Cinergi's 28 kWh / 4 kW Solar / 10 kW inverter RV build

Gazoo said:

It's just leakage.

Heltec BMS' (up to 350A) with Active Balancing & Independent Active Balancers | Page 5 | DIY Solar Power Forum (diysolarforum.com)

There is no mention of either of the terminals being tied to the aluminum shell in any of the spec sheets I have read.

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Thanks for the reply. I appreciate it. I'm trying to put together my own 16 X EVE 280Ah, 48V system with only a digital design and software engineering background.

This BMS design from @BiduleOhm is definitely looking interesting, based on the problems I've seen with some of the less expensive BMS..

The last of 36 cells will have been tested tomorrow. Whew!

I've completely disassembled my battery and am toying with a completely different setup. I'm going to try 8 packs of 4 cells with molex and anderson connectors so I never have to unscrew a terminal again and to keep the system modular. Here's the area in the RV in which the cells and equipment will go.



Cells across the bottom, two rows (I'll have them build a shelf). Most of the equipment in the upper right will be deleted and replaced with my 48-12v converter and 12v LFP battery. To the left and above the cells will be the various Victron equipment.

In this picture you're underneath the hitch of the 5th wheel, facing into the basement. There will be two LARGE doors providing equipment access. The area is part of the heated basement. The other side of the wall is the basement/storage. As such, I won't build a battery box - just 8 small fixtures to hold 4 cells each. That's the thought, anyway.

I plan to parallel the cells with the provided bus bars but I will serial-connect each of the two cells to their pairs/mates using 2 separate 4 gauge wires for an effective 1 gauge setup. Even if I turn everything on in the RV I won't pull more than 150 amps. Picture will be easier - once I have it. So, cell 1 positive connected to cell 2 positive with bus bar. Cell 3 negative connected to cell 4 negative with bus bar. Cell 1 positive connected to cell 3 negative with 4 gauge. Cell 2 positive connected to cell 4 negative with 4 gauge. Cell 1 negative and cell 2 negative become battery negative and cell 3 positive and cell 4 positive become battery positive (again using two independent 4 gauge wires). Two 4 gauge wires is exactly a single 1 gauge wire so I can stuff two of them into a 1 gauge lug, crimp, and get my battery connections. This way the cells are "perfectly" in series and the bus bars are only fixing small current differences / balancing the cells. It's a lot of wire and crimping. I will start with 32 wires directly connecting in series and test that this holds up. If it does, I'll invest in the Andreson connectors (not cheap!). The molex connectors are for the BMS leads. Then, the groups of 4 cells can be independently serviced and transported. It also means I have a LOT less to worry about with respect to proper compression fixtures for strings of 8 cells and greatly reduces the possibility of cell movement. After watching how loose my cells got in my fixture when they got to near 0 SOC, this is the way to go for me in this mobile application. It's either this, or 8-cell fixtures with springs. I could still be convinced to go that way. 8 fixtures is a lot, 4 is easier - and while I'll incur the cost of springs, I'll reduce the cost of Anderson connectors.

One thing on my mind is that if a cell becomes a lot weaker than its mate, one of the two wires will take more current .. and perhaps my design needs to include worst-case current for a single wire and not depend on the current being relatively evenly divided. Unlike my previous ruminations, the cell pairs will be matched by capacity (as opposed to pairing highest with lowest) - so the chance of this happening should be low. But I don't want to burn down my RV

The RV's due date is moved out to March 30th now At least I have time to continue experimenting with the design.

Cell testing complete! Raw results (sorted):

268
269
270
270
270
270
271
272
273
273
273
274
275
276
276
277
277
277
277
277
277
278
278
278
278
278
278
278
279
279
279
280
280
280
280
281

10 of the Panasonic High Efficiency 335 watt panels (https://www.altestore.com/store/sol...efficiency-solar-panels-p40891/#PAN335HITMONO) are on their way to my RV builder (New Horizons). For now, I will use a 2s5p configuration and a single MPPT 250/70 SCC.

