Dynamo

Post by **Morris57** » Mon Nov 09, 2009 9:19 pm

Hi I have had problems with the ignition light staying on all the time,checked the voltage reading at connections D and E on the regulator as suggested by the haynes manual and it was only 6.3 Volts.Ordered a replacement dynamo and fitted ignition light still on but unable to check voltage as battery on multimeter flat.Assuming that the replacement dynamo is fine its a recon,could I have wired it wrong There is a large spade terminal and a small spade terminal in the loom.There is no small terminal on the replacement dynamo,but there is a bolt with a washer on at the rear is this an earth connection and if so does the small spade connection need to be connected to this?

Thanks

Post by **bmcecosse** » Mon Nov 09, 2009 9:39 pm

Both wires will need to be connected! It's not an 'earth' connection - it is the Field connection - without it = nothing! DO NOT connect your small spade to earth! Where did you get the replacement dynamo ? Take it back and get one with 'spade' connections.
Note - dynamos need to be 'polarised' to suit the car system. Are you running +ve earth - or -ve earth ?

Post by **PSL184** » Mon Nov 09, 2009 11:06 pm

I think this car is neg earth ;-)
Why did you not just replace the dynamo brushes...? Was there some other problems?

Post by **bmcecosse** » Mon Nov 09, 2009 11:24 pm

Dynamos are generally (!) used on +ve earth cars - so this one may need polarising. But - only after both cables are connected!

Post by **mike.perry** » Mon Nov 09, 2009 11:47 pm

If the dynamo has screw thread terminals not spade terminals is the body stepped towards the back or is it straight for the whole length?
If it is the latter then it is probably the earlier C39 type which has a lower ouput and is used on Series MM/IIs

Post by **Morris57** » Tue Nov 10, 2009 2:11 pm

Thanks for the info,the dynamo is on my friends Minor it is +ve earth,when I have both terminal connected how do I go about polarising the dynamo.

Thanks
Craig

Post by **mogbob** » Tue Nov 10, 2009 2:35 pm

Craig
"To change a positive earth unit to negative earth, connect a negative lead from the battery to the dynamo case.Take a positive lead from the battery and touch it briefly on the dynamo small terminal and then on the large termnal -- you'll get a harmless blue spark from each.And that's that ! For positive earth, reverse these instructions. "
Quote from Haynes Classic Car Electrical Systems Repair Manual
...Dave Pollard

Hope this is what you need.

Bob

Post by **Morris57** » Wed Nov 11, 2009 3:15 pm

Thanks Very Much Bob.

I will give it a go

Post by **bmcecosse** » Wed Nov 11, 2009 8:29 pm

You only have to touch it to the Field terminal - the small one!
DO NOT touch it to the large terminal - big discharge as you 'motor' the generator.

Post by **littleblackflash** » Sat Nov 14, 2009 1:06 pm

Hello All,

Sorry to hijack this thread but I have the same problem.
On my first Morris outing we broke down and the battery was flat. After wiggling some wires and cranking with the handle it fired up.

After a lunch break, she started again and drove fine. Stopped off on the way home and the battery was completely flat.

The red light bulb had blown so we couldn't see what it was doing. But I guess if the bulb had gone, we wouldn't be charging the battery. And hence when the revs were low the dynamo couldn't produce enough power for the engine, lights and wipers.

Bulb is now fixed but stays on all the time. I've fitted a new regulator and new bushes in the dyno but the light stays on. The light does dim when I rev the engine.

Could someone tell me which pins are D & E on the regulator so I can start to measure voltages. What voltage should I get?

The car starts and runs perfectly with a charged up battery.

Post by **PSL184** » Sat Nov 14, 2009 1:25 pm

The terminals on the regulator are marked but from memory they are the middle one and the one to the right of middle. First check voltage across battery when running at idle and at fast idle. Max charge into a fully charged battery should be around 14 volts. Also check the voltage between earth and the small field terminal on the dynamo - again, this should be what you are seeing at the battery. If not the regulator needs adjusting or is faulty so check the D & E voltages at the reg. The D is the regulator cut in (above 7 volts) and E should be the same as the battery charge voltage. When you changed the dynamo brushes did you clean the brass bit (commutator) that the brushes run on? Also, check that the springs are holding the brushes tight on the commutator ring.

Post by **littleblackflash** » Sat Nov 14, 2009 1:40 pm

Thanks for the quick reply. I couldn't find any markings on the regulator but I will check again.
I'll try and do what you said this afternoon but I have someone coming to buy my car and I also have to dodge the rain and high winds.

Post by **littleblackflash** » Sat Nov 14, 2009 3:41 pm

I've noticed the A,F,D,E markings now, I was looking right next to the terminals.

So, Battery Voltage 12.5v regardless of engine speed.

Between pins D&E, 1.5v to 2.5v depending on speed.
Between pins F&D, same, 1.5v to 2.5v again depending on speed. 2.5v is probably about 3000rpm not a fast idle.

So I guess my dynamo is faulty. I've checked the bushes and they spring in and out ok. All connections are good. The dynamo centre is clean and a defined gap between the copper segment.

Anything else I should try?

Post by **PSL184** » Sat Nov 14, 2009 4:13 pm

Sounds like the windings have gone O/C - Easier to get a recon dynamo....

Post by **bmcecosse** » Sat Nov 14, 2009 4:19 pm

Test the dynamo by 'motoring' it - take the fan belt off - remove the electrical connections - join the two dynamo terminals together with a bit of wire - then using a jump lead (or other decent bit of wire) - make contact from the non-earth side of the battery to the joined up terminals. If the dynamo runs as a motor - - it's fine. Turn your attentions to the regulator - or the wiring between. Surprised to hear the red light had 'blown' - how did that happen ?

Post by **littleblackflash** » Sat Nov 14, 2009 4:33 pm

Good idea. I'll do that in the morning. I've put her away in the barn for the night with the cover over her.

Will report back my finding. Many thanks for the help.

Post by **littleblackflash** » Sat Nov 14, 2009 5:31 pm

Been thinking.

When my battery went dead and the dynamo only kicks out 2.5v, how did the engine run? When I cranked it with the handle, it started first turn and ran perfectly, no miss fire even on the steep hills in the wet.

Post by **bmcecosse** » Sat Nov 14, 2009 5:41 pm

It will fire the coil ok - but the mystery is - how did the fuel pump run! The answer is - either the battery is not completely dead - or the dynamo is charging!
Any chance the battery has been connected wrong way round ?

Post by **PSL184** » Sat Nov 14, 2009 5:51 pm

or a bad intermittant connection somewhere in the charging circuit....

Post by **littleblackflash** » Sat Nov 14, 2009 5:58 pm

I checked all the wiring conections today and the continuity along them. All seamed fine. Battery is only a few months old and terminal look ok.