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Discussion Starter #1
My 851 Superbike will not charge the battery. I read that it is common for the alternator wires to overheat and create a poor connection in the harness causing a failure to charge and ruin the regulator. I checked for this fault and sure enough, I found melted insulation. I repaired the wiring but the charging condition remains faulty. The battery light in the instrument cluster illuminates when the engine isn't running and at idle but extinguishes when RPMs exceed 1000. Before I replace the regulator I'd like to know if someone can explain how the warning light works and If it indicates that my problem lies somewhere else. The battery can be charged by a battery tender and when fully charged indicates about 12.4 volts.
 

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with the bike running you should be making a minimum of 12 volts. anything less and the regulator is done is my rule of thumb. if the battery voltage starts to decrease while the bike is running the charging system is not working (bike is just running the battery down). also check your stator, cant remember exactly for the two phase as to the output voltage but with the bike running hook your multimeter up to the stator leads and see how many ac volts are coming out.
 

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Old Wizard
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Wire repairs.

The error that most people make is replacing only the 6-inches or so of the crispy portion of the stator lead wires adjacent to the connector. Even though not visibly damaged, the adjacent section of wire should also be replaced with a larger gauge all the way back to where it enters the engine casing. This is because the entire wire has been overheated and has lost its electrical insulation properties which then allows the wires to short together, usually at the higher voltages produced at higher engine speeds but sometimes also at lower rpms.

This wire shorting will damage the regulator at some point.

For single phase charging systems, at idle speeds below 1,000 rpm the light will come on if there is significant electrical load such as lights, fans, computer, fuel pump with a plugged filter etc. If it comes on at higher rpm you'll need to replace the regulator.

The other reason regulators fail is they get too hot inside the fairings so they should be moved to a cooler location.
 

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Discussion Starter #4
Thank you for your extensive responses. I'll check the voltage across those two yellow wires and report what I get.

Shazaam, you're right, I replaced only the connectors where the insulation seems to be good.:eek: I have sufficient yellow 12-gauge wire to replace all of it but is there really any improvement if the stator leads inside the engine case retain the original wire?
Is it correct for me to understand that my regulator is probably still working and that the low voltage to the battery is due to some other fault? It isn't clear to me what mechanism actuates the battery warning light. Is it the regulator? I have a shop manual and wiring diagram but I'm unable to identify that warning light and its circuit.

I'd like to ride this bike again some day. I like looking at it in the garage but my friends really like the way it sounds on the open road.
 

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As the other mentioned above, the voltage output from the stator should be around 50 VAC.

You can disconnect the stator wiring, without the engine running and check the continuity from each wire to the case (ground). Any continuity to ground is bad news. Then check the stator voltage output by starting the engine with the stator wires disconnected. Be careful there is a lot of energy coming out of the leads. The age of your 851, if it's the original stator, is enough to question the stator integrity.

Check this site for rebuilt/rewired stators www.ricksmotorsportelectrics.com
 

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Discussion Starter #6 (Edited)
I see that my post has been moved to the Superbikes forum. Thanks. Its nice to know where I belong. :) (Or was I just kicked out of Ducati Chat?) :D

I just took a reading across those two yellow wires and at 4,000 RPM there are 65 volts AC. I didn't record the output at idle but there was a smooth increase in output as the engine speed increased.

I reconnected everything and with the engine off the battery voltage is 12.7 V and with the engine running I get 11.8 V at all engine speeds.

The battery charge light goes out when the revs are increased above idle but obviously the system isn't charging. I'd be happy to replace the regulator if that's where the problem is but I don't want to overlook some other possibility.

I haven't mentioned it before but the battery terminals are clean and the wiring "looks" like its in good condition.

Just trying to organize my thoughts here...

Is it possible for the battery light to operate the way mine does (illuminated at idle and extinguished at higher RPM) if the regulator is faulty?

If the answer to that question is yes, I’ll get a new regulator.

Is the ElectroSport ESR510 a good choice?

Thanks again for looking at my problem.
 

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Old Wizard
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The rule-of-thumb for sizing wiring is that if it needs to carry 20 amps use 12 gauge wire; 30 amps needs 10 gauge; 40 amps needs #8 gauge. Early bikes have 350 watt/29 amp two-wire charging systems so 10 gauge should be used.

The wires inside the engine casing are physically separated so they can't short together when the insulation gets damaged. The wires outside the casing run in a common sheath which is where they short together at higher voltages, in your case above 65VAC. Remove this sheath and making sure they don't touch anywhere along their length, then check your AC voltage output again.

If the DC voltage across the battery terminals doesn't rise from the usual 11.8V at idle (battery is discharging) to 13.5-ish at higher rpm the regulator function of the RR is damaged.

The regulator function of the device limits the voltage to the battery - the excess output is sent to ground through a resistor that dissipates it as heat, the rectifier function converts AC to DC.
 

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Discussion Starter #8
Don’t ya hate it when a problem is described, helpful suggestions are made, and there’s not a follow up to describe the resolution of the issue? I think these threads would be much more helpful in the archive if they included the often-missing final chapter.

Well, here’s my report.

I put a little more effort into studying the wiring diagram and finally it makes sense. I took a chance and bought a new regulator unit since I couldn't find any fault elsewhere in the system. I found out the answer to my question.... Yes, it is possible for the battery indicator light to behave as mine was. I guess the fact that the alternator was working was sufficient to operate the warning light system even though the battery was discharging.

With the new regulator in place, the warning light still operates the same way but now the battery is charging also. Road testing confirms the repair. I'm delighted. :)
Thanks for your help.
 
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