Based on the clamor for it, you would think regeneration (regen), is the “holy grail” of electric vehicles. There is something inherently appealing to the concept of re-capturing energy. Everyone wants it. The only thing is, it is practically useless for electric bikes. Due to a bicycle’s low mass, there is very little kinetic energy to convert. Then there’s the electrical conversion efficiency. Battery packs require a specific charge voltage and current that must be regulated. Going up and down several hills is the best case scenario, but even then you usually only get 2-3% back. There is a possible downside to regen. Without the proper circuitry, you can damage the battery, especially if it is a lithium pack.
The main problem with using regen on a lithium pack without additional protection is that the BMS will not protect the cells from over-voltage. You might be thinking that the BMS has OV (over-voltage) protection so the cells will be safe. In the case of regen, this is not the case. What happens whenever the BMS detects an OV condition? It turns off the *charger* mosfet, not the discharge mosfets. So when you are zooming down the hill generating 60V+ into a 36V pack, you will cook the cells, because you are pumping current into the output, which is not turned off in an OV condition. The current must be directed into the charger input, so the BMS can interrupt the circuit when a cell reaches maximum voltage. One way to do this is by inserting a blocking diode in the negative discharge path, while connecting the charger’s negative input directly to the controller. You can also use a relay to switch the controller from the discharge path to the charger input, if you don’t want the power loss from the diode. Using the BMS to protect the cells from regen is dicey at best. An external voltage and current regulator circuit would be a lot safer. Some regen controllers are supposed to regulate these, but they are not accurate. Regen is generally not worth the risk, but it can be done with proper design. Contact Hightekbikes for more information before you fry your expensive battery pack.
As countries realize the next big industry involves Green Technology, the scramble is on to position themselves to take advantage of this huge market. In the Electric Vehicle Industry, which includes electric bikes, motorcycles, and cars, China is taking a leading role. There has been great fanfare over the few offerings by American companies such as the Tesla, but few people can afford them so they will have limited market penetration. Meanwhile, Chinese companies have been quietly researching, manufacturing and perfecting electric vehicle technology with the help and encouragement of the government. Not being tied to the petroleum/combustion engine paradigm, their plan is to leapfrog American technology and dominate the EV industry. Having manufactured electric bikes for close to twenty years, they own this sector outright. There are only a handful of companies outside of China (notably Bionx in Canada) manufacturing electric motors for e-bikes. China is also the leader in Lithium Battery production, which power all electric vehicles.
In the coming years, American companies will have to invest huge sums of money to catch up. GM has already invested heavily in the Chevy Volt and other manufacturers will have to follow suit. In the electric bike sector there is new interest in complete e-bikes as well as hub motor conversion kits to retrofit existing bikes. Smaller companies are starting to invest engineering time and funds to develop improved products better suited to the American market. One example is Hightekbikes, an electric bike company who is currently looking for investors to setup a motor design and manufacturing facility in California.
As the market heats up and competition increases, there will be situations where a company takes shortcuts, such as taking a competitors product, have it copied in China, then import and sell it at a discount. They save time and money on development by piggy-backing on another companies investment. Don’t think it would happen? It already has. In this case an American company worked with a Chinese factory to produce an improved motor, investing tens of thousands of dollars. When they released the final revision and it was selling well, another American company went direct to the factory and began importing the same motor kit. Evidently, the concept of Intellectual Property is not well known in China and exclusive contracts may not be honored. Hightekbikes has been fortunate to have good relations with all our partners and vendors. Other companies might not have been as lucky. There will be more conflicts and lawsuits over intellectual property in the future as countries, particularly the U.S. and Chna, battle to dominate the Green Technology industry.
Sites with additional information on IP:
http://en.wikipedia.org/wiki/Intellectual_property_in_the_People’s_Republic_of_China
http://advice.cio.com/intellectual_property_chinas_three_realities
http://www.bnet.com/article/protecting-your-intellectual-property-in-china/204803
http://www.mckinseyquarterly.com/Protecting_intellectual_property_in_China_1643
http://news.wustl.edu/news/Pages/5691.aspx
Hightekbikes has recently released our new Power Cruiser series of Direct Drive Motors. These e-bike kits come in front and rear versions and are disc brake compatible. Direct drive motors are optimized for high speed and high power applications. Designed in the USA, these motors are absolutely the finest quality on the market. They have been copied, but not duplicated. For the ultimate performance and latest design, the Power Cruiser Model 10H stands head and shoulders above the competition. This hub motor conversion kit includes a high power 22A controller, advanced throttle, brakes with cutoff switch, and power switch that mounts to the handlebars. Typically, direct drive motors can be “over-volted” and this model is no exception. The controller is 48V compatible and the motor can be run up to 72V with an optional controller. Running at a higher voltage gives you more speed. On a 26″ wheel, the speed will be 20-22mph when powered by a 36V lithium pack. At 48V, that increases to about 24-26 mph. With the larger 700C wheel, the speed increases another 2-3mph. Note that the legal limit in the USA is 20mph without getting a moped license so please consult your local regulations.
