DIY: Dynamo to Alternator conversion

In my previous post I went into some detail of how I installed a budget stereo system. With the UK’s colder weather, earlier sunsets and my stereo’s power draw I’ve noticed the car is sometimes hard to start, with the original starter motor spinning free or making a horrible screeching sound. To remedy this and make the car a more reliable daily driver, I opted for an alternator conversion kit from Moss Europe.

DISCLAIMER: I’m not a professional! My blogs are written for my own and my readers’ entertainment. If you choose to follow my DIYs, you do so at your own risk and responsibility.

The original dynamo (or generator) as fitted to our Spridgets essentially does the same thing as a modern day alternator, though with many limitations. The dynamo has a set of brushes running on a rough-surfaced commutator that can slowly wear out and foul the commutator – requiring both brush replacement and cleaning of the contact area on the commutator. The dynamo also has a lower limit to how fast it can spin, reducing maximum electricity generation while also severely limiting idle and low-RPM output. As RPMs rise, an old dynamo will also increase it’s own internal resistance, sapping more power from the car’s motor to spin it.

The Moss Europe alternator upgrade kit

The Moss Europe alternator upgrade kit

Meanwhile, an alternator is generally mechanically simpler and easier to maintain. It also uses brushes, though they rest against a smooth slip-ring rather than a commutator, increasing their lifespan. An alternator can also spin at a much higher speed, generating enough current to charge the battery at idle and maintain most electrical accessories. For the record, the Moss kit comes with a 45A alternator – the Sprite’s dynamo was rated at 43A maximum output at 3000RPM when new, though mine generates maybe half that these days. As an added bonus, alternators leech  less horsepower from the small motor.

A common quirk on these cars is when you idle with the headlights or high beams on and rev the motor, the lights will shine brighter then dim again. This usually doesn’t happen with an alternator.

With that out of the way, let’s get into the installation!

Materials & Tools

1x Alternator Conversion Kit (£99 from Moss Europe)
Optionally, a 6-way female bullet connector (£7 from Moss Europe)
1/2″, 7/16″ and 5/16″ sockets and wrenches
22mm socket or wrench
Wire cutters / strong scissors
Wire crimpers


Note: My 1967 Sprite originally came as negative earth. Earlier cars will need to be converted from positive earth.

I started by assembling the alternator before removing the dynamo. As the car is my daily driver, I couldn’t risk having everything taken apart only to lose time on the alternator. Looking back, I’m glad I did!

To start off, fit the fan to the alternator so that the top flat edge is facing away from the alternator body. Next, fit the woodruff key (the small semicircular piece of steel) into the slot on the alternator shaft. Now for the fun part: slide the pulley onto the shaft, with the woodruff key slotting into the gap on the pulley. You may need to use a small flat blade screwdriver to hold the key in place. I used a rubber mallet to lightly whack the pulley to get an even fit. Finally, use a 22mm socket to fit and tighten the nut (or, for a lack of proper equipment, a wrench!).

Note: I spent hours upon hours struggling with the woodruff key and the pulley. Eventually, I figured out the slot in the pulley wasn’t cut properly and had leftover material, preventing the key from fitting properly. 15 minutes with a fine steel file later and it fit.

A slight imperfection in the woodruff key groove led to hours of frustration - and a simple fix!

A slight imperfection in the woodruff key groove led to hours of frustration – and a simple fix!

First step when dealing with the electrical system is to always disconnect the battery. Mine has a quick-disconnect dial on the ground side that makes this step easy. Otherwise, use a 1/2″ wrench to loosen the battery clamps. Always disconnect and re-connect the ground terminal first to prevent sparks.

Next, disconnect the wires from your dynamo. Mine had spade connectors, though earlier cars or Midgets may use ring-type connectors requiring 5/16″ or 7/16″ wrenches. If you purchased the Moss kit like I have, you’ll need to replace the ring connectors with the provided female spade connectors.

We’ll need to remove the dynamo, so first loosen the nut that attaches the adjustment link to the motor block. This will let you rotate the dynamo downwards and remove the fan belt. Next, remove the bolt that attaches the adjustment link to the dynamo’s bottom mounting tab. Using both a 1/2″ wrench and socket (two wrenches work too!), remove the nuts and bolts on the rear mounting bracket and on the water pump tab to remove the dynamo completely. Finally, remove the original mounting bracket from the block.

The motor with dynamo removed

The motor with dynamo removed

The kit comes with a shiny new black bracket, which will replace the one that was just removed. Use the same two bolts from the old bracket, but leave it slightly loose so it can adjust itself as the alternator is installed.

Take the assembled alternator and fit it to the block. There’s many ways to do this – I had luck first attaching the nuts and bolts included in the kit (or re-use the old ones!) to the water pump tab and the new mounting bracket. Then, attach the adjustment link to the bottom alternator tab. Leave the bolt loose so the fan belt can be tightened later on.

Now for the wiring. As I mentioned before, I got lucky and already had spade connectors fitted. They only fit one way so it’s straightforward enough. The “D” wire from the generator goes onto the “Battery” post, while the “F” wire goes to the “Ind” post on the alternator. Mine was clearly labelled and had the unused connections blocked off. If you have to replace the ring connectors, cut them off and strip a few millimeters off each wire. Crimp the small red connector to the brown/green wire and one of the larger connectors to the brown/yellow wire. The kit came with heat shrink that can be used to cover your crimp as well.

The external voltage regulator isn’t needed anymore, meaning it can be safely removed and re-wired. Some like to open it up and modify it to keep the appearance, I just left it in place and changed the wiring. My method of re-connecting the wires was messy, and needs to be fixed in the future!

Here's the external Lucas voltage regulator - no longer needed as the alternator has one built-in!

Here’s the external Lucas voltage regulator – no longer needed as the alternator has one built-in!

First, remove the wires from the A and A1 terminals on the regulator. These should be brown and brown/blue. These two wires need to be securely connected as they deliver power to the rest of the car. I cut off the connectors, stripped the wires and soldered / shrink wrapped them together.

Next, remove the two wires from the D terminal and connect them together. These make the “Ignition” light on the tachometer work, which, if illuminated, indicates the battery isn’t charging. These wires should be brown and yellow.

The black wire on terminal E is a ground, which is no longer needed. I simply wrapped the end in insulating tape. I did the same with the brown/green wire on terminal F.

With everything hooked up and re-connected, fit the fan belt around the crank pulley, then the fan and finally the alternator. The belt I received with the kit was MUCH too small, so I went to my local Euro Car Parts and bought a slightly longer one, using the old belt for reference. Pull the alternator upwards so the belt is nice and tight, then tighten the adjustment link on the block. Next tighten the link on the lower alternator tab, then the rear mounting bolt, then the new mounting bracket. Make sure the belt moves around a quarter of an inch, measuring in the middle between the alternator and fan pulleys. Tighten everything up one final time.

At this point I double-checked everything, especially the old regulator wiring. Any short-circuit or wrong connection could damage the alternator, battery or burn the car down. At this point it was getting late and I forgot I didn’t own a voltmeter! Road test it is.

I turned the ignition on and checked for any sparking or smoke. So far so good! I fired him up, the ignition light went out and everything seemed fine. As it was quite dark now, I did the headlight test I mentioned at the beginning. Flip the headlights on, rev the motor a few times and look for a brighter and dimmer light. Instead, I noticed I had much brighter lights that didn’t dim as the motor idled.


I don’t expect any issues with the alternator conversion, though I’ll write an update if something goes amiss!

As always, thanks for reading!

By | 2018-10-07T11:40:40+01:00 May 6th, 2017|DIY / Tech Tips|0 Comments

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