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Here are some photos of the final build of my Arduino BMS, fitted in the van. I'm quite pleased that I managed to squeeze all the electrics under the front passenger seats: 2x U27-12XP batteries, charge controller, battery protect, fuse box, inverter, RCDs, etc. The BMS code can be found here...

Final version of my Arduino BMS is now online, complete with schematic, stripboard layout, build photos, etc. https://github.com/seb303/Arduino-XP-BMS

I just created a github repository for my BMS... https://github.com/seb303/Arduino-XP-BMS Designed to provide monitoring of Valence XP batteries in order to: Keep the Valence internal BMS awake so the intra-module balancing is active. Provide a signal to a charge controller to disable charging...

The wake-up message sent by the BMS / Valence software is not battery specific, only the data read requests. And yes, it's certainly possible to make a simple BMS with a few £ worth of components. I have done exactly this: https://github.com/seb303/Arduino-XP-BMS

As you have assumed, you need an external BMS connected for the internal stats to update. In any proper commercial application, there would always be an external BMS used with these batteries; they are simply not designed to be used without one. If you got the batteries from a DIYer who wasn't...

Interesting tests, nice to get some confirmation of the internal hardware. Regarding top-balancing: yes, 100% sure, the bleed resistors will not activate unless the internal BMS is awake (LED flashing every 5 seconds). Sure, it's never completely asleep as it's flashing the status LED and...

You usually won't see the cells go out of balance much unless you are charging the batteries (or discharging them really low but try not to do this!). To get the cells balanced you should hold the higher charge voltage for a while with the internal BMS active. The internal intra-cell balancing...

To be fair, my device isn't just a keep alive tweak for the internal BMS. It's a functioning external BMS which can monitor multiple batteries and signal an external load disconnect relay and charger. Personally I prefer the idea of using theses batteries with the intended internal balance...

This doesn't seem to be the case (at least not most of the time). I am measuring 0.5mA on the RS485 5V wire regardless of whether the 2 batteries are asleep (20secs LED flash) or awake (5secs LED flash). The current usage jumps around a bit while the RS485 data is transmitting, so I stop the...

Been loving this thread, so much useful information about the XP batteries :) The guy I bought my batteries from said they only needed 5V on the RS485 connector to keep the internal BMS alive. As pointed out here, this isn't actually the case. Since I only have 2 parallel batteries in a...

Regarding inter-battery balancing for series setups: in theory the batteries have the capability to do this themselves without any extra hardware, using the internal bleed-off resistor banks. But it's unlikely we will be able to crack this without analysing the communications of the actual...

They look pretty well balanced to me, within 15mV. The internal intra-cell balancing will only activate when cell voltage is >= 3.36V *and* > 40mV above the lowest cell.

Yes, you could add a low temp cutoff to stop charging when very cold. But better if your charge controller has a sensor which can reduce the charging current say below 0C but only absolutely stop charging when say below -20C. If you search the code for OverTemperature and OT, you'll see the...

I presume he's saying that the voltage of half of the series pair is going out of balance with the other half? The total parallel voltage should not be able to differ unless the wiring is unbalanced. Peregrine, how are you wiring the batteries. Do you have the mid points of each series pair...

With series arrays you need to find a way to balance each part of the series string. The Valence batteries can do this internally, but it's hard to reverse engineer the serial comms to do this - would need access to the official Valance U-BMS hardware and a serial monitor/interceptor. As far...

Interesting. The diagram for the 4 channel balancer linked by Sycamore showed the midpoints connected, and I've also seen it recommended in other places. Like in this Victron PDF for example: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf (p21) I assumed connecting the...

I would have said 1 of these would work with the midpoints of the 3 strings connected, but Travis's experience suggests you need 3 of these balancers (1 for each 24V string in your 6 battery setup).

Thanks for spotting the bug! It is indeed ignoring the PCBA values. The temps[j] can stay as it is, only the if statement to fix. I did it like this: I'll upload the fix to github now... Cheers, Seb

Actually, this would probably be better: if (j < NumberOfCells) { In case of batteries with other numbers of cells.

I would have thought that where the current flows has more to do with the battery voltage rather than the internal resistance, and batteries in parallel will naturally keep their voltages in sync (assuming external wiring is balanced). If it works to run batteries in parallel to increase the...

It is an interesting question whether in a vehicle it might be better to power the external BMS from say the starter battery rather than the expensive LiFePO4s. And perhaps have a mode where the external BMS allows the internal BMS in the batteries to go to sleep if the voltage goes...

Should be easy enough to measure the power usage then ... I'll give it a try and report back.

Hi nickskethisniksk, There are a couple of bugs in the existing BMS.ino file so I'd recommend to wait a couple of days as some updates are coming. Yes, essentially there are 2 different baud rates used: 9600 to wake up the batteries when they are in storage mode, and 115200 for the main...

See point #13 here: https://diysolarforum.com/threads/valence-xp-super-thread.5683/#post-58455 Where it talks about 2/4-channel balancers

The Victron Battery Protect units will act as relays and require only a low current 12V signal, so should be able to run directly of the external BMS (I've no direct experience with the MIUSA-BMSLV though - I wrote my own BMS running on inexpensive Arduino hardware). You might be able to...

Understood. I'm sure the Nano is more than capable if you are using SPI comms. It's only the lack of a spare hardware UART which has me looking for alternatives. Reliable 115200 baud serial comms is an essential requirement for the Valence batteries. I know there are other hardware...

My charge controller's highest LiFePO4 setting is 14.6V. I believe it doesn't hold this voltage for longer than 1 hour per day though, falling back to 13.8V, and floating at 13.5V once it determines the batteries to be fully charged. I'll give this mode a go, and leave it for several days if...

Sure, I was just trying to design it to run on absolute minimum hardware :) But I've come to the conclusion it's a better idea to use a proper driver for the RS485. As you rightly say, it can be driven by any digital I/O pins from the Arduino, no need to use a hardware implemented serial port /...

Great, it seemed that it should. Time to dive into learning how to program these Arduino things then :)

I'm familiar with hobbies that get out of hand ;) I just PMed you a new version of the code. The output is cleaner and has different debug levels, so you can turn off the continuous status output for example. The EEPROM logging is also improved - it logs the battery data (V, T, SOC) only for...