How Power Assist Works
The information on this page can help you to understand better how electric assist systems work and how an electrically powered bicycle functions. This page can help you identify the type of electric power system most appropriate for your particular cycle, and for your type of usage. If, after going through this page, you still have any questions at all, please call us.
On this page you will find:
How we use electric assist, the types of systems available, and the advantages and disadvantages of each type. This information is relevant to all Lightfoot models and to most bikes on the market. We also discuss how to calculate the range of your electric bicycle, the cost per mile of operation, and regulations concerning electric assist bicycles. On the separate Electric Assist Systems page, you will find a list of available systems that can be used on Lightfoot cycles. Lightfoot cycles are specifically designed to accommodate almost any electric assist system available on the market today.
PLEASE NOTE: To successfully use an electric assist on your cycle, you need to know a few basic facts about the system (just as you need to know some basics to operate a car), and you need to be willing to pay attention to a couple items of simple maintenance (just as you would on a car). This page will teach you much of what you need to know, and if you are buying a Lightfoot, the rest of the pertinent information will come with your cycle.
The Basics of an Electric Assist System for Bicycles
Virtually all electric assist systems for bicycles consist of these 6 basic components:
- an electric motor,
- a battery to store power,
- a battery charger (plugs into a wall outlet),
- a controller (the ‘brain’ of the system),
- a throttle with which to control your speed, and
- cables that link everything together. (Some systems may require additional mounting brackets and transmission components.)
Virtually all electric power assist systems, once installed, are very easy to use.
Electric Assist and Exercise
Electric assist can greatly reduce the need to pedal. A moderately athletic human can put out 100 watts of muscle power for several hours, or 200 watts for a few minutes. An elite athlete can produce perhaps 300 watts for up to an hour. Power assists common on the market can provide 500 to 1000 watts, making them stronger than even the most athletic rider.
An electric assist’s greater power can be used judiciously to supplement pedaling (especially for climbing hills) or it can totally replace pedaling (at least for the range of the battery.) You have to be disciplined if you want to get physical exercise with a power-assisted bicycle, tricycle or quadracycle. Our mid-drive setups integrate the motor into the transmission in such a way that the motor doesn’t replace the rider’s power so much as magnify it. Such as system helps maintain the incentive to pedal, giving you the best of both worlds. The beauty of the electric motor/battery assist system is this: when cruising on level ground the energy cost of pedaling a moderate weight system is very low, and, when climbing, the system pushes its own weight as well as that of the bike and rider. A possible drawback of electric assist for some people will be that, after using electric assist for a while, pedal-only bikes will seem slow.
“I’ve had your Lightfoot Greenway trike since 2006 (six years) and love it! But I’ve had some physical problems develop…. so (I am adding) electric assist.” — Martha N., NC
TYPES OF ELECTRIC ASSIST SYSTEMS ON THE MARKET
Roller-drive type motor systems may be appropriate for the least demanding conditions. This type of transmission, with the motor spinning a small roller which pushes against the tire tread, may not work well in snow or rain, in sandy and gravelly conditions, nor with knobby or studded tires. Fenders interfere with the roller.
Hub Motor systems use an electric motor built into the hub of the wheel, either the front or rear wheel. Most rear-wheel hub motors hold a freewheel cog-set to provide multi-speed gearing for the rider’s pedaling, but the motor itself is single-speed and cannot be geared down for climbing steep hills or pulling heavy loads. Rear-wheel hub motors preclude the use of shift-when-stopped internal-gear hubs on bikes, but not on Lightfoot trikes and quads. Some models do not accommodate disk brakes. Almost all Lightfoot bike, trike and quadracycle models will accept hub motors on any wheel, front or rear.
Single-speed Chain Drive systems generally use a motor mounted over the rear wheel of a bike, with a chain from the motor to a large sprocket on a specially modified wheel hub.
Multi-speed Chain Drive systems can be shifted down for climbing, or shifted up for faster cruising. Though electric motors have a wide torque band compared to internal combustion engines, they do have limits to how much they can lug down before they “power out” or overheat; the shiftable drive is much more adaptable to varying load and changing terrain. Shiftable systems also help keep the incentive to pedal high, so that the rider is less tempted to stop pedaling and let the electric do all the work. One Custom version of the multi-speed chain drive that can be used on Lightfoot trikes and quadracycles is created by using a hub motor (without spokes or rim) in a “mid-drive” position.
