Renogy battery shunt resetting

[Dameon]

I'm currently trying to switch my travel trailer from a Led Acid to Lithium battery. I have a Redodo 200ah battery attached to a Renogy battery monitor. It was not yet connected to shore power. I drained the battery until it reached the cutoff I set in the Renogy, 10.8 volts. I connected to shore power and the WFCO converter started chargin the battery. It starts charging at ~25A, per the battery monitor. It then jumps up to ~50A after a few seconds. It runs there for about 20 seconds at which point I hear the shunt disconnect and the monitor goes to 0A charging. After a few more seconds I hear the shunt re-connect and it goes through the whole process again, 25A -> 50A -> 0A.
This is my first foray into Lithium so I'm at a loss as to where or what to check. I have it wired just like the diagram in the booklet that came with the monitor.

 

[NWC100]

My Renogy shunt doesn't make any noise, are you sure that's not the battery BMS disconnecting, check the recommended charge level, a quick search shows as 40a recommended, it's possible the battery doesn't like 50a and is protecting itself via the BMS, is there a way to reduce the charge rate down to 25a and have it hold there. Definitely the shunt cannot disconnect the battery, it's a fixed device with no open or close setting, always open.

 

[Dameon]

I got pretty close to the shunt and it sounded like it was the one opening and closing. But it is close to the battery so I'll have to check again and really pay attention to where it's coming from. I'll also try and do a resistance check between the B- and P- on the shunt when it does this to see if it's open or not. As for the battery BMS, you are correct, the documentation does say 40A recommended but it also says Max Continuous Charge Current is 200A. It also mentions that if charged at 100A it takes 2 hrs to charge, so it must be OK at those Amperages. I don't think there is a way to reduce the charging current on a WFCO converter without re-engineering the thing, but it's something I can look into.

 

[Dameon]

You were correct NWC100, the sound is not coming from the shunt. It's coming from under the front of the camper (my batterie and other things are inside). It almost sounds like it's coming from the Positive bus bar. I'll have to get in closer and see.

 

[mikefitz]

The shunt cannot disconnect anything, its just a low value resistor in series with the battery negative cable.

One of two things are occurring, either the BMS in the battery has entered protection mode and stopped the charge process, or the overload system in the WFCO converter is cutting power.
Your statement that you 'hear' the disconnect suggests the converter may be 'upset '.

In general its not a good idea to run a lithium battery completly flat but it seems its accepting charge.


What model of WFCO do you have, it may be unsuitable or less than ideal for lithium batteries?

 

[Dameon]

The sound was coming from under the very front of the camper where the positive bus bar is. The convertor is near the rear, so I knew it wasn't that.
I had run the battery down to the 10.8v since the WFCO 8955-AD needs to do a full charge to "detect" if you have a lithium or led acid battery. Though I've heard that it doesn't do that very well. May want to replace it at some point.
I think I found the issue, although I'm not sure why it would have caused it. When I was discharging the battery I disconnected the Solar panel from my Solar controller, but only the negative side. The positive side was still connected. When I started charging the battery through the converter I didn't reconnect the negative. I've since reconnected the negative back into my Solar controller and the system is charging fine at ~50A. I have no idea why that would have fixed it or if it's just a coincidence.