Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > 748 probs

[Nigel C]

more strange things! had trouble with the neutral light not working which only came on when i pressed the horn button seems to have cleared itself .

as it's going in for it's mot on friday is the charging prob likely to get picked up during the mot test???

[AK]

As long as everything works Nigel, they wont pick up on it.

By the way - Friday is a bank hol - do they do MOT's then?

Alan
ps - good to meet up with you today at Bogs'ill

[Nigel C]

yeah i thought that too but when i questioned it they said they are open !!

[stewmcc]

sounds to me like a bad earth some where, check all the connectons behind the headlight.

stew

[Nigel C]

Finally traced the problem the block connector behind the battery tray (with the two yellow wires from the left hand side of the engine is burnt out alf's(my dealer) suggested replacing it with two bullet connectors and running the wires across under the engine as opposed to over and move the connection from behind the battery tray and moving it ahead of the battery (apparently they do this mod to all dukes as a matter of course) would connectors capable of taking 15v + be sufficient ??

[Nigel C]

it wasn't to move the regulator itself just the connection of the two yellow wires from the regulator to wires from the left hand side of the engine at present it is stuck behind the battery tray where i presume bieng out of the airflow next the the belt covers has caused it to fry hence moving it out from behind the battery tray

[Shazaam!]

It's not the engine heat that damages the insulation, it's heat from the copper conductor itself.

The wires running from the stator to the regulator are seriously undersized .

The general 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 wire should have been used. 1999 (and later) three-wire 500 watt alternators produce a little over 40 amps so #8 gauge wire was needed (but not used.)

So you ought to replace the wiring all the way back to the stator with a larger gauge.

These wires have to pass high amperage continuously. There’s an electrical phenomenon called I-squared-R loss. That is, if you run 30 amps through a corroded or loose connector or undersized wire having (say) a 1/2-ohm resistance, the heating effect is 30 X 30 X 1/2, or 450 watts. That’s a lot of continuous heat. This heat just conducts down the wire, cooking the insulation as it goes.

Just like you can’t put your hand on a 450 watt light bulb while it’s lit, you can’t expect a plastic connector or electrical insulation to survive radiating 450 watts of power either. A corroded or loose connector always has a higher resistance than the adjacent wires and it will heat up enough to melt connector plastic parts and adjacent insulation. That’s why it’s best to solder the wires directly together and eliminate connectors entirely.

Generally though, it is the connectors heating up that causing the insulation and conductors to melt and short out.

On my 916, for example, the stator wires got so hot that the insulation became brittle and cracked near the regulator connectors. A closer examination showed that the damage extended along the wire all the way back to the engine casing. I could scrape off the softened insulation with my fingernail.

So even if the stator wire resistance measurement and the voltage output checks out OK, the output to the regulator is unreliable because the insulation between wires (that run in a common sheath) breaks down at the higher voltage levels at higher RPM.

Damaged insulation will complicate troubleshooting the system. The wires run in a sheath that causes them to touch along their length and particularly at the point where they enter the engine. If the insulation is heat damaged, it breaks down at higher charging rpms so the voltage between the stator wires will measure below spec.

The only solution is to replace the wires. I was able to avoid removing the flywheel cover by pushing an insulation sleeve over the wires at the point where they exit the casing.