24 replies to this topic

[soopercooper]

As it turns out, my mini has a dynamo rather than an alternator. Question is, are there any major advantages to having an alternator rather than a dynamo?

Also, how easy is the conversion - I understand that an alternator will just bolt into the same place as the dynamo, but I also understand that the control box will have to be bypassed - any idea how to go about this, or any idea how much it might cost to get a mechanic to do the conversion?

any advice appreciated!

[Dan]

Very worthwhile, that's why cars don't have dynamo's any more. Dynamo's don't supply charge at idle, so whenever you are idling not only isn't the battery being charged but the car is running off the battery making it even flatter. Also dynamo's don't last anywhere near as long or provide very much output at all.
And the seperate regulators tend to go out, meaning your supply voltage can vary quite a bit with temperature.

You do need a different rear bracket for the Alternator as it is shorter than the dynamo, but the wiring changes are fairly simple as I understand it.

[soopercooper]

thanks for the reply - think I will get it changed for an alternator then. Do you know if the rear bracket is an 'off the shelf' item and any idea where to find out about the wiring?

[Guess-Works.com]

I did a dynamo ro alternator conversion, but I cheated.... complete new loom... however, without much trouble you can figure the differences from the change in the wiring diagram.... also, if you can find the front half of a later model mini loom on ebay will same a lot of peeing around with connectors...

as for a fitting bracket... http://www.minispare....aspx?pid=34727

I'll clip the appropriate bits out of a wiring diagram and post later...

[Guess-Works.com]

Ohhh... just had a blinding flash hit me...

Are you +ve or -ve earth ( easiest way is to check which of the battery terminals is connected to body )

In the unlikely event that it is +ve earth, then there's a whole raft of things which may need tinkering

[soopercooper]

Ohhh... just had a blinding flash hit me...

Are you +ve or -ve earth ( easiest way is to check which of the battery terminals is connected to body )

In the unlikely event that it is +ve earth, then there's a whole raft of things which may need tinkering

The negative terminal is attached to the body.

Why would anyone have a positive earth, not knowing about these things as I do!

[Guess-Works.com]

You'll be surprised, a lot of pre 70's cars were +ve earth , and all Mk1 & 2 minis, I think they changed to -ve earth with the MK3.

But, dug out the wiring diagrams for the 1275 GT ( dynamo and alternator )

and there's very little difference, in fact you can overlay one over the other !! lol

but.. you need to ditch the dynamo and also the control box ( the big black thing on the side of the car with 5 terminals ). Fit, the alternator... now this is where an appropriate bit of loom from a later mini comes in handy...

Of the wires which use to be connected to the control box....

(NU) Brown with Blue trace (x2)
(NG) Brown with green trace
(N) Brown (no trace)
(NY) Brown with Yellow trace (x2)
(B) Black (earth)

One of the Brown/Yellow wires will be removed with the dynamo, as will the Brown/Green

The Black can be attached to the body at an appropriate Earthing point.

This leaves you with four wires...

The two Brown/Blue wires of which one is linked to the lights and the other the ignition switch, can both be connected to the main battery feed on the starter solenoid

The two remaing wires now need to be connected to the Alternator which has three terminals two wide and 1 small...

Your Brown goes to the middle wide terminal
Your Brown/Yellow goes to the bottom smaller terminal

For the top terminal you will need to connect a new wire from that terminal to the battery feed on the starter solenoid.

And that seems to be it..

[Guess-Works.com]

Appropriate section of wiring diagram for Dynamo...

[Guess-Works.com]

And Alternator

[soopercooper]

You'll be surprised, a lot of pre 70's cars were +ve earth , and all Mk1 & 2 minis, I think they changed to -ve earth with the MK3.

But, dug out the wiring diagrams for the 1275 GT ( dynamo and alternator )

and there's very little difference, in fact you can overlay one over the other !! lol

but.. you need to ditch the dynamo and also the control box ( the big black thing on the side of the car with 5 terminals ). Fit, the alternator... now this is where an appropriate bit of loom from a later mini comes in handy...

