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Alternator Stuff

Alternator Output Currents

Most Minis used the Lucas 16 ACR and 17 ACR alternators, but there have been others:


Manufacturer Model Output (amps)
Lucas 15 ACR 28
Lucas 16 ACR 34
Lucas 17 ACR 36
Lucas 18 ACR 43
Lucas 20 ACR 66
Lucas A127 45 & 55

The A127 alternators fitted to the later SPi Minis are a straight swap for older 1x ACR models.

Lucas A127 alternators have also been fitted to a variety of other ARG cars; some casings are different but the internals are apparently the same. Ratings differ and rise - there is one available rated at 120A for an export version of the Range Rover, but expect to pay around UKP2 for each Amp of output!


It appears from correspondents that there is a Lucas A127 alternator for a 1998 Ford Escort Diesel which is rated at 75A. Aside from possible issues with pulley size and alignment, this is likely to be cheaper than the equivalent Rover/Land Rover/Range Rover alternators, particularly second hand.

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Alternator, how to check if it is working

You can resort to using proper diagnostic tools like these.

Two simple ways to test if your alternator is charging the battery:

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Alternator problems, not charging

If the red ignition light on your dash is burnt out or disconnected the regulator won't be able to find it's reference, and this can cause the alternator to not charge, or even worse, not regulate the system voltage, blowing up electronic ignition etc (see also Charge warning lamp).

DO NOT discount the following possibilities before going to the cost and hassle of changing or reconditioning the alternator:

UKP3 for a fan belt, UKP2 for a pulley, UKP45 for a reconditioned alternator unit!

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Alternator, reconditioned units

"I used to work for Robert Bosch Ltd in the "Tech Support Department" and I can say that a good rebuilt unit is as good if not better than a new unit, as long as three things are in good order when you strip it:

The Lucas or Magneti Marelli alternators that where used on all minis up until about 1989 are very easy to rebuild. Please note where all electrical connections go as it differs car to car:

All parts such as bearings, brush sets, fans and pulleys are available in the UK; the only problem is that the cost of the parts may be more expensive than an off the shelf rebuild/recon unit."

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Alternator Wiring

The three wires are Fat feed, thin feed, and sense.

The sense wire goes to + via the dash red lamp. You must have this connected to allow the alto to reference itself and give out 13.8V or whatever. I wrecked my electric ignition by having this unconnected. Rev up and + goes to >15V.

Out of the other two only the fat one is needed. They are connected in parallel anyway. I have cut out the thin one and it is fine.

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Alternator Swaps

Added by FB 7th May 2003

Anything goes really, but........................................................

There are several things to watch for if you intend fitting an alternator from another vehicle on to your mini

1) The pulley on the alternator is the right diameter - if it is wrong the alto will over or under rotate leading to excess enegy consuption if the pulley is smaller and UNDER charging if too big BUT the alternator may be designed to work at higher/lower revs relative to the Mini one - can't help you there! talk to Denso, Lucas, Fisher-Price etc etc

2) The pulleys do not line up properly: this will lead to fanbelt slippage and fraying/premature failure - use a straight edge along the face of the pulleys to check they are in line.. space the alternator along with washers on the mounting points and/or machine down the back face of the pulley to suit. (Caution the pulley rotates at high speed and may vibrate/break up if incorrectly modified)

3) different pulley V sections: some fanbelts are different in cross section to mini ones- if you are a "guru" fit the mini pulley to the donor alto OR at least get the fanbelt off the donor car and check its profile is the same. fit the wrong fanbelt section and you will get slippage or premature wear. NEVER overtighten to get more grip.......

4) Overtightened fanbelts to accomodate 2 & 3 can lead to burned out alto bearings- fanbelt is usually checked for tightness with a torque wrench ( it slips in the belt at X lb/ft on the pulley bolt) or by being able to twist the longest extent of the belt by sideways by about 90 degress.

5) Wiring - alternators have different connections: what is common is.....

A) a BIG wire to put charge into the battery (this goes to the solenoid on the same side as the fat battery lead)

B) a wire to the charge light - this is normally disconnected from earth by the alternator when it starts charging to disconnect the (+) at the dash board end of the bulb from ground HOWEVER be sure you understand how the alto is wired up on the donor car, there are lots of variations.

Mini alternators may use a voltage sensing wire to tell the alto the state of battery voltage and/or another wire feeding 12v to the alternator to get it working, the "exciting" wire.

Other than having to rotate the plug by 180 degrees I found that a 65A alternator off a Rover 820 saloon had the same wiring configuration as my 1275GT 1978 mini.

If you choose a UK donor you may be able to easily cross reference the wire colour codes

BE VERY CAREFUL........ alternators are not all protected from abuse- NEVER run an alternator up on a car WITHOUT connecting its CHARGE wire to a load (ie. the battery) you may fry the diode pack (£££ +messy). ALSO the alto may be FAULTY already if unchecked at a scrap/breakers yard.

WHY do you need to swap one? unless you are running 420W high beam like me and/or a massive in car entertainment system REMEMBER the alto will use energy (AKA BHP) to generate power regardless of what watts you need.

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