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Archive for March, 2010

With the arrival of our Agni 95 series permanent magnet motor we began testing to see its performance at low currents. Nominally it should be able to handle 400 Amps and deliver 12 to 16 kW.

With a max efficiency of 90% at around 200 A the at least 80% of the range of operation will lie between 0 and 300 A.

Because such high voltages and currents are required to run the motor it can be quite difficult to test without a complete electric system that can sustain the required power. Furthermore, the battery system is not built yet so testing has so far only been completed on the small scale.

However, there is good news- it works. Three “no-load” tests have been performed to test the basic functionality of the motor controller in unison with the Agni motor.
Test 1 – 62 VDC, 2-3 A

Test 2 – 62 VDC, 2-3 A running at equivalent speed of 5.5 MPH

Test 3 – 4 12 VDC LiPo batteries in series. 48 V, 25 A

All three test showed that the motor and motor controller produced linear and smooth operation across its current range. The next steps will be to construct the battery system and run the motor at its full potential.

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With the arrival of the batteries, the beginning of the end for the electric system has started. The first design step for the accumulator was to arrange a battery array capable of powering our electric motor. The following photo displays this.

The batteries are arranged as six packs in series that are in four parallel sections.

The Zippy Flightmax 5S batteries consist of five 3.7 V Lithium Polymer batteries stacked together and wired in series, for a total voltage of 18.5 V. Four of these packs in series produce 74 Volts, well within the necessary range for the motor controller.

To produce the proper current, 6 of these 74V strings will be placed in parallel. The nominal current capacity of the system will be 30 Ah. The maximum continuous current rating of the Flightmax batteries is 25C, and in this configuration yields a maximum continuous current of 750 amps.

Usage of the batteries at this level is generally not recommended and greatly reduces battery life. Approximately one half this value, or 375 amps, is recommended for those wishing to maintain capacity for 100s of cycles. The Agni motor chosen can use at maximum 400 amps.

Battery casing is required to support the structure of the accumulator in addition to providing electrical isolation.

These acrylic cases will provide for these needs. Inside them 12 battery packs will be placed. They will be connected via solid copper bus bars capable of handling past 400 amps. After the system is set up it will be tested with the battery management system in addition to the charging system. In our next post we will discuss what the mechanical engineering team has done to fabricate a chassis from scratch.

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