LiFeP04 Batteries for Solar & BMS

[Living Large]

Unfortunately all the BMS systems are intended to Top Balance. However they do everything required for Bottom Balancing. Trick is you just program Top Balancing out or defeat it.

Spoke with a few user groups who Bottom Balance on the Robot side of the house. Are you open to Arduino? Real simple to do and most of it has already been done so no circuit design or code writing. Takes three circuit boards, a display, and some fabrication. Then dump the code in. Dirt cheap!

The thought occurred to me that it may be possible to disable top balancing. Since you aren't working with dumb boards, that makes sense. Great.

I have seen references to Arduino, and haven't looked into it. Seems the time has come. I think Jack mentioned it in the video. Clue me in - how would Arduino fit in here? Would it be an interface to the BMS, or something else? I'm seeing RS-232 as part of Aduino, but I saw no other interface at a glance - would that be the communication with one of these BMSs?

[Sunking]

The thought occurred to me that it may be possible to disable top balancing. Since you aren't working with dumb boards, that makes sense. Great.

I have seen references to Arduino, and haven't looked into it. Seems the time has come. I think Jack mentioned it in the video. Clue me in - how would Arduino fit in here? Would it be an interface to the BMS, or something else? I'm seeing RS-232 - would that be the communication with the BMS?

Arduino is a family of circuit boards used by Robotis and Electronic Hobbyist to do about anything you want. They are a family micro controllers and what they call Shield boards. The controllers have up to 54 digital inputs and 20 Analog inputs. You right code to process what they do with the input information. The Shields are various I/O interfaces for WiFi, Bluetooth, USB and Display. I have used them to make a 8 channel RC remote control using a computer joystick. It is all Open Source Code and Circuit Designs. Literally hundreds of user groups to make anything you want. Think of it like Linux.

For voltage you just use a A/D converter for 0 to 5 volts and it converts it to 10 bit number from 0 = 0 volts and 1023 = 5 volts and input it into one of the digital inputs. Do that 16 times for each cell. Then write the code to do what you want to do with with it like switch a output when the voltage goes to 2.7 volts for more than 15 seconds is you LVD control. Another code line to through another output if any input goes to3.7 volts your charger disconnect. Then the code to drive a Display anything you want based on the inputs to a LCD screen.

Custom BMS to your likes at half the cost of a commercial unit.

[Living Large]

Arduino is a family of circuit boards used by Robotis and Electronic Hobbyist to do about anything you want. They are a family micro controllers and what they call Shield boards. The controllers have up to 54 digital inputs and 20 Analog inputs. You right code to process what they do with the input information. The Shields are various I/O interfaces for WiFi, Bluetooth, USB and Display. I have used them to make a 8 channel RC remote control using a computer joystick. It is all Open Source Code and Circuit Designs. Literally hundreds of user groups to make anything you want. Think of it like Linux.

For voltage you just use a A/D converter for 0 to 5 volts and it converts it to 10 bit number from 0 = 0 volts and 1023 = 5 volts and input it into one of the digital inputs. Do that 16 times for each cell. Then write the code to do what you want to do with with it like switch a output when the voltage goes to 2.7 volts for more than 15 seconds is you LVD control. Another code line to through another output if any input goes to3.7 volts your charger disconnect. Then the code to drive a Display anything you want based on the inputs to a LCD screen.

Custom BMS to your likes at half the cost of a commercial unit.

Oh. Ok. I was thinking of an interface to the BMS, to program it and display parameters. It's possible that could be done, but you appear to be saying DIY BMS for our LFP bank, since we know what actions we want to do based on voltage (not really an accurate statement since we need to account for sags under load). I like your thinking. And there won't be any top balancing to disable.

One bit would be 0.005V, which works, assuming there is accuracy across channels. You could calibrate that with a table though, if necessary. Of the top, it sounds like a definite candidate. The challenge would be integrating with the rest of the system, I suppose.

One bit would

[Sunking]

Oh. Ok. I was thinking of an interface to the BMS, to program it and display parameters. It's possible that could be done, but you appear to be saying DIY BMS for our LFP bank, since we know what actions we want to do based on voltage (not really an accurate statement since we need to account for sags under load). I like your thinking. And there won't be any top balancing to disable.

One bit would be 0.005V, which works, assuming there is accuracy across channels. You could calibrate that with a table though, if necessary. Of the top, it sounds like a definite candidate. The challenge would be integrating with the rest of the system, I suppose.

