Blake Smith

This is the final blog post in a series on converting a 1978 Puch Maxi Moped from fuel combustion, to electric powered.

Read Part 1 here. Read Part 2 here. Read Part 3 here. Read Part 4 here. Read Part 5 here.

Today, I took the moped for it’s first successful test drive!

Look at her go! We’re affectionately naming her “The Blueberry Rocket”.

It’s hard to believe that it looked like this just 5 months ago:

I’ll share a few final details of the build, for those who might want to follow along. I plan on doing one more less technical post for those that might be interested in reading about the build from a high level.

Final Wiring

The last step was to complete the final motor circuit for the 48V electrical system. This means connecting all the different electrical components (circuit breaker, shunt, battery disconnect, 48 to 12v DC converter) together in the black electrical box.

I used some nice hydraulic crimpers to make the mating Anderson cables that connected to the battery. After connecting this all together, the motor turned, and the shunt lit up!

Only two problems:

1. After some consideration, I realized that the 14 gauge cable I used was too thin gauge to push the 30+ Amps necessary to drive the motor.
2. The motor was spinning in the wrong direction.

I recabled the circuit with 8 gauge wire, using the hydraulic crimpers to add ring connectors. I originally didn’t want to spend the money on the hydraulic crimpers, but it was so worth it, especially to make solid connections on this thicker gauge cable.

I toggled the “reverse connector” on the motor controller to make the wheel spin the other way, which presented another problem: The wheel was spinning in reverse, but was going really slow.

Turns out, that “reverse connector” on the motor controller also makes the wheel spin much slower. I needed to switch the rotation of the motor by switching the phase of motor power cables, as well as switching the hall sensor cables around. Configuration 2 from this forum post worked like a charm for me:

Standard Phase wire configuration:

U = Yellow V = Green W = Blue

…With the Green and Yellow Hall sensor wires transposed, transpose the phase wires:

Blue and Yellow Phase wires transposed (This is the working combination for the 10kW BLDC motor with the Green and Yellow Hall sensor wires transposed) U = Blue V = Green W = Yellow

After that, it ran at high speed just great!

Wrapping it Up

There are some other odds and ends that I’ll slowly work on: Cleaning up and hiding the cabling better, protecting the battery and electrical systems from the elements better, getting a custom decal made for the frame, getting the brakes to be more responsive. It’s fall here in Chicago, so I’m going to slow-burn some of this final work over the winter to be ready to really ride in the spring.

It’s still hard to believe that it works! This has been 5 months of continuously solving problems and clearing roadblocks. It’s been a really fun challenge, and is a joy to ride. I set out to learn about how EVs work, and I definitely accomplished that. I was able to restore a beautiful bike and make it totally zero emissions in the process.

Who knows? Maybe next it’s time to get a solar panel to charge the thing. :-)

This is a blog post in a series on converting a 1978 Puch Maxi Moped from fuel combustion, to electric powered.

Read Part 1 here. Read Part 2 here. Read Part 3 here. Read Part 4 here. Read Part 5 here.

I have two small updates to share in my moped conversion project:

1. I fixed the motor shaft problem, have the motor mounted, and the main drive chain on and aligned.
2. The battery pack arrived, and successfully took its first charge.

Motor Shaft Fixes

In my last post, I shared some of the challenges I faced with the motor shaft not being long enough to clear the moped frame and align properly with the rear wheel sprocket.

A neighbor friend was able to connect me with a machinist who helped fashion an adapter for the motor shaft (in exchange for a nice bottle of whiskey):

This threads onto existing left-handed shaft, and then has a 3/32” roller pin driven through it to hold the adapter in place.

It also extends far enough out, to line up correctly along the chain line!

A few nice properties:

1. The shaft now accepts a standard 1/2” bore sprocket, which are readily available and easy to find.
2. In theory, the adapter can be removed, if ever need be. In practice, this is unlikely to ever be necessary.

I’ll need to stress test the roller-pin to make sure it can handle the torque from the motor. If not, I might have to upgrade to stronger pins that can withstand the force. More to come on this front.

I can’t tell you how good it felt to finally get the main drive chain sized and onto the bike.

Here’s what I ended up using for everything:

• 14 tooth sprocket, for #41 chain size. 1/2” bore.
• 420 sized motorcycle chain. This has the same pitch and roller width as ANSI #41 chain sizes (the sprocket), and the same pitch as a #415 chain, with a slightly larger roller width (which should fit). Puch’s usually come standard with a #415 chain and sprockets.
• The existing rear wheel sprocket. I might eventually replace this with some new stock from Treatland, but not yet.

Figuring out chain sizes was quite frustrating. There are many tables in various parts of the internet, here are the relevant size from the components I mentioned above:

The most important pieces that need to line up:

1. Pitch, the distance between chain pins.
2. Roller width, the width of each link. A #420 chain is slightly larger than a #415, so this will work. Smaller width creates a problem.

Mechanical Niceties

Because the center-stand on the moped was coupled to the motor, I opted to go for a side kick stand that worked quite well.

I cleaned up the chain tensioner, and sized up a new pedal-side chain:

The pedal cranks just barely clear the protruding motor. I might need to file / sand down a few places on the pedal cranks to make it consistently clear without accidentally striking anything. This is the downsides of using a bigger motor.

