Cable Lengths When Wiring Each Battery to Lynx Distributor

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josiahjlee asked Nov 20, '20

Cable Lengths When Wiring Each Battery to Lynx Distributor

I’m considering wiring each of my 4 LIFPO batteries to the Lynx Distributor separately. I’m wondering if anyone with experience has thoughts on the following:

1) Do the wires to each battery need to each be the exact same length? I know it’s important in traditional parallel wiring for wire lengths to be equal, but haven’t seen anything on this when wiring directly to the Distributor.

2) Is battery balancing impacted with direct wiring as compared to traditional parallel wiring each of the batteries together with diagonal positive and negative terminals wired to the Lynx Distributor?

3) any thoughts on cost efficiencies of wiring each battery directly to the Lynx Distributor? Smaller wires, but more fuses, etc.

battery charging lynx shunt battery connection

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Answer 1 · 2020-11-21T01:07:34Z

Alistair Warburton answered · Nov 21, 2020 at 01:07 AM

The cost of the aditional copper to keep all 4 th same lemgth will be tiny in the greater scheme of things. However if the batteries have the BMS on-board it probably will not make any practical difference.

4 seperate circuits are going to be significantly easier to handle, due to the smaller wire size...

You may find a 'Lynx power in', just a bus essentally, with external fuses and isolators will work out cheaper, especially if you use NH style DC fuses which, with a handle, removes the need for isolators too.

If you are talking about 4 seperate banks of 4 cells with an external BMS then NO you cant without bridging all the cell-cell nodes although you could still use 4 seperate BMS modules.

You do mean LiFePo4 right? LiPo are essentally bombs!! Great for RC but folk keep then in metal boxes for a reason.

Keen to learn if I am missing something mind you...

Al

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Kevin Windrem commented · Nov 21, 2020 at 03:04 AM

LiFePo4 batteries are considered safe in most situations. These are not at all the same as what's found in RC cars, airplanes and drones. The Lithium Ion batteries in these devices are prone to thermal runaway. LFPs have a chemical makeup that intrinsically prevents thermal runaway.

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Alistair Warburton Kevin Windrem commented · Nov 21, 2020 at 03:27 AM

Sorry that is what I meant, but I see it isnt at all clear now I read it back. I was concirned the origional poster had not apriciated the different chemestry, given the typo in the type name.

In my head I said " You DO mean LiFePo4, right? ", inference, They are fine, but dont confuse those with LiPo or other Lithium variants.

Unfortunatly I didnt say that explicitly and I can see why you, and anyone else for that matter, read the complete opersit.

Point taken I will be more carefull, thanks for clarifying, my reply clearly needed it.

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Answer 2 · 2020-11-21T04:44:25Z

josiahjlee answered · Nov 21, 2020 at 04:44 AM

Yes, these are the Battle Born LiFePo4, so definitely the safer kind and have the onboard BMS.

if I’m reading your response correctly, it may be easier to wire each of the 4 batteries directly because I can use smaller size wires and fuses, and since the batteries have onboard BMS, even if the cables weren’t exactly the same length between each battery and the Lynx, it probably wouldn’t matter much. The difference would probably be less than a foot (or 300mm I think) between any of the 4.

the only downside I could think of at this point was future expansion of battery capacity since the Lynx has just the 4 terminal posts. So if I added a battery or two later, I might have to redo the whole wiring and go back to parallel wiring anyway with larger cable and same length wire between each battery and diagonal battery posts to the Lynx.

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Alistair Warburton commented · Nov 21, 2020 at 05:34 AM

If you go with Lynx 'Power In' it will be much cheaper.

It still only has 4 ways but adding another Lynx unit would be fine, they just connect together.

You will probably be able to fit two cables on each post anyway, because the cable are smaller and will stack, and you can always use the two bus bar ends.

Obviously you need fuses as the power in hasnt got any. NH fuses are center tags, pull out with a handle, have a good breaking capacity and are available in DC. Using them as an isolator is common. (Shrouded of course)

You will need to check but size 00, in whatever current rating you need, will probably be about right. 00 gos to 160A in AC not sure about the DC spec. If 00's dont go high enough then use a size 1 (0)

Al

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Daniël Boekel (Victron Energy Staff) ♦♦ Alistair Warburton commented · Nov 21, 2020 at 11:05 AM

I prefer to use a Lynx Distributor for battery connections, as it is so much easier to fuse each battery connection with it.

https://www.victronenergy.com/live/dc_distribution

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Alistair Warburton Daniël Boekel (Victron Energy Staff) ♦♦ commented · Nov 21, 2020 at 07:36 PM

I didnt mean to overstep... Comments based on Victron distributors advice when discussing this very issue.

Also NH format fuses, in a cheap disconnector chassis, seemed like a good plan.

If I am mistaken I am happy to learn...

That said I do like the idea of the fuse monitoring in the Lynx Distributor, in fact the whole thing is definatly a neet easy solution IMHO.

Al

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Daniël Boekel (Victron Energy Staff) ♦♦ Alistair Warburton commented · Nov 21, 2020 at 10:59 PM

That works fine (NH fuses) but is much more expensive and also much more work and takes more space. so the Lynx distributor will be a better choice for most systems.

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Alistair Warburton Daniël Boekel (Victron Energy Staff) ♦♦ commented · Nov 21, 2020 at 11:19 PM

Thanks, I will look at my options... Blinkered this end I guess. Dont want to hijack this thread though so will leave it at that.

Cheers.

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