Message edited by author 2007-05-26 11:57:22. |
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05/26/2007 11:50:00 AM · #5 |
Originally posted by Spazmo99:
It sounds like the alternator/generator needs replacing.
Does the battery hold a charge? I mean, if you charge it right after you mow, does it start the next time you mow? |
Yes, I charged it last weekend after mowing, and it started right up this weekend without having to charge again. |
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05/26/2007 11:57:34 AM · #6 |
Originally posted by eqsite:
Originally posted by Spazmo99:
It sounds like the alternator/generator needs replacing.
Does the battery hold a charge? I mean, if you charge it right after you mow, does it start the next time you mow? |
Yes, I charged it last weekend after mowing, and it started right up this weekend without having to charge again. |
Unfortunately, the alternator on this model is integrated with the engine flywheel so it's not a really simple repair. If you are as inexperienced with mechanical repairs as it seems from your posts, you're better off waiting or looking elsewhere for service. |
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05/26/2007 12:01:01 PM · #7 |
| If it is a two cylinder four stroke petrol engine, then there is a good chance that it doesn't have an alternator, but has a magneto. This is a fairly simple and cheap job if done by someone who knows what they are doing. But if you have limited experience, best leave it to those who know. |
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05/26/2007 12:01:11 PM · #8 |
Originally posted by Spazmo99:
Unfortunately, the alternator on this model is integrated with the engine flywheel so it's not a really simple repair. If you are as inexperienced with mechanical repairs as it seems from your posts, you're better off waiting or looking elsewhere for service. |
Hmmm, ok. I'm sure you're right about waiting. Is there a simple way for me to test the alternator to see if that really is the problem? |
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05/26/2007 12:02:40 PM · #9 |
Originally posted by formerlee:
If it is a two cylinder four stroke petrol engine, then there is a good chance that it doesn't have an alternator, but has a magneto. This is a fairly simple and cheap job if done by someone who knows what they are doing. But if you have limited experience, best leave it to those who know. |
I definitely have limited experience, but I'm not afraid to try. I probably should be, though ;) |
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05/26/2007 12:50:39 PM · #10 |
Originally posted by eqsite:
Originally posted by Spazmo99:
Unfortunately, the alternator on this model is integrated with the engine flywheel so it's not a really simple repair. If you are as inexperienced with mechanical repairs as it seems from your posts, you're better off waiting or looking elsewhere for service. |
Hmmm, ok. I'm sure you're right about waiting. Is there a simple way for me to test the alternator to see if that really is the problem? |
Define simple. If you have a meter that can measure DC voltage in the range of 10-15 volts (you can get cheap ones at Radio Shack) then do this:
- Charge the battery, and check the voltage. Put the red lead on the positive (+) ternimal and the black lead on the negative (-) terminal. The voltage should be about 12.8 volts.
- Now start the engine, and with it running (needs to be running faster than idle) check the voltage again. If it's charging, the voltage will be around 14.5 volts. If not, it will not have changed from the first reading, or may be very slightly lower.
If it's not charging, there are a few possibilities:
- Alternator. Reference Spaz's post, sounds like he knows this model (I don't).
- Voltage Regulator. Sometimes these are separate, sometimes integrated with the alternator. Not sure about this model.
- Wiring. Check for broken or corroded connections between the alternator, regulator (if separate) and battery.
Message edited by author 2007-05-26 13:09:52. |
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05/26/2007 01:08:33 PM · #11 |
Originally posted by kirbic:
Define simple. If you have a meter that can measure DC voltage in the range of 10-15 volts (you can get cheap ones at Radio Shack) then do this:
- Charge the battery, and check the voltage. Put the red lead on the positive (+) ternimal and the black lead on the negative (-) terminal. The voltage should be about 12.8 volts.
If it's not charging, there are a few possibilities:
- Alternator. Reference Spaz's post, sounds like he knows this model (I don't).
- Voltage Regulator. Sometimes these are separate, sometimes integrated with the alternator. Not sure about this model.
- Wiring. Check for broken or corroded connections between the alternator, regulator (if separate) and battery.
