Switched ADC BMS

[johu]

Finally got around to some more BMS testing, now with two modules, i.e. the configuration that kept blowing up back in London. With the opto coupler armada the problem seems solved. Restarted around 20 times and it never smoked.

I did hook up one module completely the wrong way around. It seems this killed the upper two channels, they show too low readings. Will replace the mosfets and see. Apart from that no damage.

[Sector7e]

I'm considering using 112 LiFePO4 batteries in my 96 Nissan Hardbody 4x4 Leaf swap. Is there a limit to the number of cells this can manage, or would I be able to utilize 7 boards for my BMS? Will these be available in the openinverter.org shop when you finalize the design?

[johu]

By design there isn't a limit, only the CAN bus bandwidth. The software currently limits to 6 modules but that is easily extended.
I've done all tests that I'm currently capable of and have done a minor design change that isn't super critical. Before selling larger quantities I'd wait for feedback from a few projects.

[Proton]

@johu

I would like to order one and test it on my solar system. How do you monitor it? can you connect it to a computer?

[johu]

It's got CAN comms. Will write out some specs on the wiki soon. Spoiler: you can query individual and accumulated cell voltage data via CAN SDO. The most important stuff is always on the bus.

[Proton]

I have no clue how to work with can yet. there is any tool I can use for that?

[Sector7e]

By design there isn't a limit, only the CAN bus bandwidth. The software currently limits to 6 modules but that is easily extended.
I've done all tests that I'm currently capable of and have done a minor design change that isn't super critical. Before selling larger quantities I'd wait for feedback from a few projects.

I'd be willing to be an early adopter with my 112 cell battery pack. Where would I order 7 when the latest revision is ready?

[Jacobsmess]

I'm yet to begin my EV conversion pathway BUT I do have possibly 240 7ah 12V lead acid batteries I'm configuring into some home storage and I'm wondering, would this be an option for balancing and monitoring of these? I'll be wiring them in 4S10P banks so 48V and 70ah and up to 6 banks depending on how many of them are in good health.

[johu]

Put the BMS up for sale, "early adopters edition": https://openinverter.org/shop/index.php ... duct_id=74

[Proton]

Put the BMS up for sale, "early adopters edition": https://openinverter.org/shop/index.php ... duct_id=74

I tried to order one but the shipping is $47. do you have a different shipping method?

[johu]

I tried to order one but the shipping is $47. do you have a different shipping method?

Ah yes that is the super duper insured shipping. The smallest parcel is 12€. I think it has no insurance so if it's lost, it's lost...
You can order with the current shipping and I'll just refund the difference via paypal

I also started a wiki page: https://openinverter.org/wiki/16-cell_BMS

[Proton]

I just ordered it. yes please do the cheaper shipping method.

[Sector7e]

I'll order when there is a quantity* of at least 7 available.

[0tik]

Do I understand this correctly? BMS in itself can't control contactors as in it doesn't have overvoltage/undervoltage output signal?
>Keep BMS running even with car shut off if a lot of balancing is needed (on ESS applications the BMS runs 24/7 anyway
Perhaps you could make your BMS manage OEM chargers(over canbus) or make it compatible with openinverter board.
OIBoard have pin19 for BMS input, but that's for shutting down inverter, not a charger.
PS. Adding https://openinverter.org/wiki/16-cell_BMS to shop page of BMS could be helpful.

[SciroccoEV]

Do I understand this correctly? BMS in itself can't control contactors

Having the BMS control contactors is generally a bad idea because disconnecting the battery under load is a good way of killing inverters.

You can get away with it in low power aplications, like power tools (they generally use MOSfets to connect/disconnect the battery) and in fact it's very common to do it that way as the tool/charger were often designed for other battery chemistries and having the battery just drop in is a real advantage.

Really the BMS should be just sending out data to the inverter/charger and they will adjust the demanded/supplied current.

There is an argument for letting the BMS open contactors if cell parameters go significantly outside normal range, especially a large overcurrent.

[0tik]

I do know that battery shouldn't be disconnected under load. I'm wondering how to integrate this BMS with BrainBoard, it's charging mode or/and any external charger like the one from outlander or volt.
I did read paragraph "Calculating current limits" but that still doesn't clear the question if it communicates with BrainBoard out of the box or not.

[johu]

No, not out of the box. The CAN mapping needs to be set up on the inverter side for idcmin and idcmax
For chargers the info will need translation via VCU or custom mapping on the BMS side

[EV_Builder]

Having the BMS control contactors is generally a bad idea because disconnecting the battery under load is a good way of killing inverters.

