Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > Sport Touring: ST4 / ST3 / ST2 > Is it the reg/rec ?

[Phil Butler]

While out on the bike the charging light came on, yep the dreaded Reg/Rec problem, or is it?

checking around I found that the plug on the alternator leads was burnt. Plug replaced with more substantial item, light is off great!! er...not really the light came on again after about 5 miles. No problem with the connections, good and tight.

The light comes on and goes off randomly, I have checked the alternator output it is more than 14 volts at tickover.

I have since been out and done over 60 miles on the bike without problem even though the light is still doing it's thing.

Is it a problem with the lamp circuit from the reg/rec and it needs replacing

If so which is the best. the existing one is the original so it's 7 years old do I go with a Ducati part or try Electrex or Newtronic which is the best, oh yes are the alternatives much cheaper than a genuine part.

CheersPhil

[rockhopper]

When my connector burnt out the light didnt come on. Dont know if that helps you or not!!

Whats the voltage across the battery at 3000 rpm?

[PaulC]

Having had 2 reg/rec fail so far it would appear they don't necessarily go the same way each time. The first one gave no real indications of problems other than the battery light stayed on permanently. The second one, no light on but after riding for an hour or so the bike would start to slowly break down and then finally stop. Checking the reg/rec indicated that when cold it was charging fine, but went out for a ride with the multimeter in the map holder and after 20 minutes the voltage started to drop off until it was obvious it was just running off the battery. I now have an upgraded starter motor lead, headlight gizmo (as mine is hardwired) and optimate to try to help the whole system (as the reg/rec problems are supposedly linked to it getting overworked if your battery is getting drained) and an Electrix reg/rec. Was a bit cheaper although the attachments were not correct so I had to rewire original ones (from the old reg/rec) on. No problems for the last 18 months, so fingers crossed.

[fatduke11111]

I never had the light show once - just crap at turning over progressively worse after charging the batt, and the fuel guage / clock jobbie reset to 'all zero's' a couple of times.

Which pointed to the Reg so I had the wiring resoldered around the dreaded infamous plug and also put some heavier gauge cables for starter motor and earth as it was slower at turning over.

Charging ther batt regularly seems to keep it in trim - bit similar to PaulC about 12months so far.

[Shazaam!]

It’s not the lamp circuit it’s the charging circuit. Put a voltmeter across the battery and ride around - you’ll see that the voltage is dropping below 12V when the light comes on.

The most common reason for an erratic charging voltage is that the stator lead wire insulation is heat damaged allowing them to short together, especially after the engine heat further reduces the electrical insulating capability of the wires. Ducati has supplied seriously under-sized wires - given that they have to carry 30-plus amps continuously. Replacing the wires between the engine casing and the regulator with a heavier gauge cures the problem - if done soon enough. If not, the voltage surges from the wires being shorted together end up damaging the solid state components in the regulator/rectifier and you’ll soon end up having to replace it as well.

So first replace the wires from the stator to the regulator need to be replaced. At first glance it may appear that the high current being carried by the wire had just overheated a few inches of insulation next to the high-resistance bullet connectors. But when you remove the common sheath that the wires run in back to the left engine cover, you likely find that overheating (from the current, not the engine) has softened the insulation to a degree where you can damage it with your fingernail. A multimeter will say it's continuity is OK, but at the higher AC output levels at higher rpms, the insulation can’t prevent the wires from shorting together. Remember, the wires are held in physical contact along the entire sheath length.

You don’t need to remove the engine cover to do this. Inside the engine the stator wires don't touch each other. The approach that I took was to replace the damaged wiring up to where it exits the side cover. I pushed a piece of shrink-wrap tubing over each of the wires and into where they pass through the seal in the cover and left the internal portion of wiring alone since they are separated inside the engine. Again, the main problem is where they touch each other along their length where they run in a common sheath.

I also took the oportunity to relocate the regulator itself to the licence plate holder to get it away from the engine and exhaust heat.

You can read the full explanation here:

http://ducatisportingclub.com/contro...d.php?tid=2042


You need to use SWG 12 gauge wire between the engine case and the connector to the R/R. Any wire, no matter what size, has resistance (so many ohms per foot) so any wire will heat up. Obviously the larger the wire, the less resistance it will have to current flow, and the less heating that will occur for a given current.

The type of insulation on the wire is also important to this discussion. Different insulation materials have different temperature allowables for continuous operation. For example for 10 gauge (AWG) wire in 30ºC (86ºF) free air:

55A will heat high density polypropylene to 90ºC allowable
58A will heat polyvinyl chloride (PVC) insulation to 105ºC allowable
75A will heat Kapton, Teflon, and silicone insulation to 200ºC allowable

So for example, silicone insulated wire should be used for higher current ratings or for hotter operating environments.

The environment that the wire sees is important, and this is where Ducati engineers screwed-up. The above temperature ratings assume that the wires are located in 30ºC free air. The stator wires run first internally to the engine, and then are enclosed on a sheath that passes over the engine and internal to the fairing. So the insulation on these wires don’t see adequate cooling, they exceed their performance rating, and loose their insulation properties.

The portion of the stator wiring that run in the sheath is where insulation failure is critical. The stator wire are held closely together and insulation breakdown from heat causes them to short together at the higher output voltages at higher engine rpm. Get rid of the insulating sheath, the wires will run cooler. Add some shrink insulation where the wires contact grounded components.

The wires inside the engine don’t come in contact with each other until they exit the cover. Even if the insulation overheats it can’t damage the regulator, and because of the hot environment, a larger gauge wire inside the cover isn’t going to reduce insulation operational temperatures much in this section of wire.

The leads attached to the regulator/rectifier are a smaller gauge but they also see a cooler environment than the sheathed wires. Sure, they’ll be heated more than the larger gauge replacement wires but they have better cooling. So, just make a low resistance splice to the RR wires.