OTHER IMPORTANT CONSIDERATIONS
Quality varies widely among systems on the market. More expensive systems usually are more weather-proof, have thermal-overload protection, have better electrical connectors, are more resistant to corrosion, and have better warranties and service. Poor quality systems may have few safety features and inadequate assembly instructions, potentially leading to dangerous and expensive wiring mistakes.
Batteries of Lithium Manganese and Lithium Iron Phosphate, when well made, are presently among the most capable, longest lived, fastest charged, least temperature-affected, least toxic, and most powerful (for their weight) batteries on the market, as well as the most expensive. Because the Lithium cells and the battery management technology needed to run them are still cutting-edge, there is, unfortunately, some poor quality product being offered for sale. Lead acid batteries are tried and true, very heavy, and inexpensive. For proper performance, a battery cannot be so small that it cannot provide sufficient power (amperage) when the motor demands.
Power of the motors used in assist systems typically varies from 200 watts to over 1000. Some systems, such as the BionX, offer selectable power levels, with levels as low as 75 watts. 75 watts will not push you up a hill by itself, but offers a very noticeable ‘tailwind’ push on level terrain, rationing power for many hours of riding. 300 watts will push a moderate sized bike and rider up a moderate hill with your pedaling assistance, and can help you hold 20 mph on the level. 700 watts will power almost any single-rider cycle past 25 mph with some pedaling. 1000 watts will power a tandem or cargo cycle to 25 mph on the level with some pedaling, and a single rider to 30 mph if gearing allows. The US federal power limit for electric bikes is 750 watts “continuous” (not “peak”) power. In Canada the limit is 500 watts continuous, and in Europe the maximum power allowed is typically 350 watts continuous.
“Pedelec” features (these ‘pedal-electric’ features are common on European systems) require that the cycle be moving at several miles per hour before the assist will kick in. For those operating in a hilly environment, this means that the rider does not have power assist at the moment when it is needed most–starting from a stop on a hill. For riders in urban conditions, power is not available for the first few moments of pedaling, as when attempting to accelerate across intersections. Pedelec systems also are usually speed-limited to 20 mph in the USA, and 20 kph in Europe.
System voltage is usually 12, 24 or 36 volts. High power systems may use 48, 60 or 72 volts. Low voltage systems are in some ways safer for the home do-it-yourself electrician. Higher voltage offers measurably higher efficiency and more power per pound of motor. The motor, battery and controller all have to have the same voltage.
OBTAINING YOUR SYSTEM
We can help you select and procure a system.
Lightfoot has been putting electric assists on our cycles for over a decade, and we have gained a lot of experience in what works and what doesn’t. We know that certain sophisticated systems are needed for demanding applications, while simpler and more affordable systems may be adequate for less demanding jobs.
Some electric assist systems are available from their manufacturer as kits, and if you have a little mechanical and electrical aptitude, they can be installed by you.
If you already have an electric system, and wish us to install it, you can ship it to us immediately after you order your cycle. We will install and test the system, charging you an installation fee by the hour for the time required.
There are a couple of systems that we can help you obtain and we can then install that system on a cycle we are building for you. When your electrified Lightfoot cycle is completed and shipped to you, it will be ready for you to get on and go.
If, after reading through this information, you still have questions about what to order and from whom, please call or email us.
USING ELECTRIC ASSIST
The range provided by electric assist varies, depending upon manner of use, cycle/rider weight, system efficiency and type/capacity of the battery used.
CALCULATING RANGE: Conservatively; each 100 watt-hours of usable battery capacity should provide about 2-3 miles (3-5km) of pure-electric level-road cruising power. The number of watt-hours in a battery is calculated by multiplying battery voltage X battery amphourcapacity X the percentage of useful capacity (90% for Lithium, 40% for Lead-acid). Hill climbing uses substantially more power per mile; steep grades can easily triple or quadruple energy consumption. Coasting on downhills does nothing to regenerate electricity, but serves instead to rest the rider and conserve the remaining stored power. Regenerative-braking systems (such as in the BionX hub motor) can recapture a small percentage of the energy of momentum normally lost to braking. USED AS ASSIST: (An example) By using the electric assist 1/3 of the time for moderate hill climbing, by coasting on downhills, and by providing the other 2/3 of power through pedaling, the electric power system can provide an assisted range of 5-9 miles per each 100 watt-hours of battery capacity. This type of assisted-riding is more feasible if the battery pack is lightweight.
