the BMS communication is broken on -48V telecom system

Question

question

alp-ar-tunga-jabbarli asked May 7, '24

the BMS communication is broken on -48V telecom system

Good day dear friends. We have installed a system consisting of victron and pylontech products for a telecom company. The telecom side needs -48V DC. After installing and preparing everything, when we connect the 1x50mm2 cables going to the telecom side to this victron system, the communication is broken on the LV-Hub and Cerbox GX side and we cannot see the information in the system in any way. When we disconnect the power cables to the telecom side and restart the system, the communication is restored. But when we reconnect the power, we have the same communication problem. I'm very curious as to why this might be happening. These are the products we are using:

Pylontech Battery 20 pcs.

Pylontech LV Hub

3 units Multiplus II 48/5000 Inverter

1 SmartSolar MPPT 450/100

1 SmartSolar MPPT 450/200

4 Victron Lynx Power In

1 Victron Cerbo GX

1 Victron GX Touch 70

1 Victron Smart Shunt

cerbo gx pylontech lv hub

2 |3000

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

duivert answered · May 07 at 02:23 PM

Hi you need a dc dc converter from victron between the 48v bus and the telecom equipment,

You can not attach equipment directly!

2

2 |3000

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

alp-ar-tunga-jabbarli commented · May 08 at 03:31 PM

First of all, thank you very much for your opinion. Why can't we connect directly? I think we can connect to the telecom system in reverse polarity. We can release the positive and negative power cables coming out of our main +48V busbar to the reverse connection on the telecom side.

0 ·

duivert commented · May 08 at 03:40 PM

Reading your post and answer, this is not possible at all!

You want -48V, that means negative 48volts

System is positive 48volts

Simply swapping positive and negative is not -48v

Its still +48v since there is no 0V reference

0 ·

Modifications Space

Node Red Space

Answer 1 · 2024-05-08T17:42:30Z

Alexandra answered · May 08 at 05:42 PM

@Alp Ar Tunga Jabbarli

I have never done a telecom system so my knowledge is pure theory. I do have some thoughts though.

It will have something to do with the grounding on bms can maybe (comms loss). Remove the ground wire from the can cable maybe as a test. (Pin 3)

How is the rest of the system grounded?

@duivert telcoms uses -48v because of corrosion/electrolysis.

Positive in a victron system can be grounded.

2 |3000

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

question