Energy storage is the weakest element of any otherwise well-designed electric vehicle. The person who comes up with a much better rechargeable battery than what we have today will be very, very well rewarded. Compared to, say, a gas tank, batteries are very heavy, bulky, expensive, and slow to refill.
Battery technology is being driven not by large, high-energy applications like vehicles, but by portable electronics like cell phones, laptops, and
toys hobbies like radio-controlled model aircraft. This means that if you want to use the latest technology for a vehicle, you tend to need to hook up a large number of small batteries intended for smaller devices. This introduces more labor costs, and every connection introduces electrical resistance and mechanical vulnerability. Charging and discharging large series of batteries in a safe, controlled way is then another problem. It’s hard to find stable, cost-effective sources for such technology, especially for small-fry startups like Cleverchimp.
Starting with Xtracycles as a platform has made more things easy than hard in designing Stokemonkey, relative to regular bikes, but coming up with good battery offerings has still been tough. After trying lots of different things, I’ve settled on nickel-metal hydride packs in two sizes: 324 and 468 watt-hours. These are good for about 40 and 70 minutes of high-rate discharge, which riders can portion out over the course of rides of any length. Customers can get singles or multiples of these packs to suit their needs best. The packs consist of thirty cells in series, spot-welded together and shrink wrapped.
I took it as a sign from the universe that when arranged in a near-cylinder, these packs fit just about perfectly in standard (cheap) 4″ ABS pipe for physical protection (several packs in less robust enclosures failed from physical shock in testing). I drill out the packs for ventilation and cooling, and cap them with standard rubber pipe caps for bumper cushioning. An adjustable strap makes carrying the packs for off-bike charging and theft prevention easy. The prototype shown in the photo below isn’t quite indicative of the production design, but it’s close. The packs fit in the Xtracycle’s inner velcro-flapped pouches, or right out in the main cargo slings. They can be lashed in any opportune place as well, including in the front triangle.
One of the sweeter touches are locking Neutrik Speakon connectors–far-and-away the nicest available for applications like this. One 4-pole connector serves for both charging and discharging.
I’m planning to import extra packs, and sell them independently of Stokemonkey to anybody with 36-volt needs. Ordering a surplus will help me get my sea-freight volumes up to the economical minimum, permitting smaller and more frequent shipments of other Stokemonkey components.