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The batteries of the Whisper™ have been grouped to limit the possible danger in the event of inadvertent contact. The current configuration features four strings of seven Lithium-ion batteries, which are individually monitored and controlled. When deemed necessary by the operator or the e-Traction® Energy Management System, individual batteries or entire strings can be shut-down, without noticeably affecting the vehicle's performance. The e-Traction® Bus and the Whisper™ are each using 28 Lithium-Ion batteries from Valence Technologies. The e-Traction® Bus is using the 45 Ah U1 variety and the Whisper™ uses the 100 Ah U24. The batteries are grouped in strings of 7 and placed in closed containers that are air-conditioned. The individual batteries are supervised and managed with the same CANopen system that controls the other vehicle systems, such as the e-Traction® direct drive traction system and auxiliary power supply.
The air-conditioned container with 28 U1 batteries is placed right above the e-Traction® Bus APU. The initial version of The Whisper™ used, during its brief existence, 80 Ah Nickel-Zinc batteries with surprisingly disappointing results. As part of the search for a solution we have visited with various manufacturers and studied the benefits of the alternatives that were deemed technically viable and/or financially feasible. With an eye on cost containment, we also looked into future the mass production possibilities and anticipated future economies of scale. In the end a choice was made to develop a supply line for Lithium-Ion batteries.
The Whisper™ has two air-conditioned battery storage compartments. Placed on each side of the directly behind the rear axle. The combined these two containers, which can easily be removed with forklift equipment, weigh just 280 kg or 616 lbs. Saphion Technology Comparison
* Based on run time of 5 amp motor, cycles to 80% DOD and purchase price. Performance may vary depending on, but not limited to, the following conditions: installation and use, charging rate, depth of discharge, temperature.
Detailed Specifications (click for link to manufacturer specifications)
Lithium-ion batteries and Safety (click for link to research document) Fundamental properties of lithium iron phosphate, the core of Valence’s SAPHION® technology make for an intrinsically safe cathode material for lithium ion applications currently available. When fully charged, no excess lithium is left in the cathode (unlike LiCoO2 where 50% still remains). The Redox voltage is low enough to ensure no electrolyte decomposition occurs. The company has also demonstrated that this material has a high resilience to oxygen loss, which would otherwise result in a significant exothermic event upon heating. Furthermore, Valence’s polymer technology provides a system with no free electrolyte, unlike the commercially available liquid based batteries, thereby further adding to its safety characteristics. |
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