Why would a mower melt 20 amp fuses?

   / Why would a mower melt 20 amp fuses?
  • Thread Starter
#31  
Hope this helps. Especially for anybody willing to take the time to look at it and help me understand what's going on here. This is the link to my wiring diagram.

If the link is messed up, its on Page 75


The fuse that is melting is the 20 amp fuse with the yellow wires.

The yellow wire goes from the Engine Adapter Harness to the key. I think. It shows to just end by the key. I'm going to take it apart now and see if that's right.

When the fuse melts, the blades stop turning. Sometimes I can put in another fuse and keep on mowing. Other times, I have to wait, and when it cools off, I can keep on mowing. But now it's worse, and it heats up a lot faster. SUPER FAST!!!

The other thing is that my temperature gauge stopped working when all this started. I'm guessing that the two problems are related.

Thank you!!!
 
   / Why would a mower melt 20 amp fuses? #32  
That's pretty much the same schematic I was finding but easier to read with a few more clues. I'll look at this later but diodes could be suspect. Polarity on the clutch is important because it has a diode.
 
   / Why would a mower melt 20 amp fuses? #33  
Here's my take on it.....
It isn't a short, because the fuse doesn't blow instantly. I think it's an electrical overload.
Second, it cannot be supplied with "too much power" or "too many amps" and I doubt the system has more than nominal 12 volts, and even if the volts were in the 15 volt range, that only helps the fuse to carry more current. (Volts times Amps equal Watts). When you energize the clutch, it DEMANDS a certain amount of WATTS, which it gets by drawing amps thru the circuit. The higher the volts, the less current (amps) it needs to draw thru the wires, switches, connections, fuses, etc. Volts dont cause heat, only amps do that.

Also, your electric clutch switch energizes a copper-wire-wound coil, which creates a magnetic field, which is supposed to pull in a piece of ferrous steel to tighten up the disc and drive the blades.
If the ferrous steel armature can't get to a position that "neutralizes" or "equalizes" the coil, current flows to try to make that happen. The further out from neutral, the higher the current flow. When the armature is in the right position, current flow is much reduced.

Could you bypass all the circuitry from the battery to the connection closest to the clutch coil? Make sure you are hooking the positive battery post to the positive terminal on the clutch. Use about a 12 gauge wire and alligator clips.
Monitor the wire for heat, because if a 12 gauge wire gets hot, that's about how much current it takes to blow that 20 amp fuse.

The goal is to see if there is some fault or deficiency in the original tractor wiring. Your extra wire will supply power directly to the clutch, bypassing (augmenting, really) ALL tractor wiring.

But I suspect there is a problem in the clutch itself, either a faulty winding or something that's preventing the armature from finding "home". (altho I see in your first post, you already tried a new clutch)
These devices are difficult to disassemble, depending on your ability and knowledge, your access to tools, etc. but if you get a new clutch and it works, i recommend that you try to take the old one apart to see how it works and what's inside. Nothing to lose, if it's already junk.
Anyway, try the helper wire, and monitor that wire temp to prevent damage and see if that helps.
 
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   / Why would a mower melt 20 amp fuses? #34  
Unfortunately, the link only goes to page 71 before the warranty statement & flipping to Spanish.
Can we sort out some terms, to be sure everyone's on the same page?
In the OP, you said 'PTO generator'. That means the electric clutch for the blade drive, right?

And the switch you're talking about is the 'cutter engage switch', figure 4-3 on pg 15 of the linked pdf?

Air cooled version, or liquid cooled? (Next step for docs would be the wiring diagram for your particular engine, which isn't shown in the linked pdf.)

The previous tips about using a light bulb instead of a fuse make sense, but I'd disconnect *both* wires from the clutch before starting the test. That way the lamp should light *only* if you have a partially shorted wire.

Looking back at the OP, the pic of the fuse makes it look like it melted (and the plastic actually burned) starting on the 'human' end of the fuse, and to one side. Where exactly is that fuse *physically* located? That looks like heat damage from an external source.

And additionally from the OP, could you be talking about the actual alternator built into the engine, and not the electric clutch? There seems to be no direct path for the yellow wires & related fuse to the clutch.