- Now start the engine, and with it running (needs to be running faster than idle) check the voltage again. If it's charging, the voltage will be around 14.5 volts. If not, it will not have changed from the first reading, or may be very slightly lower. |
Yep, I have a voltage meter and I even sorta know how to use it :) I'll give this a try. Assuming I can figure out which parts are which, is it just a simple matter of checking voltage in and out of each component? (i.e., from alternator into regulator, from regulator into battery -- do I have that right?) |
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05/26/2007 01:12:14 PM · #12 |
| Ack, I see I buggered up my previous post. I've edited it for clarity. The only point you really need to check is between the battery terminals. It's a two-step procedure as detailed (now correctly, LOL) above. If it's not charging, first check connections, and if they seem OK, then have it looked at by a knowledgeable service person. |
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05/26/2007 01:15:07 PM · #13 |
If it has an alternator, take a small pocket screwdriver (or similar) and carefully let it touch the alternator pulley when it is running. If teh alternator is charging, the pulley will be magnetized (assuming it's steel) and draw the screwdriver blade to it.
If it is not charging, and while running, take a hammer and whack (reasonable whack - not driving a railroad spike whack) the alternator housing and recheck with screwdriver, though if it does start working, you will more than likely hear the change.
The hammer trick can free-up stuck brushes, and may get it working for now, but if the brushes are stuck, it's usually because they are worn and at the end of the spring tension behind them, and the alternator will need replacing/rebuilding.
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05/26/2007 01:16:32 PM · #14 |
Originally posted by kirbic:
Ack, I see I buggered up my previous post. I've edited it for clarity. The only point you really need to check is between the battery terminals. It's a two-step procedure as detailed (now correctly, LOL) above. If it's not charging, first check connections, and if they seem OK, then have it looked at by a knowledgeable service person. |
OK, thanks. I'll see what I can figure out from here. |
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05/26/2007 01:17:03 PM · #15 |
Originally posted by Brad:
If it has an alternator, take a small pocket screwdriver (or similar) and carefully let it touch the alternator pulley when it is running. If teh alternator is charging, the pulley will be magnetized (assuming it's steel) and draw the screwdriver blade to it.
If it is not charging, and while running, take a hammer and whack (reasonable whack - not driving a railroad spike whack) the alternator housing and recheck with screwdriver, though if it does start working, you will more than likely hear the change.
The hammer trick can free-up stuck brushes, and may get it working for now, but if the brushes are stuck, it's usually because they are worn and at the end of the spring tension behind them, and the alternator will need replacing/rebuilding. |
Interesting. I'll give this a try as well. Thanks! |
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05/26/2007 01:40:11 PM · #16 |
Originally posted by Brad:
If it has an alternator, take a small pocket screwdriver (or similar) and carefully let it touch the alternator pulley when it is running. If teh alternator is charging, the pulley will be magnetized (assuming it's steel) and draw the screwdriver blade to it.
If it is not charging, and while running, take a hammer and whack (reasonable whack - not driving a railroad spike whack) the alternator housing and recheck with screwdriver, though if it does start working, you will more than likely hear the change.
The hammer trick can free-up stuck brushes, and may get it working for now, but if the brushes are stuck, it's usually because they are worn and at the end of the spring tension behind them, and the alternator will need replacing/rebuilding. |
I have a couple of these engines, and the alternator is under the flywheel, which has permanent magnets in it. The A/C voltage/current comes from under the flywheel on one or sometimes 3 wires, and there is usually a diode and fuse in the line before it goes to the battery.
First look for a fuse or fuse holder somewhere in the wire, or under the ign switch. With a one wire system, the diode if it has that system looks like a bump in the wire covered with a piece of heat shrink tubing. It works like a check valve and allows one phase of the A/C coming from the coils under the flywheel to go to the battery as D/C current. It's called a "half wave rectifier" in electrical terminology.
If you can connect your meter to the alternator wire coming from under the flywheel, and to ground there should be A/C voltage, about 16 volts or so, there with the motor running at mid speed.
