Lynx Smart BMS: Allow to charge “Yes” but ATC contact open

Q&A and troubleshooting
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1

Very simple installation setup:

  • 4 LFP Smart 12.8 V / 160 Ah batteries in series

  • Lynx Smart BMS 500 with Lynx Distributor

  • Venus GX for data access via Modbus TCP/IP

  • Contactors to isolate loads/chargers according to ATC and ATD contacts

The issue:

On VictronConnect, it shows Allow to charge: Yes, but the ATC contact is open.

I already replaced the BMS, and it worked fine for a few hours, but then the same issue came back.

This system has been working flawlessly for 2.5 years without any problem.

We are passing battery voltage through the ATC contact (~52 VDC), making sure that no more than 0.5 A flows there (with a fuse). The ATC contact is used to control a contactor coil.

Any ideas? Initially, I was sure the problem was with the BMS, but since the new one only worked for a few hours before showing the same behavior, there must be another issue somewhere.

Thanks!

2
  1. A 0.5A fuse could allow a higher current for a short period.
  2. Switching a contactor can result in voltage / current spikes if flyback diodes are not used. We often see people damaging the control relays on equipment by driving contactors / large relays.
3

Thanks for your answer.

I understand your point but I have some questions regarding:

-the BMS has resettable fuses on that contact(ATC) in that way I suppose that is possible to diagnostic and reset an issue like overcurrent?

-in that case is not more probable the contact fails in close position instead of open position?

Thanks!!

4

I expect that the resettable fuses are PTC self resetting fuses so no diagnostics.

Welding closed is one option, but there could be arcing as the contacts open eroding the contacts or overheating the contacts and warping them so that they do not close.