Creating An Experimental Electric Car At Home by Craig Moore

Author:Craig Moore [Moore, Craig]
Language: eng
Format: epub
Published: 2016-01-29T23:00:00+00:00

Battery Discharge Timer and Fuel Gauge Sending Device for electric vehicles.

Intended for use in GM cars with a resistive fuel gauge sender which is operated by a float in the gas tank. The circuit replaces the sending unit in the tank which is removed with the tank.

The circuit is a variable rate timer and fuel gauge sender. Since it is impossible to look inside a battery and to determine the exact state of charge, this circuit provides a reasonably accurate estimate of remaining battery charge by closely matching the discharge rate of the battery. The circuit is powered by the motor power battery which is the same battery that is being monitored. The timer self corrects itself by running faster or slower depending on the voltage of the battery while under load. A comparator constantly compares the unregulated battery voltage with the regulated voltage that powers the timer. The circuit has only 5 wires. Red (motor power battery positive) and green (motor power battery negative) power the circuit with 96 volts to 124 volts. White with red stripe connects to the ignition wire or a key switch that supplies 12 VDC from the 12v accessory battery. Black wire with white stripe connects to chassis ground. The blue wire connects to the car's fuel gauge sending wire which supplies 5vdc. This last wire is usually purple and was connected to the original fuel gauge sender in the gas tank. The printed circuit board is marked to indicated the wire connections previously described. As the timer progresses, the fuel gauge inside the car will indicated F or, E and all points in between. The rate of the timer can be adjusted with potentiometer RV3 to either extend the time or shorten it. This adjustment is necessary the first time that the circuit is used.

When the timer is adjusted properly, the fuel gauge on the dash will indicate full when the battery has been fully charged and empty when there are a few miles left out of the full range of the vehicle. After charging, the timer is reset automatically when the power cord to the charger is pulled. This is why it is recommended to fully charge the battery each time. A partial charge will reset the timer to indicate full but the gauge will move more quickly toward the empty side of the gauge as the charge is depleted.

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