MG-Rover.org Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Evening All,

Just bought myself an MGTF 1.8 , drove home fine but not long after when sitting ticking over the battery light illuminated so assumed not charging,checks i have done...

From alternator body to alternator main + output , voltage registered as 11.7v which is exactly what the battery reads when disconnected and tested on bench so that says to me its not charging.

I have checked back from the alternator main + output to 80a fuse located between cross braces (mounted on back of engine - cockpit firewall) , have continuity (i believe the cable runs via the starter so that should be okay)

Checked above 80 amp fuse , all okay.

It looks like the alternator has died , but before i replace are there any other checks/things i,m missing?

The plug connector on the alternator is two wire , i think one goes to dash light to make it go out when alternator has output (cancelling the 12v + from the battery by putting 12v or more on other side of the dash light) , but whats the other wire do ,does it go to ECU? if so could this affect anything , ie does it tell the alternator to output? don,t think so but like to rule everything out and understand its operation.

I have removed the alternator (Bosch YLE 102430) and removed the diode pack and brushes have plenty left on them and pick up on alternator shaft looks okay.

Are there any other fuses to check which could cause this issue on the wire feed from the ECU (if thats where its coming from ) perhaps?

Any advice/opinion gratefully accepted.
 

·
Registered
mg_tf
Joined
·
389 Posts
The second wire to the alternator is to allow the ECU to adjust the output to match the load, this is effectively an economy device so that if the load is light the alternator isn’t using engine power unnecessarily.

I would suggest the most likely item to have failed is the regulator, I’ve replaced a couple of these.

See link to video below, it says it’s for Skoda and VW but it’s the same alternator

 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
Thanks mgbob, was tempted to try a regulator but wasn,t sure with the brushes having plenty of life, have you had them fail where they still have plenty of meat on the brushes?

Is there any way to test the regulator to confirm?
 

·
Registered
mg_tf
Joined
·
389 Posts
The length of the brushes is irrelevant as long as they’re long enough. I did a post-mortem on one and the issue was the regulator chip had separated from the substrate, this caused the hair fine wires to break and stop it working. I suspect its vibration that caused the chip to become detached.

You could test the diodes but testing the regulator would be a challenge.

The regulators are readily available on evil bay, from memory the ones I fitted were generic but worked ok
 

·
Registered
1995 MGF Mpi
Joined
·
692 Posts
Here in Canada, most automotive electrical shops will test the alternator for free.

That is a good video, I have watched it before. As mgbob suggests, probably best to just replace the regulator.
 

·
In the Garage
MG TF
Joined
·
32,849 Posts
With the TF if the alternator diode pack has failed then generally there would be no battery light at all even when the ignition has been turned on and the warning lights come on as a check.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #7
Thanks for input guys,an update,ordered and fitted new regulator/diode pack and thought I'd try and test alternator on bench before refitting.

So not sure if this would/should work with the Bosch type but below is what I have done.

Connected + from main alternator output post to + on multimeter,connected alternator case to - on multimeter.

Then using a socket in a drill span the alternator to my drills max rpm which is 1450 rpm,(above cars normal tick over speed) and registering only 0.3v output which indicates to me the alternator is u/s.?

Or am I missing something as i do not have L or FR connected? Does this matter?

All comments/advice gratefully accepted before I put back on car and find it's not working 😁.
 

·
Registered
mg_tf
Joined
·
389 Posts
I’ve never tried this but my observations would be:-

Although your drill at 1450 rpm is above the normal engine tick over, the crank pulley is over double the size of the alternator pulley, so if we assume 2.5 times the size and a tick over of 700 rpm, that give an alternator speed of 1750 rpm. So your drill isn’t fast enough to reach tick over speed.

When the alternator’s installed in the car there’s 12V being supplied from the battery, I suspect it may need this to get the alternator and its electronics working.

You don’t have the connection to the ECU, I suspect it would work without this but I couldn’t be sure.

If you’ve got the engine cover off it wouldn’t take long to re-fit it, you could be lucky and you’ll save yourself the cost of new one. If it’s still bad all you’ve lost is an hour or so.
 

·
Super Moderator
Joined
·
11,000 Posts
It's very unlikely that the alternator would have any output at drill speed. Also it will need to be excited via the ignition warning bulb circuit.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #10
I’ve never tried this but my observations would be:-

Although your drill at 1450 rpm is above the normal engine tick over, the crank pulley is over double the size of the alternator pulley, so if we assume 2.5 times the size and a tick over of 700 rpm, that give an alternator speed of 1750 rpm. So your drill isn’t fast enough to reach tick over speed.

When the alternator’s installed in the car there’s 12V being supplied from the battery, I suspect it may need this to get the alternator and its electronics working.

You don’t have the connection to the ECU, I suspect it would work without this but I couldn’t be sure.

If you’ve got the engine cover off it wouldn’t take long to re-fit it, you could be lucky and you’ll save yourself the cost of new one. If it’s still bad all you’ve lost is an hour or so.
That's a good point about the pulley gearing ,hadn't considered that,if fr is the field regulation supply from the ECU and needs to be present I guess I could put 12v supply on here🤔,or as you say just refit and see what happens.
 

·
Registered
mg_tf
Joined
·
389 Posts
Be cautious about putting 12V on this terminal, the signal from the ECU may not be 12V. It's my understanding that the ECU can vary the output of the alternator, if this is the case it could be a data signal.
 

·
Registered
mg_tf
Joined
·
389 Posts
As I thought it's a data connection, see link below, this isn't specifically about a Bosch alternator but I'm sure it's not that different

 

·
Registered
Joined
·
6 Posts
Discussion Starter #13
Refitted alternator tonight but ran out of daylight to test, charging battery off the car overnight.

Will report how it goes tomorrow when I get chance to start her up and see if any output from alternator now.
 

·
Registered
mg_tf
Joined
·
389 Posts
If you want to know how to bench test an alternator take a look at this.

Awesome alternator or what!

 

·
Registered
Joined
·
6 Posts
Discussion Starter #15
Refitted alternator today with new regulator/diode pack and it's now charging battery at 14.3v at tick over,result.

Thanks for all the assistance/input on the issue,still skeptical as to how long it will last till I get a few more miles on it but so far so good. :)
 
1 - 15 of 15 Posts
Top