Hunting, bikepacking, or just living off-grid is way better when you have an eBike. You can carry more gear, travel further, and get out of tight situations without straining too hard.
However, one major drawback of electric bicycles is the limited range. Despite their convenience, you have to recharge the battery regularly. Doing so can be difficult when you’re outside unless you have an inverter with a battery or portable power source. (Such as solar panels or the battery on a gas-powered car.)
So, if this is the case for you, you might be wondering: How can I size up an inverter that will be able to recharge my batteries just like the wall outlet in my home?
As a rule of thumb, you should buy an inverter with more power than your battery charger (usually twice the wattage). With such a high-power inverter, you won’t overload the inverter, and it will be able to operate at safe temperatures without shutting down or overheating.
That said, if you can’t understand how much power is required by your charger, or have trouble figuring out which inverter to pick, don’t worry because I’ll cover everything you need to know about inverters using topics such as
How to size up an inverter for an eBike charger?
How to set up your first inverter
Common questions regarding eBike batteries and inverters
How to size up an Inverter for an eBike Charger?
In this section, I’ll elaborate more on how you can calculate the amount of power drawn from your eBike battery charger, understand how an inverter works and figure out several alternatives that could work for you.
Understanding Volts, Amps, Watts, and Watt Hours
Whenever you are looking for a new inverter, battery charger, or e-Bike batteries, you will come across several electrical units such as voltages, amperes, watts, and watt hours. Although the most important spec when sizing up is the wattage, understanding the intricacies of volts, amps, amp hours, and watt hours will be very beneficial.
Before we move on to the wattage, let’s understand voltage and current (amps).
Voltage (otherwise known as potential difference) is used to “gauge” the pressure at which an electrical power source can pump electrons. Devices with higher voltage will be able to push in more current, whereas ones with a lower voltage won’t be able to keep up at the same pace.
In the context of bike batteries, a typical eBike battery pack will consist of either 36V or 48V. The voltage rises when the batteries are fully charged (higher potential) and drops down when the batteries are drained (lower potential). For example, a 48V pack has a maximum voltage of 51.2V when it’s topped up (100% charge) and a voltage of (around) 41V when fully drained. At this lower voltage, the batteries cannot power the eBike motor.
Also, the battery charger for such a 48V battery pack will have an output voltage higher than 48V (typically 58V). This high voltage output from the battery charger guarantees a significant potential difference between the drained battery and the charger, allowing the charger to push in more amps to the batteries, recharging them efficiently.
Amp is a unit of measurement used to define the amount of electrical current that is flowing through a circuit. When there’s a voltage difference between a power source and a load (a resistor) current will flow through the load, providing electrical power to said load.
When you are riding an eBike, the battery pack acts as a power source and the electrical motor (regardless of whether it’s a mid-drive or hub-drive) will act as the load/resistor. When you twist the throttle or pedal (using a pedal-assist mode) the batteries will give out electrical current to the motors where it will start turning. The motor will run even faster when more current/amps are allowed to pass through.
Amp Hours (Ah)
Another spec you might come across when dealing with amps is the amp-hour(Ah) specification. Most eBike battery manufacturers use the Ah specification to specify the capacity of batteries in the same voltage range. For example, a 20Ah 48V battery will have more capacity than a 14Ah 48V battery.
The Amp hour measurement defines how much current you can draw from the battery in one hour. Therefore, with a 20Ah/48V battery, you will be able to draw 20A within one hour or 10A within two hours (and so on) at the same voltage level.
Unfortunately, the Ah system of measurement is not very reliable to compare battery capacities because the inverter, eBike charger, and car batteries all use different voltages. Therefore, we need a more “universal” form of measurement, and that’s where watts and watt hours come into play.
Measuring power using voltage and current can be confusing since different types of devices have different voltages and current limits, so to measure and compare the power requirements more reliably, the unit of watts was introduced.
Simply put, power (in watts) is the product of voltage and current. This rule applies to both alternating current (AC) and direct current (DC) sources. (Although the calculation gets a little more complicated with three-phase power.)
