Strange electrical problem

[BigBen]

Hello,

Have a strange electrical problem on my Rover K powered Atom

Symptoms as follows:

-Lights flash at 1-2Hz
-Dash lights also flash (flash = get dimmer and brighter not on/off in both cases)
-fan runs at inconsistent speed.

Diagnosis so far:

Battery is ok (over 12 V unloaded)
Alternator is ok (15 odd volts with engine running)

So next step is to identify what kind of load could cause a voltage drop on the car, only one thing being the starter motor so today I started the car then disconnected the wiring to the starter motor. The problem went away ! The starter relay is not being fired so it is something else.

Any thoughts / suggestions ?

Ben

[stevieturbo]

I guess if you have removed the starter and the problem is gone....something strange would make you think the starter itself is at fault...although it would be very odd.

I'd have first thought its a poor grounding issue.

[spend]

Is the alternator connected via the starter motor by any chance and you have actually disconnected the alt also?

[BigBen]

spend said:

Is the alternator connected via the starter motor by any chance and you have actually disconnected the alt also?

That is an excellent point, did not measure the voltage at the battery once the starter was disconnected. That has identified my next test.

Will keep everyone posted

Cheers

Ben

[BigBen]

BigBen said:

spend said:

Is the alternator connected via the starter motor by any chance and you have actually disconnected the alt also?

That is an excellent point, did not measure the voltage at the battery once the starter was disconnected. That has identified my next test.

Will keep everyone posted

Cheers

Ben

Thinking about this (have not had a chance to try yet) they are on the same wire but in series so removing the connector from the starter does not remove the alt from the circuit. Going to swap for a different alternator later as it is easy enough and alts are often the source of strange electrical behaviour IME

Ben

[annodomini2]

You need a high frequency oscilloscope to see the problem, would bet its the alternator rectifier has failed.

[BigBen]

annodomini2 said:

You need a high frequency oscilloscope to see the problem, would bet its the alternator rectifier has failed.

It does look like it. I have got a scope more than capable of doing the necessary but frankly swapping the alternator seems less bother !

[Steve_D]

BigBen said:

annodomini2 said:

You need a high frequency oscilloscope to see the problem, would bet its the alternator rectifier has failed.

It does look like it. I have got a scope more than capable of doing the necessary but frankly swapping the alternator seems less bother !

I bet connecting a couple of probes is cheaper but I suppose that depends on what rate you charge yourself.

Steve

[BigBen]

Steve_D said:

BigBen said:

annodomini2 said:

You need a high frequency oscilloscope to see the problem, would bet its the alternator rectifier has failed.

It does look like it. I have got a scope more than capable of doing the necessary but frankly swapping the alternator seems less bother !

I bet connecting a couple of probes is cheaper but I suppose that depends on what rate you charge yourself.

Steve

This is a good point, but taking stuff to bits is much more fun than putting a probe on it !

[BigBen]

BigBen said:

Steve_D said:

BigBen said:

annodomini2 said:

You need a high frequency oscilloscope to see the problem, would bet its the alternator rectifier has failed.

It does look like it. I have got a scope more than capable of doing the necessary but frankly swapping the alternator seems less bother !

I bet connecting a couple of probes is cheaper but I suppose that depends on what rate you charge yourself.

Steve

This is a good point, but taking stuff to bits is much more fun than putting a probe on it !

But putting a probe on it confirmed that the regulator was most likely not doing its job. Swapped the alternator for one I had in stock and all seems well. Will drive the car to work tomorrow and see what happens

Ben

ETA can anyone suggest a source of alternator spares ? need brushes / voltage regulator pack for a Marelli 63321239 !

Edited by BigBen on Monday 16th March 22:44