dmq avatar image
dmq asked

Multiplus 2 switch off battery supply voltage


if I disconnect the 48VDC supply voltage (Pylontech battery stack) to the Victron MP II, will it immediately turn off when there is still a connection to AC IN / Grid 230VAC? I want to disconnect my battery stack to top balance it - at the moment my setup passes main parts of my installation on L1 through AC Out 1 of MP II. I can switch it back to grid supply (through a emergency power switch) but I do no want to swich my consumer devices off.

Thanks in advance

2 |3000

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

3 Answers
Alexandra avatar image
Alexandra answered ·


You should only disconnect your batteries when the system is powered off.

If you have a GX device in the system then the pylontec would manage their own balancing charge and discharge needs. We usually on install leave them on keep charged for a few days for everything to settle down.

The MP is not designed to have no battery attached and be powered on. It is best to have a bypass installed then. But you cannot have the best of all the worlds unfortunately at some point during your propsed idea the power has to be off and consumers off.

Even if you were do disable the internal charger, so you did not have to disconnect the MP to prevent further charge, would need a restart to set it up.

1. Get a GX let the pylons self manage

2. Install a bypass for any further maintenance requirements so consumers are only momentarily inconvenienced.

2 |3000

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

dmq avatar image
dmq answered ·

Thank you very much @Alexandra

I have a Cerbo GX device connected - the pylontech communicates through CAN with the Cerbo GX device. BMS is integrated. So far so good - but when I read out the pylontech (4x US3000C) stack through the console port - I see slight differences. I my ESS configuration I set the battery SOC discharge limit to 15%. One battery has a SOC of 11% another of 15% - strangely the minimum and maximum battery voltages of the stack members do not differ so much: 3259 - 3263.

What makes me crazy is, that the stack drops Alarms on the Cerbo when I am on the SOC limit level of 15% for about 12 hours. I get the "famous" Pylontech internal battery alarm "failure". Pylontech says (based on reference of many other posts here in our community), that this is not a critical error but just a warning.

Today I got the error at 04:54 o'clock. When I check the state of the battery in the Cerbo: 48.90V, 14% SOC. When I check the state through RS232, I see that battery two is absent:

Power Volt   Curr   Tempr  Tlow   Thigh  Vlow   Vhigh  Base.St  Volt.St  Curr.St  Temp.St  Coulomb  Time                 B.V.St   B.T.St   MosTempr M.T.St  

1     48905  0      20200  17100  17200  3259   3262   SysError Normal   Normal   Normal   11%      2021-12-18 15:33:01  Normal   Normal  18400    Normal  

2     -      -      -      -      -      -      -      Absent   -        -        -        -        -                    -        -       

3     48906  0      19700  16900  17000  3259   3262   Idle     Normal   Normal   Normal   14%      2021-12-18 15:33:00  Normal   Normal  18000    Normal  

4     48905  0      19300  16500  16600  3259   3261   Idle     Normal   Normal   Normal   17%      2021-12-18 15:33:00  Normal   Normal  18000    Normal  

Because of that I wanted to top-balance the whole stack manually again based on that advise:

Do you have an idea why there are SOC differences (see above, 11%, 17%) - do you know, why battery 2 is absent (it will reappear automatically when the stack starts to charge).

Thank you,


1 comment
2 |3000

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

Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Give them a fully charge with a small current and they will balance at 100%.

Using the batteries in low SOC states for a longer time will always result in cell imbalance. Thats what "Optimized (with BatterieLife) is for. It will increase the SOC discharge limit step-ba-step to ensure the battery will get a 100% charge from time to time.

0 Likes 0 ·
dmq avatar image
dmq answered ·

FYI I will activate ESS BatteryLife and observe the situation again.

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 ·

Pylons like to get up to full charge, if they have not been doing that then you see these issues as matthias mentioned. The other cause it current sharing from your stack. The optimizated with battery life is definitely the way to go.

Or keeping them at full charge for a few days before cycling again.

0 Likes 0 ·
dmq avatar image dmq Alexandra ♦ commented ·
Thank you Alexandra - I will go with BatteryLife (at least in winter months).
0 Likes 0 ·

Related Resources

Additional resources still need to be added for this topic