Of the wires which use to be connected to the control box....

(NU) Brown with Blue trace (x2)
(NG) Brown with green trace
(N) Brown (no trace)
(NY) Brown with Yellow trace (x2)
(B) Black (earth)

One of the Brown/Yellow wires will be removed with the dynamo, as will the Brown/Green

The Black can be attached to the body at an appropriate Earthing point.

This leaves you with four wires...

The two Brown/Blue wires of which one is linked to the lights and the other the ignition switch, can both be connected to the main battery feed on the starter solenoid

The two remaing wires now need to be connected to the Alternator which has three terminals two wide and 1 small...

Your Brown goes to the middle wide terminal
Your Brown/Yellow goes to the bottom smaller terminal

For the top terminal you will need to connect a new wire from that terminal to the battery feed on the starter solenoid.

And that seems to be it..

many thanks for this info.

My car is a 1968 Mk2 cooper although the engine was changed around '91 for a 1275 unit, but the - terminal on the battery is definately connected to the car body. Does this mean it was converted at some point then? (and why on earth was an alternator not fitted at the time!!!??)

[Guess-Works.com]

Things get a little foggy going that far back, but MK2 coopers started being produced October '67, and it was in 69 the MK3 came out, and I think the change to -ve earth happened in the middle of that... the manuals are typically vague about this...

But, yes why they didn't change to an alternator at that point I don't know..

[dklawson]

My Mk1 was generator equipped as GuessWorks said. However, a previous owner converted it to negative ground. You asked "why wasn't an alternator fitted at that time" regarding your car's conversion. There are many possible reasons, most of them probably financial. In a lot of instances the ground conversion is/was made to allow the use of modern accessories like late model tachometers or radios. It may have been an unnecessary expense to install an alternator at the same time.

There are two excellent articles on the Mini Mania / Mini Spares web site covering alternator conversion. Take a look at:
http://www.minimania...e//ArticleV.cfm
and
http://www.minimania...e//ArticleV.cfm

The first article describes how to make the conversion using a gutted old control box as a junction box... thus allowing you to keep your wiring harness intact. The second article mentions running a second heavy gauge wire to the starter solenoid to carry the extra current. If you want your car to look "original" use the junction box method while running the extra wire to the solenoid.

Succinctly, (after you've made sure your car is set for negative ground) at the control box connect the three heavy gauge wires together. Similarly, at the control box connect the two (non black) small gauge wires together. (Do not use the black ground wire at the control box, it is unnecessary). Remove the generator and it's rear bracket, replacing them with the alternator and alternator bracket. Take the two wires that used to go to the generator and connect them to the alternator. The large wire goes to one of the two large spade lugs, the small gauge wire goes to the indicator lamp terminal (small spade lug). Run a second heavy gauge wire from the second large spade lug on the alternator to the "hot" battery terminal on the starter solenoid.

[siggy]

DK I converted my 71 - 1275GT as per KC. Gutting a control box and soldering the relevant wires. Looks far better than chopping the loom.

Siggy


Parts needed:
bracket 12G1053
pulley 12G1054
fan C37222A
belt GCB10825
1. Disconnect battery
2. Remove regulator box from car, carefully marking all connections.
3. Remove dynamo, etc.
4. Fit alternator, new bracket, and new belt.
5. Dismantle regulator (use junk regulator if you have one). Remove coils and contacts. Remove connections to blade terminals.
6. Solder links between terminals A, A1, and D, connecting all three.
7. Solder a link between terminals F and E.
8. Reconnect loom to correct terminals-EXCEPT-connect ignition warning light (brown/yellow) to terminal E.
9. Connect alternator to loom: Large wire to large terminal (output), and small wire to small terminal (sensing).
10. Reconnect battery

[dklawson]

Siggy, I did the same thing. My intention was to leave the car so any future owner could quickly and easily restore the car to original condition. It does look much cleaner and original using the control box as a junction box.

[Guess-Works.com]

good plan, as I say I cheated and put in a new loom...