One bit would

Accuracy as I understand it is completely dependent on the 5 volt supply. There is a Forum called Endless-Sphere a E-Bike enthusiast group. Over there there are two threads running. One is an Arduino BMS that sound slike a commercial product development, but anyone can get into the action and buy a test unit. If you can help with development they will sale it to you at cost. Sounds like a Chi-Com manufacture ripped them off already and beat them to market. Since it is open source not squat they can do about it. The have all the code and schematics right there to be downloaded so anyone can copy. Might be a bit more work that I am willing to put into it.

The other thread is using a CellLog charger. That is a RC Hobby Charger and can charge or do anything with up to 8 cells, so it would take two of them for a 16S pack. I have something similar but is called an iCharger.

There are lots of ways to skin this cat. Might even be a biz to be born for Bottom Balancess since no commercial product exist. Everything is built around Top Balance.

As you can tell I am kind of all over the place with it evolving. Perhaps we can work together on a common goal. You want RE, I want EV. Really makes no difference what the application is.

[Mike90250]

Once the weakest (lowest capacity cell) has been located, is it possible / reliable to use it as a pilot cell to monitor the battery pack, and have it control LVD and 90% full charging ? Spending a couple hours for the initial set up, and a monthly verification that the chosen cell is still the weakest, would eliminate a rats nest of wires and fuses and a couple handfuls of questionable quality BMS sensor board, thereby increasing the overall system reliability ?

[Sunking]

Once the weakest (lowest capacity cell) has been located, is it possible / reliable to use it as a pilot cell to monitor the battery pack, and have it control LVD and 90% full charging ?

On paper yes Mike. But would you be willing to bet $2500 to $15,000 on it? Intially assuming you correctly dead nuts bottom balanced to 0% it would be the one weak cell driving the train.

Spending a couple hours for the initial set up, and a monthly verification that the chosen cell is still the weakest, would eliminate a rats nest of wires and fuses and a couple handfuls of questionable quality BMS sensor board, thereby increasing the overall system reliability ?

OK fair point, wrong picture in your minds eye. If you Bottom Balance, then you eliminate the boards on each cell unless you want to monitor temperature. For RE applications temperature is not needed because the charge and discharge currents are so low there would be no heating issues. EV is another story coupled with the elements.

Rats nest well depends on how you look at. For a 48 volt 16S pack all you need is a 16 wire ribbon cable running right across the top of the pack breaking one wire out at each cell. One wire connected between each cell to monitor voltage of each cell. In addition to that you would need a pair of small gauge power wire from the batteries to power the BMS. Keep in mind the inter-cell connections are not wire and lugs like you use on lead acid. LFP uses buss bars. So all you have is a neatly placed ribbon cable running across the tops of the batteries neatly secured and dressed in. IMO or my eye is a work of art, not a Rats Nest.

Does this look like a rats nest even with the Balance Boards?

[Living Large]

Once the weakest (lowest capacity cell) has been located, is it possible / reliable to use it as a pilot cell to monitor the battery pack, and have it control LVD and 90% full charging ? Spending a couple hours for the initial set up, and a monthly verification that the chosen cell is still the weakest, would eliminate a rats nest of wires and fuses and a couple handfuls of questionable quality BMS sensor board, thereby increasing the overall system reliability ?

This is a very interesting suggestion. But what happens if one of the other cells kicks the bucket at some point, and you aren't monitoring it?

As for the questionable quality BMS boards, with the Arduino you wouldn't have it - you would have 17 wires. Having done digital circuit design and construction, I'd willingly go the hobbyist route. Dereck won me over with bottom balancing, so I would seek to not use shunts. I am *guessing* that some of the BMS units listed at the site above do not have individual boards, but I could be wrong. I agree with you that eliminating boards across your expensive cells would be desirable. If it is just a sensor and not a shunt I would feel better about failure modes.

[Living Large]

Accuracy as I understand it is completely dependent on the 5 volt supply. There is a Forum called Endless-Sphere a E-Bike enthusiast group. Over there there are two threads running. One is an Arduino BMS that sound slike a commercial product development, but anyone can get into the action and buy a test unit. If you can help with development they will sale it to you at cost. Sounds like a Chi-Com manufacture ripped them off already and beat them to market. Since it is open source not squat they can do about it. The have all the code and schematics right there to be downloaded so anyone can copy. Might be a bit more work that I am willing to put into it.

