My first Brompton conversion was completed a few months ago with a Freedom Ebikes kit I ordered online. You can read the original conversion notes I made here. Since then, I have been using that first Brompton as a 'test bed' for my second Brompton conversion project.
I began work on the second Brompton a week ago after the last major component I ordered - the motor and wheel - arrived. As most of the conversion is similar to the first build, I will only highlight the major differences in the second build. As with the first one, this Brompton will be used only for short-distance errands within my home community where I need electric-assist for steep slopes.
PAS vs Throttle
I flip-flopped between going down the PAS-only route vs PAS+throttle or throttle-only. In the end, I decided on a minimalist approach with a throttle-only setup like I had on my first Brompton. I chose a thumb-throttle as it seemed more natural and comfortable to me than a twist grip one.
Wheel and motor
I initially tried to order a built motor and wheel from Freedom Ebikes. But they never responded to my order request, for some reason. I found their communication somewhat spotty anyway from my first experience ordering the kit for my first Brompton. It was just as well they didn't reply as I was able to source the wheel and motor for a fraction of the price Freedom was going to charge me.
I ordered the 80mm Tongxin motor - the original so-called 'Nano' motor, not the newer Goldant one - from Outrider in China. The motor was USD80 (GBP52). And I decided to get them to build the entire wheel as it would only cost USD35 (GBP23) for the CR18 rim, spokes and labour. The order took more than five weeks to ship. I was very patient and I did 'prod' them along the way but repeatedly got the excuse that their factory was very busy. The truth was probably that they gave low priority to single orders from individuals. In the initial communication, I said I wanted the 260pm, 250W, 36V Tongxin motor. But I received a 180W motor instead. A quick check of the final purchase order (that I signed and agreed to) showed that the motor power was not specified. So it was partly my fault for not catching that. After waiting five weeks, I certainly wasn't going to return it and wait an indefinite amount of time for a new motor and wheel! Besides, the motor power output is determined by the controller and the main difference between the 180W and the 250W motors is probably the gauge and length of wire using in the motor windings.
And as luck would have it, the CR18 rim came drilled for a Presta valve because I didn't specify that. Fortunately, I had the correct-sized bit to enlarge it for a Schrader valve. As anyone who has tried to put a tyre on a 349-sized CR18 rim knows, it is a real PITA. Having had difficulties with this on my first Brompton conversion, I armed myself with both the VAR tyre lever as well as the Simson Tyre Mate. Did these help? Nope! After struggling for a long time (something like an hour), I managed to get the tyre on. But I pinched and punctured the tube in the process. I was too exhausted to take the tyre off again. And I didn't have a tube repair kit. So I brought it to the local bicycle store. The technician did it in five minutes flat. They didn't bother patching the tube and charged me only HKD50 (GBP4) for a replacement tube and labour.
KU63 Controller
I bought the KU63 controller from BMSBattery.com. It costs only USD15 (GBP10) each so I got two. I wired it for sensorless operation. When I first connected the controller to my original Brompton for testing (replacing the controller from Freedom Ebikes), I could not get it to work with the throttle. It turns out that I had to snip one wire on the controller board to disable the PAS Start feature (which I didn't ask for). This sort of thing sometimes makes ordering direct from China a crap-shoot. For those interested, here is the link to the thread I started on the Endless-Sphere Forum: KU63 Controller problem
The KU63 controller is shipped with the current limit set to 15 Amps. By shaving the current shunt on the circuit board, I was able to reduce the current limit to about 8.3 Amps. That limits the power of the motor to about 300W peak at a nominal voltage of 36V.
Anti-spark
The Freedom Ebikes kit I installed on my first Brompton had Anderson Powerpole connectors which gave a healthy spark when you connected the battery to the controller and the capacitors in the controller charged up. There are several anti-spark strategies that are used by others. One method involves a transistor circuit to limit the current during the initial connection. A simpler one involves making an initial connection through a resistor and then making the main connection after. In keeping with my desire to keep things simple, I came up with an adaptation of the second method using a DPST switch, a single resistor and the 'Enable' input of the KU63 controller. The switch also serves as a 'Master' switch to turn the controller on/off.
1. With the switch in the 'OFF' position, connecting the battery will allow the controller to pre-charge in a fraction of a second without a spark. The KU63 controller remains in standby state drawing less than 2mA after the capacitors are charged.
2. Turning the switch 'ON' will bypass the resistor and make the main current connection as well as turn the controller on via the 'Enable' input.
