Video: Generator to Alternator Conversion

Alternator conversion and alternator change

Some of us have given up our old generator and moved ahead to an alternator. Some of us have moved from an old style alternator to a more modern and more efficient alternator. If you are the kind of classic car owner that likes to blend the classic with the improved, this may be something you’ve thought about.

What’s the difference between a generator and an alternator?

They both make the same kind of electricity. One doesn’t make “better” electricity than the other.
The biggest differences are…
1 Although they both make alternating current, AC, they differ in how they convert that current to the direct current, DC, that our cars use DC.
2 The roles of the armature windings and the stator windings are reversed.
3 Generators use external regulators. Alternators usually use internal regulators.

In a classic generator, the stator windings (statue, stationary – fixed in place) affixed to the inside of the case serve as the field windings. The windings on the armature (the part that rotates) are the current generating windings.

As you learned in school, when you pass a magnet past a coil of wire, (or you pass a coil of wire past a magnet) you create electricity in the coil of wire. The field windings (stationary) in the generator serve as an electro-magnet. The windings on the armature spin past the magnetism of the field windings. This creates electricity in the current generating windings mounted on the armature. SIMPLE. TWO THINGS.

At the end of the armature we have a series of conductive bars. Traditionally we have a pair of brushes that make contact with the bars. That’s how the electricity is directed out of the generator and to the rest of the car.

Generators are heavy, and often large.
They also have another shortcoming. Having the current generating windings on the armature means there is a limit to how fast you could spin it without harming it.
To keep the RPM’s of the generator under control, generators were usually set up with a large pulley to lower their RPM’s. That protects the generator from high RPM damage, but it leaves the generator almost valueless at low RPM’s. Also, running all that current through the bars at the end of the armature and through the brushes is tough on the brushes. DEMO This calls for additional regular maintenance.

An alternator was a logical evolutionary step. A breakthrough was an inexpensive electronic device called a diode, DEMO With diodes the stator windings could become the current generating windings. The smaller lighter field windings could be put on the armature. SIMPLE. TWO THINGS.  (Field, Current Generating)
Lighter armature windings allow the safe RPM’s of the alternator to be much higher than a comparable generator. A smaller pulley could be put on the alternator. It could spin faster which made it capable of generating current even at low RPM’s.
Also, the relatively small amount of power needed so the field windings can become an electro-magnet, can be sent to the armature via a pair of small brushes that would ride on slip rings on the armature instead of bars. The brushes last a very long time. Sometimes  the life of the car.

Installing an alternator in place of a generator, or upgrading an older style alternator to a more modern alternator, is usually not hard to do. The challenge for many of us is how to wire the upgrade. Generators had external voltage regulators. Alternators usually have internal voltage regulators. That means the alternator is a nice neat all-in-one package, but it leaves us with a number of wires and the old regulator that need to be dealt with.

If we go from an old style alternator to a more modern one, we may be surprised to find some of the early alternators had external voltage regulators like generators did.
Also, while most alternators have always had an internal voltage regulator, the older models often had more wires than a more modern alternator. So, we are left with dealing with wires again.

Let’s talk about wiring.
A relatively modern alternator only needs two wires to do its job.  It needs a small wire that goes to the light on the dash, and it needs a heavier wire that carries the current out of the alternator and to the rest of the car. Two wires isn’t intimidating at all. We can deal with two wires.

To know what to do with the two wires. Watch the video.

Moss Tech Services


'Video: Generator to Alternator Conversion' have 9 comments

  1. March 15, 2013 @ 3:31 pm Ron King

    Expand the vido to shhow what else has to be done if you have + ground. What has to be changed? Thanks ron


  2. May 28, 2013 @ 5:01 pm LarryT

    Excellent Tech Video! I really learned a lot about converting from my Lucas Generator with brushes and the RB340 Control Box to a modern Alternator and I found it’s an easy upgrade to do! Having an alternator that operates at low rpm’s really adds to the electrical convenience of my 66 MGB. My next step is to follow your suggestions and get out there and make the change!



  3. May 28, 2013 @ 5:04 pm LarryT

    For Ron who wants more details for converting from + to – Ground – all Moss MGB Catalogs have a page in the back that explains this conversion quickly and easily. The Instruction Page may be near the electrical parts in the catalog.

    Good luck –


  4. June 16, 2013 @ 11:28 am David Pethig

    found video really good and instructive know how to convert to an alternator now thanks just one thing you said the vehicle had to be neg earth but on the diagram it shows the battery as pos earth is this right or MUST the battery be neg earthed thanks again will try it out on my Ford 100E


  5. December 31, 2013 @ 5:32 pm bill

    I noticed that the battery in the diagram was positive ground too. This should be changed to negative ground on the battery and wire from the starter solenoid should go to the battery positive terminal.


  6. January 7, 2014 @ 5:13 pm Rod T

    Great video, I learned a lot and want to switch my 62 MGA to an alternator. Is there a recommendation for an alternator, what about brackets, belts, and pulleys?


  7. January 8, 2014 @ 8:27 am carlbergs

    We offer a kit to convert your MGA to an alternator. The link is here


  8. July 23, 2015 @ 12:09 pm John

    Good video but the wiring diagram shown for the alternator has the battery connections the wrong way round. ie positive (+) earth. Should ( as stated in video) be negative (-) earth


  9. August 21, 2016 @ 12:41 pm stephen heaney

    There are other small spade terminals 180 degrees opposite the three main connections , one is marked is marked with a number 57 the other appears to be at one end of the diode bank.
    what is their purpose?


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