Electric Hub Motor - Geared or Direct Drive?
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 electromagnets 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. 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 free-wheel and three planetary gears which transfer the rotation to the outer case and wheel. The gear ratio is typically 4:1.
Geared motors are smaller and lighter. Due to the gear ratio, they have good torque, even at low speeds. Due to their small size and the physical strength of the gear assembly, there is a limit on the maximum power/voltage that they can handle. The internal free-wheel isolates the wheel from the motor so there is no resistance when turning the wheel.
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. It also is at least 15% more efficient, which means you will get more distance out of the battery per charge.
For high speed cruising over low to moderate hills, the direct drive works well. It can go faster than the geared motors and handles lots of power/voltage. If you can live with a heavier bike, you can load up with batteries and carry a heavy load very far and very fast.
Electric Bike Kit Motors
Motor power ratings are specified in watts. Watts(W) = Volts(V) x Current(A). For example, a motor running at 36V and (x) 22A is pulling 792W. The thing that not everybody realizes is that motors don't have an exact value for watts. Consider the specified rating to be a general value as each motor will have a power range. Sometimes motors are purposely under-rated as in the case of electric bikes sold to Europe, which by law are limited to 250W. Ever wonder why there are so many motors rated for 250W ? Taking one of these motors as an example, first calculate the current. 250W/36V = about 6.9A That current is too low for 90% of ebikes so it doesn't add up. The lowest E-Bike controller current is at least 10A, and many are 15A or more. So 36V x15A = 540W, twice what the specified rating is. Of course you can run at a lower voltage, and 24V is still common, especially for smaller bikes. In that case you have 24V x 15A = 360W.
The point is that motors can be run at different power levels. They will be most efficient at a specific power level. Below this level ,they will bog down and waste power for example when they are going slow under heavy load. At the higher point of the power range, the motor will start to get hot as it cannot dissipate the heat and will waste power.
The standard way to rate a motor is test it on a sophisticated motor testing apparatus. It puts it under measured loads and plots the various parameters including efficiency and output power. The power rating corresponds to the point of peak efficiency. There's actually a simpler method anyone can do. While not exact, it gets you in the ballpark. Simply increase the power level supplied to the motor while under load and measure the temperature of the motor. The power level at which point the motor is slightly warm when run continuously (under load) is the optimum operating level.
You will see motors advertised as 1000W on sites like Ebay and you might think, wow what a great deal on a powerful motor! The problem is any power level can be slapped on a motor. Most of these are actually 500W motors. Both our direct drive and geared motors operate very well at more than 1000W with a 48 volt battery (especially the direct drive); however, that is not where they operate most efficiently. They are most efficient cruising at 500W for the direct drive and 400W for the geared. So don't get caught up on power ratings or fooled by exaggerated advertising claims. For more information on your power requirements, contact us at 707-439-3179.
|LifePO4 Battery Break-in Process|
Battery Break-in Process
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 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 a chemical process going on with-in 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 really ride it hard to check the power and range. Unfortunately, that is not the best thing to do. It is recommended to perform 5 to 10 cycles of low discharges followed by full charges. A low discharge would be drawing 1-3 AH or riding 2-5 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 much lower than the others. They have to be kept within a certain range of each other. In addition, leaving the pack on the charger over night gives the BMS time to equalize the cells. You may see the charge LED (green light) on the charger blink between red and green during this process. The pack is charged in "serial mode" where the charge current is passed through each cell to get to the next one. So each cell has to share part of the voltage going in, typically 44V for a 36v LiFePO4. During the critical break-in period some cells will accept current more than others. Thus, it is critical to follow the break-in process to optimize the performance of the pack.
Once properly broken in the pack will stay in balance if charged after each use and not left for long periods without charging. While rare, it is possible that a pack can become unbalanced even after being broken in. The solution is to charge up each cell separately until they are equal. This is not something the customer can do as working on the cells is dangerous. Not all suppliers have the technical ability to do this. At Electric Bike Solutions, however, we offer this service to our customers and can even replace individual cells in the unlikely event one goes bad.
So the bottom line is when you receive a new pack, for the first 5-10 times you use it, ride the bike only a few miles followed by charging.
Electric Bicycle Battery Technology
All “Lithium” batteries are not all the same... yet they all seem to fall under the title “Lithium”. In fact over twenty different Lithium chemistries exist. Most of these chemistries fall under the grouping of Primary Cells like button cells and are not generally rechargeable.
Under a separate category there are Lithium Ion, rechargeable, batteries. These Lithium Ion batteries are considered the best type for automotive propulsion. These are a type of rechargeable battery in which the anode (positive Electrode) contains lithium in some form while the cathode (negative electrode) is made of a type of porous carbon. In this category there are three general groups. These groups are made up of a wide variety of materials. These materials are:
Advantages of Li-ion Technology
Lithium Ion batteries are lighter than other energy equivalent batteries – often much lighter. A key advantage of using lithium ion (especially LiFePO4) chemistry is the high open circuit voltage that can be obtained in comparison to aqueous batteries such as lead acid, nickel-metal hydride and nickel cadmium.
Lithium ion batteries do not suffer from the memory effect. They also have a slow self discharge rate of approximately 5 – 10% per month compared to over 30% in common nickel metal hydride batteries and 10% per month in nickel cadmium batteries.
Lithium-ion versus Lithium-iron (more than just an "r")
Contact Doug, the owner of Electric Bike Solutions, with your questions at the numbers and email below.