I spent some time looking at the Arduino BMS link. For the BMS, he's using a TI BQ76PL536A chip, which handles 6 cells. Can be stacked using more chips up to 192. Surface mount device with 64 pins... maybe more work than I would be willing to invest at my old age. It does LVD and HVD for each cell, has a "Pack" level alert as well, 2 temperature sensors, and optionally does balancing if you add external FETs. Communicates via a SPI interface, which the Arduino has.

This is an example of the building block needed to do just what you suggest. One or more of the devices in the list at the link you provided might have 3 of these or similar chips in it and be ready to go. Wouldn't it be great if you could connect an off the shelf device with the front end to an Arduino, to minimize the amount of work? I just scratched the surface, but this looks very promising.

[Sunking]

I spent some time looking at the Arduino BMS link. For the BMS, he's using a TI BQ76PL536A chip, which handles 6 cells. Can be stacked using more chips up to 192. Surface mount device with 64 pins... maybe more work than I would be willing to invest at my old age. It does LVD and HVD for each cell, has a "Pack" level alert as well, 2 temperature sensors, and optionally does balancing if you add external FETs. Communicates via a SPI interface, which the Arduino has.

This is an example of the building block needed to do just what you suggest. One or more of the devices in the list at the link you provided might have 3 of these or similar chips in it and be ready to go. Wouldn't it be great if you could connect an off the shelf device with the front end to an Arduino, to minimize the amount of work? I just scratched the surface, but this looks very promising.

I think the reason they use the TI chip is for the A/D converters and its precision 5 volt supply. If you were to use the Arduino you would have to use A/D converters of some sort for the Arduino to work with

[Living Large]

I think the reason they use the TI chip is for the A/D converters and its precision 5 volt supply. If you were to use the Arduino you would have to use A/D converters of some sort for the Arduino to work with

I need to do more looking at the various links you gave. Basically, I was envisioning an A/D interface, monitored by the Arduino. For some reason, as I looked at the TI datasheet, my mind lept past the custom development boards they are using (because I didn't like the thought of dealing with SMD) to thinking that one of these off the shelf BMSs would have the TI or similar part in it, and would perform the function of the custom board. And I could link to the Arduino via SPI. Maybe that is not possible - because hey, why would they be making their own A/D interface? I've never worked with a SPI, and it's very possible they are not meant to go from discrete unit to discrete unit, but rather on the same circuit board or boards mounted close together in the same box. You can see I've just scratched the surface, not familiar with pretty much any of the building blocks. I'm trying to run with the right shoe on the left foot and visa versa.

[Sunking]

I'm trying to run with the right shoe on the left foot and visa versa.

You are not alone. Myself I am just going to go with the Orion Jr as I know it will do what I want. I just will not use the Top Balance feature it has built-in which eliminates balance boards. That is the difference between active and passive Top Balance. Tight now my cart has passive Balance Boards. 16 independent boards that do not communicate with anything. They are in their own little world oblivious to anything around them. They turn on at 3.65 volts, and turn off at 3.55 volts. That is all they know.

[Living Large]

You are not alone. Myself I am just going to go with the Orion Jr as I know it will do what I want. I just will not use the Top Balance feature it has built-in which eliminates balance boards. That is the difference between active and passive Top Balance. Tight now my cart has passive Balance Boards. 16 independent boards that do not communicate with anything. They are in their own little world oblivious to anything around them. They turn on at 3.65 volts, and turn off at 3.55 volts. That is all they know.

Back to the starting gate. Your cart has individual boards, and they are passive. The Orion Jr advertises that it has "integrated passive balancing," but there are no external cell boards. For some reason I was going to guess the Orion would be "active".

Seems like this product would do what I would want for the PV system we have discussed, and your bottom balancing scenario. It is programmed via RS-232 and a PC, and I notice it draws 1.2W typical (nice). Has a battery backup. My expectation would be the PC can be disconnected and this runs autonomously.

Here is the advertised list of inputs and outputs:

-2 digital signal outputs for controlling charge and discharge limiting mechanisms
-1 digital signal output for controlling a battery charger
-1 CANBUS 2.0B interface [optional] (both standard and extended IDs supported)
-1 digital RS-232 interface for programming and diagnostics
-2 multi-purpose outputs with software assignable functions
-1 multi-purpose input with software assignable functions
-3 analog 0-5v outputs that represent the following signals: Charge Current Limit (CCL), Discharge Current Limit (DCL), State of Charge (SOC).
-2 thermistor inputs (additional monitoring possible with thermistor expansion module)

These "digital" outputs - do you think this means logic high and logic low? The voltage swing appears to be the battery bank voltage, which is a little surprising. EDIT I found the wiring manual, which says the outputs are open drain, which is why they go to the PS voltage.

