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

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...

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

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

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...

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...

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...

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.

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...

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...

Technically the RS485 spec is A-/B+ (= logic 1), but common RS485 chips such as the MAX481/MAX483/MAX485/MAX487–MAX491/MAX1487 have it the other way round in their datasheets, hence why many adapter boards are labelled the other way round.

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 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...

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).

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 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...

It's not necessarily bad for the controller to have the batteries removed while still connected to PV. You need to check the no-load voltage spec of your panels and compare this to the maximum voltage spec of your controller. I'm no expert on large PV systems, but for an RV system I would have...

You don't need to place a relay between your panels and charge controller. To protect against over-charging/over-voltage you would put a relay between the charge controller and the batteries. Or if your charge controller supports it, directly signal it from the BMS to stop charging in an...

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...

Well I could if the batteries weren't already bolted into a tight little space under my passenger seat :) But it's pretty clear from the current measurements that in normal operation, the internal BMS is not being powered from the RS485 5V line. The fact that the internal BMS stays active for...

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...

Just added a couple of new features: Now reads Current from the batteries, and logs to EEPROM if a battery triggers a status change. Added a new console command: "debug 2 <n>" https://github.com/seb303/Arduino-XP-BMS

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...

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

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...

That's a fair point. While the UV shutdown will disconnect almost all loads, my external BMS will still be powered, using I guess around 20mA (I should measure it and check!) Plus the internal BMSs in the batteries will remain active - I don't know how much power these consume. I'll up my...

Thanks for the advice. I'll change my shutdown threshold to 3.9V, as I wouldn't want it to shut down the charger during the process of cell balancing. The warning is only an indicator, so I'll probably leave at 3.6V for now, just out of interest to see whether it hits this level with normal...

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...

I just fixed a potentially serious buffer overflow bug so please download again if you already downloaded... 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...

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...

Actually thinking about your setup of 20 batteries, it would probably be better to log only the values of the 1 battery which triggered the change of status. Otherwise the EEPROM is going to get used up pretty quick....

That's a fairly sizeable setup you have there :) I'm running only 2 batteries, just enough to power the 12V and small inverter of a campervan. About the output mess: it's on my to do list to make the debug output neater and more compact. I also noticed that when my new code logs the battery...