INCREASING CAPACITY: Twice the battery bank will provide twice the range. Lightfoot bikes (two-wheelers) can usually carry one set of batteries, and a dual pair may be supported by a custom-made underseat pannier rack. Lightfoot road trikes carry a single set in the cargo pod, and can usually add a second set of lightweight batteries. Large batteries can be supported by custom brackets or cargo boxes. As a rule of thumb, you should get a larger battery capacity than you will absolutely need. This is especially important if using lead-acid batteries; they should not be drawn down more than 50% except very infrequently, and should never be deeply drawn down in sub-freezing weather. CHARGERS: Batteries and Chargers usually are designed as matching sets; a charger usually cannot be changed from one battery bank or system to another.
WEIGHT: Adding extra weight makes hill climbing, acceleration and lifting the bike more difficult. Unsuspended battery weight is “dead” weight, hammering at the frame and wheel rims when bumps are hit; this is especially an issue with large lead-acid batteries. Hub motors, being part of the wheel, cannot be suspended from road shock except by high-profile (fat) tires. Batteries take up room, reducing the amount available for cargo. Optimal sizing of the battery pack is very important for these reasons. Weight of batteries varies by type and number. The 10 apmphour BionX LiMn battery weighs about 8 pounds. A 20-amphour 36-volt LiFePo4 battery weighs about 14 pounds, not including the weight of its container. By comparison, a 30-amphour 24-volt (a pair of 12-volt units) lead-acid battery pack would weigh about 45 pounds, though it would only have the same available power as the LiFePo4. Per unit of stored power; the Lithium battery weighs 1/6 as much and costs 4 times as much. A heavier battery is also going to require a stouter and heavier and more expensive carrying case/bracket.
COST EFFECTIVENESS OF ELECTRIC ASSIST
CALCULATING ENERGY COSTS: If we assume that electrical power can be provided at 10 cents per kilowatt hour (this is conservative for Montana residences, which are paying 5-7 cents in mid-2008), and if we assume that the internal efficiency of the charger/battery/motor/transmission is such that 70% of the electricity provided to the battery charger is actually delivered to the drive wheel, and if we further conservatively assume that 40 watt-hours of stored power provides 1 mile of travel when using a chain-drive electric assist on a Lightfoot trike; we can then calculate that the electrical charging needed to travel 1 mile would cost almost exactly 1/2 cent, and thus the electricity to travel 100 miles would be 50 cents. This calculation shows that the money needed to buy a single gallon of gas at $4/gallon would buy enough electricity to take a Lightfoot cycle with chain drive electric assist 800 miles (without pedaling); therefore, we are justified in claiming, for illustration’s sake, that such an electric motor system at least gets “800 miles per gallon”.
To go further with this comparison, we can justly claim that meeting half of the cycle’s power needs by pedaling (burning food calories, which in modern America are often “excess” calories) and the other half with electric assist, constitutes a vehicle that “gets 1600 mpg”. (It has been calculated <reference needed> that, when one compares the caloric value of gasoline and that of food, the human engine gets 3000 miles per gallon.) Even with very modest amounts of pedaling, we can easily claim the attainment of 1000 mpg as a rule-of-thumb for the efficiency of electrically-assisted Lightfoot cycles.
CASE STUDY: Calculating energy costs for the BionX assist was done in 2009. The 360 Watt-hour capacity BionX battery can move a heavy rider (who is pedaling) strongly at least 25 miles (as our experience confirms) at almost 20 mph. At a conservative 10 cents per kwh for electricity, charging the battery once should cost 3.7 cents. Assuming a 15% charging inefficiency, we can calculate that a single fill-up actually costs 4.3 cents. This 4.3 cents assists us for 25 miles, as we have shown, or we assist it, since it may be providing the majority of the power used (depending on efficiency, weight and aerodynamics of the cycle being ridden) needed to travel at 20 mph. If we spend our $4 on electricity instead of a gallon of gas, we can charge the battery 93 times, which is enough to travel 25 assisted miles 93 times, which is to say; 2325 miles for the cost of a gallon of gas. This conclusion more than supports our rule-of-thumb claim of 1000 mpg for our electric assists.
