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Discussion Starter #1
The wiring to my stator in my '95 900ss is shorted together right at the windings on the stator. I have read other posts that say not to replace the wiring inside the case. Can it be done and be alright? If so I wanted to solder the new wires on but I am not sure if they would get too hot and melt the solder. Anybody else tried this?
 

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Old Wizard
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Winter Project

Here’s the basic problem.

The loops of wire that comprise the stator itself are coated with an insulation coating that prevents the wire loops from shorting together. So failure of the stator itself almost never occurs. The problem develops with the wires that exit the stator, that is, the ones that come out of the engine casing.

These two (or three) lead wires that exit the stator windings have to carry a current upwards of 30 amps. The voltage differential between these lead wires increases with engine speed to around 70 VAC.

If the insulation on these lead wires can’t hold back this voltage they’ll short together somewhere along their length where they physically touch, or short to a grounded component, at some intermediate voltage/engine rpm. If you short out these wires, your voltage regulator/rectifier that they connect to will be damaged and need replacement.

Adding to this problem is that the lead wires are partially routed in close physical contact with each other within a common sheath. This sheath is intended to provide supplementary insulation to prevent shorting between the wires and adjacent grounded components. Unfortunately, when the insulation gets damaged the lead wires will short - inside this sheath - where they are forced to touch.

So, the insulation gets damaged by heat and looses it’s ability to prevent shorting to adjacent components. It gets hot inside a superbike fairing (and this doesn’t help) but engine heat not the main cause of insulation damage.

Ducati could have used a larger gauge wire and a better heat resistant insulation, but again, this is not the primary reason for RR failures.

The damage occurs because the in-line connector that allows the regulator/rectifier to be detached/replaced develops a higher and higher resistance as it develops corrosion and/or loosens under normal usage. This causes I-squared-R heating at the connector, and because copper wire is an excellent conductor of heat, ALL the adjacent wiring gets hot, really hot. For example, a small one-half ohm increase in resistance at the connector causes a typical 30 amp current to develop 450 watts of heat.

The mistake most owners and shop workers make is to cut-out and replace only the crispy portion of the wiring. Not good enough.




Here’s the basic solution.

You have to replace all of the wiring that was heat damaged and take steps to assure it won’t happen again. Otherwise you’re going to be replacing your regulator again, and soon.

As luck would have it, the stator lead wires do not touch each other inside the engine casing, so even when the insulation is damaged (like in the picture below) they can’t short together. So there’s no NEED to replace the wiring inside the casing.






So my advice to ALL Ducati owners is to make this a winter project. Replace all the wiring between the engine casing and the regulator leads with PVC-insulated AWG 12 gauge from Radio Shack. Larger 10 gauge is even better, less resistance per foot. Then solder the wires together to eliminate the heating source. Remove the common sheath to physically separate the wires and use stand-off insulators where the wires come close to grounded components.
 

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Discussion Starter #3
The insulation on the wiring inside the casing was melted because the sheath was run all the way to the stator. So about 1/2" from the stator was where my problem was.
I went ahead and replaced the wiring all the way to the stator with 10awg wire.
The picture with the stator shows that the wires get hot and discolored the insulation and it gets brittle and cracks so that was where I had problems.


Thanks
 
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