Victron LFP NG Battery & Lynx Class-T

DIY
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1

Hi,
I want to built myself a Lynx LFP System onboard.

  • 4x 200 Ah Victron LFP NG Batteries
  • 2x Class-T Lynx
  • 1x Lynx BMS NG 1000
  • 1x Lynx Distributor

My Question is now regarding how to connect the 4 batteries to the Class T.
According to Victron you just connect each battery (+/-) to the Lynx Terminal. According to Wiring Unlimited on Busbars you should make sure, that the current flow from the minus-bar goes left, while the plus-bar goes right (visually speaking), so the distances on the bus bar always stay the same. Another way of doing this would be to distribute the minus and plus cables from the batteries, so the batteries switch minus and plus on the bus bar.

Lynx Straight
Lynx Straight1224Ă—816 160 KB

Lynx Star
Lynx Star1224Ă—816 167 KB

Am I overthinking this? Is the Lynx Busbar already configured this way? I didnt find any information on this.

Thanks for the help…
Marcus

2

Have a look here for photos and the manual which should make it clear. In short connect batteries to lynx class -t and lynx’es together.

3

I read each manual of the BMS, the Class-T, the Distributor and the Batteries twice and checked the diagrams. According to those you just connect the batteries directly straight - without going through the hassle of star-connecting, but I havent understood yet, why?
Because the Electrician in me tells me: You have to make sure each battery has the same distance from the distributor, unless the Lynx has someway of connecting to the left, instead of the right, the distance from the far right battery (to the distributor) is shorter, than the distance of the far left battery (to the distributor).

4

It’s a fundamental limitation with how Victron’s (current) series of batteries works. The batteries have no means of reporting their own SoC and they don’t communicate to each other to aggregate the overall SoC. You need a Victron NG BMS and a battery monitor, both of which are separate from the batteries. In your case, the battery monitor and BMS are both located inside the Lynx BMS NG, along with a few other components. This effectively forces you to put all the batteries on one side of the Lynx BMS, and your sources and loads on the other side. But it’s not all bad news. You have multiple options, some of which are:

  1. Don’t worry about it. Your system appears small and you won’t come close to exceeding current limits of the bus bars or contactor inside the Lynx BMS. In our testing and calculations, the Lynx system can easily handle 400A continuous and 500A if there is good air movement. Go to a 24V system vs a 12V and you will halve the currents.
  2. Victron has a means of using multiple battery banks with multiple Lynx BMS in parallel, in which case you can better distribute currents across the bus bars, but at significant added cost.
  3. Use 3rd party batteries with BMS’s that can communicate with each other, then the limitation of funneling all current through a single battery monitor allows you distribute currents across the bus bars. See here for an example of what I’m talking about: https://youtu.be/xCZEvgtnihk?si=0_KWOiCKFSkPoQQN

The majority of Victron systems operate just fine using option #1, and for your system that’s what I would recommend. If I’m wrong and you’re looking to build a larger system where any localized currents exceed 400A, then consider #2 or #3. My suggestion is if you go with 3rd party batteries, then look for something on Victron’s supported 3rd party battery list. But, at 12V there aren’t going to be many batteries on that list with batteries that communicate like I mean in #3.

In short, I think option #1 is for you. Let me know if I have misunderstood the underlying question you posed.

5

Hi,
for simplicity sakes I just didnt draw the Lynx BMS, the distributors, the loads, etc. :slight_smile:

I wanted to direct the question exclusively to the question of how to connect to the Lynx Busbar, as it is counter-intuitive to just connect the batteries - like in the drawing 1 - instead of doing the star-approach (keeping each battery to distributor length the same) - like in drawing 2.

The real application of my case is drawn here:

6

Got it. Drawing number 1 is the way you would do it. You just want to keep the positive cables all the same length and the negative cables all the same length. The goal is to, within practical limits, to keep each parallel circuit the same in an attempt to equalize loads and charging across the batteries. At the currents you will be pulling, the bus bars resistance just won’t make a notable difference in power lost. What you have shown in drawing number 2 is important when you are paralleling batteries together at their terminals. If you land each battery separately on the bus bars as in #1 you will be fine.

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