CALCULATING LIFE-CYCLE COSTS: If we assume the following–that our motor system can serve for 20,000 miles, that a Lithium Iron Phosphate battery pack can maintain reasonably good efficiency for 1000 full discharge cycles, and that each full discharge provides 20 miles of travel–then we can calculate that both batteries and motor might serve for approximately 20,000 miles (though a brushless, gearless motor might last a lot longer). The $1500 motor/battery set would then have provided each mile of travel for 7.5 cents. Total Life-Cycle cost per mile of the electric assist system then would combine 7.5 cents per mile equipment costs with 0.2 cents for fuel for a total per-mile cost of 7.7 cents. Since the battery system does not contain heavy metals, since the rest of the system is largely recyclable, since bicyclist impact on roads and infrastructure is minimal, and since we are using very minute amounts of fuel, we can assume that the external costs (which are borne by the local community, the planetary ecology and all world citizens, and not solely by the cycle’s user) are very small, especially when compared to the very large externalized costs of automobile use. Total combined direct and external lifecycle costs per mile for an assisted cycle might total something like 10 cents, as compared to perhaps $1.50 per mile for automobiles (as calculated at Commute Solutions http://www.commutesolutions.org/calc.htm (which demonstrates that cars have external costs much greater than their direct costs), giving us a per-mile cost for an ‘electric bicycle’ that is 1/15th that of an automobile.
Charging batteries can be accomplished with photovoltaic modules (“solar panels”). This technology has high up-front financial costs and low long-term costs. It is technologically simple and ecologically benign. It is most appropriate for use in sunny desert or Mediterranean climates. We have extensive experience with designing photovoltaic solar charging systems, and can help you evaluate and configure such a system. A lightweight and durable module (“solar panel”) of a type very appropriate for portable mounting on a cycle (an “on-board” system) is available, along with an appropriate voltage controller, from a long time solar business associate of ours, at http://www.pvsolarmodules.com/Marine-grade-solar-modules.html. We can install an on-board system on your cycle, or your local photovoltaic systems provider can install a non-moving charging station at your home or business using standard type modules and controllers. Modules for charging lithium batteries should have a peak output voltage of 1.4x nominal system voltage for full and efficient charging. While we can use solar to charge batteries on most of the electric assist systems that we use, those few electric assist systems which integrate electronics with the battery, such as the BionX, cannot use solar charging. “I just spent a full day riding…(my son’s Lightfoot electric bike). It was a great day. (He) now has 3300 miles (on his cycle). With some minor fixes the bike has been a great bike for him. His only means of transportation.” — Rick H., TN
NOTE: WE CANNOT MAINTAIN YOUR ELECTRIC ASSIST SYSTEM FOR YOU. For trouble-shooting a malfunctioning system, you should first contact the manufacturer of your system, or their dealer/representative. It is for this reason that we encourage you to purchase your system directly from the manufacture of your preferred electric assist, or their dealer, and not from us, the bike manufacturer. If you have a non-standard system or if the manufacturer of your system has gone out of business, you can contact a local shop with expertise in electric golf carts, electric scooters or electric wheelchairs.
Some batteries are made of toxic materials (lead-acid and nickel-cadmium especially) and all batteries (even the benign lithium batteries) should be recycled at the end of their life. We do not at this time recycle batteries. Large lead-acid batteries can be recycled at auto repair shops. “D” cells as found in many systems can be recycled at Best Buy, Target, Circuit City, Wal-Mart, Home Depot and Radio Shack stores. Battery Solutions (www.batteryrecycling.com) recycles batteries. Check with the Rechargeable Battery Recycling Corporation at www.rbrc.org, and click on the “consumers” icon for recycling information. The toxic materials of some batteries are well contained within the battery casing; please take care not to damage the casing even if they are no longer usable.