It’s not widely known that lithium battery packs, especially LiFePO4, have to go through a break-in period. The pack is made up of several cells connected in series, for example a 36V LiFePO4 pack has 12 cells. When new, the cells do not charge up and discharge at the same rate. One reason may be a chemical inhibitor that is added to slow down self-discharge. At any rate, there is some chemical process going on with new cells that cause them to perform differently when new. Often the first thing a customer will do when buying a pack is to go out and hammer on it, checking the power and range. Unfortunately that is the worse thing you can do. It is recommended to do 5 to 10 cycles of low discharges followed by charging, preferably over night. A low discharge would be drawing 1-3 AH or riding 1-3 miles, without heavy loads.
Since the cells will discharge at different rates, the first cell to reach the minimum voltage will trigger the detection circuit in the BMS, which shuts off power. The range will be low and the customer thinks they have a bad pack. By doing short cycles the cells have a chance to equalize and not get far out of balance. The BMS has a balancing circuit but it does not have the ability to bring up a cell that is alot lower than the others. They have to be kept within a certain range of each other. Leaving the battery pack on the charger over night gives the BMS time to equalize the cells. You may see the charge LED on the charger blink on and off during this process.
Once properly broken in, a lithium battery pack will stay in balance if charged after each use and not left for long periods without charging. Ideally the supplier would perform the break-in process before shipping the pack out. That’s currently not posible due to the time involved and equipment required, at best they can do a short cycle. So for now it’s up to the customer to take the time to do it and resist the temptation to “see what the pack can do” when they first get it. So to summarize: for the first 5-10 times you use a new LiFePO4 battery pack, ride the bike only 1-2 miles followed by extended charging.
There are two basic types of motors in wide use today for electric bikes, direct drive and geared. The direct drive has no internal gears or other moving parts except the actual case which rotates around the axle on sealed bearings. The coils are wound around an assembly that is fastened to the axle and remains stationary. The outer ring of the case has a ring of magnets that rotate in close proximity to the electromoagnets formed by the coils. As the coils are energized in a specific pattern by the motor controller, the magnets are attracted and repelled causing the wheel to rotate. The outer case directly drives the wheel of the bike. The geared motor has the same basic configuration, but does not directly drive the case. Instead, there is an intermediate gear assembly driven by the motor. This consists of a freewheel and three planetary gears which transfer the rotation to the outer case and wheel.
Geared motors are smaller and lighter. Due to the gear ratio (typically 4:1), they have good torque, even at low speeds. The gears make a little noise but usually not very noticable. Due to their small size and the physical strength of the gear assembly, there is a limit on the maximum power that they can handle. The internal freewheel isolates the wheel from the motor so there is no resistance when turning the wheel. This prevents the motors from becoming a generator, so can not be used for regen.
Direct drive motors are bigger and heavier but can take more power. Their larger size, bigger magnets and coils, allows them to dissapate more heat. They are totally silent. There are less parts to go bad as they do not have the internal gear assembly. Depending on the motor, there may be some drag due to the magnetic attraction. DD motors turn into generators when rotated so they can be used in regeneration (regen) applications.
Which should you choose?
For riders who want assist but still want a light bike with the least amount of change in how it rides, the geared motor is best. It can get you up most hills with the right power level, but has an upper limit.
For high speed cruising over low to moderate hills, the direct drive works well. It can go faster than the geared motors and can take lots of power. If you can live with a heavier bike, you can load up with batteries and carry a heavy load very far and very fast. If you want regen, you have to use the DD motor.
Winter is here and you may have noticed a decrease in your range. That’s because a battery’s capacity is directly related to ambient temperature. At freezing temps, the capacity of a lead acid battery (SLA) can decrease up to 60%. Lithium packs are also affected to a lessor degree, maybe 30-40%. The recommended charge current also changes. The best thing you can do is keep the pack as close to room temp as possible. Don’t leave it outside and keep it insulated when in use.
We have just released a new 1000 watt motor. There are front and rear versions and it is disc brake compatible. The front version fits normal forks, the rear model fits a larger 155mm spacing between dropouts.
We also have a limited supply of ebikes using this motor in stock. The setup uses the rear motor in a full suspension mountain bike frame. A 36V10AH lithium battery in an aluminum case, slides onto the rear rack. Price is $1500.
Greetings, this is Terry Reilly, owner of Hightekbikes. I’m starting this blog to better communicate with our customers and the public in general. I’ll be posting the latest information on the electric bike industry and on our products in particular.
