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REC Master 9M - Startup Pieps - CAN Problem

Hello REC Community,

I have a REC Master Slave config with one 9M Master Unit and three slaves. (Large Li-NMC 48S / 20kWh system).


Everything works great except the CAN communication to the inverter.
You can see in the Webclient that the master finds the three slaves, all voltages are correct and all looks great as it should be.

However the CAN bus is dead!
I checked cabling, termination, changed CANF to other values. Thanks to many hints 🙂
And, I am familiar with CAN cabling and did this many times before.
I even connected a general CAN Monitor. No messages on the CAN connector of the REC Master at all!

Wondering if my Master device is broken.
The REC Master boots up with one, followed by three pieps. See the short video here:


While there is documentation on LED blink errors, there is no documentation by REC on the pieps.
After finding the Clients on the RS485, the LEDs go out. There is no error blink error. There is no error in the ERRL? command. There is simply no error message anywhere. But the CAN output is dead.

Could somebody who did a Master Slave configuration tell me, if the

"piep - 3 x piep"

startup of the master is normal or my device is broken?

Thank you so much.


(I am really desperate, as my local REC dealer in Germany is not supportive)

This is what my demo unit looks like during startup.


The bright green LEDs at the end are the contactor enable relays.

Uploaded files:
Stefan Ried has reacted to this post.
Stefan Ried

Thanks Rick for making the video. This helps a lot.

So it looks like that the sequence after the boot piep is normal and counts the number of found slave devices.

You have two slaves, so it boots with piep - 2x piep

I have three slaves and it boots with piep - 3x piep.

I come more and more to the conclusion that I need to replace my master device.
I'll try to approach REC directly, as my dealer in Germany seems to be out of business.

Thanks again for the great help Rick.