Jason Leeman

What battery do I need for a 48v 500w or 1000w or 2000w motor?

Your electric bike is essentially a conventional bike with a battery, a motor, and an acceleration mechanism. However, knowing how the bike works goes beyond understanding the basics; you need to know your bike's power train details.

 

In this article, we will discuss the bike's motor and battery.

 

First, Does the bike charge as you pedal?

The technology for electric bikes to charge as one pedals exists. Some bikes can charge as you pedal. However, the technology is uncommon among electric bikes for two reasons.

 

Firstly, the self-charging e-bike weighs more. The additional weight slows down the bike, regardless you're pedaling or getting motor assistance. It, therefore, might not be too useful to have a bike that charges while you're pedaling if you will have to pedal harder to get the bike moving.

 

The second reason is the electric returns from a self-charging mechanism generating power from pedaling. It is estimated that the bike is only able to generate a 5% to 10% return when the rider pedals to generate power. To put this statistic into perspective, imagine having to pedal for 10km to get back 1 km in battery range.

 

The technology around peddling to recharge the e-bike is too unrefined to be of significant value to the everyday rider.

 

There are bikes that can recharge when you brake. The technology is called regenerative braking. If you're an electric vehicles enthusiast, you might have heard of the term.

 

Regenerative braking generates power by negative motor action.

 

Allow me to explain.

 

A motor is essentially a generator. Motors can generate power. There were bikes that had dynamos used for lighting the headlamp. That dynamo is essentially a motor working in the opposite direction.

 

Regenerative braking forces the motor to act as a dynamo when braking. Rather than rotate forwards, the motor rotates backward, thereby generating power. The idea is to use the braking energy typically dissipated as heat by the brake pads to recharge the battery.

 

Again, the gains are low. It is unlikely that the bike will have enough braking force to generate any significant power for storage in the battery. Regenerative braking in cars is used to dissipate heat more than it is used for power generation.

 

How do I know what battery to get for my electric bike?

There are four main types of batteries in the market; lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion batteries. Nearly all e-bikes use lithium-ion batteries.

Lead-acid batteries

Lead-acid batteries are bulky and unsuitable for bikes.

Nickel-cadmium batteries have more capacity than lead-acid batteries, but they lose charge significantly even when unused. A nickel-cadmium battery can lose 70% capacity through self-discharge within 24 hours. As a result, you might park your bike only to come back and find the battery nearly fully drained despite the bike not being used.

 

The nickel-metal hydride battery has about 40% more capacity than the nickel-cadmium battery. However, the battery has significant self-discharging. Additionally, the nickel-metal hydride battery is significantly expensive.

 

Lithium-ion batteries

The best batteries for your e-bike are lithium-ion batteries. There are three types of lithium-ion batteries available to e-bike owners. Available battery types are lithium manganese batteries, lithium cobalt batteries, and lithium-ion polymer batteries.

 

Lithium manganese batteries have durability and range. The batteries are favored by many e-bike manufacturers. You might want to know that some hybrid cars use lithium manganese as their batteries of choice.

 

Lithium cobalt batteries came before the lithium manganese batteries. The main advantage the lithium cobalt batteries offer is higher energy density. That means you get more range per battery compared to other lithium-ion batteries of the same size. Lithium cobalt batteries are also light and reliable.

 

Lithium-ion polymer batteries are closely comparable to the other lithium-ion batteries in terms of performance and weight. The main difference is that lithium-ion polymer batteries can be shaped into a variety of shapes. That allows manufacturers to fit a battery to the shape and aerodynamics of the bike.

 

The way to determine which battery to get for your bike is to evaluate your needs. If you are looking for light-weight batteries with sufficient range at an affordable cost, your best option would be among the lithium-ion prospects. That stated, the exact battery you need for your bike depends on the kind of motor your bike features.

 

To understand the concept of batteries and how they fit into their motors, you need to know a few technical details on batteries.

 

Important battery attributes

Batteries are categorized for their voltage, amperes, and watts. Voltage refers to how fast the electrons move. Amperes indicate the volume of electrons that can flow. Watts is a product of multiplying voltage by current, and it indicates the electrical power available.

