Lighting circuit problem

[Lewes96]

Out for a ride today and lights went dim then out after a couple more mins. Tested across the battery terminals with engine running at 5k revs shows 12.5v and lights back up but out again when revs dropped. Charged the battery so it showed 13.5v then back in the bike and same thing again. Does this sound like a knackered battery? It is about 3 years old but gets very intermittent use though I do trickle charge it every couple of weeks or so. Any thoughts welcome.

[MickeyMoto]

If you read the blue book there is a section on fault finding the charging circuit. I would say that 12.5 volts across the battery at 5k rpm is a bit low. Your regulator may be faulty.

You may want to check the earthing points, too.

[Lewes96]

Yes time to dig out the blue book I think!

[norbert]

Do you have 12 V on the brown cable entering the regulator with ignition on? If not the regulator won´t work.

[Lewes96]

Not sure on that one yet. I will check. Am also wondering the best way to check if the battery is knackered?

[Lewes96]

Checked through the wiring as amp flow from generator was nowhere near what it should have been after the regulator. Cleaned up the terminals and the fuse holders etc and …. back to 14.5 volts across the battery terminals at 5000 revs. So seems it may just have been dirty spade connectors.

[MickeyMoto]

Perfect.

How satisfying finding a fault that only cost time!

[morini_tom]

Checked through the wiring as amp flow from generator was nowhere near what it should have been after the regulator. Cleaned up the terminals and the fuse holders etc and …. back to 14.5 volts across the battery terminals at 5000 revs. So seems it may just have been dirty spade connectors.

Glad you found the problem.

It is very common for the spade terminals to get a bit corroded but also, the construction of the fuse box is such that the grouped spade terminals are riveted together on the back of the fuse box.

Over time, the rivets loosen, and corrosion between the bars increases the resistance. All of this increases the load on and reduced reliability of your electrical circuit. Additionally, the fuse holders can go a bit loose meaning poor or intermittent connection through the fuse.

It is WELL WORTH taking the fusebox apart, drilling out the rivets, cleaning everything up, and then re riveting, or bolting back the terminals, and added solder across the joint for belt and braces too. This will restore spring to your fuse holders and prevent unnecessary robbing of power by the fusebox.

It’s not too hard if you’re methodical, and the end result is very satisfying and may well save you hours of chasing sporadic gremlins down the line

[Lewes96]

Yes indeed sounds like a job worth doing!

[Lewes96]

May have spoken too soon. Have yet to tackle rivets etc on terminal connector unit so this could still be that but:

- with ignition switch in second position (no lights possible in this position) 14.5 volts across terminals at 5000 revs
- with ignition in second position(but with only the rear light on, which comes on automatically 13.5 volts across terminals at 5000 revs
- with ignition in second position (with side light on at front) stays at 13.5 volts across terminals at 5000 revs
- with ignition in second position (with either main or dipped beam on) at 12.4 volts across terminals at 5000 revs and at 12 volts at 2000 revs

ie the bike struggles to keep the battery charged unless running quite fast.

Does that sound normal?

[MickeyMoto]

What is the wattage of the headlight?

The alternator chucks out about 140W at high revs. Brake light and two indicators are +/- 60 Watts. Add in your headlight and tail light and what is left has to charge the battery. Run at slower speeds, the output drops.

My BMW has a voltage of 14volts with no lights and 13.ish with the lights on. Different animal, obviously.

[scbond2@yahoo.co.uk]

Ill remember to tell the fuzz that

[MickeyMoto]

Ill remember to tell the fuzz that

Luckily I did not post in Scotland so no hate crime against Morinis has been committed!

[Lewes96]

Headlight bulb is 35watts

[George 350]

Hi.
Alternator output on earlier (pre electric start) 350's was only given as 100W - and no data was ever given as to how many revs were required to achieve that. Add in age, demagnetised flywheels, poorer connections, ridiculously thin wires in the switches etc, then they will struggle.
For what it's worth, my Strada has the earlier type alternator, and with new (better in my book) loom, non CEV switches and modern fusebox balances a 45W main beam at 3500rpm. Also add I no longer have an electric fuel tap to rob watts.
Hope that this helps,
George