Converted Finiss MTB with a Bafang BBS02 motor with lights and P850C color LCD display ($442), 48 Volt x 17.5 Ah (840 Wh) down tube battery ($422) and new chain ($16). Total of $880 (includes VT tax and shipping, NH residents would pay 6% less).
Why DIY?
If you are the type of person who likes to work on your house or your car, you can build a very nice Ebike with specs that are better than most Ebikes on the market for under $1000, resulting in significant savings and a custom ride to fit your needs.
First a little bit of the background story leading up to this DIY workshop: the UV EV Expo and the UVEL. If you just want to work on your bike, skip to the next section.
Here in the Upper Valley of the Connecticut river in Vermont and New Hampshire, our group of energy committee members have now held 5 UV Electric Vehicle Expos. (I wrote about the first one back in May 2014 in this post "Upper Valley Electric Vehicle Forum and Demo".) These developed into a very big outreach for us- to give you an idea of the effort there were usually around 2 dozen vendors and exhibitors, speakers, food, (and of course Ebikes in every one), here are the attendance totals:
2014 Norwich, VT 250 people
2016 New London, NH 350 people
2017 Hartford, VT 550 people
2018 New London, NH 375 people
2019 Hartford, VT 550 people
These were most likely the largest EV events in New England each year, and it was actually nice to have a break in 2020 when COVID restrictions were imposed. However we still had a little bit of money left from the 2019 budget, so we decided to use it on an Ebike library (with disinfecting the bikes, distancing, and masks the safety precautions turned out well). Back in 2010 when I was just starting to figure out Ebikes as a substitute for my car, Dave Cohen of VBike down in Brattleboro was also starting work on a consulting service for ebikes. He arranged for a few Ebikes that he could loan out for short trial periods to people who wanted to see if an Ebike would fit into their lifestyle. After a few years of doing this, our statewide bicycle organization Local Motion up in Burlington ramped up the concept into a widely available library of several Ebikes. However the bikes were often not in the Upper Valley, and we Expo people decided we needed our own library. With Local Motion's help, we combined our Expo funds with donations and bought a Specialized Turbo Como 3.0 ($2800), a RAD Wagon longtail cargo bike with a child handrail ($1800), and I converted a Specialized Hard Rock MTB ($977) for loaning out.
The DIY Specialized Hard Rock conversion for the UV Ebike Library. It has a Tongsheng TSDZ2 500 Watt motor, a 48 Volt x 14.5 Ah (696 Watt hour) battery, with new tires, brakes, chain, lights, fenders, rack, and mirror for $976.96 (including VT tax and shipping).
The Parts:
At this point I've installed hub motors (MAC, MXUS, Leaf, and generic cheap ones) and bottom bracket (BB) motors (Bafang and Tongsheng). I'm finding that the BB motors work all around the best. These have been my preferred parts for the last dozen bikes:
Motors (both of these are street legal in VT and NH):
First choice: Bafang BBS02 48V, 750W, 120 Nm torque, about $435. This is a very good, strong motor, and I recommend it for riders who are experienced, carry loads, or have distance to cover. By programming the first two assist levels to be less, this motor on the Finiss bike conversion feels pretty close to the Turbo Como bike in our library, while still having more power at the top assist level.
Second choice: Tongsheng TSDZ2, 48V, 500W, 80 Nm torque, about $365. This is a good quality motor. and because it has less output and a torque sensor it is very smooth and an easy ride. I recommend it for beginner riders or people who haven't ridden in a long time, smaller bikes, or shorter distances.
Batteries
Bike handling is better using a down tube battery than one in the rear rack. I'd now use a rear rack battery only if I needed 1 kWh or more of capacity, or a battery couldn't be fit any other way. The latest down tube Reention DP-6 case with 4 mounting tabs down each side plus heavy duty flat contacts (drain water better than round) and a full length aluminum mounting channel is a very nice package.First choice: 48V x 17.5 Ah, (840 Wh), about $405
Second Choice: 48V x 14.5 Ah, (696 Wh), about $320
Workshop step by step video
All the bikes held up well over the season with only minor repairs, (there were about 230 borrowers from 7 towns), and the Hard Rock generated a lot of DIY questions from people who wanted to convert their bike. We decided to hold one more DIY conversion workshop, but this time we had to hold it online because of COVID. Norwich Energy Committee arranged with our local Community Access TV to film a step by step conversion that I did outdoors in the doorway of my barn for COVID distancing, and once that was edited we used the video for a Zoom meeting. (A thank you also to Norwich Women's Club for funding parts for one of the bikes!) This recording covers much more than I could write in this post, so I'm going to go straight to it, and then end this post with six small tips that I didn't cover in the recording.
E Bike Conversion Workshop
-On a Mountain Bike often the shifter cables are routed through a plastic guide underneath the bottom bracket, and this guide sticks out so far that the motor won't slide in. Remove the guide, and then route the cable to the rear derailleur through a piece of cable housing running over the top of the BB instead. You can keep the factory cable housings at the handlebars and at the derailleur, and just cut a new piece that fits between the cable braze ons on the downtube and the chainstay.
-Do not convert a carbon fiber bike, tightening the motor nuts may crack the bottom bracket.
-Roughly half of the bottom bracket motors have loosened up the large retaining nuts after riding a couple hundred miles. After a second tightening they have stayed tight. I now use the upper end of the recommended torque range for the nuts instead of the middle.
-I didn't say enough about the Tong Sheng speed sensor- it is very sensitive to the gap, requiring an extremely large one of 10 to 15 mm. I've had to mount the magnet on a spoke on the other side of the wheel to get this gap.