 

An e-bike battery will have a sticker indicating its amp hours. Amp-hours is the number of amps the battery can produce for one hour. Typically, amp hours for e-bike batteries range between 10 and 20 Amp-hours (Ah).

 

E-bike battery packs also indicate their watt-hours (Wh). The watt-hours refer to the battery's ability to deliver power in hours. A 450Wh battery, therefore, can deliver 450 watts of power for one hour, or 225 watts for 2 hours, and so forth.

 

Please note that the Wh measure does not indicate ride time; e-bikes do not use their battery packs continually.

Going by the metrics discussed, you can estimate that a 48v 750w motor running for an hour requires a 15.6 A battery. For other motor sizes, refer to the table below.

  

Voltage

Watts

Battery

48v

1500w

31.25 A

48v

1800w

37.5 A

48v

1200w

25 A

48v

500w

10.42 A

48v

2000w

41.67 A

How long will a 48v 20ah battery last?

You get your estimated battery time by multiplying the volts by the amps. In this case, the multiple is 48*20 to yield 960 watts for one hour. How long your battery lasts depends on what kind of battery and how you ride the bike.

 

You should be able to get at least 57.6 minutes on a 48V 20ah lithium-ion battery with continuous use. A lead-acid 48V 20ah battery will only give you about 288 minutes of riding. That is because lead-acid batteries should not discharge below 50%.

 

Going by the same formula, a 48v 10ah lithium-ion battery will last 28.8 minutes, while a similar lead-acid battery will offer 14.4 minutes of riding time.

 

How Do You Get the Most Value Out of the Battery You Buy?

 

There are four major factors that will affect your battery's longevity. These are charging patterns, frequency of use, bike maintenance, and bike technology.

 

Charging patterns

You might be tempted to charge your bike to full capacity when you're about to head out for a ride. It is completely understandable considering the very real concerns around charge anxiety. You want to have that power when you need it.

 

But you would be wrong.

 

It is recommended that you charge your battery to about 80%. That allows you to avoid completing a discharge cycle. A discharge cycle happens when your battery moves from 100% to 0%.

 

All batteries have a finite discharge cycle count. That means a battery with 1000 cycles will break down after 1000 100% to 0% discharge cycles. To avoid getting to 1000 cycles, for example, avoid charging up to 100% every time.

 

That stated you need to charge the battery fully every once a while to balance the cells.

You also need to avoid letting your battery be discharged completely. When the battery hits 30%, it is okay to recharge it to about 80%. Again, hitting 0% completes a discharge cycle, thereby affecting your battery's longevity.

 

Frequency of use

It goes without saying; the more you use your bike, the more you degrade the battery. If you want to enjoy that battery for long, go easy on the throttle. Cycle via pedals until it's absolutely necessary to hit that throttle.

 

Bike maintenance

Think of the bike and its load (you) as a burden for the battery. When you use the throttle, you are asking the battery through the motor to move that load. To make it easy for the motor, the bike should be efficient.

 

An efficient bike has its moving parts well-lubricated and its tires inflated to the recommended pressure, for example. Maintaining your bike to ensure that all mechanical parts are not only lubricated but clean will extend the battery life.

 

The battery through the motor will be running an efficient machine. Power will not be lost compensating for losses such as friction or sub-optimal wheel rotations.

 

Bike technology

Earlier, we discussed regenerative braking. Now, if your bike has regenerative braking technology, it is likely that you will get some marginal gains on the battery's longevity. A bike that recharges its battery in small quantities as it moves is more efficient than a bike that does not.

 

Another impactful technology is pedal assist. If your bike has a pedal-assist, it uses more power than the typical bike. Every time the pedal assist kicks in, the battery is asked to power the motor.

 

Conclusion

To understand and care for your e-bike's battery, you need to be familiar with the concepts we have discussed here. Do not be intimated; it gets easy, even intuitive, once you get the initial hang of it. 

About the author 

Jason Leeman

Jason Leeman is an engineer, tech geek and personal electric vehicle enthusiast. He loves testing the latest in urban personal transportation and sharing his love of wheels with his kids and his blog readers.