Buswire Check

Evening,

Could someone please double check the bus wire thickness I plan to use. I would appreciate it.

Full setup:
14s x 40p ( x 10)

I'm planning to build 40 cell packs, fused with 1 amp fuses, so each pack can not do more than 40 amps. Planning to do 10 strings in parallel. So, for the bus wire on the packs, I'm looking at 11 guage, or 4.17mm2 with just over 40 amps.

Is this correct for the individual 40 cellbatterysetup?

Appreciated.

With 1A fuses on cell level that pack cannot do more than around 10A... Cell level fuses are NOT for fusing max current. Max current is the main fuse and that one should be well below the cell fuses.
Do you want to change 40 fuses or 1?
I recommend 5A fuses on cell level for 1A continues. Then you add a 40A main fuse instead. This will ensure you blow the correct fuse....

For 40A i would use 6mm2 buss wire or equal. I use 6*2.5mm2 for 80A bus wire here.

its all about how much drop you want. And the drop depends on resistance and length of the wire.

Thanks for reply.

Ok, so the 1A glass fuse on the packs are too small at 1A. Average Joe is using 0.5A, if i'm not mistaking. So, how much amps would you draw out of a 100 cell pack with 0.5 amp glass fuse? I'm planning a 400 cell pack, in essence. 10 x 40.

For the bus wire on the 40 cell pack, is 80A not too much. I'm planning in using 10 cells in parallel, so that would be then 800A. That is a lot! @ 42V that is 33kw!

It reads as if you expect 80a from 1 pack and 1 pack has 40 cells. If follows that 80amps / 40cells = 2amps per cell.
A single pack will have 4.2v @ 80a. When you put 10 packs in series the voltage increases to 42v but the amperage stays at 80a. 42v * 80a = 3360watts or 3.360kw.

PS.

I'm looking at a 5kw inverter, 10kw spike. So, maybe 10kw max. If I do 40A, in a 14s setup, that is 40A x 42V or 1.6kw. Times that by 10, equals 16K max. Even this is more than twice my heavy load.

BTW, just been watching your DIY spot welder vid. Might be a good option. Thanks.

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OFITC,

Thanks man. No, not a all.

I'm building 10 strings of 14 series strings. So, 40 18650's in a pack, times 14 for 14s, and then times the whole by 10, for a 40+kw wall.

Joes fuses are way to low for most People. Cell level fuses should be 5x the max rating per cell and total current. Do not base it on tested instant blow current because its not the same as the rated current. A 1a fuse is max load 1a. And Cell level higher than pack fusing

Why do 10*14s ?? Going to have 10 bmss?? I would go for 4strings instead. Aka 4* 14s100p. A lot more economical. And i would use 4-5a fuses and pack level fuse at 100a. Then you know that 2 strings are needed to cope with the load and you can work on the others IF needed.

Always think ahead!

Daromer,

Thanks. I see while reading through the posts, AJw22 also using 1a axial fuses.
https://secondlifestorage.com/t-AJW22-s-7-5-75kWh-PowerShelf

No, I'll be using 1 BMS, since the 10 strings will be paralleled together. In essence creating one large 14s. Each of the 400 cell packs will be broken up into 10 x 40 cell packs.

So, regarding the fuses, is a 1A fuse too small for a 400 cell pack to deliver maks spike of 10kw. That is then 0.59a per cell. Or working load of 5kw it will be 5000w/42V/400cells or 0.28 a per cell.

Yes it is to small. DO YOU want to change 400 fuses when it blows?
The cell fuse should be 5x as big as your main fuse atleast. Or else you will end up with a chain reaction where they all blows.
1A fuses and such small just ads resistance. Their purpose is dead short protection and not current limiter or heating element.

Your calculation only works if all your cells are 100% equal and they arent in a powerwall from 2nd hand cells.

I dont get the fact that you build 14 strings and then join them all together in every point. Looks to me like extre time to work with it but perhaps you have a good system doing it. Neither less the main fuse is more important that you think of than your cell fuses. And I have not seen you mention it once yet. That one is for short protection over the whole battery bank. That one is important.

Daromer,

Thanks for the above. As for the 10 strings, I'm building a modular wall with smaller units, so I can put each in a fire-box. Primarily I don't want one large 200 or 400 cell battery. This is just my design. More work up front definitely, but I can expand it and maintain and trouble shoot smaller packs of 40 cells better. Also the heat and possible fire on a 40 cell pack, should have less of an impact than larger packs. Also, I don't want my system in an outhouse, so I'd like it to be safe for the garage. I will also put a temperature gauge on each of the 140 batteries or 40 cell packs.

As for the main fuse, you are correct, I have not mentioned it yet. What size would you recommend as per the discussion? Do you fuse it for the maks spike value of your inverter, at 10KW?

Main fuse is determined by your least denominator. Most likely the inverter and it is in its manual....

Its not easier to work with smaller multiple packs vs larger since you plan to have em all connected. IF One pack fall behind you Still need to find that cell... Only way to make it easier is 1bms per string or One that can monitor each of your xxx packs