As an e-bike owner, you need an inverter to charge your bike when you don’t have access to a traditional power outlet. But before you pick out just any inverter, you must know what size you need for your bike.
If you pick out the wrong size, you may run short or cause damage.
A few factors can affect what size inverter you need, though. Let’s take a look.
Factors That Influence What Size Inverter You Need
The battery capacity of your bike is one of the more important things to keep in mind. A higher battery capacity means you’ll need more energy to charge it, which would mean a larger inverter that can provide that much energy.
E-bike battery capacity is usually measured in amp-hours (Ah). You’d need to multiply the Ah rating by its voltage to get the battery’s capacity. For example, a 10 Ah battery of 48V will have a total capacity of 480 watt-hours (Wh).
Type of Charger
Another factor that affects the inverter size is the type of charger. There are generally two types of chargers: constant voltage (CV) and constant current (CC).
CV chargers are usually slow and, as the name suggests, provide a constant voltage to the battery while it charges. CC chargers instead provide a constant current and are faster at charging.
CV chargers have a lower charging rate, so you may not need a large inverter to charge your battery. On the other hand, CC chargers need more power to supply the high charging current, so the inverter will have to be larger.
Remember, though, that CC chargers can generate more heat and damage your battery long-term, while CV chargers are gentler and better at maintaining battery health.
Another thing to keep in mind is the efficiency of the charger itself. Not all the energy used to charge your battery is stored. Most charging processes are inefficient, with a cap of about 80-90%. So, about 20% of your inverter’s energy will be wasted.
If you want to make sure your battery is fully charged, you’ll have to account for this loss and pick an inverter of a size larger than your battery’s capacity.
To calculate the charger size you’d need at minimum, you can divide the battery capacity by the charger’s efficiency rating. For example, for the 480-watt battery capacity we calculated earlier, a charger with a 90% efficiency would need 533 watts to charge (480 watts ÷ 0.9 = 533 watts).
Battery Voltage & Amperage
Your battery’s voltage and amperage are major contributors to the size of the inverter you need. This rating would likely be written on the battery itself and indicates how much power you need to charge the battery, which dictates the inverter’s size.
We already went over how to use voltage rating to calculate the wattage and battery capacity. If you are using your inverter to charge multiple batteries, calculate the total wattage for all of them to determine how much power you will need to charge them.
The charging time of the battery is also something to keep in mind. Not all chargers work at the same rate – some are slower than others, while others are faster.
It may seem like the charging time isn’t very relevant, but if you’re using an inverter to charge your battery, it’s probably because you’re on the go and don’t have time to wait for your bike to charge anyway.
The charging time for batteries depends on different things, including the battery capacity, the charging current, and the charger’s efficiency.
Larger batteries will take longer to charge, as will lower charging currents. Higher charging currents are faster, but they will take up more power, which means that the inverter you use will need to be bigger.
To calculate the charging power, you can multiply the capacity with the voltage (to find the wattage) and divide it by the time it takes to charge.
For example, if you want to charge your 480-watt battery in 2 hours, you’d need an inverter that can supply at least 240 watts (480 ÷ 2 = 240) to manage that.
Keep in mind the charger efficiency, though! If we stick with the charger we used earlier with a 90% efficiency, we’d need 533 watts of power. To charge that in 2 hours, we’d need an inverter that can supply at least 267 watts (533 ÷ 2 = 266.5) of power.
Make sure to account for charger efficiency when making calculations! If you’re charging more than one battery, you’ll want to account for the capacity, efficiency, and charging time for each one.
If you don’t need to charge your battery within a specific amount of time, you can use an inverter of any size, provided it can supply the required amount of power, without worrying about charging time.
Sometimes the charging method can also make a difference. For example, trickle charging uses a low current, which could require a smaller inverter, but comes at the expense of charging time.
Because trickle charging is used for maintaining a charge for long idle periods, it’s not a good way of fully charging the battery and can take several hours, if not days, to work.
If you’re using trickle charging, the inverter you need isn’t particularly powerful.
On the other hand, fast charging uses a high current in a short period. With fast charging, you can quickly charge your bike’s battery – sometimes in less than an hour – but it needs much power to manage that. That means you’d need an inverter with more power to charge your bike.
Fast charging saves you time, but it’s not recommended for most battery types since it can reduce lifespan.
Standard charging is something of a middle ground between these two. With standard charging, the current isn’t too high or too low. It takes longer than fast charging but not as much as trickle charging. It also doesn’t affect the battery’s lifespan too much.
The charging method you use can affect the required inverter size. For fast charging, a larger inverter is necessary, while for trickle charging, a smaller one may work. Standard charging will require something in between.
Surge capacity is what it sounds like—the capacity of an inverter to provide a brief burst of power. It is usually needed to start a device, and isn’t meant to be long-lasting.
When you plug in your e-bike charger, the inverter may need to send a surge of power to start it up before it settles into a more sustainable, lower-power mode. The inverter you choose should have enough surge capacity to start your battery charger. Otherwise, the battery won’t get charged at all.
Other Devices Being Powered
If you use your inverter to charge more than one device, whether just multiple bike batteries or other devices, get an inverter large enough for all of them.
We already went over the wattage requirement – add up the total wattage needed for all your devices, and that’s the amount of power your inverter should be able to supply.
Keep in mind other factors, though. Different devices and batteries may have different charger types, charging methods, and even surge capacities, so you’d have to account for all these things.
In general, it’s best to get an inverter with a higher output than the minimum you need, to ensure there’s enough to go around. It can also keep your devices and batteries safe from any potential damage.
While this has more to do with the physical size of the inverter, sometimes the portability is also an important aspect to keep in mind. This is especially true if you’re heading out to a place where you won’t have a traditional power output to charge your bike with.
In such cases, you want an inverter large enough to provide the energy needed to charge your bike but not so large that you have trouble carrying it around.
Choosing the right size inverter is important when picking one out for your bike’s battery. You don’t want to risk causing your battery damage by using one with the wrong output.
While you can use each of the points mentioned above to determine the minimum amount of power needed for your battery, it’s always a much easier option to ask the manufacturer about it, or simply use an inverter with a much higher power output than you need.
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