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Topic: Battery Pack, individual cell voltage measurement (Read 4 times) previous topic - next topic

phoyt

Hello,

I need to be able to monitor the individual cell voltages within a pack of 45 lithium cells. Each cell's voltage woud range between 2.5 and 4.0 VDC. I've read that I could use my Arduinio Mega to monitor voltage up to 5 VDC but that measurement depends on a connection to ground.

Obviously, to measure the voltage of one cell in the middle of the pack, I can't measure between a cell terminal and ground.

So are there any options that I can use with an arduino to measure individual cell voltage?

Ideally, I'll want monitor all 45 cells and stop charging the pack when any one of the cells hits a preset voltage.

Thanks,
Pete

retrolefty


phoyt

Yes, the pack is normally kept between 134 and 151 VDC. This is the traction pack on an Electric Vehicle.

I have an off-the-shelf battery management system installed but it is failing and I can't afford to replace it.

Thanks,
Pete

Graynomad

#3
Nov 30, 2012, 06:29 am Last Edit: Nov 30, 2012, 06:38 am by Graynomad Reason: 1
There are many ways involving relays, muxes etc but my preferred method would be to use 45 small processors each powered from the cell being measured and with an isolated serial link.

I stress that I haven't actually done this yet so there may be a gotcha, but I do have what I think is a workable idea I plan to build up soon.

_____
Rob
Rob Gray aka the GRAYnomad www.robgray.com

phoyt

Since I'm more of a software than hardware person, I'm unsure how to even get started with this idea. But currently have 46 wires running from each of the 45 cells, to a junction box full of terminal strips where the current Battery Managment System (BMS) is housed. I'm hoping that anything I can come up with, can be used with those existing wires because they were put in place during the build of my EV and it is not practical to run new wires at all.

The current BMS monitors individual cells and exchanges information between each of those 45 monitoring circuits and in theory, the first cell to reach 3.65 volts, should shut down the charging system. It seems to be starting to fail or feeling the effects of some other problem. So I'm hoping to use an Arduino to monitor all of the cell voltages and apply the appropriate logic to determine when a charge cycle must be terminated. I've got a LOT of money in the batteries and will do just about anything to make sure they last as long as possible. At the moment, I'm manually monitering each charge because I don't trust the BMS or the charger to cut off charging at the right time.

I'd LOVE to find something like the digital temperature sensors that I used with the Arduino. They all share the same +5 power source and they all share the same data line to the Arduino. They are individually addressed and are polled individually, ever few seconds. Based on that information, I'm switching on and off 6 solid state relays connected to heating elements in the boxes. It actually uses a product called FlexiWatt to provide the heat. That is a product used to warm reptiles in pet stores or at home.

Somehow, I don't think this is going to be easy.  :smiley-eek:

Peter

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