Good day.
Hoping there are still some smart folks around here with experience in the weirder setups.

I have recently upgraded from my Victron Multiplus II 3000/48/35 system to a Deye 12kWh hybrid inverter. Installer was full of confidence that the BYD battery will work, no problem!

However, problem.

Seems the BMU CAN comms are not ayoba with the Deye inverter.

If hooked up "correctly" (batteries daisy chained, highest address goes to BMU, BMU goes to inverter) , then battery shuts down when mains fails (or turned of for testing). Which is not very helpful.

Installer swears it needs a firmware upgrade. I kinda suspect the inverter is not doing the needed keep-a-live signal, but what do I know. Maybe all of the above.

After support calls to BYD(?) (by the installer), they apparently can't do it (on which I call bullshit, but whatever).

BYD (or anointed support outfit) can apparently come out and do a firmware upgrade though. Have not asked about costs of THAT yet.

FWIW, the previous installer (that did the Victron/BYD system) upgraded the firmware of the battery modules some years back. So I know it is possible. I also know BYD is not exactly forthcoming with firmware+tools for this battery model, so that maybe does say something. I found an 2019 update bundle from a random AU site after MUCH digging.

Anyway, the installer got the battery working by bypassing the BMU, and setting 2/3 of the battery module addresses to 0, and the one that has Ethernet cable going to inverter to 1.
This feels shaky for me. But again, what do I know.

So the questions:
1. Anybody here got experience / advice with a similar setup? Deye with older BYD battery models (circa 2017-2021)

2. Any thoughts/concerns on running the battery as described? Photos can be supplied if needed.

Things SEEM to be working ok, but since I can't actually SEE the CAN-supplied data, I can't really verify either way.

Thanks in advance.

PS: if anybody has a link to an archive of BYD Battery-Box firmware updates and tools... don't be shy?

Edited June 17Jun 17 by demaniak

As a follow up, I can already say that what I THOUGHT would happen, does seem to be happening.
Since there is no coordinating BMS between the battery modules, it looks like the SOC of each module (as shown by the LED indicators) are not in sync.
The oldest module seems to be consistently "behind" in terms of charge, as self reported.

On 2026/06/21 at 9:00 PM, demaniak said:

As a follow up, I can already say that what I THOUGHT would happen, does seem to be happening.
Since there is no coordinating BMS between the battery modules, it looks like the SOC of each module (as shown by the LED indicators) are not in sync.
The oldest module seems to be consistently "behind" in terms of charge, as self reported.

How are the batteries connected to the inverter - through a busbar, or with cable going from one battery to the next? (thinking that if one cable is longer than the others it could result in under-charging...)

Also, were these batteries all fully charged/balanced individually before connecting them to the inverter? (if not, then it is possible that the less charged battery will progressively become even less charged, as the inverter could stop the charging when the first battery signals that it is fully charged...)

On 2026/06/17 at 8:20 PM, demaniak said:

... Things SEEM to be working ok, but since I can't actually SEE the CAN-supplied data, I can't really verify either way.

I'm not sure if the Deye's software is similar to that of the Sunsynk (I do believe it is...), but if it is then you could download *some* battery data (more than displayed on the inverter screen or software. I discuss the process here: https://powerforum.co.za/topic/34104-finding-and-understanding-the-sunsynk-operation-data/

I can unfortunately not advise directly, as I do not know this battery - but I hope that someone can help you.

Thank you for the reply @HennieL

As far as I'm aware and can see, the batteries were installed in the cabinet according to the manual ( https://www.manualslib.com/manual/1482649/Byd-B-Box-2-5.html?page=6#manual ) - so busbar, then up to inverter.
Have kept an eye on the battery SOC LEDS over the last week or so - it does SEEM like all modules reach full charge (just not when the inverter reckons it is 100% - at that point, batteries are usually still taking as much PV as can be provided). And the oldest module is perhaps struggling a bit more than the newer ones - might simply be seeing effects of age ☹️

I do still believe the inverter's idea of SOC and the real SOC is not always aligned, meaning any inverter setting that is based on SOC is kinda a hit and miss situation.

Will also try a cable that I made up that cuts out pins 1 and 2 (RS485), as I got this weird idea that might be a source of confusion for the inverter. Or the battery?
The battery BMU DOES have RS485 capability on that rj45 socket (as well as CANbus), but afaik that is only to enable firmware updates (in the times when updates were still available). But since the inverter apparently can also talk RS485 via the comms port - I'm suspecting it does not like what it finds on the BMU side when it tries. Or the battery does not like what IT sees there. I will see when I try my cable. If nothing else, that will eliminate one potential source of trouble.

I will take a look at your linked thread, thanks :)

Edited 10 hours ago10 hr by demaniak

Hi @demaniak

With 3× older BYD 2.5 modules 7.7 kWh at 0.5C, you’re limited to roughly 3.8 kW continuous charge/discharge.

The 12kW Deye is too big for this bank it pulls hard on grid failure and trips the BMS.

Recommended settings:

• Set battery to Voltage mode (not SOC)

• Max charge current: 70–75A

• Max discharge current: 70–75A

• Discharge stop: ~48–49V

• Charge end: ~54–55V

This should stop the shutdowns.

Long term you’ll need more storage capacity for a 12kW inverter that can charge and discharge at 240A 12.3 KW

1 hour ago, Powerforum Store said:

Hi @demaniak

With 3× older BYD 2.5 modules 7.7 kWh at 0.5C, you’re limited to roughly 3.8 kW continuous charge/discharge.

The 12kW Deye is too big for this bank it pulls hard on grid failure and trips the BMS.

