Electric Bike Conversion
Adding electric power to my bike has eliminated the barrier of steep hills. My travel range has extended and ebike is now my preferred method of transport. I enjoy quietly cruising in the open air without arriving sweaty. My ebike’s economical, friendly on the environment, and I can park right outside my destination.
DIY electric bike conversion
This conversion was a very welcome Christmas present from my husband Mike, and our children, who worked on the project together. Most of the fiddly work was done by Mike and his process is explained below. The kids understand how the new technology works and they’ve enjoyed being part of building a special one-off gift.
Turning a bike into an ebike
Below are Mike’s details of the kit and the conversion process.
We looked around at the options. We read a lot of forums about electric bike conversions and chatted with people who’d recently converted bikes. We decided that, since we live at the top of a Wellington hill, the best choice was a mid-mounted motor that powers the front crank. Other options included a hub motor that replaces one of the wheels.
The mid-mounted motor keeps the weight in the centre of the bike
A mid-mounted motor gives the advantage of the motor being able to leverage the gears. When you choose a gear, the motor assists you in that gear. With a hub motor it’s linked directly to the speed of the wheel. The mid-mounted motor also keeps the weight of the motor in the middle of the bike, so it’s better balanced, which is especially good off-road.
There are a number of kit options available. It came down to buying from Ali Express, ie. directly from China, or we could buy a more locally supplied conversion kit. It can be hard to tell the quality of the kit or the battery pack when purchased from an unknown Chinese supplier. The availability of the battery pack was important too, because you can’t air freight lithium batteries.
We bought the conversion kit, battery and charger from Luna Mate. The motor and controller was shipped from Australia and the battery pack from within New Zealand. The 52V 13.5AH Shark battery pack can be charged, either on or off the bike, using the corresponding 52V charger.
It was just as cost-effective to buy from Luna Mate as it was to buy from Ali Express. The benefit was the peace-of-mind of dealing with an Australasian supplier. If we have any technical, warranty or return issues, they have a local support team.
The kit we used is Bafang BBS02 and it comes complete with a motor and front crank, front chain ring, crank arms, brake handles, controller and a gear change sensor. We chose the biggest available battery pack that would fit within the frame.
A key decision was what size gear chain to get. With three options we went for the default 46-tooth chain ring. In hindsight this was probably a bit big for the gear set. To fix this we’ll get a replacement chain ring manufactured by Lekkie.
Fitting the kit
This was reasonably straight forward but it did need the right tools. We were fortunate to borrow a complete tool set from avid cyclist Carl Penwarden who has converted his VW Beetle car to electric, but none of his bikes (yet!). Specifically, we needed a tool to remove the pedal crank arms and another one to undo the bottom bracket. Once that was done we took out the bottom bracket, and gear set, and bolted-in the motor and front gear set.
The battery holder mount didn’t match the water-bottle mount
One of the challenges was fitting the battery. The battery came with a well designed holder, but it assumed that the battery was mounted on the frame where the water-bottle holder would normally go. It also assumed where the holes for the holder were. This didn’t match our bike and you can’t buy an adapter.
We made an adapter bracket to mount the battery at the right place on the frame. We created it from a 25x3mm steel strip. We bolted that to the bike first, then to the battery holder. We primed the adapter in a coat of a rust preventer. We also covered it in heat shrink to protect it from scratches and bumps. This step took the most time of the whole conversion.
With the parts all sorted we mounted a new brake lever. Only one lever could be mounted because the Shimano gears had the gear change built into the brake lever so we couldn’t remove the lever that controlled the back gears. If we did that there would be no way to control the gears.
New lever on the front brakes shuts off the motor
We attached the Bafang gear brake lever to the front brake because it has a cut-off switch built into it. This means that when you apply the front brake, the motor automatically cuts out. This prevents the motor powering the rider over the handle bars.
Next we mounted the controller and LCD display onto the front crossbar. We plugged-in all the cables and tidied things up with cable-ties, being careful to leave plenty of movement for both general use and turning extremes.
Cabling and connectors are tucked up inside the loom
We wanted the cable connections to be protected from the weather and from knocks. We used some plastic split loom tubes purchased from Jaycar, and put the cables/connectors inside it, to hide connectors and loose cables. This was particularly useful for the battery cable which is thick and has big connectors. To cover the end of the loom tube we found a 25mm round plastic furniture foot at Bunnings. It stops water running down the tube. The result is tidy and weather-resistant.
After charging the battery pack, using the charger ordered with the kit, we took it for a test ride. It worked well the first time!
We’re still to sort-out the battery charge indicator on the display. It assumes a 48V battery and we used a 52V battery so the percentage charge indicator always shows the battery being more charged than it actually is. As an interim measure we turned on the battery voltage reading so you can see the actual battery voltage. We added a label to help figure-out how charged the battery is.
The charger is good but it has a reasonably noisy fan. It takes a few hours to recharge the battery. With daily use we’re charging the ebike about once a week.
Reflections on the conversion
One of the optional extras we bought was the Luna Mate tool for doing up the bolts to mount the motor. This was good because it was reasonably cheap and fits the new bottom bracket nut perfectly. After the first few weeks of use, the bike’s bottom bracket mount had loosened and it needed to be retightened using this tool. It’s a spanner, not a socket, so it can’t be attached to a torque wrench to tighten the bottom bracket nut up to the right torque level, so you have to guess the torque.
Specific tools made the job much easier
Having the right tools made the job really easy. When we needed to retighten the bottom bracket we purchased a crank arm puller because we’ll probably need to tighten these up again in the future.
The motor has a theoretical maximum output of around 750w and can be power-limited to the NZ electric bike assist power limit of 300w via the motor control display on the bike.
We were pleased that we bought a good quality conversion kit. It was well put together, came with everything we needed, and it has a warranty. For something so heavy, the shipping costs of returning items effectively negate any warranty for a kit from China.
The ebike is quick, reliable and beautiful to ride. It’s a pleasure to use and the kids love borrowing it. The conversion was a fairly easy project and it’s been a great Christmas gift that is used every day.