Craftsman GT3000 - Is some hotness normal on the 30 amp power fuse

[Valhalla3]

My Craftsman GT3000 with a Briggs & Stratton Platinum 20HP, OHV Turbo Cool Vtwin Intek, blew a 30 amp main power fuse over a month ago. I thought it was the fuel shut off solenoid at first but then it looked like it was more likely the electric PTO clutch. But now I'm questioning that too. The PTO clutch reads 2.3 to 2.7 ohms across its coil. A new one they say is about 3.5 ohms. But with the engine off, and the pto clutch switch engaged, that 30 amp fuse and socket get hot within about 15 seconds. With the PTO clutch disconnected and the ignition switch in either the run or the run/lights position, nothing gets even warm. Actually the fuel shut off solenoid starts getting warm after a minute or so. Left on, it will get a little hot but you can still have your finger on it even after a couple of minutes or so. The fuel shutoff solenoid measures about 32 ohms across its coil. By run/lights position I mean where the switch lands by default after letting go of the sprung position to crank the engine. BUT..... when the engine is started, the 30 amp fuse and socket and wires start getting warm within about 20 seconds or so. I thought it was starting to get hot right on the top of the fuse so I shut it off not knowing if this was normal and not wanting to blow the fuse or chance hurting anything else. I have only a 20 amp fuse in the socket for now and that did not blow in the time frames I mentioned. It seems that the only thing that is going on with the engine running that is different from when it is not, is the regulator and alternator charging the battery. The magnetos provide the power for the spark plugs right?

So, is that normal operation for the 30 amp fuse and wires to get warm to hot while running? What else can I do to troubleshoot this? Something caused that 30 amp fuse to blow the first time while I was mowing. Please help....my grass is going on 2 months high.

Thanks!

VH

 

[Roadworthy]

Your fuse should not get hot. Based on your resistance reading the PTO clutch should draw just over five amps - well within your thirty. However when you engage the PTO it will initially draw far more, hence the thirty amp fuse. Your coil may have some shorted turns or some internal leakage when it gets hot. Try to borrow a dc ammeter which can handle perhaps fifty amps so you can troubleshoot your circuit.

 

[tomplum]

Your PTO clutch OHM reading is OK. How are the terminals in your holder and through the switch? I use one of those fuse buddy things, really convenient. Feel your harness from the PTO switch to the clutch for a diode and check that if it applies here.

 

[DarkBlack]

Something quick to rule out: put a voltmeter on your battery while running and verify your dc voltage isn’t getting too high, then switch your meter to AC volts, and make sure your not getting any appreciable AC voltage. You’re ruling out a shorted diode

 

[CalG]

Something quick to rule out: put a voltmeter on your battery while running and verify your dc voltage isn’t getting too high, then switch your meter to AC volts, and make sure your not getting any appreciable AC voltage. You’re ruling out a shorted diode

Speaking of 30 amp fuses.
I recently needed to replace a 30 amp fuse on the Hurlimann. The tractor would not start without it.
Starter relay and glow heaters

Went to the FLAPS (NAPA) to buy a replacement, and the only product offering was green, but OPAQUE! Not the see through translucent plastic housing typical of Buss brand fusses.
How is a fella going to determine a blown fuse in the field if you can't see the open conductor? Does the plastic show some discoloration when burned open?

 

[Valhalla3]

Something quick to rule out: put a voltmeter on your battery while running and verify your dc voltage isn’t getting too high, then switch your meter to AC volts, and make sure your not getting any appreciable AC voltage. You’re ruling out a shorted diode

Thanks for the reply! How much DC voltage is too high? How much AC voltage is too high?

 

[Valhalla3]

Your PTO clutch OHM reading is OK. How are the terminals in your holder and through the switch? I use one of those fuse buddy things, really convenient. Feel your harness from the PTO switch to the clutch for a diode and check that if it applies here.

Your PTO clutch OHM reading is OK. How are the terminals in your holder and through the switch? I use one of those fuse buddy things, really convenient. Feel your harness from the PTO switch to the clutch for a diode and check that if it applies here.