Between the digital and the two multi-purpose outputs, do you think LVD and HVD for a PV system can be implemented? EDIT I sent Orion's manufacturer a question of if voltage above/below a threshold can be detected and control outputs.

Based on the description of Columb counting, would you expect that the SOC function on this is accurate, compared with the "meters" built into some equipment? Orion has its own optional meter, but with the analog output you could make your own or just use a multimeter.

Would the CCL and DCL functions be used, in your opinion? We've been focusing on voltage.

EDIT One thing I don't see is if there are timers to allow for voltage sags to avoid false tripping a LVD.

At a glance, this looks like a good candidate. All that would be left is determining how to interface it to the actual system.

[Sunking]

Back to the starting gate. Your cart has individual boards, and they are passive. The Orion Jr advertises that it has "integrated passive balancing," but there are no external cell boards. For some reason I was going to guess the Orion would be "active".

Seems like this product would do what I would want for the PV system we have discussed, and your bottom balancing scenario. It is programmed via RS-232 and a PC, and I notice it draws 1.2W typical (nice). Has a battery backup. My expectation would be the PC can be disconnected and this runs autonomously.

Here is the advertised list of inputs and outputs:

-2 digital signal outputs for controlling charge and discharge limiting mechanisms
-1 digital signal output for controlling a battery charger
-1 CANBUS 2.0B interface [optional] (both standard and extended IDs supported)
-1 digital RS-232 interface for programming and diagnostics
-2 multi-purpose outputs with software assignable functions
-1 multi-purpose input with software assignable functions
-3 analog 0-5v outputs that represent the following signals: Charge Current Limit (CCL), Discharge Current Limit (DCL), State of Charge (SOC).
-2 thermistor inputs (additional monitoring possible with thermistor expansion module)

These "digital" outputs - do you think this means logic high and logic low? The voltage swing appears to be the battery bank voltage, which is a little surprising. EDIT I found the wiring manual, which says the outputs are open drain, which is why they go to the PS voltage.

Between the digital and the two multi-purpose outputs, do you think LVD and HVD for a PV system can be implemented? EDIT I sent Orion's manufacturer a question of if voltage above/below a threshold can be detected and control outputs.

Based on the description of Columb counting, would you expect that the SOC function on this is accurate, compared with the "meters" built into some equipment? Orion has its own optional meter, but with the analog output you could make your own or just use a multimeter.

Would the CCL and DCL functions be used, in your opinion? We've been focusing on voltage.

EDIT One thing I don't see is if there are timers to allow for voltage sags to avoid false tripping a LVD.

At a glance, this looks like a good candidate. All that would be left is determining how to interface it to the actual system.

LL I am going to put you in contact with a sales rep for Orion products. He is a avid DIY EV guy. Not a Bottom Balancer, but he knows all about it and how to make the unit work This takes me out of the middle. Send me a PM with your e-mail address please.

[Living Large]

LL I am going to put you in contact with a sales rep for Orion products. He is a avid DIY EV guy. Not a Bottom Balancer, but he knows all about it and how to make the unit work This takes me out of the middle. Send me a PM with your e-mail address please.

Dereck, I received an email back from Chris Ewert. Good news:

"Yes, absolutely. That is a core feature of the Orion Jr BMS. There is
an output called "Discharge Enable" and one called "Charge Enable".
Those outputs turn on if everything is OK, and turn off if any one cell
drops below the min. cell voltage, or goes above the max. cell voltage
respectively."

I'll email you my address, so I can ask further questions. Thanks a lot.

[Sunking]

Dereck, I received an email back from Chris Ewert. Good news:

"Yes, absolutely. That is a core feature of the Orion Jr BMS. There is
an output called "Discharge Enable" and one called "Charge Enable".
Those outputs turn on if everything is OK, and turn off if any one cell
drops below the min. cell voltage, or goes above the max. cell voltage
respectively."

I'll email you my address, so I can ask further questions. Thanks a lot.

Can LVD be done on time delay? Say 2.6 volts if greater than 15 seconds? Check your email and PM