Battery charging solutions offer EV roadside assistance

Article By : Bill Schweber

Three battery charging solutions address EV driver anxiety by developing portable units for roadside emergencies.

One of the issues that proponents of electric vehicles (EVs) worry about—whether actual or potential purchasers—is the possibility of running low and then out of sufficient battery charge. That is the equivalent of running out of gas with an internal combustion engine (ICE)-based vehicle, or both gas and electrons for a hybrid electric vehicle (HEV).

There is no comparably convenient solution to the “out of fuel” problem for EVs, at least not until recently. What’s missing, in colloquial terms, is the equivalent portable “can of electrons.” Given the concerns and realities of low EV-battery reserve energy while on the road, I was intrigued when I saw this partial-recharge system from SparkCharge.

SparkCharge has developed a portable unit that is built up of battery modules using the common 18650-format cylindrical lithium-ion (Li-ion) cells—the same cells used in the Tesla Model S and Model X. The battery modules can be stacked physically and electrically to increase energy-storage capacity, and are connected to a single charger module (Figure 1). The company also claims a refill rate of about a mile per minute.

annotated diagram of the SparkCharge system of stackable battery modulesFigure 1 The SparkCharge system uses a set of stackable modules for the energy-storage batteries as well as for their charger. Source: SparkCharge

Portable EV charger

The charger module supports a maximum continuous 40-A output at 500V. The DC fast charging complies with the CHAdeMO standard while the combined charging standard (CCS) compatibility is planned for a later stage. The key specifications are:

  • 20 kW DC charger (9 kg) with CHAdeMO or CCS combo plug is coming
  • Single module (22 kg): 3.5 kWh (3.2 kWh usable) and 159 Wh/kg (145 Wh/kg usable)
  • Battery modules can be recharged using traditional 110V or 220V household outlets
  • Up to five modules:
    • One module (22 kg): 3.5 kWh (3.2 kWh usable) for 14-15 miles of range
    • Two modules (44 kg): 7 kWh (6.4 kWh usable) for 28-30 miles of range
    • Three modules (66 kg): 10.5 kWh (9.6 kWh usable) for 42-45 miles of range
    • Four modules (88 kg): 14 kWh (12.8 kWh usable) for 56-60 miles of range
    • Five modules (110 kg): 17.5 kWh (16 kWh usable) for 70-75 miles of range

photo of the SparkCharge unit in the back of a roadside-service vehicleFigure 2 By allowing uses to set the modularity, the SparkCharge unit can fit the available space in roadside-service vehicles, which also must carry lots of other spares and tools. Source: SparkCharge

The product is designed to be carried by a standard roadside-service truck, the one that also carries gas cans, a battery booster, and tire changing gear. The company is partnering with local roadside operations, including the well-known AAA network in some localities.

SparkCharge is not the only innovator to realize that there’s a need for charging of EVs away from formal charging stations. FreeWire Technologies has unveiled the Mobi EV Charger, a Level 2 AC and DC fast-charging station on wheels to be used in place of conventional charging stations in contrast to fixed-in-place roadside emergencies (Figure 3).

photo of the Mobi EV ChargerFigure 3 The Mobi EV Charger targets on-site portability rather than roadside support. Source: FreeWire Technologies

Likewise, Lightning eMotors, formerly Lightning Systems, has a mobile charging system mounted in a towed trailer or self-contained van, targeting large commercial trucks and buses (Figure 4). All three of these systems are battery-powered; they do not use gasoline-powered or similar generators internally. Of course, they do need to be recharged somewhere and somehow when not in use.

illustration of how the Lightning eMotors mobile charging system fits into a vanFigure 4 This mobile charging system is designed to fit into a van or be towed on a trailer behind a small truck. Source: Lightning eMotors

Design issues and tradeoffs

I won’t offer an opinion about SparkCharge’s business model or their financial prospects, as there are plenty of pundits and analysts out there who will do that. What I’d like to know more about, however, are the electrical and mechanical design issues and tradeoffs they faced. Unfortunately, the available collateral on that is non-existent. I do like the aspect of having the power modules themselves snap together for fairly simple boost in total battery capacity and energy storage.

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It allows the unit to be tailored to the available space in the service vehicle and also decouples recharging the battery units from the travel unit; it is somewhat analogous to families of power tools with their interchangeable rechargeable battery packs. I do wonder how the gradations in the number of battery modules and thus stored energy in use affect components such as connectors as well as different thresholds of regulatory approvals.

What’s your view on the technical challenges facing this approach to bringing “electrons in a can” to a stranded EV? What would you like to see as a solution? What changes would you make or features would you add or eliminate, if you could? Your comments and feedback on these issues are welcome.

This article was originally published on EDN.

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.

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