First time battery bank build.

[TheHappyNomads]

I'm about to place an order for the initial supplies to build my first DIY batter bank. My goal is to build two banks of 16s 48v packs to hit a goal of ~29kWh (connected to (2) LV6548s

(32) Envision Grade B 305ah Cells
(2) JK-BMS 200A Continuous/350a Peak - 2A active balancing
Zketech EBC-A40L Capacity Tester

I know I'll need fuses, buss bars, and other items. Any pointers on what would work best for me?

 

[DIYrich]

If it is your first time, I recommend grade a cells. Might not even need the battery tester. Charge it up with the inverter, and dump the power to the grid or water heater.

 

[TheHappyNomads]

I would but the Grade As are a bit cost prohibitive for me. I don't mind a challenge, unless it really is a ton more difficult.

"Charge it up with the inverter, and dump the power to the grid or water heater."

I have gas water heater and these will not be grid tied.

 

[chrisski]

The capacity tester will discharge the batteries. How do you plan on top balancing these batteries?

Have you figured how long to top balance, capacity test, and then top balance each cell? I could see this taking me three weeks to do all 32 of these cells. Real limit is how long it takes to charge and discharge a single cell when it comes to matching the cells.

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EDIT: I see this is a charge and discharge tester. Could take a month, easy.

At the full 40 amps should take around 16 - 24 hours per cell depending on how these cells were delivered. Up to 8 hours to charge depending on the state it was delivered; 8 hours to capacity test; and then 8 a final 8 hours to top balance.

With the equipment I was using, would have taken me two weeks to capacity test my 16 280 ah cells, including things like chores and work. I opted for grade A cells and the data from the distributor had them evenly matched, so I randomly placed them in two groups of 8.

 

[Robbert]

Building your own battery is a fun project. I made two in a shelf (as in the picture).
Don't mind the cable-mess. That is cleaned up now

I will build a third one, but now will use a battery box (EEL or Seplos).
You might want to consider battery box as well. In the end it looks nicer and also from a cost perspective it is not a bad idea.

When i added up all the costs of addtional stuff i needed (switches, breakers a pre-charge circuit and buttons etc) i think that the battery box is cheaper after all.

 

[TheHappyNomads]

With the equipment I was using, would have taken me two weeks to capacity test my 16 280 ah cells, including things like chores and work. I opted for grade A cells and the data from the distributor had them evenly matched, so I randomly placed them in two groups of 8.

Per the distributor: "Capacity tested, sorted, and matched for consistent performance."

How does this differ from the same for Grade A purchases?

 

[chrisski]

Per the distributor: "Capacity tested, sorted, and matched for consistent performance."

How does this differ from the same for Grade A purchases?

It differs in no way.

That to me is a “red flag” and something to look into about getting grade A cells at a grade a price. If you’re not the first to purchase from this vendor you can expect the same results they got.

I purchased my grade A cells three years ago. Perhpas these cells are sorted as advertised.

 

[TheHappyNomads]

It differs in no way.

That to me is a “red flag” and something to look into about getting grade A cells at a grade a price. If you’re not the first to purchase from this vendor you can expect the same results they got.

I purchased my grade A cells three years ago. Perhpas these cells are sorted as advertised.

Sorry, I'm a bit confused about the red flag -- what do you mean? As far as I have researched this is a reputable supplier of batteries which is why I didn't have any reason to doubt their statement describing the condition and sorting of the cells. There are reviewers of these Grade B cells that all appear to be positive.

 

[RV10flyer]

If you buy grade A cells from 18650 battery, you won’t need a capacity tester. I have several unused testers. After the first few batteries, I found it to be a waste of money and time. Hook them and run them. JK will go good on grade A’s to 57V or more on some. So, what are you going to do if the capacity is 295aH? Ship them back? Not worth the shipping cost. Get yourself some 2” and 4” polyamide high temp tape, 3ea 1” cargo straps per battery (they stretch and tighten when charging so don’t over tighten to start with) , oak boards for each end to slightly compress 16 cells, 18-22ga x 1/4” ring terminals, double pole dc breaker, class T fuse, 2 ga battery cable, 2 ga x 1/4” lugs (I have fit 2 ea 7ga wires into 2ga but other times with newer cells I use two 6ga x 1/4” lug), 2 ga butt splices for connecting to the two 7ga BMS wires, hydraulic crimping tool, carbon conductive grease, 400 grit alum oxide sandpaper, scotchbrite, 91% alcohol or acetone, a good multimeter and a good 100A clamp on amp meter. Good luck. Have fun. 210+kWh of diy LFP and counting

 

[SupraSPL]

The more cells that are in series the more that matching well comes into play. I recently built an 8S pack with those 305ah envision cells and (spoiler they're legit) I think they are the best deal out there right now and I just ordered another batch.

 

[SupraSPL]

They come in boxes of 4 and will be well matched in those boxes. Each box will have a different state of charge and that will take a little work to balance out.

To quickly get them closer without any fancy equipment, connect all in parallel. Once current drops below 3 amps, doesn't take long (clamp a jumper wire between the highest and lowest cell without buss bar if you want to see how much current is moving) then you can connect them into series and charge them up (with MPPT set to say 53V) until a cell hits 3.4V. Then back into parallel and repeat the process until they are all at 3.5V or so. The trick is to never let a cell run above 3.65V and probably no need to go above 3.55 or 3.6 anyway. Then let the BMS dial them in.

My BMS only has a small passive balancer so I used a few 3.2v 3.5v leds to bleed high cells, to get the battery into service quicker.

57V (3.55V) is no problem for these cells and they could balance higher if for some reason you wanted to.

Did you pull the trigger today? I hesitated when I saw the EVE 304 As on sale for $135. I've read they are 315Ah actual and of course they wouldnt be bloated the way the Envisions are (3-5mm) but ultimately $89 for 306Ah+ sold me.

 

[Aridom82]

- Often the busbars come with the batteries, so you dont need to buy them.

- If you are planning to operate them near that 200 amp max you have to study how to do very good connections (terminals-busbars-bms)

- Some separation/insulation layer between the cells is recommended. I use the 3240 insulation epoxy 0,5mm thick sheets already cut so size you can find in aliexpress, they are quite cheap when compared to fr4.

- A 16kwh battery pack weights around 85-90 kg so think about where are you going to put them and how to support them.

- You will need a dc breaker and a T fuse for that 200 amp target.

- There is a lot said about compression, i am including it in my prototype pack using traction springs, even if there are ways to use compression springs also.

- And last but not least be very patient and extremely aware when you tinkle with these batteries, wear glasses and never risk shorting them so keep that allways in mind when you are using metal tools over them or there are loose wires.