Blair is a guy who works as a mechanic at a foods processing plant, and over the years he has seen cordless tool batteries improve quite a bit. He recently decided to build a custom ebike using DeWalt 20V battery packs, and here is the result. Blair posted Ten videos to document the entire process from start to finish. If you want to see the end result walk-around, go straight to the last video.
Blairs first ebike version, a Trek cruiser and BBS02 with Headway cells
Blair was happy with the Trek bike and the 48V Bafang BBS02. The headway cells were “OK” but the BMS that they came with ended up damaging some cells, over the winter when he stored the ebike in his garage for a few months.
Video length 6:26
Building a charging station
Once Blair had made the decision to switch to DeWalt cordless tool packs, he knew he was going to need a charging station right away. DeWalt has chargers that can charge two packs at the same time, but Blair found out that two single chargers cost less than the double-pack charger. So, He purchased six of the single chargers (the DCB107), and clustered them for mounting on his garage wall.
Length is 19:18
Getting stock battery packs to work
Blair gets six DeWalt DCL040 flashlights in order to cut off the battery interface so he can mount those onto the ebike frame. He is using the 5-Ah packs, so each one is 5S / 2P using 18650-format cells that are high-discharge 2500-mAh each.
Part-1, length is 9:23
Modifying and combining parts from lights, USB chargers, and battery pack cases
Blair modified and combined parts from several different DeWalt components. The DCL040 flashlight, the DCB090 USB adapter, and the DCB205 battery packs.
Part 2, length 23:46
Switching the battery yellow tops for black from DCB200 packs, and adding faux chrome trim.
Part 3, length 12:27
Cutting off the flashlight bases, and making them into adapters
Part 4, length 3:51
Adding voltage meters and a low voltage alarms
Part 5, length 7:02
Fabricating the aluminum frame-mount to hold the batteries
Part 6, length 3:18
Mocking up the parts locations
Part 7, length 4:18
The finished product
Blair is using a 750W 48V Bafang BBS02, with a 15S battery pack. The stock BBS02 controller has 63V capacitors (with a little safety margin, of course), so this is the absolute highest voltage that the stock controller can run. However, the stock Low Voltage Cutoff (LVC) will not work with this voltage, so that is the reason it was vital for him to install voltage gauges, in order to keep track of the State Of Charge (SOC)
One interesting custom touch is that Blair installed heated handlebar grips, and his awesome heated jacket runs off the ebike battery pack (instead of it’s own DeWalt cordless tool battery, as it was originally designed to run on)
Part 8, length 9:31
Conclusion, and some Editorial opinion
When any group of people sees something like this, half will want something similar, and the other half might wonder…why? A system like this only has 10-Ah of range, and…once you add up the cost of all the parts (not counting all the time to adapt all the parts to work like this), a conventional 10-Ah ebike battery will cost less. There are actually a few reasons that this might be a useful way to go.
The hardest part of ebike systems is the battery. It is also the most expensive. If you make a mistake on your battery system design, your expensive investment can seem like you threw a lot of good money away, if…it dies an early death.
Blairs first Headway cell battery pack died due to a faulty Battery Management System (which we sometimes call a Battery Murder Suspect). Cordless tools have a very sophisticated, robust, and mature design of BMS in order to reduce warranty returns on their battery packs. Battery dies too early? take it to a DeWalt dealer, and they will prorate the replacement. If you only used half of its rated life, you will get 50% off a replacement pack.
The other reason someone might want something like this is “future-proofing”. If there is a trade war with China, then…ebike battery packs that use Chinese parts will be unavailable for a while. On the other hand, there are tens of thousands of cordless tool packs in warehouses right now. DeWalt, Makita, Bosch, and Milwaukee will never go out of business, and they will never stop making cordless tools.
If you like the idea of cordless tool packs for an ebike, here are some options
The DeWalt “20V” packs are 5S , meaning that each pack has either 5 or 10 cells configured to provide a nominal 3.7V X 5S = 18.5V, and when they are fully charged to 4.2V per cell, it is 4.2 X 5S = 21.0V
I don’t know if the available 14S cordless tool packs (for yard maintenance equipment like mowers, edgers, and chainsaws) would be cheaper than this DeWalt “3 X 20V” system, but…it may be useful to investigate the “56V” EGO packs, and the “58V” Echo packs. In spite of the labeling, they are both 14S using high-discharge cells. 14S has a nominal voltage of 3.7V X 14S = 51.8V, and when fully charged they are 4.2V X 14S = 58.8V.
Both brands have a 4-Ah pack available, so two of them would be 8-Ah, and three of them would provide 12-Ah, which is what I would recommend as a minimum (four might make a sweet 16-Ah V-twin?).
[edit: after some additional investigation, I feel the “56V” EGO packs are the best possible cordless tool pack to experiment with ebike systems. They have lawnmower packs that are available with 5.0-Ah and 7.5-Ah]
[edit: never plug in a full battery pack to a harness with a low battery pack. They will try to equalize rapidly, and may get so hot that they catch on fire. Charge and discharge them all at the same time]
If you want to use 15S (like the “3 X 20V” packs shown above), then the Snapper brand has a single 15S “60V” pack providing 4-Ah each (again, use three or more).
What cells are inside the DeWalt 20V packs?
DeWalts light slimline packs (which have only five cells inside) use very high discharge cells (The most likely suspect for this 1.5-Ah cell is the 30A HB6 from LG). However, the 5-Ah packs that Blair is using have ten cells inside, so each cell doesn’t need as much amp-producing capability to work at the power levels that this line of tools demands. Since each pack is 5-Ah and we know they have ten cells inside in a 2P configuration, each cell must be a 2500-mAh cell.
After some research, I am fairly certain this model of DeWalt pack uses the HE2 cell from LG-Chem, in South Korea. The factory rates these as a 20A peak cell, so in a 2P configuration, it should be able to occasionally put out 40A.
Blair has two pack strings (capable of 80A!), which he did in order to have adequate range, but…I had originally wondered if using a single three-pack string to power his ebike would be straining the packs? The BBS02 stock controller maxes out at 25A, so now I am comfortable stating that Blair will not be getting these packs hot, even if using only three of them, instead of the full six packs.
Written by Ron/spinningmagnets, January 2017