The pre-charge resistor can be anything from about 50 Ohms to 500 Ohms. And it can be a low-wattage resistor as it does not have to carry the main current. The switch does have to be able to carry the main current. I used one rated for 10 Amps.
Battery pack
I bought two LiFePO 6s1p 2.3Ah packs from A123RC.com and connected them in series to make the equivalent of a 2.3Ah 12s1p pack. I am not proud of the wrapping job I did on the pack so I will not show the completed pack here!
Chainstay hook
After experimenting with various setups, I decided keep the original chainstay hook arrangement with minor mods to the motor axle cap supplied with the wheel. To protect the chainstay, I wound a length of spiral cable wrap around it and secured it with zip ties. The result is a snug hook action.
Throttle, brake levers and shifters
I replaced the original Brompton brake levers with BMX levers because the mounting block on the original levers took up so much space on the handlebar and left too short a grip length with the thumb-throttle unit installed. I also switched the two-speed derailleur and three-speed hub shifter units to the opposite sides. This allowed the more often used three-speed hub shifter with the left hand while simultaneously using the right hand on the thumb-throttle. Ergon grips were added for comfort.
Wiring harness
In my wiring harness, I used 2mm and 3.5mm banana connectors popular with RC hobbyists. They appear to make wiring joins with good contact while allowing disconnection if I need to change components in the future. Sugru was also great in encasing joins.
For the main connection between the controller and bicycle, I used Neutrik 6-pin connectors - three pins for the motor and three for the throttle. The pins are rated for 7.5 Amps each which is more than adequate for this setup. The connector housing diameter is such that a section of an old handlebar grip would slip on snuggly for protection against knocks.
Conclusion
Sourcing parts on my own instead of buying a kit saved me a lot of money. It cost me less than half of what I paid for the Freedom Ebikes kit. And it allowed me to choose the exact parts I wanted. However, it was time consuming. For those that are new to the e-conversion scene, the route you choose will really depend on how much your time is worth to you.
The future
I plan to make changes to my first Brompton to make the wiring neater like it is on this second one. The KU63 controller has a Cruise Control function. I had it temporarily enabled when testing the controller on my first Brompton and I quite like the feature. However, enabling the Cruise Control feature means a brake lever cutout switch is necessary.
I began work on the second Brompton a week ago after the last major component I ordered - the motor and wheel - arrived. As most of the conversion is similar to the first build, I will only highlight the major differences in the second build. As with the first one, this Brompton will be used only for short-distance errands within my home community where I need electric-assist for steep slopes.
PAS vs Throttle
I flip-flopped between going down the PAS-only route vs PAS+throttle or throttle-only. In the end, I decided on a minimalist approach with a throttle-only setup like I had on my first Brompton. I chose a thumb-throttle as it seemed more natural and comfortable to me than a twist grip one.
Wheel and motor
I initially tried to order a built motor and wheel from Freedom Ebikes. But they never responded to my order request, for some reason. I found their communication somewhat spotty anyway from my first experience ordering the kit for my first Brompton. It was just as well they didn't reply as I was able to source the wheel and motor for a fraction of the price Freedom was going to charge me.
I ordered the 80mm Tongxin motor - the original so-called 'Nano' motor, not the newer Goldant one - from Outrider in China. The motor was USD80 (GBP52). And I decided to get them to build the entire wheel as it would only cost USD35 (GBP23) for the CR18 rim, spokes and labour. The order took more than five weeks to ship. I was very patient and I did 'prod' them along the way but repeatedly got the excuse that their factory was very busy. The truth was probably that they gave low priority to single orders from individuals. In the initial communication, I said I wanted the 260pm, 250W, 36V Tongxin motor. But I received a 180W motor instead. A quick check of the final purchase order (that I signed and agreed to) showed that the motor power was not specified. So it was partly my fault for not catching that. After waiting five weeks, I certainly wasn't going to return it and wait an indefinite amount of time for a new motor and wheel! Besides, the motor power output is determined by the controller and the main difference between the 180W and the 250W motors is probably the gauge and length of wire using in the motor windings.