I'm charging up the last 5 cells from my test and will assemble a 2p16s pack. I think I'll use 1 gauge wire for the series connections (50mm^2), each of which is about the same as 2 of the provided bus bars. Since I'll be using 2, I'll have approximately 100mm^2 (3/0 equivalent) available for carrying current, assuming the amperage is evenly divided. This should make for a ridiculously low-resistance battery pack. If this design is to my liking, I'll add the Anderson connectors (which will add resistance - that's fine). Right now all the cells are on two shelves (16 on each) and I'll play with this configuration ... assuming I like the idea of 8 packs of 4 cells, I'll get to work building the compression boxes. I will try adding 1/16" neoprene between cells and underneath the cells & cell fixture for maximum vibration resistance. The fixture will have two rods along the sides of the cells and 2 rods underneath the cells to make sure they can't drop down and put strain on the cell terminal. More to come!

Man, it must feel good to have finally made it through the individual cell tests even if some of the results are not what you hoped, that is a lot of work/time.

I know you have mentioned it before, but could you restate the cliff notes of your single cell methodology for reference?
The basics is all I am asking for (charge rate, discharge rate, charge termination, discharge termination, approx ambient, and test/measurement equipment)


Your top (highest in Ah lowest on your list) 16 would make a pretty solid 16S pack. Within 1.5% of minimum rated capacity, and within 2% of eachother.
16: 281-277

Your next 16, are not so stellar, but not so bad either. Within 5% of rated (promised) capacity, and within 3% of eachother
16: 277-270

Another way to go about it would be to use the 32 lowest capacity cells, and sell the top 4 as a tested and capacity matched set.

I think you are planning 2P16S now, how do you plan to match/pair the cells?

Dzl said:

Man, it must feel good to have finally made it through the individual cell tests even if some of the results are not what you hoped, that is a lot of work/time.

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You have no idea! LOL Plus I want to get my system back online.

Dzl said:

I know you have mentioned it before, but could you restate the cliff notes of your single cell methodology for reference?
The basics is all I am asking for (charge rate, discharge rate, charge termination, discharge termination, approx ambient, and test/measurement equipment)

Click to expand...

Dzl said:

Your top (highest in Ah lowest on your list) 16 would make a pretty solid 16S pack. Within 1.5% of minimum rated capacity, and within 2% of eachother.
16: 281-277

Your next 16, are not so stellar, but not so bad either. Within 5% of rated (promised) capacity, and within 3% of eachother
16: 277-270

Another way to go about it would be to use the 32 lowest capacity cells, and sell the top 4 as a tested and capacity matched set.

I think you are planning 2P16S now, how do you plan to match/pair the cells?

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I'm going to match the capacities. I was originally going to pair highest with lowest but now I think that's a bad idea. I'd rather not have cell inconsistencies and rather just be limited to my lowest-performing pair (currently 270).

@Michael B Caro , the vendor, and I are working to see where to draw the line for warranty on these.

I'm also receiving 4 Lishens which I could easily drop into place if they test over 273 and then I'm at 273. And if I can warranty, say, the bottom 4 and their replacements and the Lishens are >=276 then I'd be at 276. That would be cool. At the end of the day, a few Ah will probably not matter to me. It just feels "dirty" to have 280Ah cells not get used to their potential because there are 270's in the mix. This is my first solar system and I'm making a LOT of assumptions about my solar generation and my usage.

You sure are persistent cinergi. I lost steam after capacity testing about 30 cells.
Thanks for sharing your experience.
My cells are probably similar to yours. That is probably normal.
And that would be fine if we weren't lead to believe we would get the full 280Ah.
Your solution of 4 replacements seems fair in my opinion.

Buying a bunch of spares at a reduced price would save a ton of work for us. Then we could just swap out the obvious duds.
You can see the duds with the BMS without testing anything.

