leitmotif
Member
In the Electrical Vehicle world the "big deal" is Battery Management (Monitor) System (BMS). As they discuss it is basically an undervoltage or overvoltage to prevent damage to Lithium Phosphate cells. Often the "solutions" are a board mounted to cell terminals that puts a shunting resistor across the cell. These often cost about $100 per cell - ballparking this it is about 1/2 cost for a circa 100 amp hour cell.
One of the critical factors of batteries is often overlooked - temperature of cells. I have seen Li cells that have swelled and theorize this is caused by overheating.
The state of charge is basically done by measuring current discharged or charged to battery. These modules often run about 3 to $500.
I wondered if I could beat the $100 per cell cost using a PLC. I looked at Automation Direct and a package to monitor 16 cells came out to about 50 per cell and with temperature monitoring 75 per cell.
So design parameters for 100 cells
1 Monitor cells for individual cell voltage
2. Monitor using shunts both battery current and motor current. In case of VFD and AC motor this may be done with a current signal provided by VFD.
3. Monitor total battery voltage
4. Monitor individual cell temperature
OUTPUTS
1. one or two for each cell to place one or two shunts across cell. I like two to give 3 levels of shunting. 200 outputs right there.
2. Display temperature and cell number on a panel meter. Possible alarm function 2 outputs
3. DIsplay battery and motor amperage. Possible alarm function 4 outputs
4. Display total voltage 1 output
5. Control signal to battery charger that would regulate battery charge voltage adjusted for temperature. one output
6 Control signal to charger to shut down charger when complete. one output
I think PLC can scan the inputs say temperature decide the high level and then dump that value and cell number to a buffer or temporary file which can be used to provide output.
Reason I like PLC for this
1. Well proven technology - dont have to write software
Customer would have to enter only his parameters to monitor his battery.
2. Eliminate the circuit cards bolted across cells make cleaning and maintenance easier.
3. Off shelf stuff widely available factory support.
4. PLC and other controls can be remotely mounted in passenger compartment to keep clean and out of rain road splash.
Downsides
expense - customer lack of familiarity AND expertise - environment problems such as vehicle vibration, temperature and humidity.
High traction battery bus voltage ie 325 VDC. This is not referanced to ground.
OK I need to hear from devil advocates on stuff I have not thought of and or why wont work.
Car parked for week (or??) - how do I avoid drain of 12V or 24V battery and avoid losing the program and customer inputted parameters. Same thought for disconnecting the battery.
I would also like recommendations on whose product to use - ideally 12 VDC but know 24 VDC will give more options so can accept 24 VDC.
Dan Bentler
One of the critical factors of batteries is often overlooked - temperature of cells. I have seen Li cells that have swelled and theorize this is caused by overheating.
The state of charge is basically done by measuring current discharged or charged to battery. These modules often run about 3 to $500.
I wondered if I could beat the $100 per cell cost using a PLC. I looked at Automation Direct and a package to monitor 16 cells came out to about 50 per cell and with temperature monitoring 75 per cell.
So design parameters for 100 cells
1 Monitor cells for individual cell voltage
2. Monitor using shunts both battery current and motor current. In case of VFD and AC motor this may be done with a current signal provided by VFD.
3. Monitor total battery voltage
4. Monitor individual cell temperature
OUTPUTS
1. one or two for each cell to place one or two shunts across cell. I like two to give 3 levels of shunting. 200 outputs right there.
2. Display temperature and cell number on a panel meter. Possible alarm function 2 outputs
3. DIsplay battery and motor amperage. Possible alarm function 4 outputs
4. Display total voltage 1 output
5. Control signal to battery charger that would regulate battery charge voltage adjusted for temperature. one output
6 Control signal to charger to shut down charger when complete. one output
I think PLC can scan the inputs say temperature decide the high level and then dump that value and cell number to a buffer or temporary file which can be used to provide output.
Reason I like PLC for this
1. Well proven technology - dont have to write software
Customer would have to enter only his parameters to monitor his battery.
2. Eliminate the circuit cards bolted across cells make cleaning and maintenance easier.
3. Off shelf stuff widely available factory support.
4. PLC and other controls can be remotely mounted in passenger compartment to keep clean and out of rain road splash.
Downsides
expense - customer lack of familiarity AND expertise - environment problems such as vehicle vibration, temperature and humidity.
High traction battery bus voltage ie 325 VDC. This is not referanced to ground.
OK I need to hear from devil advocates on stuff I have not thought of and or why wont work.
Car parked for week (or??) - how do I avoid drain of 12V or 24V battery and avoid losing the program and customer inputted parameters. Same thought for disconnecting the battery.
I would also like recommendations on whose product to use - ideally 12 VDC but know 24 VDC will give more options so can accept 24 VDC.
Dan Bentler
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