-The motor gear housing on one of the dozen bikes with BB motors pressed against the chainstay when the large nut was tightened up. Some people dent the chainstay in for clearance, but a better way is to use shim washers on the motor. (The Chinese vendors often call these narrow washers "gaskets".)
-Several people have asked if the Bafang motor could be made slow for puttering along. This is easily done by simply turning the assist off, but for those who wish to have a tiny bit of assist, I've reprogrammed the first (and sometimes second) assist levels to about half of their original settings. This has turned out to be the main motor programming I do, another is to set the thumb throttle to a continuous medium power level so that an inexperienced rider can't burn the motor out by holding the throttle down at a stop.
Bonus Material! An updated "Operating Tips for Owners"
In the earlier DIY post I finished by copying the 2 pager handout of tips. The handout has since been redone 4 times for the parts I'm using, here is the latest version:
As with any bike, please check tire pressures, the brakes, and take a quick look for any problems before going out on a ride. The chain should be lubricated at least every several hundred miles depending on riding conditions.
The Bafang BBS02 motor is a globally proven design with several million produced, and is on it's third version with robust gear and electrical improvements. 10 display styles are available, I use a P850C display.
-It is 750 Watts (the legal limit in New Hampshire and below the 1000 W limit in VT) and 48 Volts
-It has both a cadence sensor (about 1/4 turn of the pedals to activate) and a thumb throttle for turning on the motor
-There are switches on the brake levers to be sure the motor shuts off in an emergency situation
The downtube style lithium battery is removable with a water resistant plastic case. It has a quality Seiko battery management system (BMS) that monitors the charge levels of the Samsung brand cells to balance them, and also provides short circuit and low voltage protection.
-The battery size is 48 volts by 17.5 Amp hours, or 840 Watt hours
-An extra water bottle mount has been installed on the downtube to strengthen the battery attachment.
-Order a 46 tooth front chainring for 26 inch wheels to provide a normal pedaling cadence range, maxxing out around the legal e-assist limit of 20 mph. The rear cassette or freewheel should be a wide range 11 or 12 tooth top gear to a 32 or 36 tooth low gear size range to have a good gear for all situations.
-Test rides that I've taken have averaged around 15 Watt hours per mile. This gives a range of about 50 miles with an 840 Watt hour battery (rated capacity less a 10% safety factor, divided by an average 15 Watt hours per mile). Your range will probably be different depending on factors such as how much you pedal, heavy loads, hills, wind, etc.
-The 2 Amp charger takes 10 minutes of charging time for every mile traveled. This is about 9 hours to charge a completely empty battery.
-There are 10 displays available for the BBS02 motor, I use the P850C model because it has the most info for the best price, has a USB port for phones or GPS devices, has a light switch with auto dimming built in, and has one of the largest and easiest to read displays.
Bicycle operating tips:
Keep your cadence between 60 to 90 rpm, (which is the normal recommended range for regular bicycling). The motor is more efficient the faster it is running, and it will turn all the way up to 120 rpm. Don't pedal slowly with the motor doing all the work, because when the motor is turning slowly it is not moving you down the road and most of the energy going into it is coming out as heat, not as a rotating shaft doing work, and this heat could burn the motor out. Shift down for hills just like on a regular bike to keep your cadence in the regular bicycling range, and the motor will also be in a good speed range.
The thumb throttle is great for getting rolling under difficult circumstances, such as getting started at an uphill intersection, and (just like a regular bike) it works much better if you have remembered to shift down to a lower gear before you stop. Note that using the thumb throttle will reduce your range.
Battery operating tips:
The battery will last the longest if you keep it charged in the middle of it's range, and don't go below 10% or above 90%. It's best if you store it half full or a little above that, and keep it in a cool (but not below freezing) place. Charging it fully a day ahead of a ride is fine, but keeping it sitting there over a long storage period all the way full or all the way empty eventually causes chemical changes inside it that will shorten it's life. With poor storage the battery will last a year or two, with good storage it can last 4 to 5 years.
If you want to keep the battery charged enough for a spontaneous ride, then storing it at 3/4 full is OK, just not as good as 50% to 65% full. A battery of 17.5 Ah at 48 volts, (840 Wh), is on the larger side and there is room within it's capacity to run it at less than a full charge for making several smaller trips before recharging.
Don't charge below freezing. The electrolyte inside the battery is similar to water, and doesn't work very well below freezing. Never charge the battery below freezing because the thick electrolyte can trap chemical reactions in small spots in the battery and damage it. It is OK to ride below freezing, (down to around 0 F) because the battery is releasing energy when it is discharging and this helps keep the electrolyte moving around. However the electrolyte is sluggish when discharging below freezing and as a result the battery will have less power and range.
If you want to monitor your battery more exactly than on the bike's display, there are DC meters available with 4 functions (Volts, Amps, Watt Hours, and Time) that can be spliced in between the motor and battery. A second way of monitoring is to use a Kill A Watt household appliance meter when charging the battery. However this measures after the ride not during it, and it is less accurate because you will need to figure in about a 10% to 15% loss due to efficiency of the charger, (the battery is getting 85% to 90% of what the Kill A Watt meter reads for Watt hours.) For example if the Kill A Watt meter reads 0.10 kWh (100 Wh) when the charger finishes and the light turns green, then about 85 Wh went into the battery and 15 Wh were lost inside the charger. You can divide this 85 Wh by the number of miles you rode to find out your Wh per mile.
