Morris Minor Owners Club

My dynamo isn't charging the battery.

The brushes are fine however. Is there anything else that can go wrong?

Car has a new loom

OK if brushes are good then is the belt in good order and correct tension? Are all the electrical connections sound?

otherwise you may need to look at the regulator points, and or its calibration and operation.

somewhere.... I had a really good link that described how the regulator works and how to set one, I'll see if I can find that.

that would be great. I can't see the connections being the problem, they are all new, as the car has a new loom.

I have driven the car for two days now, and I still have lights

Prehaps its just the tell tale light playing up?

It's not, tried that out tonight.... Engine cuts out just after the lights turn themselves off

I only just got home after getting lost around here

ONNE, I quote from the workshop manual. switch off all accessories and
disconnect the dynamo leads Dand F. connect the dynamo terminals with
a short piece of wire then start the engine and run at NORMAL running speed. Connect a voltmeter on 0-20v scale between the dynamo terminal
and the dynamo body. GRADUALLY increase engine speed when the voltage reading should rise rapidly but do not rev engine( approx 1000rpm should suffice) do not let reading reach 20 volts.
The clues from this are: NO READING=check brush gear. LOW READING
(approx 1V)=possibly field windings faulty. LOW READING(approx 5V)=
possibly armature winding fault. If you manage this the next stage will
identify faults further along the line.

Excellent! I will print this off, and try it

To check if the control box is faulty - just run a feed directly from battery +ve to the field terminal on the dynamo - if it's working it will charge like mad!! This is strictly a test/check method - I don't suggest you run like this for any length of time, although I had this arrangemnt (through a switch) on my rally Minor - to give maximum charge when running with all lights on. But if done during the day - it will fry the battery.

Another idea I will try out.

Funnily enough, by way of coincidence my traveller has just developed simmilar battery charge problems too. Its not the dynamo as it runs all eletrics ok, its not the battery as that charges fine from a charger. Must be the regulator?. Rob Jennings- I too would be interested in that useful link on the regulator- never had cause to fiddle with one before, therefore its a bit of a "black box" to me ;-)

typical....

I can't find it and was so sure I'd bookmarked it

but found this one instead which also show how it works and how to adjust.

http://www.mgoctagoncarclub.com/articles/regulation.htm

Chicken - why do think it's not the dynamo 'because it runs all the electrics ok' - what exactly is the problem if it runs all the electrics ? Is the battery going flat overnight ?

Because the red light is on when the ignition is on but engine not running. With engine running, red light goes out and the lights, wipers, heater motor etc are all powered OK with no loss of performance. The problem is over a number of days the battery goes flat.

Starting the car on the handle with the flat battery and all is well, lights work again etc, but even 50 miles on the motorway would not charge the battery.

The battery happily accepts a charge from a mains charger.

Therfore my conclusion is dymano is working, battery OK, but regulator is not allowing the battery to receive current from the dynamo.

I admit, electrics are not my strongest area on the car!

Brushes in the dynamo might be on the way out? I would check that before thinking about regulator adjustment/clean.

Unfortunalty the light means very little and only really indicates total failure of the charge system. You can assume from what you describe that the dynamo voltage is high enough to turn out the light, but that its current is too low to efficiently charge.

Good suggestion Rob, however-
I doubt its dynamo brushes as I renewed those not that many miles ago (about 12,000 miles ago before the traveller was retired for its re-build). I believe they are supposed to last many more miles than that.

John,
have you checked the belt tension? I had the problem that the belt was turning the alternator enough to keep the ignition light out but not enough to keep up with lights and wipers. After 7 miles I tried to restart the car and the battery was flat.

Good idea Jim, as are all the other suggestions. I'm going to have a proper look this weekend in daylight provided the weather holds. The belt probably could do with a re-tension anyway.

I agree with tighten belt solution. The reg boxes don't usually 'ever' need adjusting.

Yes, I hope so, it would be the easiest fix!

Chicken, yes the life of the dynamo brushes is much much longer than
that but if they are sticking in their holders you could experience trouble
at any mileage. You should be able to check their 'slideability ' without
removing the unit. Also, check that the little earth lead which is found
bolted to the bulkhead behind the vertical wiring loom about 7"below the fuse block this is the earth for the control box and can give many strange
faults. You say the battery accepts a charge but does it hold it? You could find that it doesn't for long. If it holds a charge off the car but doesn't on the car then you have something draining it when it is seemingly off.