13 replies to this topic

[soopercooper]

Hi I have an old mk2 mini with a dynamo rather than alternator. I've been noticing that when I use the additional front spotlights at night (aftermarket add-on), it seems to drain the battery even when travelling at speed. Could this be attributed to wiring issue, or more likely a dynamo output issue? when car is revved the voltage only goes from about 12.2v to 12.3v using a multimeter to test - is this enough, and/or would a new dynamo be any better?

thanks

Edited by soopercooper, 05 October 2012 - 12:36 PM.

[Cooperman]

Check the voltage regulator as these were a problem when running extra lights.
You can get an up-rated dynamo - well you used to be able to.
If you want to keep the originality of a dynamo, there is an alternator available which is built into a dynamo casing and looks standard whilst giving around 48 amp output.

[soopercooper]

Check the voltage regulator as these were a problem when running extra lights.
You can get an up-rated dynamo - well you used to be able to.
If you want to keep the originality of a dynamo, there is an alternator available which is built into a dynamo casing and looks standard whilst giving around 48 amp output.

Thanks for this - can you give me a clue how to check the regulator? - I've previously left that black box on the side of the engine bay well alone

[Cooperman]

I think you run the engine at about 2500 rpm and measure the voltage from thje regulator. I do believe they are adjustable, but it's going back almost 45 years for me as I've fitted an alternator to virtually every Mini I've had since about 1969.
Try looking for advice on Lucas voltage regulators on-line. The only thing which will cause a dynamo to fail to give the correct output is worn brushes, but then it will simply fail to charge at all.

[bmcecosse]

A dynamo should easily handle 2 extra lights - may struggle with 4 extra. The method for adjusting is in the workshop manuals. You should get 13.8 volts when revving - with nothing much switched on.

[Cooperman]

I remember rallying with dynamos and we used to sit at controls when we were a bit early and run the engine at 3000 rpm to try to put a bit of charge back in the battery in time for the next section where we would run 3 spotlights with 2 headlights.
Then along came alternators in the mid-60's and it was never a problem again.

[tiger99]

Unless your vehicle is something special and needs to be kept original, I would suggest fitting an alternator. My first Mini had a dynamo, never again! In fact, every car I had with a dynamo (Ford 100E, Triumph Herald, Rover P4) was always struggling to keep the battery charged, withoud any added electrical bits.

[Cooperman]

On the 1964 850 I'm shortly going to start restoring I intend to use one of the alternators which looks like a dynamo. I'll leave the voltage regulator in as a dummy fitment so it will look original.

[bmcecosse]

I used to 'force' the dynamo to full charge by having a direct feed to the field terminal - via a switch which was only put ON when actually running in the section with extra lights on.

[Cooperman]

I used to 'force' the dynamo to full charge by having a direct feed to the field terminal - via a switch which was only put ON when actually running in the section with extra lights on.

Never thought of that. What an excellent idea.

[bmcecosse]

Easy to boil up the battery though if the switch is forgotten!

[minidaves]

i remember the first time i had spotlamps on with halogen headlamps with a dyanamo and driving down across the a3 and then total darkness. then remembered my physics lesons and there was not enough grunt there to run the engine heater and all them lamps.

[soopercooper]

thanks all, think i'll try and live with it and keep original, maybe try new regulator and/or dynamo

[tommy13]

The max output of the dynamo is only just over the demand when the lights, heater and wipers are on. The addition of extra lamps could just tip the balance.
My main concern is that your battery voltage readings seem low when the engine is revving. I would therefore start by checking the tension and grip of the fan belt and a very useful test is to push on the fins of the dynamo cooling fan with your thumb (engine stopped) and see if it slips round without trying to turn the engine. If it slips round easily then retensioning and/ or a new belt is required. I also have the checking and setting procedure and illustrations for the voltage cutout / regulator. Message me if you need these.