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alp-ar-tunga-jabbarli avatar image
alp-ar-tunga-jabbarli asked

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 gxpylontech lv hub
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2 Answers
Duivert NL avatar image
Duivert NL answered ·

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

You can not attach equipment directly!

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alp-ar-tunga-jabbarli avatar image alp-ar-tunga-jabbarli commented ·

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.

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Duivert NL avatar image Duivert NL commented ·

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

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Alexandra avatar image
Alexandra answered ·

@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.

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Related Resources

Cerbo GX product page

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Cerbo GX & GX Touch datasheet

Cerbo GX Manual

Venus root access document

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