I think the terminals are ok although, when the 30 amp fuse blew, it was somewhat melted and broken in the socket. I got it out without incident. What is a fuse buddy? I looked it up and all I saw was some kind of meter? Is the diode between the switch and the connector that goes to the pto clutch down near the clutch about 8 inches from it? Or is it between that connector near the clutch and the clutch?

 

[Valhalla3]

Your fuse should not get hot. Based on your resistance reading the PTO clutch should draw just over five amps - well within your thirty. However when you engage the PTO it will initially draw far more, hence the thirty amp fuse. Your coil may have some shorted turns or some internal leakage when it gets hot. Try to borrow a dc ammeter which can handle perhaps fifty amps so you can troubleshoot your circuit.

I have a digital multimeter but it is only good for up to 10 amps. People are pretty selfish and self-centered here where I live so even if someone had a 50 amp meter they would probably not want to help.

But if I do find one, what are you suggesting? Right now the problem is not with the pto clutch because I have that disconnected. I am told that the resistance in the coil I measured is ok too. I am now suspecting something in the charging system. So where would I put the ammeter....inline between the negative connection to the battery or the positive or somewhere else?

 

[tomplum]

I think the terminals are ok although, when the 30 amp fuse blew, it was somewhat melted and broken in the socket. I got it out without incident. What is a fuse buddy? I looked it up and all I saw was some kind of meter? Is the diode between the switch and the connector that goes to the pto clutch down near the clutch about 8 inches from it? Or is it between that connector near the clutch and the clutch?

It's a meter that plugs into the fuse holder. It allows you to see real time AMP draw quite easily. Just makes life easier. You could test your harness from the clutch to the switch with an ohm meter to confirm if the diode is there that it is good and not shorted. It just legs from the + to the negative wire if yours has one. They are never shown in the IPL, so other than that you have to unwrap the harness and look for the lump.

 

[Valhalla3]

This is what we used to call an unverified failure in Aerospace. Well....I realized the pto clutch, the charging system, a hard short or a bad fuse are the only things that could blow a 30 amp fuse. I tested the charging system today. The battery voltage with the engine off is 12.62 volts. With the engine running it is 13.5 volts, so that certainly is not indicative of too much current or a bad charging system.
I = V/R so with a constant resistance which we must have or the battery would be dead from the short, and the voltage being 12.62 to 13.5, the current can't be too high....right?. I also have an ammeter on the tractor which comes directly off of the fuse, and with the engine running, it was reading 5 to 7 amps, pointing to the right (charging). I wouldn't count on that to be 100% accurate but I think it tells me something. I connected the pto clutch again and turned it on, with the engine off, and the ammeter was reading 4 amps and pointing in the opposite direction Indicating a depletion state, or discharging I guess.

Now something blew the 30 amp fuse that first time but I'm not seeing anything now that would do that. Thus the unverified failure. You can't have a short in the fuse or socket because the worst case is continuity which is the same thing the fuse is doing. I have taken the clutch out of the equation and now the charging system as well...so what is left? A power gap can cause something to heat up as this fuse and socket did and it even melted the plastic fuse case. One of you was suggesting this too. Today the fuse was starting to get hot after about 30 seconds. The socket, naturally was getting warm or hot also. The wires coming out of the socket were getting warm but not too far from the socket, nothing was even warm at all. The Ignition switch and all the wires to and from it and the wires to the ammeter were also not even warm. It was only hot right on the top of the fuse and the socket. This at least seems to point to a power gap or something in the socket....at least for the problem that is going on right now. I'm out of components that could be causing the problem so similar to Sherlock Holmes famous quote "...when you have eliminated all the things it could be, whatever is left must be the truth /problem...." lol BUT this is a two part problem. Whatever caused that 30 amp fuse to blow originally is not happening right now. It may have degraded the fuse socket in some way though. But something is causing the fuse and socket to get hot and it is only hot right at the fuse and socket and nowhere else and the current would appear to only be between 5 and 7 amps with the engine running which is the only time it gets hot. Arggg! What do you think?