question

alan-olson avatar image
alan-olson asked

Bad Battery or Inefficient Wiring?

I need the community's help to determine if I have a bad cell in a Victron Smart LFP battery or inefficient wiring in my system.


System Description

- 100% Victron system: Lynx Smart BMS; Multiplus II inverter; Lynx Power In; Lynx Distributor; 4, 200 Ah Smart Lithium batteries; 2, Orion DC-DC chargers.

- Because of space constraints, the cable lengths to each battery are not equal in length. All batteries are wired in parallel and cables run to the Power In module but the lengths increase from the positive terminal on Battery 1 (about 6 inches) to the negative terminal on Battery 4 (about 40 inches).

- System has been through dozens and dozens of Absorption-to-Float balancing cycles.


Problem Description

Cell #4 in Battery #4 is imbalanced. (System worked perfectly for about 6 months. The imbalance started about 2 months ago.)


Possible Causes for Imbalance

A) Not really a cell balance problem but a failed cell in the battery >> replace battery.

B) Unequal cable lengths finally caused imbalance >> rewire with equal length cables.

C) Other


Questions

- Would having equal length cables to each individual battery help? (Pos. and Neg. cables to individual battery equal in length but each battery would have different cable lengths.)

- Is there a definitive test to identify a bad cell in a battery?


Thanks for your help!

wiringsmart lithium
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4 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

Probably a bad battery, you could remove it from the system and test it independently.

You don't say if all the batteries are wired in parallel.

Lithium batteries are more able to cope with different cable lengths than lead acid batteries, as they have a much higher efficiency. As long as the system can meet the peak demand current of the inverter, without overloading one battery, then all should be fine. As the apparent cell failure is in the battery with the longest cables, this will have had the lower operational current, but resting time with the system at low current should allow charges to equalise.

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Alexandra avatar image
Alexandra answered ·

@Alan Olson

Put the battery on a dedicated charger. Keep it fully charged. See if the tlc helps.

You might find you need longer absorption charge to make up for the not so balanced cables.

The other way is to rotate the batteries in their service positions.

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alan-olson avatar image
alan-olson answered ·

Thank you Mike and Alexandra. I appreciate you help!

It seems there's consensus that unequal cable lengths shouldn't cause major problems. I'll focus on the battery and absorption charging.

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alan-olson avatar image
alan-olson answered ·

Follow up with final results... My authorized Victron dealer pulled the battery and confirmed that the battery had a bad cell. Battery was replaced under warranty. Cabling to the batteries was not changed.

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Related Resources

Victron Wiring Unlimited Book

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