electrical problem

robbie said:

you learn something new everyday. i was under the impression that it didnt produce any power at idle. just to confirm, it does produce current but its lower than what the bike needs so the rest of the power comes from the battery?

Click to expand...

Yeah that's exactly right mate.

Here's the power output of a couple of alternators:


You can see that they start making power as soon as they start spinning, and that the power increases as the RPM's go up.

Justin.

sir.b said:

robbie said:

you learn something new everyday. i was under the impression that it didnt produce any power at idle. just to confirm, it does produce current but its lower than what the bike needs so the rest of the power comes from the battery?

Click to expand...

Yeah that's exactly right mate.

Here's the power output of a couple of alternators:

You can see that they start making power as soon as they start spinning, and that the power increases as the RPM's go up.

Justin.

Click to expand...

but on my bike im getting 14.2V on the battery at 3000rpm but instead of it picking up, its dropping as the revs go up. i thought it was meant to get higher the more you rev, but it shouldnt climb over 15V or it would mean you have a big problem as well.

i understand that the power output doesnt depend on revs and all alternators tend to give the most charge at cruising speed, but surely on a MC22 3000rpm cant be the cruising speed...

i dont know why this is happening and why connectors are getting fried and melting. my theory is that the burnt connector pictured couldnt handle the load and its not giving the full voltage at higher rpm's? im a noob so im pretty sure i got it wrong though.... :s

first step is to find out where the wires coming into the connector are coming from and where they go and what caused it to burn and melt.... any ideas?[hr]
from what i can see on this wiring diagram the connector that melted comes from the reg/rec and runs the yellow wires from the reg/rec towards the battery. the connector sits in the battery bracket then the other end of the connector goes to the alternator. im not too sure if this is correct though..... i dont know what caused it to melt like that though????? i dont want to just changed the connector and wires if its just going to happen again. i would rather find out why it happened and fix it.

im afraid that i might have put the wrong yellow wire in the wrong slot on the reg/rec connector wires that i replaced.

any anyone confirm if im correct and if im wrong,any suggestions?

That connector is the one that connects the alternator wires through to the regulator rectifier plug.

The reason why they've melted is because of heat and/or poor contact. If two of those wires were shorting somewhere or there was a very high load current, then a lot of current would have gone through those connector terminals, which would cause obvious problems. However I expect this is from poor contacts. If the terminals aren't gripping each other with sufficient force (loose), the conductivity is low. A lot of current is going through a poor contact, and that contact will get very hot. In turn, it will oxidise and get even worse. Alternatively, it could have started with grime/dirt causing poor conductivity and the downward spiral started. A lot of modern bikes have a grease in the connectors to prevent dirt/grime from degrading the contacts. Some people wash out this grease with WD40 to expose the connector hahaaa....

I'd personally replace the yellow wires and the connector. The wires have gotten too hot and probably brittle and not provide good contact for new terminals. Otherwise, make sure to inspect the yellow wires to ensure there is not damage or melted insulation. New connector! Doesn't have to be the same one, just an automotive high current 3 pin connector.

The alternators efficiency is not constant. If fact it will peak and then go down at the high end of RPMs. The problem that Honda had, was getting an alternator that is going to pump out power across a very large RPM range. I'm not sure they target the peak at cruising speed. Rather try to optimise what they can get for the usuable RPM range. Of importance... the ignition takes power. The faster the RPM is, the more sparks that need to be generated.... more power needed. Headlights however suck a fair bit of power and are quite significant.

The CBR250's alternator does generate power at idle. Just not enough to run 60W headlights or to charge the battery with the headlights on. A battery needs a certain level above it's normal voltage before it starts absorbing power (of any significance). It's a chemistry thing. Idling at 12.5V won't do it. Seeing the voltage drop off with higher RPM is not good, but also not unexpected... ignition power consumption increases. My 675's alternator drops off a bit, and that a recent model.

But all this gets a lot more complicated when you consider the combination of the alternator and the reg/rec. The alternator is generating an AC signal, where the voltage amplitude varies with engine RPM and load. The reg/rec will clip the voltage that's too high and convert it to heat (energy lost). However if the load is high enough, the voltage might not be as high, but the current is high and the losses in the reg/rec increase proportionally (more heat). Don't think too hard about that, as it'll mess with your head.

It's not precisely straight forward to compare one bike with another, as the battery itself will present a different load on the alternator system. If the battery is low on charge or in bad health, it makes it much more difficult to determine if there is a performance problem with the reg/rec and/or alternator.

In this case... I'd recommend to fix the damaged wiring, charge the battery and re-test. Also... make sure the reg/rec has good contact with a lot of metal... so it can sink and dissipate the power.