And as luck would have it, the CR18 rim came drilled for a Presta valve because I didn't specify that. Fortunately, I had the correct-sized bit to enlarge it for a Schrader valve. As anyone who has tried to put a tyre on a 349-sized CR18 rim knows, it is a real PITA. Having had difficulties with this on my first Brompton conversion, I armed myself with both the VAR tyre lever as well as the Simson Tyre Mate. Did these help? Nope! After struggling for a long time (something like an hour), I managed to get the tyre on. But I pinched and punctured the tube in the process. I was too exhausted to take the tyre off again. And I didn't have a tube repair kit. So I brought it to the local bicycle store. The technician did it in five minutes flat. They didn't bother patching the tube and charged me only HKD50 (GBP4) for a replacement tube and labour.
KU63 Controller
I bought the KU63 controller from BMSBattery.com. It costs only USD15 (GBP10) each so I got two. I wired it for sensorless operation. When I first connected the controller to my original Brompton for testing (replacing the controller from Freedom Ebikes), I could not get it to work with the throttle. It turns out that I had to snip one wire on the controller board to disable the PAS Start feature (which I didn't ask for). This sort of thing sometimes makes ordering direct from China a crap-shoot. For those interested, here is the link to the thread I started on the Endless-Sphere Forum: KU63 Controller problem
The KU63 controller is shipped with the current limit set to 15 Amps. By shaving the current shunt on the circuit board, I was able to reduce the current limit to about 8.3 Amps. That limits the power of the motor to about 300W peak at a nominal voltage of 36V.
Anti-spark
The Freedom Ebikes kit I installed on my first Brompton had Anderson Powerpole connectors which gave a healthy spark when you connected the battery to the controller and the capacitors in the controller charged up. There are several anti-spark strategies that are used by others. One method involves a transistor circuit to limit the current during the initial connection. A simpler one involves making an initial connection through a resistor and then making the main connection after. In keeping with my desire to keep things simple, I came up with an adaptation of the second method using a DPST switch, a single resistor and the 'Enable' input of the KU63 controller. The switch also serves as a 'Master' switch to turn the controller on/off.
1. With the switch in the 'OFF' position, connecting the battery will allow the controller to pre-charge in a fraction of a second without a spark. The KU63 controller remains in standby state drawing less than 2mA after the capacitors are charged.
2. Turning the switch 'ON' will bypass the resistor and make the main current connection as well as turn the controller on via the 'Enable' input.
The pre-charge resistor can be anything from about 50 Ohms to 500 Ohms. And it can be a low-wattage resistor as it does not have to carry the main current. The switch does have to be able to carry the main current. I used one rated for 10 Amps.
Battery pack
I bought two LiFePO 6s1p 2.3Ah packs from A123RC.com and connected them in series to make the equivalent of a 2.3Ah 12s1p pack. I am not proud of the wrapping job I did on the pack so I will not show the completed pack here!
Chainstay hook
After experimenting with various setups, I decided keep the original chainstay hook arrangement with minor mods to the motor axle cap supplied with the wheel. To protect the chainstay, I wound a length of spiral cable wrap around it and secured it with zip ties. The result is a snug hook action.
Throttle, brake levers and shifters
I replaced the original Brompton brake levers with BMX levers because the mounting block on the original levers took up so much space on the handlebar and left too short a grip length with the thumb-throttle unit installed. I also switched the two-speed derailleur and three-speed hub shifter units to the opposite sides. This allowed the more often used three-speed hub shifter with the left hand while simultaneously using the right hand on the thumb-throttle. Ergon grips were added for comfort.
Wiring harness
In my wiring harness, I used 2mm and 3.5mm banana connectors popular with RC hobbyists. They appear to make wiring joins with good contact while allowing disconnection if I need to change components in the future. Sugru was also great in encasing joins.
For the main connection between the controller and bicycle, I used Neutrik 6-pin connectors - three pins for the motor and three for the throttle. The pins are rated for 7.5 Amps each which is more than adequate for this setup. The connector housing diameter is such that a section of an old handlebar grip would slip on snuggly for protection against knocks.
Conclusion
Sourcing parts on my own instead of buying a kit saved me a lot of money. It cost me less than half of what I paid for the Freedom Ebikes kit. And it allowed me to choose the exact parts I wanted. However, it was time consuming. For those that are new to the e-conversion scene, the route you choose will really depend on how much your time is worth to you.
The future
I plan to make changes to my first Brompton to make the wiring neater like it is on this second one. The KU63 controller has a Cruise Control function. I had it temporarily enabled when testing the controller on my first Brompton and I quite like the feature. However, enabling the Cruise Control feature means a brake lever cutout switch is necessary.
Last edited:
