As usual with all my articles, you can click the photo in the article for a larger version.
Any "builder" will tell you ... expect the unexpected.
Refer to the bicycle anatomy photo at the right (photo courtesy of Wikipedia). The battery I bought will not fit the down tube – that's where it is normally located. On my bike, the length of the battery will fit the down tube, but the height is too high and would not fit with the top tube blocking access.
I had to figure out where to put the battery. And, replacing the battery is not an option ... this battery cost over $800. The options are:
- Install a rear rack and install the battery on (or under) the rack
- Figure a way to install on the seat tube
- Figure a way to install on the top tube
The seat tube is not an option. It is not high enough to accommodate the battery.
The rear rack is not practical ... already we have extra weight in the rear hub motor and the type of battery does not lend itself to a proper installation on the rear rack.
That leaves the top post. It might even look a bit like a motorcycle gas tank ...
The problem, of course, is how to secure the battery. The battery has two parts. Refer to the photo at the right. The box is the big black part. The power interface is the part that the battery slides in and out allowing for charging the battery off the bicycle. The power interface is constant, mounted on the frame, and sending the battery power through the plug to the controller. The four slots shown in the aluminum portion is how it is secured to the frame of the bicycle. Those slots are designed to be screwed into the bottle cage mounting bolts.
The two holes in the bike frame are rivnuts. They are not even with the frame, they stick up a little bit. Rivnuts are designed to work on thin metals. They are typically aluminum and compress to the thickness of the metal providing a screwing platform for holding water bottle cages. And, double-duty as mounting holes for ebike batteries.
To mount this battery on the top post, the options are limited to a custom designed platform, a series of clamps or zip ties, or a custom set of rivnuts identical to the down post. I'm sure this isn't new to pros, but it is new to me and many of my readers.
Rivnuts come in several flavours. As I mentioned, aluminum is probably the most popular. In the context of an expensive battery, though, I'd suggest that another option may be better: either stainless steel or carbon steel. I decided to use non-aluminum, and particularly carbon steel. Actually the decision was made for me. I dropped by Bolts + and all they had was M6 rivnuts at $0.37 each. The standard size for a water bottle cage is M5 x 0.80 bolt. The ones I purchased are M6, again not much of a choice, that's all they had and anything else was custom ordered.
The photo at the left shows the rivnuts in the down post of the bike frame. I'll be putting two similar rivnuts in the top post.
The next article in this series will show how I do that, discuss the parts and costs involved, and how I drilled the holes into the bike frame.
[EDIT] ... here's a video to explain how a rivnut works