kirs-ten-henson avatar image
kirs-ten-henson asked

Pylontech battery and Multiplus showing different SOC

Hi, I have on off-grid system with 3x Pylontech US2000C batteries and a Multiplus II 48/5000/70. I believe I have set up the system such that the Multiplus BMS overrides the battery BMS. I have manually set the charging limits advised by Victron ie absorption 52V, float 51V through the VictronConnect App

Currently the Pylontech batteries indicate a charge of 100% at 52.2V.

However, the Mulitplus shows a SOC of only 67.5%. The sun is shining and no charge is being pushed into the batteries, they are reading idle.

This appears to be okay for the batteries but I am unclear as to why the SOC reading is so different between the Multiplus and the battery BMS.

In addition, the smart solar indicator light suggests it is in absorption mode, however when I check on the victronconnect app the system never records an absorption nor a float phase.

I am new to all of this and have been playing with settings and reading docs for a while now, so any help (in language for beginners) very welcome!

Multiplus-IIbattery chargingPylontech
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

kirs-ten-henson avatar image kirs-ten-henson commented ·

Somew screenshots of data readings from today...not sure if this helps figure out what I've got wrong here?

screenshot-27.png screenshot-28.png

0 Likes 0 ·
screenshot-27.png (93.9 KiB)
screenshot-28.png (142.8 KiB)
kirs-ten-henson avatar image kirs-ten-henson kirs-ten-henson commented ·
0 Likes 0 ·
1 Answer
nickdb avatar image
nickdb answered ·

Why would you want to not use the battery bms?

The multi does not have a bms, it has an internal meter, one that does not "see" the power flows from the solar chargers so it is always inacurate.

A basic search here will show many articles on this topic.

It is not supported to run in this way and it will affect your warranty, so please follow the pylon setup guide properly.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Alexandra avatar image Alexandra ♦ commented ·

Do you have a GX and are using the Pylontec to control the system?

1 Like 1 ·
kirs-ten-henson avatar image kirs-ten-henson Alexandra ♦ commented ·

I have the Multiplus II GX, so yes I have a GX. I had understood that I should use this to control the system rather than the Pylontech BMS- is that not correct?

0 Likes 0 ·
kirs-ten-henson avatar image kirs-ten-henson commented ·

I thought I had read somewhere that the Multiplus should be used instead of the battery BMS. But I have read and reread so many different things I am no doubt very confused!

For the battery monitor in settings I can select either the Multiplus on VE Bus or Pylontech battery on CanBus or automatic. I currently have the Multiplus selected. Is this correct?

Just to note that I have DVCC switched on and settings as per this document Victron & Pylontech UP2500, US2000, US3000, US2000C, US3000C, US5000, US5000B, UP5000, Phantom-S, Force-L1 & L2 [Victron Energy]

0 Likes 0 ·
pwfarnell avatar image pwfarnell kirs-ten-henson commented ·
@Kirs ten Henson As nickdb answered above, the Multiplus does not measure the solar charge so the battery monitor in the Multiplus is not correct, the Pylontech on CanBus sees all current in and out of the battery so choose this as your battery monitor.
0 Likes 0 ·
kirs-ten-henson avatar image kirs-ten-henson pwfarnell commented ·
Thanks pwfarnell, I will change the settings and see if this brings the SOC data more in alignment. I understand that the multiplus and pylontech readings may differ. I was somewhat amazed at the massive difference though - 100% vs 65%!
0 Likes 0 ·
kirs-ten-henson avatar image kirs-ten-henson kirs-ten-henson commented ·
so this has done the trick in that the data is being pulled from the batteries and showing 100% SOC at around 52.2v. Thank you @pwfarnell!

My next query is then why does the solar charger never go into float and absorption but always seems to be in bulk mode? I have set the MPPT charge controller Absorption voltage at 52v and float voltage to 51v via the VictronConnect App with an adaptive absorption time as we generally are only at the home thurs to sun and therefore during the week the batteries are more or less full.

Should this in fact be left at the default for LiFePo4 batteries? Ie 56.8v absorption 2h absorption time and 52.8v float voltage? or does this even matter if it is the pylontech batteries that are controlling the charge behaviour?

And as an full charged batteries with no load should the solar charge relay state be Open? I haven't quite got to grips with this relay state thing...

0 Likes 0 ·