I also replaced the rear brake cable, since the one that came on the bike was broken.

Battery Arrives, Initial Charging

I received the 20 Amp Hour battery that I ordered from AliExpress. It’s fun getting mail direct from China. :-)

It comes with a 5 Amp charger, so it only took a few hours to charge the battery up fully.

This battery size fits perfectly underneath the seat on the luggage rack. I’ll need to figure out how I’m going to strap / fasten this down for security, and protect it from the elements. More to figure out here.

In the Home Stretch

I need probably a solid day to finish out the electrical wiring for the motor circuit. We’ll see how she runs, stay tuned!

Next: Read Part 5 here.

This is a blog post in a series on converting a 1978 Puch Maxi Moped from fuel combustion, to electric powered.

Read Part 1 here. Read Part 2 here. Read Part 3 here. Read Part 4 here. Read Part 5 here.

They say that 80% of the work comes in the last 20% of a project. That’s the current mode that my Puch Maxi electric conversion project is in. After getting a lot of the frame put back together, I’ve come down to a lot of the necessary detail work that’s required to get the thing moving.

12 Volt Electrical

Since I selected a motor and controller that operates at 48v, I knew I’d probably need to have a different voltage system to power the other peripherals on the bike:

1. Front headlight.
2. Rear brake light.
3. Horn.

The common voltage standard on most motorcycle and automotive systems is 12v DC, and so I decided to go with that. This has the benefit of making parts easier to source, and components easier to find. 12v DC is in contrast to the 6v AC electrical system that’s present on a stock Puch Maxi. Compared to the sometimes strange wiring scheme of a stock Maxi, the wiring for the conversion is quite straight forward.

I took apart the stock headlight and brake lights on my Maxi, measured the diameters of the light bulb sockets, and found some modern, 12v replacement 1157 sized LED bulbs that matched the dimensions!

The locking tabs on the sides of the bulbs didn’t go in perfectly at first, but with a little bit of plastic reshaping, I was able to make them fit great.

The headlight uses the same style light, but in white instead of red. A word of warning: Use red tail bulbs, even if your light has a red cover over it, otherwise your light ends up looking more pink than red!

The tail light has two LEDs: One that turns on when I turn the main headlight on, and one that’s wired into the brake switch that activates when the brake lever is squeezed.

I also opted to purchase a new horn for the bike, since the existing one didn’t seem to work on DC current.

I used my bench-top power supply to verify that all the 12V components were working. All the wires are pretty nasty looking at the moment, I promise I’ll clean them up later!

Main Electrical

The 48v system has a few necessary pieces that need to be integrated into the system:

1. A safety circuit breaker. Should there be any electrical failures, short-circuits, or current overruns, we want the system to shutoff for protection. This is the first item connected to the battery.
2. A master disconnect switch. I wanted a way to disconnect all the electrical systems, especially with curious children who might play with the bike when it’s parked in the garage.
3. A volt / amperage meter, with shunt. This can be used to measure voltage / amperage levels in the system, and can also provide a “capacity guage” to know charge level.
4. A 48v to 12v DC-DC converter. Since the main battery runs at 48v, and the peripheral systems run on 12V, we need a way to step down the voltage to supply power to the lights and horn.

I laid out all these devices on a piece of paper (which would eventually become a board of wood), and wired them all together.

The volt / amperage meter display was designed for a panel mount arrangement, so I needed to 3D print a display holder that will mount on the handlebars (OpenSCAD code is here).

I also bought a really small outdoor circuit box that matched the sizes I need to fit these electrical components on the back luggage rack of the bike. I spray painted it black to blend in better with the rest of the bike’s color scheme.

The eletrical box, while not being the prettiest thing, is a great solution:

1. Because it’s meant for electrical, it already has the appropriate holes to route in and out of the box.
2. It’s also easy to lock shut, for extra safety in case of snooping children.

Motor Shaft Problems

I encountered some other motor alignment issues, that I should have thought of earlier in the project (live and learn!). After getting the motor mounted into the frame, the motor shaft length on my motor was just a few centimeters shy of clearing the frame along the chain line:

The result of which would be the chain rubbing up against the side of the frame, and not lining up nicely with the rear sprocket. This problem is further compounded by the fact that my motor doesn’t have a replaceable shaft, and uses a non-standard sprocket mounting scheme that’s not widley supported in the rest of the industry.

Learn from my mistake and choose a motor that either has a nice standard shaft size that’s easy to align to your needs or purchase adapters for, or pick a motor that can easily have its shaft swapped out for a different one.

My initial plan to fix this was to purchase a new 1/2” keyed shaft, use a lathe or drill press to drill a hole into the shaft, and then thread the shaft with a left-handed tap onto the end of the existing shaft. This would allow me to extend the existing shaft, and at the same time, convert it to a standard shaft size that can take a plethora of different sprocket options that are available on the market.

Turns out the left handed thread would just unscrew the shaft extension due to the rotational torque of the motor.

My neighbor is helping to connect me with a machinist who has some ideas of how we can solve the problem. I’ll keep you posted on progress and updates.

Up Next

Progress has slowed down, due to the difficulty of the problems I’m working through. I’m hoping by my next post, I can have my shaft & chain alignment sorted out, and have the rest of the electrical system wired up. From there, I can size out my batteries, and get things rolling. Stay tuned!

Next: Read Part 4 here