In today's post we'll help you decide which battery choice is the best fit for your DIY electric vehicle project. Navigating the world of voltages, amps, and capacities can be confusing, so let's break it down to make your decision easier.
Key takeaways:
- More Ah = More range!
- Match battery voltage with controller/motor to prevent damage.
- Amps (A) = Acceleration.
- Use Watt-Hours to estimate potential distance.
- Ensure battery size/shape suits your needs.
- Choose batteries with a reliable Battery Management System (BMS).
- Match controller's amp demands for safety.
Voltage (V): Your EV's Electrical Flow
Most DIY projects generally operate in the 36V-110V range. Common builds lean towards 48V, 52V, 60V, or 72V setups. Higher than 72V often means turning to custom battery builds.
What Battery Should I Get to Match My Controller and Motor (or Vice Versa)?
Your controller dictates the maximum amps drawn from your battery. This is why you would want a battery that matches with the controller or vice versa, and ideally matches your motor's rated voltage too.
Let's say you have a controller rated for 48V. If your controller is designed for 48V, putting a 72V battery into the system could cause severe damage to the controller, regardless of the motor's potential tolerances.
While some EV enthusiasts slightly overvolt their controller for performance gains, you would have to make sure you can run your controller on these higher voltages either out of the box, or with some modifications as its your controller that ultimately sets the hard limit. For motors you would need adequate cooling to get away with substantially overvolting it past its limits, for example; to be able to run a 48v motor anything over lets say 60 volts, you would need to start looking at very good cooling setups so you don't fry your hall sensors or worse, burn your phase wires or coil windings. That would be a disaster!
Its usually capacitor voltage ratings within your controller that determines this limiting factor, you can get a away with running a 52v battery with a 48v controller because your controllers capacitors will be rated at least 25% higher than your battery it is rated for.
Feel free leave a comment on this post if you have any confusions!
What Size Battery Will I Need: Why Watt-hours is King
Watt-hours (Wh) is the true indicator of how far your battery can take you. To calculate this figure, multiply your battery's voltage by its amp-hour rating (Voltage x Ah = Wh).
Think in terms of "Watt hours per Mile": Find out how much power your EV consumes at your preferred cruising speed. You can get a rough estimate of this by multiplying your battery voltage by your controllers rated current limit/draw. eg "48volt battery x 30 amp controller = 1500w (full throttle)" This calculation will help you gauge the battery size needed for your desired range.
For Example: If traveling at 15mph uses 500 watts constantly, a 1000Wh battery pack gets you 30 miles, regardless of voltage.
Amps (A) & Capacity (Ah): Power & Range Explained
- Amperage (A): Amps are the power behind your EV. This figure directly influences how much power your motor can produce, dictating acceleration and peak output.
- Ensure your battery can meet your controller's peak amp demands: Your battery needs to be up to the task of supplying the amps your controller might request. An inadequate battery could become damaged, or worse, overheat, potentially risking thermal runaway wh. A well-built battery's internal BMS will protect it from these dangers.
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Capacity (Ah): Imagine amp-hours (Ah) as the size of your EV's 'gas tank'. A higher Ah rating typically gives you extended range before needing a recharge.
Power: The Driving Force
The true performance metric to target is power (measured in watts). Watts emerge from voltage multiplied by amps (Voltage x Amps = Watts). Aiming for high watts unlocks stronger performance and higher top speeds. Remember, voltage has a major influence – many motors gain speed capabilities as voltage increases.
Think about your priorities:
- Do you crave raw power or are you focused on maximizing range?
- Can you accept the weight and cost of a high-performance battery, or do you need a more practical setup?
- Most importantly, does your battery physically fit within the constraints of your EV design?
Safety First: Batteries store substantial energy. Always prioritize packs equipped with reliable Battery Management Systems (BMS) that protect against overheating and other potential hazards.