Alternator / dynamator??

[peterheywood52573]

Can anyone identify the alternator fitted to my MK2. I would like to get hold of a datasheet or manual for it. It has never let me down but the battery voltage shows 12.5V, with the engine stopped or running.

[piman]

Hello Peter,

I can't help with identification, but it's obvioisly not charging. One check, which is quite a long shot, is the ignition warning light coming on?
While alternators tend to keep residual magnetism, if it is not strong enough the back feed from the ignition warning light starts the generating process.
Otherwise it is Google to find suppliers of alternators made to look like a dynamo. Does it have a seperate regulator?

Alec

[piman]

Hello Peter,

I was on the SNG Barratt website and I see they sell a similar unit, maybe they can help with information?

Alec

[peterheywood52573]

Thanks Alec,
I looked on the SNGB website. It seems Powerlite handle their warranty, so they are probably the SNGB supplier. It does not look like mine though.
I must try and make sense of the wiring. It is weird:
The battery has 12.5V .
switch on ignition, the ign light come on, but still 12.5V.
I then turn on the headlights , still 12.5V but ammeter shows discharge. I had not noticed this before. Switched off lights.
Start the engine. Still 12.5V. switch on lights >> still 12.5V. Ammeter in middle.
I'm planning on taking the engine out at sometime, so I would like to know if the alternator is OK or more probably NOT OK.
Peter

[piman]

Hello peter,

what are you measuring the voltage with? It is odd that the ammeter is showing discharge with the lights on but zero when the engine is running as I would expect a discharge as there appears to be no alternator output. What happens if you put the lights back on with the engine running. If the alternator is faulty, as it seems to be, then the ammeter should go into discharge?
Two common alternator faults are brush or diode failure.

Alec

[peterheywood52573]

Thanks for the help Alec,
I am measuring voltage across the battery terminals.
I f the lights are switched on with the engine running, it does not show a discharge.
All of the wiring instructions do not show the ammeter. I was wondering if it was meant to be disconnected.
My car has been converted to negative earth. It does have a relay mounted next to the regulator. I am not sure what this does. Powerlite require a relay for positive earth applications but then mounted behind the dash. Is the relay standard? I cannot find one on the wiring diagram. It would be nice to have another car to compare.

Peter

[piman]

Hello Peter,

I'm fairly certain that relay in your picture is for the horn. I know the manual doesn't show one in the wiring diagram but the purple wires show that it is a battery fed fuse, i.e always live for the power circuit. It is peculiar that the relay control is ignition fed (green wire) though?

I see the dynamo relay is still in place, although I notice there is a crimp connection which probably indicates that it is now just a connection block? If you drop down the instrument panel it should be obvious if the ammeter has been by passed (I intend to fit an alternator to my car and will replace the ammeter with a voltmeter.).
However this doesn't help with solving the problem with your charging. Are you confident in dismantling it and doing some basic fault finding?

Alec

[peterheywood52573]

Thanks again Alec,
it got to the point when nothing would work. I lowered the instrument board. One of the spade terminals had fallen to bits.

I have now fixed that and things work again. I am not sure of the charging though. I will take some measurements tomorrow.
Peter

[piman]

Hello Peter,

unusual but a likely culprit. That would be incapable of passing any real current.

Alec

[peterheywood52573]

I ended up changing the battery because the specific gravity of the cells were marginal.
Now the ammeter still does not indicate any charging with the engine running. The ammeter will show a discharge with the headlights on and the engine not running. If the engine is started, the lights can be switched on and the ammeter will not show a discharge or charge. The alternator is clearly powering the lights and doing something.
I will try and find out how the ammeter might be wired. I would like to understand whats going on.

[piman]

Hello Peter

the ammeter is wired between the generator and the battery.

With the engine running and showing near zero on the meter, if you then switch the headlights on do you see a momentary kick to discharge?
If so that would indicate that the sytem is working normally. Have you a meter to check the sytem voltage when running with load?

It would seem that it is working as as if with the egine running and lights on it would show a discharge otherwise.

Alec

[peterheywood52573]

I was hoping the regulator would be recognisable as a Lucas, Bosch or other mainstream source. I was a bit stopped in my tracks though by the brush, which runs on its corner on the slip ring.