Connecting the battery or a strong charger to the system backward is what usually blows the fuse and/or rectifier diode.
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05/26/2007 01:47:53 PM · #17 |
What  Rainmotorsports hasn't commented on this thread yet. JEFF, WAKE UP!!!!!!.
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05/26/2007 01:49:41 PM · #18 |
Originally posted by MelonMusketeer:
I have a couple of these engines, and the alternator is under the flywheel, which has permanent magnets in it. The A/C voltage/current comes from under the flywheel on one or sometimes 3 wires, and there is usually a diode and fuse in the line before it goes to the battery.
First look for a fuse or fuse holder somewhere in the wire, or under the ign switch. With a one wire system, the diode if it has that system looks like a bump in the wire covered with a piece of heat shrink tubing. It works like a check valve and allows one phase of the A/C coming from the coils under the flywheel to go to the battery as D/C current. It's called a "half wave rectifier" in electrical terminology.
If you can connect your meter to the alternator wire coming from under the flywheel, and to ground there should be A/C voltage, about 16 volts or so, there with the motor running at mid speed.
Connecting the battery or a strong charger to the system backward is what usually blows the fuse and/or rectifier diode. |
Thanks, that sounds promising. It would be like me to have put in the battery backwards. I seem to recall that the batteries come in two styles, with their leads reversed. That probably means that at one point I bought the wrong one. |
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05/26/2007 01:51:18 PM · #19 |
Originally posted by Lowcivicman99:
What Rainmotorsports hasn't commented on this thread yet. JEFF, WAKE UP!!!!!!. |
He's probably out enjoying the holiday weekend, like the rest of us should be! |
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05/26/2007 02:05:44 PM · #20 |
You did not say what brand the motor was. Most gasoline J D's use either Kohler ( the older ones) or Kawasaki. There is usually an electric clutch that engages the pulley for running the blades, and this will use up a battery charge in a few hours if the charging system is not working. Both brands of motors use magneto ignition, so the motor will actually run with no battery at all after it has been started.
The red wire goes on the + post on the battery.
The larger Kohlers have a rectifier regulator assy mounted thru the flywheel cover with 3 wires plugged on it. They are about 3 inches long with a screw at each end, and look like a block with fins on it inside the flywheel housing cover. The terminals tend to rust off of the regulators.
If you can't identify the motor, take pics and post them. We want images! It's a photo site here.
Message edited by author 2007-05-26 14:15:05.
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05/26/2007 02:20:05 PM · #21 |
| If I'm not mistaken it has a 20hp Briggs and Stratton. Maybe the "V" twin. It's a budget Deere model you can buy at most home improvement stores. Deere doesn't put the good engines on these models. |
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05/26/2007 02:39:41 PM · #22 |
See? I know nuffin about small stuff.
Here's what I use to check alternators though:
 
And fuel pumps:
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05/26/2007 02:43:44 PM · #23 |
If you are handy with gadgets, here's a link for you.
Briggs support site
You can get the manual for it there.
Cool pics Brad. I used to use a standard electronics "O" scope for that stuff. Now it is cheaper and quicker to just change out the part, except for the fuel pump with a stuck brush. They used to be mechanical when I was working on cars.
Message edited by author 2007-05-26 14:52:50.
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05/26/2007 03:19:10 PM · #24 |
Originally posted by NstiG8tr:
If I'm not mistaken it has a 20hp Briggs and Stratton. Maybe the "V" twin. It's a budget Deere model you can buy at most home improvement stores. Deere doesn't put the good engines on these models. |
That's exactly right. Briggs and SStratton Twin V. |
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05/26/2007 03:20:20 PM · #25 |
Originally posted by eqsite:
Originally posted by NstiG8tr:
If I'm not mistaken it has a 20hp Briggs and Stratton. Maybe the "V" twin. It's a budget Deere model you can buy at most home improvement stores. Deere doesn't put the good engines on these models. |
That's exactly right. Briggs and SStratton Twin V. |
Same engine as used on Countax Ride-On mowers, and they have a magneto. |
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