Lithium batteries need individual fuses?

[John E Davies]

I ran across this diagram from a Victron battery installation manual. 

 

 

 

 

I am having a hard time understanding why separate fuses would be desirable if the main line has a suitably rated one. I just hooked up the big 4/0 inverter cables as before, and jumpered the two battery positives and the negatives with short cables. I emailed the vendor that sold me the batteries for advice.

Does anybody know if this would be a good idea and why? Does Oliver fuse each battery? I have not yet completed my cable configuration, I may do this, just in case, and mount the two fuses on the sidewall, inside the box with the batteries... and run a separate 00 gauge cable to each battery positive post, with enough length to allow the tray to come out part way. 

FYI, here is an excellent reference for the Victron batteries. I wish I had found this before I started this project. It is very complete, but it may be intended for more complicated electrical systems like in a yacht. Many of the marine system parts and interconnections are not needed in an RV.

https://www.victronenergy.com/upload/documents/Manual-Lithium-Battery-Manual-EN-(P).pdf

Thanks for any comments.

John Davies

Spokane WA

Edited December 19, 2020 by John E Davies

[mjrendon]

I have not had time yet to read your reference material but I believe that Victron recommends a fuse on each battery  to prevent an issue with battery imbalance. This can occur when installing batteries with different charge states or if some "event" happens while the batteries are connected in service.  If the batteries are not balanced, there can be large current from the higher charge state battery to the lower charge state battery.  A BMS board should limit this current, as would a fuse.

From the images posted here I do not believe that Oliver is fusing the two LifeBlue batteries. Someone would need to verify this.

Mike

Edited December 19, 2020 by mjrendon

[mjrendon]

It looks like the Victron batteries are monitored internally by the BTV, but the controls to prevent excessive charge/discharge rates is done using an external BMS.   Did you or are you installing the external BMS as part of your setup?

from the battery manual on the Victron website

"Our LFP batteries have integrated cell balancing and cell monitoring. Up to 5 batteries can be paralleled and up to four 12V batteries or two 24V batteries can be series connected, so that a 48V battery bank of up to 1500Ah can be assembled. The cell balancing/monitoring cables can be daisy-chained and must be connected to a Battery Management System (BMS).

The BMS will: 1. Generate a pre-alarm whenever the voltage of a battery cell decreases to less than 3,1V (adjustable 2,85-3,15V). 2. Disconnect or shut down the load whenever the voltage of a battery cell decreases to less than 2,8V (adjustable 2,6V-2,8V). 3. Stop the charging process whenever the voltage of a battery cell increases to more than 4,2V. 4. Shut down the system whenever the temperature of a cell exceeds 50°C."

Edited December 19, 2020 by mjrendon

[John E Davies]

Yes, I have a had separate Victron BMS for a year now. The batteries do indeed shut down the charging by themselves, for example, I had one cell that was over voltage, it simply shut down all charging. When the converter was turned off, the cells in both batteries equalized over a short period of time. The only thing I am concerned about is the BMS cannot actually control the Oliver installed Progressive Dynamics charger (I added the lithium charging section). With a smart (connected) Victon charger, the BMS will turn it on or off, or cycle it, to control this stuff. Unfortunately the biggest smart Victron charger is only 30 amps. I would hate to lose the 45 amps of my present one. I will also be adding a Victron MPPT solar controller, which the BMS will be able to fully control.

Over voltage alarm:

 

After turning off the charger. (The second battery cell voltages were almost identical).

 

I think these Victron batteries take a few cycles to “settle down”, in terms of cell balance. They can only compensate for small variations at a time. I have no clue how the other brands deal with it.

John Davies

Spokane WA

Edited December 19, 2020 by John E Davies

[mjrendon]

From what I read, the BTV (internal to the Victron battery) controls the cell imbalance.  The charge/discharge rate protection offered by the BMS relies on communication to the Victron charge and load controllers.  I believe that you are correct in that the PD controller lacks the ability to be controlled by the Victron BMS. However, you might leverage the DC disconnect relay.  If I am understanding the Victron setup correctly, a fuse between each battery would be prudent.  I am not sure why Victron chose to design their system this way.

The Battleborn BMS is an internal battery device and performs temperature control, balancing and charge/discharge rate protection.  
 

 

Edited December 19, 2020 by mjrendon