Electric Car CANbus project

Hi All,

Wanted to get a few thoughts before I make a purchase.

I have built an electric Mazda RX8 (see below link) and I'm looking to add rapid charging.

to manage the communication between the car and the chademo charging station I need to build a device that reads in battery parameters in analogue form and squirts them back out in canbus. Parameters would be things such as voltage (0-350vdc), current (0-1000A), temperature etc.

I'd also be interested (in the future) in reading in parameters from my motor controller (continuous udp log stream over Ethernet/RJ45) and also display all this data on a ~7" screen located in the satnav housing.

No-one seems to have a way of reading up to 350v DC safely.

Any recommendations or pointers?

Cheers,

Mike

Welcome to the forum Mike.

I'm guessing you are using Lithium chemistry as the primary battery source, is this correct?

Normally, you only measure the voltage of each cell in your battery pack, using a board such as this BMS12 from Zeva.

Zeva is here in Australia and the small company operator has converted a number of vehicles including an RX7.

The guy there, Ian Hooper is very helpful and seems knowledgeable in both electronics and electric vehicle conversions. He even converted a mobility chair which is able to perform wheel-stands.

The BMS12 board is a CAN bus board and you can set the CAN address of each board thus allowing you to string a series of these boards together.

The board offers programable settings for each cell, for example, under volts, over volts and the balancing threshold.

I've looked into using this board for a different situation, my off-grid renewable energy system, where I am installing 400Ahr at 25.6 volts of Winston Yittrium LiFeYPO4 cells.

I have an Arduino DUE which has CAN bus already built in, and just needed to buy a a few little CAN bus transceiver boards.

The DUE will be CAN bus master and communicate with the BMS12 to get and set data.

Is it possible that you use such an idea to get the voltage reading you need?
Then for the current sensing, you can use a number of methods, but for being able to read up to 1000Amps, maybe a good sized current shunt with an op-amp to feed back into the system, via CAN bus.

I use hall effect sensors, but in the order of 50 to 100 Amps, and so these won't cut it in your case.

I started to have a read of the thread, and can (no pun) see it details many things over many pages.


Paul

Thanks Paul,

We are using LiFePO4 (98* Sinopoly 100AH cells), 3.5v max charge voltage and 3.34v open circuit voltage.

We do not use a cell level BMS. We have a lot of R&D in that area and haven't seen it as necessary.

I found this: rechargecar.com which seems like it ticks most of the boxes for me.

I just need a way of reading voltage accurately and safely and I think I can order and start coding.