Can any dynamo / electrics experts diagnose this?
Discussion
This is slowly doing my head in ...
The car is a sixties Fiat 500 running a dynamo, separate regulator, points and wasted spark ignition.
All was well until a few weeks back the ignition light came on at speed on the motorway. Car drove fine but at anything above about 2500rpm the ignition light came on.
Have since had the dynamo checked out and apparently brushes, springs and bearings are all good.
Have fitted new regulator.
Tested in garage and light goes out once started and stays out even when revved hard - hooray!
Go for a drive and almost immediately the light comes on when revved - pretty much only goes out at idle or at less than 55km/h in top (guessing about 2400rpm), so presumably load related?
Electrics are not my thing and short of spending time and a chunk of cash replacing the apparently sound dynamo with a new one to see if it works I'm at a loss. Is this something that could be caused outside of the dynamo and regulator, eg. The wiring between or the battery or something?
Help appreciated!
Bob
The car is a sixties Fiat 500 running a dynamo, separate regulator, points and wasted spark ignition.
All was well until a few weeks back the ignition light came on at speed on the motorway. Car drove fine but at anything above about 2500rpm the ignition light came on.
Have since had the dynamo checked out and apparently brushes, springs and bearings are all good.
Have fitted new regulator.
Tested in garage and light goes out once started and stays out even when revved hard - hooray!
Go for a drive and almost immediately the light comes on when revved - pretty much only goes out at idle or at less than 55km/h in top (guessing about 2400rpm), so presumably load related?
Electrics are not my thing and short of spending time and a chunk of cash replacing the apparently sound dynamo with a new one to see if it works I'm at a loss. Is this something that could be caused outside of the dynamo and regulator, eg. The wiring between or the battery or something?
Help appreciated!
Bob
Thanks for those ideas.
The engine mounting on the 500 is very soft and positioned centrally at the back, allowing a lot of torsional movement of the engine under load.
The earth strap goes from underneath the dynamo mounting on the far left of the engine (middle of cooling fan) to the far left of the engine bay (one of the rear panel mounting bolts). If engine movement under load is pulling the strap and breaking the connection that would explain the repeatability under load, and why it could be initially fine at high revs but no load in the garage after refitting the dynamo. The problem first showed itself under high load cornering hard which would also fit.
Heading to garage as soon as I get home to check!
oakdale said:
Check the engine earth strap.
This one has got me most excited as I can imagine a situation with this that matches all the symptoms.The engine mounting on the 500 is very soft and positioned centrally at the back, allowing a lot of torsional movement of the engine under load.
The earth strap goes from underneath the dynamo mounting on the far left of the engine (middle of cooling fan) to the far left of the engine bay (one of the rear panel mounting bolts). If engine movement under load is pulling the strap and breaking the connection that would explain the repeatability under load, and why it could be initially fine at high revs but no load in the garage after refitting the dynamo. The problem first showed itself under high load cornering hard which would also fit.
Heading to garage as soon as I get home to check!
Well, checked, cleaned and where needed replaced all the contacts to the dynamo and the earth strap. Several were pretty ropey and the earth strap contact was really poor.
Put it all back together and... No change...
Check the voltage at the battery and it rises to about 15.4v and then drops straight back as the red light comes on with revs. Same story if you take the voltage from the brush terminal on the dynamo but with a higher voltage. This was all in the garage so no real movement to confuse things.
So it all points in my mind to the dynamo itself (despite assurance from the local specialist that all is good) and it is the brushes floating as the rotational speed increases.
Grrr...
Put it all back together and... No change...
Check the voltage at the battery and it rises to about 15.4v and then drops straight back as the red light comes on with revs. Same story if you take the voltage from the brush terminal on the dynamo but with a higher voltage. This was all in the garage so no real movement to confuse things.
So it all points in my mind to the dynamo itself (despite assurance from the local specialist that all is good) and it is the brushes floating as the rotational speed increases.
Grrr...
Steffan said:
In view of all the work the OP has done it does seem probable that either the Dynamo is failing or the control box is failing. I appreciate the control box is new and the Dynamo declared good but something is causing the fault to continue. I would be doubtful of those two items the OP seems to have covered the poor contacts probabilities. Best of luck to th OP electrics are always tricky on older cars.
That's my view too... And thanks!The live output just disappears into the loom and I have to admit it didn't occur to me that the starter is where it may end up. I'll check that. The starter is only a year and a half old though so it wasn't that long ago the contacts at that end were removed and cleaned. Could be the join with the connector though.
I have also managed to source some new dynamo brush springs from Europe, and some NOS brushes in case the brushes are floating at high revs. Just waiting on the post...
I have also managed to source some new dynamo brush springs from Europe, and some NOS brushes in case the brushes are floating at high revs. Just waiting on the post...
This is maddening!
Stripped the dynamo and the springs and brushed indeed look fine. Fitted the new set of both just in case, and also cleaned up the brush runners as one of them was full of slight surface rust.
Put the dynamo back together, checked it motored ok (it did) and reinstalled in car.
Exactly the same symptoms, only now the light stays on once the increase in revs has set it off, even if you then back down to idle. It did exactly this the last time the dynamo was stripped by the specialist.
So, individually everything checks out to the level I can apply.
Auto electrician here we come, if I can find one who gets these...
Stripped the dynamo and the springs and brushed indeed look fine. Fitted the new set of both just in case, and also cleaned up the brush runners as one of them was full of slight surface rust.
Put the dynamo back together, checked it motored ok (it did) and reinstalled in car.
Exactly the same symptoms, only now the light stays on once the increase in revs has set it off, even if you then back down to idle. It did exactly this the last time the dynamo was stripped by the specialist.
So, individually everything checks out to the level I can apply.
Auto electrician here we come, if I can find one who gets these...
Cheers guys. It's being looked at next week.
Sticking control box sounds perfectly reasonable, but identical (and I mean identical) symptoms with two separate boxes? Hopefully a specialist will just roll his eyes, say 'this is yer problem' and it will be a long time before I have to pull the blimmin' dynamo again! :-)
Sticking control box sounds perfectly reasonable, but identical (and I mean identical) symptoms with two separate boxes? Hopefully a specialist will just roll his eyes, say 'this is yer problem' and it will be a long time before I have to pull the blimmin' dynamo again! :-)
In theory it has finally been fixed, having resorted to an alternator conversion following multiple attempts with auto electricians, dynamo repairs, replacement dynamo, 3 different regulators including a solid state one...
I should know for sure later this week when I get the car back...
I should know for sure later this week when I get the car back...
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