You can get away with it in low power aplications, like power tools (they generally use MOSfets to connect/disconnect the battery) and in fact it's very common to do it that way as the tool/charger were often designed for other battery chemistries and having the battery just drop in is a real advantage.

Really the BMS should be just sending out data to the inverter/charger and they will adjust the demanded/supplied current.

There is an argument for letting the BMS open contactors if cell parameters go significantly outside normal range, especially a large overcurrent.

It's about who knows what and who is responsible for what.
The BMS often also knows current of the pack. So it knows when opening the coils isn't a good idea.

In the end it's a safety feature todo it correctly BMS announces it wants to open and when conditions are met it can and should open.

[0tik]

Alright. Dio I understand it right? So what I have to do is to open spot values in web interface. Find idcmin. Set values as
CAN id 0x12C
position 0000
Bits 000A
Gain 0001
RX

Then for idcmax
CAN id 0x12C
position 000A
Bits 000A
Gain 0001
RX

On the BMS side charge/dischargelim is managed by your magic code vaguely described here https://openinverter.org/wiki/16-cell_BMS (Operation - Calculating current limits)
Now a new mystery unveiled once i got so far... BMS can set idcmin/max to 0 once cell voltage reaches 3/4.2V But once voltages bounce back... What changes my idcmin/max back to their values set by me? Do BMS change idcmin/max to 0 right when it hits limits or is it a gradual change? (A limp mode at preset voltage would be a good idea.) Since BMS doesn't recieve idcmin/max from the Brainboard i bet it can't do it in a smart way.

[johu]

I received a new batch of BMSes and they will become available in the shop soon. I will sell a few more as with the "early adopters" discount then will raise the price to something viable.

Apart from that there is still some discrepancy between channel 0, 1 and 15 compared to the other 13 channels. I.e. channels 2-14 will measure the exact same voltage when applying a known input, channel 0 reads 5 mV too high, channel 1 reads 5 mV too low and channel 15 7 mV too low. This is down to different transistors being used on the lower two channels and to an extra load resistor being switched in for channel 15.

I have now decided to compensate this in software where a correction factor can be entered for these 3 channels. It defaults to something I have measured here.

[Proton]

I received a new batch of BMSes and they will become available in the shop soon. I will sell a few more as with the "early adopters" discount then will raise the price to something viable.

Trying to connect to the Openinverter BMS and start using it.
Do you still recommend inno-maker.com/product/usb2can-cable/ for connection to the BMS? or there are any other tools that I can use for CAN?

[JaniK]

Hi, I had shop tab for BMS in browser waiting for right time to order but now realized shop says product not found, is the early adopter version gone now?

[johu]

Trying to connect to the Openinverter BMS and start using it.
Do you still recommend inno-maker.com/product/usb2can-cable/ for connection to the BMS? or there are any other tools that I can use for CAN?

Sorry, missed that. I don't have much experience with bridges, just make sure it will work with oic / python CAN

[johu]

Some more BMS content

[johu]

Alright. Dio I understand it right? So what I have to do is to open spot values in web interface. Find idcmin. Set values as
CAN id 0x12C
position 0000
Bits 000A
Gain 0001
RX

Then for idcmax
CAN id 0x12C
position 000A
Bits 000A
Gain 0001
RX

Yes. I changed those to 11 bits now, see wiki to allow up to 2000 A.

On the BMS side charge/dischargelim is managed by your magic code vaguely described here https://openinverter.org/wiki/16-cell_BMS (Operation - Calculating current limits)
Now a new mystery unveiled once i got so far... BMS can set idcmin/max to 0 once cell voltage reaches 3/4.2V But once voltages bounce back... What changes my idcmin/max back to their values set by me? Do BMS change idcmin/max to 0 right when it hits limits or is it a gradual change? (A limp mode at preset voltage would be a good idea.) Since BMS doesn't recieve idcmin/max from the Brainboard i bet it can't do it in a smart way.

The BMS does a simple P-controller, so as you approach min/max it gradually limits. So if you draw less current your cells will sag less and you've essentially got a limp mode. Leaf BMS does it in the same way, so this should work.

I have worked on the software today, now also one of the temperature sensors per module is evaluated on the master. Evaluated means min and max are found, so now we can do current limiting based on that.
I also distribute global average cell voltage and idc to the sub modules so they know when it is appropriate to balance and to which value.
Also changed the CAN mapping a bit.
The number of cells on each module is queried via SDO at startup to be able to calculate total voltage from average.