ELECTRIC BICYCLE REGULATIONS
For the most part, electrically assisted cycles are welcomed throughout the US and in most other countries. We have never had a customer report that they were unable to use their electrified Lightfoot cycle. There are limits on the power of motors, and there are restrictions under certain conditions and in certain areas.
The United States Federal Low-Power Electric Bike Law
HR 727, signed by President Bush on Nov 27 2002, defines a Low Power Electric Bike for those who wish to manufacture them. It specifies working pedals, one horsepower maximum, and a top speed of 20 mph under electric assist. States are not required to have or follow this definition. There are a few states allowing 1000 watt vs. the 750 watts (750 approximately equals one horsepower), and a few allowing 25mph. However, the majority of states use the 20mph rule to identify a bike or trike under the low powered electric bike rule. If you max out at 25 mph, in many states that bumps you up to moped classification, requiring more equipment such as turn signals, rear view mirror, horn etc; some may even require registration. This law can be seen in The Federal Register / Vol. 68, No. 29 / Wednesday, February 12, 2003 / Rules and Regulations pages 7072 and 7073.
Excerpt: SECTION 1. CONSUMER PRODUCT SAFETY ACT.
The Consumer Product Safety Act (15 U.S.C. 2051 et seq.) is amended by adding the following:
`LOW-SPEED ELECTRIC BICYCLES’
SEC. 38. (a) Notwithstanding any other provision of law, low-speed electric bicycles are consumer products within the meaning of section 3(a)(1) and shall be subject to the Commission regulations published at section 1500.18(a)(12) and part 1512 of title 16, Code of Federal
(b) For the purpose of this section, the term `low-speed electric bicycle’ means a two- or three-wheeled vehicle with fully operable pedals and an electric motor of less than 750 watts (1 h.p.), whose maximum speed on a paved level surface, when powered solely by such a motor while ridden by an operator who weighs 170 pounds, is less than 20 mph.
`(c) To further protect the safety of consumers who ride low-speed electric bicycles, the Commission may promulgate new or amended requirements applicable to such vehicles as necessary and appropriate.
`(d) This section shall supersede any State law or requirement with respect to low-speed electric bicycles to the extent that such State law or requirement is more stringent than the Federal law or requirements referred to in subsection (a).’.
SEC. 2. MOTOR VEHICLE SAFETY STANDARDS.
For purposes of motor vehicle safety standards issued and enforced pursuant to chapter 301 of title 49, United States Code, a low-speed electric bicycle (as defined in section 38(b) of the Consumer Product Safety Act) shall not be considered a motor vehicle as defined by section 30102(6) of title 49, United States Code.
State Regulations of Electric Bicycles
We do not guarantee that this information is accurate or up to date. If you know that any information herein is in error, or have knowledge of important details or exceptions to these regulations, please email us at firstname.lastname@example.org.
Motor vehicle license required (most of these states also require a helmet, possibly a motorcycle-rated helmet): Connecticut, Kentucky, Louisiana, Massachusetts, Minnesota, Pennsylvania, Utah.
Minors disallowed: Arkansas (10 years of age minimum), Florida (16), Louisiana (15), Massachusetts (16), Minnesota (16), Tennessee (14), Washington (16).
Electric cycles illegal: Hawaii, New Jersey (on state roads), New York (on state roads).
Miscellaneous Restrictions: Texas (cycle cannot weigh over 100 pounds), California (1000 watt maximum), Colorado (1000 watt maximum).
The Canadian Power-Assisted Bicycle Law
The Canadian Motor Vehicle Act was recently modified to include a class of Power Assisted Bicycles. Federal Guidelinesstate that cycles with continuous motor power under 500 watts, which travel at speeds less than 32 km/hr, have no need for license or insurance on public roads. WARNING: A powerful electric motor, especially those having 1000 watts or more of power, is capable of pushing a cycle to higher speeds than most people will maintain on a non-assisted bicycle with muscle power alone. Increased speed and kinetic energy increase the likelihood and severity of accident, and increase stresses that could lead to structural failure of the cycle’s frame, fork, wheels and tires. You must inspect your cycle’s frame, fork, tires and brakes every time you ride, and it is your responsibility to recognize and ride within the safety limits of the power-assisted cycle.