Mower Blows 20 amp fuse when PTO when PTO is engaged

[Auto Doc's]

Verify the grounds (big and small) are all clean and tight starting with the battery cable and work from there. A cruddy, rusty ground or "green" corroded cable/wire creates high resistance. People always focus on the positive side and neglect the negative side of circuits.

While you are checking things, make sure the charging system is working properly, use a multi-meter. A weak or overcharging system will cause a PTO clutch to overheat and that will blow the fuse. A poorly grounded voltage regulator is also not uncommon.

 

[Freddie21]

Could you not take a wire from the battery, put it through a 20a fuse, attach it to the clutch wire through a switch to see if the fuse blows after some time? This would confirm the condition of the clutch and it's lead. You could then cut the load side of the mower's fuse holder and attach your test wire there. Take it in steps to determine where the problem lies. You would need a schematic.

 

[Reverett]

There are 2 ways to approach a problem.
Toss parts at it till it goes away or find where the actual problem is and rectify it.

A solenoid draws POWER ( Watts ) and it does not care how it gets them
So 12V x 10A or 6 V x 20A or 3 V x 40A is all the same to it.
However Amps = heat.
Heat = RESISTANCE
RESISTANCE = VOLTAGE DROP
VOLTAGE DROP = more AMPS to make the same WATTS

And thus the self feeding loop continues till the fuse can't take it any more.
Much like the self feeding loop of face book morons makes bigger & more face book morons.

9 out of 10 mowers that come in here have disgusting battery connections and in particular the ground connection
Next is the actual fuse holder itself which is not waterproof because cheapskate owners & Face Book whingers will not pay the extra 50¢ to get waterproof connectors so the factories no longer fit them.

A proper search of this site will find around 2/3 of the blowing fuses problems were fixed by replacing the fuse holder.
Half of the remaining were fixed by cleaning or even replacing the battery cables & connections.

FWIW I do around 300 service / repairs a year and am yet to need to replace a clutch but I have gone through several 50 packs of fuse holders .

You are correct about their being a conspiracy out there.
It is called a free market lead economy
So whoever makes a mower with the lowest Hp to $ ratio or the lowest blade inch to $ ratio will outsell all others and prosper while the factories that make high quality mowers that sell for a fair & reasonable price will bob along being just barely profitable while the family that runs them continues to believe in the value of making quality over cost or go bankrupt.

That is the conspiracy, got nothing to do with badly designed PTO clutched except in the narrow minds of the technically if not totally ignorant who make 99% of cyber space.

The chances of you getting a dud PTO clutch if you bought it from a mower shop is about the same as winning the lottery
The chances of you getting a dud PTO clutch if you bought it from an on line Amazon or ebay vendor is about the same as it raining on any particular day.
All of the reject PTO clutches that are made in CHina end up being sold on line cheaply, usually because they are faulty .

Bert for President!

 

[VRR.DYNDNS>BIZ]

As an electrical engineer for over 40 years, I want to provide a bit of clarification to what berts said about solenoids. All a solenoid consists of electrically is simply a coil of wire. It creates a magnetic field when, in this case, a DC current passes through it. The amount of current it draws is determined by the resistance of the coil, which is typically under 5 ohms for a PTO. A solenoid does not draw watts per se. It draws a specific current based on its resistance and the voltage applied. When you multiply the voltage across the solenoid by the current through the solenoid, you will know the wattage or energy being used. A solenoid may specify a wattage in its spec sheet, but that is only when the unit is operated at its rated voltage, and when it is cold. [as a side note, the resistance of a coil actually rises as its temperature rises, causing less current to be drawn]

A solenoid does not behave in such a way as to draw the same number of watts, regardless of the voltage applied. In other words, if you took a perfectly good 12V PTO clutch and connected it to a 12V battery, it will draw a certain amount of current(likely to be in the 3-4 amp range based on a coil resistance in the 3-4 ohm range). If you take that exact same PTO clutch and connect it to a 6V source, it does NOT draw twice the current. In fact, it will draw half the current. The power is also halved. Why? Because the resistance of the coil remains the same in both cases. Ohm's law still applies. Current=Volts/Resistance

Specific to your problem, I'd suggest using your ohmmeter and checking the circuit(with battery disconnected of course). Disconnect clutch and check its resistance first. If the value you measure is significantly below the 3-4 ohm level, then it would appear your PTO is hosed. If it's good, then I'd work my way back looking for short of some kind to ground.

I submit this with the deepest respect for berts and his extensive experience! Not trying to start a flame war, rather I just want to give Ohm's Law its due!

Keep us posted!

I was about to post similarly and thankful for this correct post. Now on to diagnosis. After checking that coil resistance, still with the fuse out and the coil disconnected, ( and the battery disconnected just for safety of the odd unknown), read the resistance of the balance of the tractors circuit resistance on the ignition switch side of the fuse under all switch settings. Record/report the lowest reading and under what condition. Lets assume a full 12.6 battery voltage is availalble and we blow a 20 amp fuse ( without the impact of connections as prior discussed), r=e/i = 12.6/20=6.3 ohms. Now some tractors have only one fuse, others have a separate fuse feeding only the PTO. that must be reviewed. If only one fuse and resistance is 7 ohms or less, continue to isolate where the resistance rises to a safe level. Besides wire shorts, the typical items are the clutch coil, the PTO switch, the ignition switch, the fuel solenoid, any fancy panels and reverse control panels, charging system diodes or regulator ( battery level will not be maintained ), and least likely are the interlock switches. When the ignition switch is on but no battery connection, the fuel solenoid resistance at play since in the run position it connects the solenoid to the battery feed given to the ignition switch. If at this point the resistance has hit the fuse blow threshold, disconnect the fuel solenoid and read the resistance. 99 out of 100 riders have no load under fuel disconnect status when the ignition switch is on so this resistance from fuse holder feeding to ignition switch to ground should be open circuit for 99 out of 100. Hope this helps.