Choosing the Right Charger for Your EV Fleet (part 1)

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Camber Team

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While selecting a charger for a single vehicle can be tricky, designing an entire charging infrastructure for a commercial fleet can feel like a huge challenge. As commercial fleet electrification moves from pilot projects to full scale conversion of fleets, facilities and fleet operators need to charge hundreds of vehicles instead of just one or two. To meet this rising need, charger manufacturers are beginning to offer various types of chargers with different power levels and numbers of charge points. Commercial vehicles typically have large batteries that need to be charged in a shorter amount of time than your average passenger vehicle. Therefore, most commercial vehicles are designed to use Direct-Current Fast Charging (DCFC or DC), which can charge a vehicle much faster than a residential AC-Level 1 or AC-Level 2 charger. 

In this first article on selecting the right charger, we will go over three main factors to consider when selecting a DCFC charger for commercial vehicles: Vehicle Specifications, Fleet Operation and Charge Times. 

  1. Vehicle Specifications

The first step in selecting a charger is finding the maximum power level the vehicle can accept. Specifying a power higher than this limit often leads to oversizing the charger and all the associated electrical upstream infrastructure. Oversizing gets expensive, and may add to project timelines as the utility needs to bring more power to the site than is needed. 

The maximum power a vehicle can accept can be calculated by the formula:

PM=VBIM / 1000

Where,

PM = Maximum Power Vehicle Can Accept (in kW)

VB = Maximum Voltage of Battery (in Volts) 

IM = Maximum Current Vehicle Can Accept (in Amps)

Do not let the equation scare you away! The vehicle OEM should have all this information at the ready with the vehicle specifications. (They should also be able to tell you the maximum charge rate, but it is always worth confirming.)

For this example, assume the vehicle has a battery voltage of 500V and has a maximum current rating of 200A:

VB = Maximum Voltage of Battery, 500V

IM = Maximum Current Vehicle Can Accept, 200A

Therefore, the maximum power can be represented by:

PM=500V*200A / 1000

PM=100kW 

In this example the maximum amount of power the vehicle can receive is 100kW. Even if a higher power charger is installed, the most power the vehicle would ever draw is 100kW. If a lower power charger is installed, the vehicle would be limited by the power output of the charger. Battery voltage and maximum charging current are limits set by the vehicle manufacturer to ensure the health and operation of the battery pack. It should be noted that the actual maximum power draw typically occurs at around 90% of the battery’s maximum voltage. From 90% to 100% battery voltage, the battery’s management system often reduces the amount of current allowed into the battery to protect battery health and increase the longevity of the battery cells. 

  1. Fleet Operation

A commercial fleet’s usage and operating schedule can vary widely among industries and uses. It is important for fleet planners to understand when a vehicle can charge, and how long it needs to charge to be ready for the next shift. Charging can only occur when a vehicle is parked and not in use. Therefore, a fleet operator must help create a charging schedule that dictates when the vehicles charge, where they charge, and for how long, in order to meet the energy demands of the shift. 

Charge windows are often dictated by shift operation, or whenever there is a significant amount of downtime or “dwell” for the vehicle. Since the maximum charge rate is dictated by the vehicle, the amount of time the vehicle needs to recharge is determined by the amount of energy used. 

In ideal circumstances, there is more than enough downtime for the vehicle to fully replenish the battery before the next shift. Having a charge window that is longer than the time needed to recharge the battery allows for more flexibility in fleet operation, as well as the opportunity to reduce charger power, or implement a charging schedule. A reduction in charger power, or a smart charging schedule can reduce site electrical demand and save on energy costs.

If, however, the charge window is shorter than the recharge time, or the vehicle’s battery capacity is too small for a full shift of operation, opportunity charging may be required. In opportunity charging scenarios, a high-powered charger is used for a short period of time in order to replenish battery energy as fast as possible. These can be on-route options or specific chargers with a depot. 

One additional consideration for fleet operation is the ambient conditions in which the fleet is operating. In very cold climates, battery energy is used to heat the battery packs and the vehicle’s cabin, reducing the amount of available energy for vehicle operation. Preconditioning allows the battery to be recharged while the vehicle is heating the battery and cabin to ensure there is enough onboard energy for vehicle operation.

In our next post, we’ll cover Charge Times and how it all comes together! 

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