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simplewrench

16 hp Broadmoor eating pto switches

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simplewrench

Had a guy offer me 3 mowers for an engine installed in his sun runner. This is one of the 38CA3CF60-AE8E-4CD8-8C47-B5BD7B625004.thumb.jpeg.fb5ceb0d63324e17f580f701b6f1eae2.jpegit’s a 16HP Broadmoor runs decent transmission seems fine. Dash tower needs some work and the deck needs lots of work, but my biggest issue is that I mowed for about an hour and the deck quit and the switch was hot and no longer had continuity to turn the deck on. I installed a different used pto switch and it worked until I turned the deck off then that set of contacts were shot. So I moved the wires in the harness to another set of contacts in that same switch and had the same results. I assume there is an issue with the clutch but I don’t have much experience with the electric clutches, so any insight you can offer would be much appreciated. 

I don’t want to sink a lot of money in this unit it may just be better to use this engine in the sun runner. I was going to use an opposed twin in it but it had a V twin in it originally. 

Edited by simplewrench

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PhanDad

The easiest thing to fix that could be wrong is the voltage regulator  is putting out too much voltage.  This would result in more current flowing through the switch and electric clutch windings.  Not good for the battery either.  

Or, more likely IMO, there’s a short somewhere in the clutch windings such that the resistance is lower and excess current is being drawn.  

If either of the above is correct, I’m surprised the switch burns before the clutch winding totally fails.  

I’m curious to hear other opinions.  

 

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kwt

I'm more tuned to AC electricity as it relates to motors and am not super familiar with DC theory. I'm used to thinking voltage drop on a constant load causes the amperage to rise. It is always due to bad connections, possibly in switches, or even an improperly designed system. Maybe an electromagnet like what is in the clutch has a corresponding rising clamping force increasing with voltage, consequently increasing load and amperage/current.

 

I do know that a bad voltage regulator on a 12 volt DC system will smoke a set of resistance heated snowmobile hand warmers in short order.

 

It's pretty easy to put a volt meter on the charging circuit while the engine is running on the governor (WOT).

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LMichaels

In any case there is extreme current flow BUT that may be in reverse. When and electromagnetic coil working on DC is shut off the electric field collapses and induces a huge back current. Which can cause a huge arc in the switch and burn the contacts.

I would check system voltage with engine running. Should be about 14V or slightly less. If so my money is on the actual clutch coil as the diodes that prevent that back "arc" are likely burned out

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simplewrench

I really appreciate all the input it definitely gives me something to work with. I’ll let you know what I find out. 

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LMichaels

I am not sure what the spec is on these machines. Maybe I will have to try my own machines (though one is a Honda) and see what I get. If it's not pulsing or fluctuating perhaps that is normal. My money then would be on the actual electric PTO specifically the coil and support circuitry. It should have internal diodes and perhaps a capacitor to squelch the huge back current from the field collapsing when you turn it off. That back current can get up to a few hundred volts and pretty high current which would account for burning out the switch

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simplewrench

Yeah I pulled the plug on the clutch and at first it was putting out 14v but crept up to 18v so l will order the regulator. 

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LMichaels

I don't think it's your issue with the switch. I still think there is an issue in the clutch itself when the field collapses. Though if 18V is not normal it may have eaten the diodes for arc suppression

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simplewrench

That would explain if it is a surge when powering down but not 18v charging when the clutch was disconnected at least in my mind. Or am l missing a piece in my mind? Or of my mind. 

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LMichaels

When you energize a coil it builds a huge magnetic field. When you  de-energize a coil/electromagnet that huge field collapses and induces a huge reverse flow of energy back through the same circuit. If something is not done to block it that same induced current will cause a huge arc across the contacts of the switch or relay contacts that energized it in the first place. Think ignition points and coil. There is a condenser to suppress the arc that would form from the coil inducing a back current and burning out the points. In that PTO clutch the same thing happens. Forget the perhaps slightly high 18V charging volts. It's superfluous to the problem at hand. Without something built into that clutch to suppress that induced voltage the switch will make a huge arc when you turn the coil off. Whether it's a diode system to bleed off or block the reverse voltage or a capacitor or any combination of them. Unless you suppress that arc the switching contacts will burn up in short order. I don't know any simpler way to explain it but OP my $$$ is on that system having failed internally on that clutch and replacing it should eliminate the issue. Now if the 18V is proven to be excessive the issue MAY come back as the excess INPUT voltage may be damaging the arc suppression system but unless and until something is done to fix the arcing in the contacts you will never "fix" the initial issue you asked about

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simplewrench

Ok I appreciate the clarification and re emphasis on that system. I just want to spend my hard earned money wisely. Thank You 

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LMichaels

This may be true as I have never checked the voltage on my own Sovereign or even my Honda. But even at that it alone does not account for the burned out switches. Unless excessive initial voltage is what has killed the PTO solenoid in the first place. If it ever stops raining here this week I will pull my Sovereign into the garage (yard is so soggy I am afraid it will sink to the axles LOL) and report my charging voltage. BTW OP don't discount the role the battery plays in the charging system. IF and I mean IF the 18V proves to be excessive try a new battery in the machine. Alternator type charging systems are VERY dependent on the battery as part of the voltage regulating system. And before you ask YES a bad battery can still run your machine. So your battery may have one bad cell which can cause the voltage readings to go wonky

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LMichaels

Fwiw I checked my sovereign and my Honda's voltages with engines running about 1800. Both read 17 volts average at battery. So op your 18 doesn't seem out of line. Certainly within variation between meters. Hope this helps.

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LMichaels

I posted a lot of info in the hopes of helping you out but see no further posts. Did you find the issue or are you letting it go? Curious what you have come up with

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jlasater

There's no reason a diode can't be added externally. I'm not sure what the spec's would be for one in that application but it could be added.

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CarlH

LMichaels has it exactly right about an inductive voltage spike when the switch is opened.  This is directly analogous to how a Kettering ignition (points, coil, sparkplug) works.  A magnetic field builds (in coil/clutch winding) while current is flowing.  When the switch/points open, the current flow stops, the magnetic field collapses, and a voltage spike occurs.  Such a spike likely killed the regulator but is unlikely to have burned up the switch.  The switch failure likely came from a shorted coil winding and increased current.  It takes time to build up the heat necessary to burn up a switch and that spike likely only lasted some milliseconds.  There is Kohler and/or Simplicity bulletin about adding a diode to the newer Wagner clutches on the Commands and a cable is available on eBay.  I think the diode would be a zener but have no idea of the shunt voltage or power rating.

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