BMS advice needed for 7s8p or 7s16p solar storage

[grossy34]

Hi im about to finish 7s8p or 7s16p for solar storage, still undecided if 8p or 16p as no idea what kind of bms is needed for smaller and bigger pack, cells used brand new 18650 eve-26v, would appreciate for any advice.

 

[OffGridInTheCity]

Eve 26v 18650 list as a 2550mah cell - https://www.18650batterystore.com/products/eve-26v-18650
16p * 2550mah = 40.8ah, which is light duty in terms of BMS balancing.

I would think any 7s BMS (with balance) that allows the load current you want would likely work - I don't see the need for worry or big $ in this case.

 

[grossy34]

thx for info.

 

[italianuser]

Possibly get yourself a BMS which can handle 1.5 / 2 times the nominal capacity of your battery. For a 40Ah battery a 60Ah BMS could be a good choice. You don't want the BMS to work at it's nominal limits all the time!

 

[grossy34]

what about that one?
if not can you post or attach photo of suitable one?

 

[italianuser]

Yes, that's it but you need the 60A version for a 40Ah battery.

The product's name is "7S 60A BMS", something like this:

 

[grossy34]

thx for info, ordered

 

[grossy34]

regarding my progress, battery still not finished as my portable spot welder was too weak to weld 0.15 nickel strip so i ordered a stronger welder and expecting it within a days, my inverter arrived and im stuck somehow with a breaker/fuse box for panels, asked seller regarding those and for my ac input 32a breaker is recommended, for a battery 120a one and for a pv panels 20a and my question is which one should i but for pv strings as there are few types but not sure if it doesn't matter which one will get or need specific one so advice needed, attached pics of them no.4 or no.5? also attached pics of my inverter details, ac input breker and battery breaker so please advice

 

[italianuser]

my question is which one should i but for pv strings as there are few types but not sure if it doesn't matter which one will get or need specific one so advice needed, attached pics of them no.4 or no.5? also attached pics of my inverter details, ac input breker and battery breaker so please advice

To be able to control each string individually you can use a DC MCB (photo 3 "TOMZN MCB 125A DC" and photo 4 "DC Circuit Breakers All Sizes") with an amperage of 1.5x/2.0x your string amperage. If a string is for e.g. 10A then a 20A DC MCB will be ok (I bought 20A DC MCBs for my each of my three 8.64A strings). You choose a slightly over-dimensioned MCB to avoid it working at it's nominal limits. It's a good practice to disconnect panels from the inverter when doing maintenance.

IMO It's a good idea to have an MCB for each string.

Some people just have a single MCB for all panels; if inverter supports two PV inputs then it would be two MCBs.

Photo n.5 is a fuse holder (looks like a model for 10x38 fuses, the numbers are millimeters), I use them in couples on both negative and positive. A good choice for the fuses is the ones with sand inside because they are more effective, when they blow, in extinguishing arcs which happen when interrupting an electrical line. I use fuses on the battery (between battery and inverter), with the amperage the closest as possible to the battery size. If your batteries are in parallel you could put a fuse holder on each individual battery; 10x38 are not the biggest fuses, for higher amps there's a bigger size (which requires it's correspondent holder, that means a 22x58 fuse holder and 22x58 fuses).

 

[grossy34]

thx for info, bought them all, not arrived yet though, need some advice regarding daly bms
as is rated 60a but output wires are 10awg/30a?
is that ok or i should replace them with 6awg?

 

[floydR]

Since the wire has 200c rated silicone insulation it should do 60A uou can up size the wires connected to the b- p- wires
later floyd

 

[italianuser]

Since the wire has 200c rated silicone insulation it should do 60A uou can up size the wires connected to the b- p- wires
later floyd

Oh wow, I was really struggling with this one! I found this other info which was about the relationship between Ampere and Power, which are not always proportional... but your answer is the correct one I think
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(https://electronics.stackexchange.c...-awg-charts-rated-in-amperes-and-not-in-watts)
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