Recommended settings:

• Set battery to Voltage mode (not SOC)

• Max charge current: 70–75A

• Max discharge current: 70–75A

• Discharge stop: ~48–49V

• Charge end: ~54–55V

This should stop the shutdowns.

Long term you’ll need more storage capacity for a 12kW inverter that can charge and discharge at 240A 12.3 KW

Thanks.
Yeah, aware of the size-problem.

This is an inflight, phased upgrade - battery is slotted as the last piece to be replaced (probably with something on the 16kWh spectrum).

Luckily load shedding is now a SOLVED problem for ever and will never "darken" our doorways again. Right? Right??

Max charge/discharge has been pegged lower than suggested settings.

I HOPE they Deye is smart enough to shutdown if higher demands come in while islanding.

I'll look into the voltage mode - as the manual says, there are gotchas with voltage mode to watch out for (esp with LiFion batts), but I hear you about that.
The damn installer dodged questions/suggestions about V mode - the more I think about it, the more I believe they actually know very little outside their very specific recipe (hardware/config).

thanks again.

3 minutes ago, demaniak said:

Thanks.
Yeah, aware of the size-problem.

This is an inflight, phased upgrade - battery is slotted as the last piece to be replaced (probably with something on the 16kWh spectrum).

Luckily load shedding is now a SOLVED problem for ever and will never "darken" our doorways again. Right? Right??

Max charge/discharge has been pegged lower than suggested settings.

I HOPE they Deye is smart enough to shutdown if higher demands come in while islanding.

I'll look into the voltage mode - as the manual says, there are gotchas with voltage mode to watch out for (esp with LiFion batts), but I hear you about that.
The damn installer dodged questions/suggestions about V mode - the more I think about it, the more I believe they actually know very little outside their very specific recipe (hardware/config).

thanks again.

Great news

Voltage mode will work fine without risk of damage and I am sure the Deye will keep loads at bay until you can make a plan on the battery these new 16KW batteries are pretty impressive and there are a few decent units under different brands available I am busy testing the Hubble AM16+ and its pretty decent there are other solid brands like the Kynee that we are also getting great feedback and will be reviewing soon and the New Pylontech Fidus is IP65 and also seems like a solid unit have not tested it yet but hope to soon.

Typically installers know the products they punt and not always interested in things outside of their realm of what they know.

Regards

"I do still believe the inverter's idea of SOC and the real SOC is not always aligned, meaning any inverter setting that is based on SOC is kinda a hit and miss situation."

This is perhaps the case on most inverters as most will be using voltage and not measure energy via a shunt if comms are not used and voltage settings.

I am wondering about the statement that the Deye might not adhere to the maximum load when in island mode. I would guess the 12kW calculates the same as the 5kW. My 5kW is set to only provide 4kW load and can confirm that it has switched of about 3 times when the setting is exceeded.

My experience is not applicable to the batteries you have but see no reason why not to run in voltage mode until you got the upgrade with other batteries and going back to using comms.

I am running 4 battery banks on voltage mode and they have their own BMS for the protection/balancing features. 2 are DIY.

Use the inverter SOC only as a guidance and not if you want to say use 20-100% of the battery. My inverter will report over 50% most mornings but it does not concern me even if the real SOC is 35 or 65%.

Edited 4 hours ago4 hr by Scorp007

2 hours ago, Powerforum Store said:

I am busy testing the Hubble AM16+

I am actually following that thread with interest :)

The Hubble AM16+ is currently looking like very good value for money.

The local support angle makes it even more attractive - BYD really screwed me over on that front.

Edited 4 hours ago4 hr by demaniak

7 minutes ago, Scorp007 said:

"I do still believe the inverter's idea of SOC and the real SOC is not always aligned, meaning any inverter setting that is based on SOC is kinda a hit and miss situation."

This is perhaps the case on most inverters as most will be using voltage and not measure energy via a shunt if comms are not used and voltage settings.

I am wondering about the statement that the Deye might not adhere to the maximum load when in island mode. I would guess the 12kW calculates the same as the 5kW. My 5kW is set to only provide 4kW load and can confirm that it has switched of about 3 times when the setting is exceeded.

My experience is not applicable to the batteries you have but see no reason why not to run in voltage mode until you got the upgrade with other batteries and going back to using comms.

I am running 4 battery banks on voltage mode and they have their own BMS for the protection/balancing features. 2 are DIY.

Use the inverter SOC only as a guidance and not if you want to say use 20-100% of the battery. My inverter will report over 50% most mornings but it does not concern me even if the real SOC is 35 or 65%.

The 1 bothersome thing with voltage mode is that the "time of use" settings on the Deye then get even more miffy, due to the very flat discharge curve of lifion batts.
But ok, all of this is temporary, until I get to that part of the upgrade. So as long as the batteries remain protected,then that is ok (well, built-in BMSes should prevent actual disaster at least).

3 hours ago, demaniak said:

The 1 bothersome thing with voltage mode is that the "time of use" settings on the Deye then get even more miffy, due to the very flat discharge curve of lifion batts.
But ok, all of this is temporary, until I get to that part of the upgrade. So as long as the batteries remain protected,then that is ok (well, built-in BMSes should prevent actual disaster at least).

I am very happy that the inverter keeps my voltage level spot on during time of use activated. Been using it for 17 months.

I am also off grid most of the time. I do switch the grid on via a timer after 4h00 just to always have some battery capacity.

I thus use as little as 100-300wh grid during the 4h to 8h30 period. Most day even in winter no grid even in this morning period. Only when thick clouds during the day like we had the last month do I switch grid on at other times but only if needed.