Most often, motors will have a power rating in terms of watts (Such as 250W, 750W, 1000W, etc.). When the wattage is higher, the motor can operate with more speed and force; hence, you can accelerate faster and climb up steep hills without pedaling too hard.
Apart from the electrical motor, inverters and battery chargers have a power rating in the form of watts. So if an eBike battery charger states that it’s 250W, the maximum product of voltage and current that the charger can consume is 250W. (So, if it’s a 48V charger, the maximum current draw is 5A.)
However, electronic devices rarely operate at the maximum power rating; hence a 250W charger will only consume around 150-200W on average. So this metric can be unreliable when trying to figure out how long you need to charge your batteries or how long the inverter needs to stay consistent; hence, the need for an additional watt-hour measurement unit.
Watt hours is the more universal and reliable measurement for comparing battery capacities. The Watt-hour measurement is crucial when you need to set up a power bank (which usually includes 12V or 24V batteries) to charge your eBike battery.
You can easily calculate the watt-hour capacity of any battery by multiplying the amp hour value by the nominal voltage. For example, a 48V, 20Ah battery has a Watt-hour rating of 960Wh; hence, to charge the eBike battery from a solar generator, you would need a power bank with a higher energy density.
Also, the watt-hour rating can be used to (roughly) determine how long you will have to charge an eBike battery. So if you use a 250W charger, it would take around four hours to top off a fully drained 960Wh (48V/20Ah) battery.
The Different Types of Inverters
Now, since we already have an idea about watts, amps, and watt-hours, it’s time to talk about inverters, the safest and most efficient method of charging your eBike batteries when you’re on the go.
Inverters are the ultimate mobile eBike battery charging tool because a well-designed inverter can mimic the AC wall outlet in your home. A properly setup inverter allows you to charge your eBike batteries using the stock charger, which is the safest and most efficient method for recharging your eBike. Apart from that, an inverter can be a great power station for charging laptops, mobile phones, and (depending on the sine wave configuration) even water pumps and refrigerators.
Mainly, there are two types of inverters, pure sine wave, and modified sine wave. Pure sine wave inverters are more expensive, but they produce the cleanest and smoothest sine wave for powering AC appliances. These pure sine wave inverters (PSW) are the most accurate in terms of recreating the AC power you have in your home.
On the other hand, you’ve got modified sine wave inverters, these devices are almost one-third the price of pure sine wave inverters (under the same wattage), but they produce a “modified” sine wave which is not very smooth.
Luckily you can safely use a modified sine wave (MSW) inverter for charging mobile phones, laptops, and eBike batteries. Anything else that includes motors, inductors, or capacitors (primary AC components) will not work very efficiently. They will produce some form of buzzing noise, generate more heat, and eventually power down.
So if you are strapped for cash and only plan on charging your phone, laptops, cameras, eBike, etc. you can rely on a decent MSW inverter.
That said, it wouldn’t hurt to have a high-power pure sine wave inverter at your disposal. Even if you don’t plan on traveling, you can still use a PSW inverter for an off-grid solar generator or backup power system.
Continuous Power vs Peak Power
MSW and PSW inverters have two power specifications: continuous and peak power. As the name suggests, the “continuous” power rating specifies the maximum power rating at which the inverter can run perpetually.
Meanwhile, the peak power rating describes the maximum power it can generate for a few seconds. Usually, an inverter would have a peak power value double (or even triple) the continuous power. This feature is designed to facilitate electrical motors, which need a short burst of power (surge) to gain momentum.
Sizing up an Inverter
Now, let’s get into the meat and potatoes: How to size up an inverter for your battery charger.
First, check the label or datasheet of your eBike battery charger and look for the rated power. If not, check the label for the input voltage (usually 120V/240V) and maximum input current.
After that, multiply the input voltage by the input current to get the rated power (for a 120V/2A charger, it would be 240W.)
The product would be the maximum amount of power required to charge your eBike battery.
Here, you can also calculate the rated power of the charger using the output DC voltage and current. Although it’s technically correct, it is less reliable as a significant amount of energy is spent on the AC-DC conversion process. Therefore, I recommend the direct power rating of the charger or using the input specifications to calculate it.
