Individual Battery Monitoring

Instrumentation for Improved Electric Vehicle Performance

*** Beta Units now available! ***

Voltage Measurement Box Specifications:

Batteries Measured: 15
Resolution: 10 bits on every module (~.015V/LSB for 15V max)
Accuracy: Worst Case +/- .10 volts, Typically +/- .02 volts
Update Time: Measures all batteries 4 times per second
Weight: 642g (lightweight packaging possible for high-performance vehicles)
Dimensions: 2.6" x 4.2" x 6"
Limit Output: [Optional] One line pulled low when any one module exceeds a threshold (15 volts)
Data Output: RS232 Serial data to LCD screen via standard DB9 connector

Display Box Specifications:

Screen Size: 4 X 20 backlit LCD display
Resolution: Individual bar graph for each battery (32 bars high, .1875 V/bar)
Scaling: 9V (min) to 15V (max)
Refresh Rate: Same as measurement rate, all batteries 4 times per second
Weight: 384g
Dimensions: 2" x 3.2" x 5.175"

Why Monitor Each Battery?

 Benefits While Driving

This battery monitor is able to give you an excellent "situational awarness" of how the battery pack is performing. Quite often, one or two modules have a capacity that is far lower than the average. These modules will become discharged first yet the driver will continue on until reaching the expected amphour capacity of the full pack. This may reverse the polarity on the weak batteries, further damaging them, and yield reduced performance and low efficiency of the pack as a whole. It is also very difficult to diagnose this problem and find the batteries that are causing trouble. In an extreme case, the low battery may pose a safety hazard and can overheat, vent, or even catch fire.


The battery monitor provides a visual graph of how each module is doing. As you accelerate, you can watch the battery voltages under load to see which ones sag the most and very quickly identify weak batteries. Combined with an E-meter, you can determine exactly the amphour capacity of the pack before the weakest module falls to an unacceptably low level. The monitor will also prevent you from ever unknowingly reversing the polarity on a module. You can easily drive less aggressively as a weak battery "shows up" to keep it's voltage positive.


Benefits While Charging

The battery monitor is also helpful while charging. You can quickly observe how well the pack is balanced and notice which modules reach full voltage first. This is also the easiest way to see if your charging system is working properly or if any modules are being overcharged. It is convenient to adjust the charge current based on individual battery voltages instead of just the total pack voltage. You can always be sure that you are not damaging your expensive sealed batteries.


How it Works

Voltage Measurement

Electronics: The battery measurement box has a connector with a voltage tap from the positive terminal of every battery in the pack. It also has a connection to the pack ground (Bat-). Inside the box, these voltages are scaled down in a precision resistor divider network. Then a microprocessor controls a bank of multiplexers to "pick off" the signals that correspond to the positive and negative of one module. These two signals are then sent through an instrumentation amplifier circuit and feed into an analog to digital converter. The microprocessor then takes the digital data, configures it to read as a set of bar graphs, and sends it out as isolated RS-232 formatted data to the LCD display. The operation of the measurement box is very intuitive and is essentially taking a digital voltmeter and placing it across each battery in the pack in rapid succession. This would be impossible for a person to do since the voltmeter is only connected to each battery for about .02 seconds before moving to the next battery.

Box Connector: The connector used on the outside of the box is a locking AMP circular plastic connector (CPC). This variety is extremely robust and rated to handle the high battery input voltages. The box is completely enclosed and relatively water resistant. However, it should only be mounted in a protected area of the vehicle where it can not be exposed to rain, dirt, or road spray.

Graphing Display: The LCD display has a small circuit board attached to it and accepts serial data directly from the measurement box. This serial communication is through a standard straight-through DB9 cable. The information is in RS-232, UART format. As already mentioned, each battery has its own column that is up to 32 bars high.

Wiring the Battery Monitor

In order for the measurement box to read the battery voltages, one wire needs to be brought from the positive terminal of each battery in the pack and the one wire from the pack ground. These wires MUST be fused near where they are connected to each battery. Nothing more than a 100 mA fast fuse is needed. This is imperative to protect the wire bundle and the box from shorts and a serious potential fire hazard. These wires all come together into one locking connector on the battery box.

For more information on installation and wiring read or download the installation guide:
(The guide is in MS Word 2000 format)
Installation Guide

How do I Get One?

The 3rd generation of this system is now in limited Beta production. The monitor is being used in several different types of EV's with both sealed lead acid batteries and Nickle Zinc batteries.

This is currently the only affordable, ready-to-use, graphical monitor available to the EV community. This system is useful in just about any EV from a neighborhood electric vehicle at 48 volts to an electric dragster at 400 volts. The ability to watch each battery is particulary useful in high-power and high-voltage systems using sealed batteries such as the Optima or the Exide Orbital.

The price for a complete monitor system while in Beta Production is now $400 (plus tax and shipping)
This includes both the measurement and display boxes, a standard DB9 cable to connect them, and a connector with pig tail wires to mate with the measurement box. The user only needs to splice the wires together or use suitable butt crimp connectors.
If you are interested in using this product to improve your EV instrumentation, please send me an e-mail with your vehicle type, the voltage you are using, and the battery type and configuration. Contact Me

 

Home Page | Electric Porsche | Electric Bike | Hybrid Trailer v2.0
Contact Me

Hits since Aug-16-03


Site Last Updated On: Aug/16/2003

Photos by: Felicia Zimmermann

403578