EV managment module
Posted: Wed Aug 13, 2008 2:18 pm
I have been working on a BMS system for use with my new Li-ion cells fitted to my Fiat 126. The car is using a Agni 95 turn PM DC motor with a Kelly KD72401 controller that gives regenerative braking. While looking for options for a BMS system I found, among others, Reap systems 14 cell boards and Cedric Lynch's cell controllers, also available from the Agni motors website. Reap's BMS is a top-end product, highly recommended with a price tag to match! Cedric's cell protectors would have to be modified to suit the lower operating voltages of these cells, but he is working on a new design that will work with the greater range of cells coming onto the market.
I decided to see what was available "off the shelf" and found that BMS boards are available for e-bikes that have the correct voltage settings for my cells. These BMS boards connect between the negative terminal of the battery pack and the controller as well as the charger. They simply shut-off the pack if they encounter a low or high voltage condition. This brings 2 problems for use in a car.
1. They can't handle the higher currents of a car, all the current goes through the BMS board.
2. They shut off with no warning, not a problem in a bike, you just pedal but not good in a car unless your name is Fred Flinstone!
Problem 1 can be addressed with a simple relay, problem 2 requires something a bit cleverer. The systems mentioned above use a PWM signal to reduce power output gradually. What I have done is come up with a system that will sound a audible alarm and warning light if cell voltages get low and start a 15 second timer before shutting down the motor/controller completely. So it will rely on the driver to reduce throttle when the batteries are getting low, and as long as the driver was the one who signed the cheque for the batteries it should work fairly well.
I have found a programmable controller made by a company called http://www.splatco.com. Their controllers will work on 12 or 24 vdc. I am using their CC16 controller. It has 16 pins that can be configured for either inputs or outputs. They also do other controllers that can drive LCD displays and have analogue inputs, etc..
I originally bought this to use as a speed limiter for my Volvo as it has some counter functions built in. Haven't gotten around to doing that yet, but I still have a couple of spare inputs, so it could possibly be added to this project. I am calling this a EV Management System as I am not directly measuring the Li-ion cells but using the measurements taken from the cells by separate boards as well as inputs from the rest of the vehicle to control when the vehicle can be driven or charged. This set-up should be able to use Peter's slave boards which have the advantage that because they are individual boards, they could be independently calibrated. It should also be possible to use this system without the battery monitoring, so that for example the car can't be driven while still plugged in!
The actual program will be in the following post. I have only done very limited testing with the simulation software provided. There may still be bugs that I haven't found. This is still very much a work in progress.
Any thoughts, suggestions, comments greatly appreciated, although due to time constraints it may sometimes take me a while to respond.
Greg Fordyce
I decided to see what was available "off the shelf" and found that BMS boards are available for e-bikes that have the correct voltage settings for my cells. These BMS boards connect between the negative terminal of the battery pack and the controller as well as the charger. They simply shut-off the pack if they encounter a low or high voltage condition. This brings 2 problems for use in a car.
1. They can't handle the higher currents of a car, all the current goes through the BMS board.
2. They shut off with no warning, not a problem in a bike, you just pedal but not good in a car unless your name is Fred Flinstone!
Problem 1 can be addressed with a simple relay, problem 2 requires something a bit cleverer. The systems mentioned above use a PWM signal to reduce power output gradually. What I have done is come up with a system that will sound a audible alarm and warning light if cell voltages get low and start a 15 second timer before shutting down the motor/controller completely. So it will rely on the driver to reduce throttle when the batteries are getting low, and as long as the driver was the one who signed the cheque for the batteries it should work fairly well.
I have found a programmable controller made by a company called http://www.splatco.com. Their controllers will work on 12 or 24 vdc. I am using their CC16 controller. It has 16 pins that can be configured for either inputs or outputs. They also do other controllers that can drive LCD displays and have analogue inputs, etc..
I originally bought this to use as a speed limiter for my Volvo as it has some counter functions built in. Haven't gotten around to doing that yet, but I still have a couple of spare inputs, so it could possibly be added to this project. I am calling this a EV Management System as I am not directly measuring the Li-ion cells but using the measurements taken from the cells by separate boards as well as inputs from the rest of the vehicle to control when the vehicle can be driven or charged. This set-up should be able to use Peter's slave boards which have the advantage that because they are individual boards, they could be independently calibrated. It should also be possible to use this system without the battery monitoring, so that for example the car can't be driven while still plugged in!
The actual program will be in the following post. I have only done very limited testing with the simulation software provided. There may still be bugs that I haven't found. This is still very much a work in progress.
Any thoughts, suggestions, comments greatly appreciated, although due to time constraints it may sometimes take me a while to respond.
Greg Fordyce