Nonetheless, I highly recommend purchasing an inverter with at least twice the continuous power rating as your battery charger. (To prevent overheating and accidental cutoffs.)
Here are some well-known inverters that offer the best performance for electric bikes’ batteries:
Bestek 300W Power Inverter: One of the best car inverters out there, no need to do additional wiring, plug it in via the 12V car adapter, plug in your eBike battery charger and drive off into the sunset. It is a very affordable MSW you can use to charge your portable devices.
VOLTWORKS 1000W Inverter: If you want a little more power and three separate AC outlets to charge your devices while on the go, you can check out this 1000W PSW inverter by VOLTWORKS, you might need to modify your car to set it up, but it’s worth it since you will be able to power fans, pumps, and refrigerators with it.
LVYUAN 3000W PSW Inverter: If money and cargo space aren’t an issue, the LVYUAN 3000W inverter is a worthwhile investment. With this bad boy, you will have more than enough power to charge your batteries while traveling.
How to Setup your Inverter
Setting up an Inverter for your Car
There are two ways to set up a car inverter, either via the 12V cigarette lighter socket or directly connecting them to the car battery on your engine.
For the latter, I recommend getting it done with the help of a mechanic since you need to set up an inline fuse, manage cables and mount the inverter somewhere inside your car (Which, unfortunately, requires some drilling.)
Also, it would be best if you never used the inverter when the engine is turned off as the lead acid batteries will drain faster (and die) when the alternator is not generating a float voltage.
Setting up an Off-Grid Solar Inverter
If you’ve already set up solar power for your RV or off-grid cabin (including the panels, wiring, solar charge controller, deep cycle batteries, etc.) you can easily install an inverter by mounting it on the wall or panel board near your batteries and installing the cables.
However, make sure to keep the cables from the battery to the inverter as short as possible, to prevent voltage drops. So the most efficient way to set up an inverter is right next to the batteries. (Approximately, no more than 7ft or so.)
Using a Solar Generator
Instead of inverters and separate batteries, you can also go for a solar generator or portable power bank. These devices include a rechargeable battery (most often li-ion batteries), solar inputs, and a pure sine wave inverter in a neat package. You can charge these power banks using an AC wall outlet, a 12V car socket (although that could take hours), or even via dedicated solar panels.
This type of solar generator/power station is easy to set up and transport. However, they are expensive, and the smaller ones don’t have enough battery capacity to charge your eBike battery more than once.
Common Questions Regarding eBike Batteries and Inverters
Can I charge an electric bike battery from my car?
Yes, with the help of an inverter, you can definitely charge your E-Bikes’ batteries from your vehicle. However, you can only use the inverter while you are driving. Otherwise, the car battery will drain out rapidly.
Can I charge my eBike batteries directly from Solar Panels?
Although it’s possible to set up DIY DC-DC converters to charge your eBike’s battery directly from solar, it is not recommended because you won’t have the proper protection circuits and intelligent features offered by the stock charger.
Can I charge my eBike while riding?
A rare selection of premium eBikes happens to have regenerative braking features (where the momentum from the brake pads is transferred to a small generator to recharge your batteries. Unfortunately, the technology is not yet refined to make it feasible for eBike riders. (As of right now, regenerative braking can only recharge 5%-10% of your full capacity and makes the bike even heavier.) If you are also curious if you can charge your ebike whiled pedaling, you can read our article discussing this.
Can I use a gas-powered generator to charge my eBike Batteries?
Yes, you can directly plug in your stock charger to the AC outlet of the generator. Gas-Powered Generators produce AC electricity in the 120/240V range (depending on your location).
Sizing up an inverter is not that difficult when you are willing to spend a little extra. More power is always better since you’ll be able to use fast chargers or charge other devices simultaneously. That said, you can get by with an affordable 500W or 300W MSW inverter, provided you size it up according to your eBike battery charger specification and use original devices from reputable manufacturers.
Andrew Strider is an electric bike enthusiast. He currently owns 5 electric bikes and is an active member of his local electric bike club where he is able to test many other models/brands a few times a month.
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