If you're really talking about the alternator, measure the voltage somewhere on the mower. There's no danger of damaging anything as long as you're using a digital voltmeter & you don't short something out. Know that if the voltage regulator has failed, and the system is outputting significantly higher than 14V, or if the diodes in the regulator assy have failed and its outputting AC voltage, it will kill your battery (and possibly any other electronic stuff) fairly quickly.

Given the wiring diagram, I'd suspect that the electric clutch is a red herring and the problem is actually related to the alternator/regulator (actually the regulator), assuming you don't have an external heat source attacking the fuse, and you don't have a bad electrical connection related to the fuseholder, as previously discussed. Still need to see the actual path of that yellow wire after it gets to the engine, though.
 
   / Why would a mower melt 20 amp fuses? #35  
Looks like the A wire should connect to the A terminal on the key switch. The yellow wire goes to the voltage regulator on the engine which would be energized with the key on. Also looks like the entire safety system is energized from the L terminal of the key switch with the key on that feeds the safety interlock module. Looks like the fuel solenoid could get its power from the safety system or the interlock module

What does the other fuse with the red wires look like. I think if it was something in that side of the system it would be showing issues also. And also what @KWentling said about the diodes. I had also thought about the clamping diode on the clutch wiring, but you said that the wires were also heating up without the clutch engaged.

Try releasing the parking brake, and then turn on the key and see if it still heats up without the engine running. Don't even need to be in the seat, that would eliminate most of the safety system from being energized.

But I am strongly leaning toward a shorted regulator/rectifier. Disconnect the yellow wire from the regulator and connect an ohm meter between the yellow wire and the metal case of the regulator. Very high resistance would be normal and very low resistance in this case could be tenths of a ohm would indicate bad regulator.
 
   / Why would a mower melt 20 amp fuses? #36  
I should have added, when doing the voltage test, do it with the engine running at near normal operating rpm (it's likely a 'dynamo' style alternator, and output drops off at low rpm). Check the DC voltage and then switch to AC on the meter & check again. DC should be around 14V; AC measurement should be zero, or no more than a volt or so at worst. Anything higher indicates a problem with the rectifier/regulator.

But I ask again, where is that fuse physically located?
 
   / Why would a mower melt 20 amp fuses? #37  
Good afternoon Eddie,sorry to hear the problem is still evading detection but stay calm,take breaks and drink plenty cold water. Alot of good advice has been offered but some is based on "sience" that is accurate but can be hard for the average guy to follow. After seeing your wiring diagram,I'm thinking pto clutch isn't where the problem lies. The yellow wire and fuse serve all accessories, including clutch. Let's try something simple and hope it turn's something up. The temperature gauge is controlled by a variable resistance sender in engine block. That sender might have gone bad causing the high resistance short we are searching for. The gauge and sender are tied together by a white wire with black strip. Whichever is easier, disconnect that wire at sender or gauge. It's entirely possible that disabling temp gauge might prevent engine running but if so we'll get to that later. With wire disconnected, start engine or if engine doesn't start,leave ignition switch in run position while feeling wire for overheating. Good luck,I'll wait for result.
 
   / Why would a mower melt 20 amp fuses? #38  
I agree with jaxs that the temperature gauge, sender, and associated wiring is worth a look.
 
   / Why would a mower melt 20 amp fuses?
  • Thread Starter
#39  
Thank you for all the advice. I've been messing with this all weekend, and I guess I lost it. I cut out all the wires and I'm going to just wire up the basics. No more safety switches, no more hour meter, no more water temperature gauge, and not one extra wire then what I absolutely have to have.

I'm going to put in a new ignition key and a toggle switch for the PTO. Both of those have been ongoing issues for at least 7 years.

I'm going to do an online search for a diagram to copy. I just need the key to start and turn off the motor, and the PTO. I need the engine to charge the battery, and that's really all that I can think of that I need.
 
   / Why would a mower melt 20 amp fuses? #40  
That wiring diagram is really poor. The person who made that should be taken to the wood shed for instructions.

There is nothing in the diagram that shows what the switches connect in the various positions.

OP - is your engine air cooled or water cooled ?

Richard
 
 
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