Even that might be a waste of effort though. Most people just use them.

ArthurEld said:

You sure are persistent cinergi. I lost steam after capacity testing about 30 cells.
Thanks for sharing your experience.
My cells are probably similar to yours. That is probably normal.
And that would be fine if we weren't lead to believe we would get the full 280Ah.
Your solution of 4 replacements seems fair in my opinion.

Buying a bunch of spares at a reduced price would save a ton of work for us. Then we could just swap out the obvious duds.
You can see the duds with the BMS without testing anything.

Even that might be a waste of effort though. Most people just use them.

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lol, I lost steam after one top balance of 8 280 Ah cells. After that top balance, I put together my 8S pack, did a discharge to 265 Ah without hitting any low voltage limits and called it good. I set my bank capacity at 250Ah in my Victron BMV-712 and Chargery BMS capacity settings and operate within that range. I use conservative charge (27.6V pack absorption, 27.0V pack float and 3.6V cell BMS cutoff)) and discharge voltage settings (24.0V inverter cutoff, 23.6V DC converter cutoff, and 2.8V cell BMS cutoff). I don't try to squeeze every last Ah out of the pack, nor do I worry about "runners". I just assumed from the start I was dealing with 250Ah batteries instead of 280Ah, stay out of the knees of the voltage curve and I'm happy. The batteries should last a long time too, before I see any capacity decrease.

bdbugbee said:

I just assumed from the start I was dealing with 250Ah batteries instead of 280Ah, stay out of the knees of the voltage curve and I'm happy. The batteries should last a long time too, before I see any capacity decrease.

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Bingo. These cells are a bargain. Qualifying and then replacing a few at 96% of specification might feel good, but it is a Pyrrhic victory that places the value of our time at something like pennies per hour, for that little extra. Just assume they’re 90% of rated, or buy 10% more than you thought you wanted. Much less expensive.

I think the disappointment comes from some who purchased these cells from the group buy and were told these cells were capacity tested. When we received the cells and tested for ourselves, we found that not to be true and rightfully assumed they would test at 280ah's or better. This is what the supplier (Basen) told Michael. This is no fault of Michaels and I place all blame on Basen because it appears they lied.

Having said that, people have different tolerances as to what is acceptable. In my case I have a total capacity of 272ah's and a useable capacity of 250ah's. Do I feel I got a bargain? Yes I do. But I was disappointed when I first capacity tested the cells thinking they would test at least 280ah's. Now in the grand scheme of things that is 97% capacity. So when I look at it that way it doesn't look so bad. And given the 280ah capacity rating, a cut in 8 amps is not the end of the world...lol.

BTW, I do recommend anyone interested in cells contact Michael for quotes. He will take care of you if there are any problems or you are not happy.

Yeah, [happiness] = [reality] - [expectations], doesn't it?

Even the high end stuff (I'm looking at you, Victron) suffers from over-zealous marketing making its way into the datasheets... it's rampant.

Don't take my rigorous testing and reporting as disappointment. Take it as wanting to inform myself for cell-matching purposes AND to inform folks here in the forum. Yeah, I can build a 28kWh bank for $4k instead of $22k of Battleborns. So I'm not really complaining.

Well, I certainly appreciate your rigor, in a very selfish way.

Gazoo said:

I think the disappointment comes from some who purchased these cells from the group buy and were told these cells were capacity tested. When we received the cells and tested for ourselves, we found that not to be true and rightfully assumed they would test at 280ah's or better. This is what the supplier (Basen) told Michael. This is no fault of Michaels and I place all blame on Basen because it appears they lied.

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However, a prudent and reasonable person knows you cannot trust everything a sales person half a world away tells you. Especially when the sales culture is known for creative adaptations of the truth in order to make a sale.

What Mom told you is true, you can’t believe everything you hear. If one does there is sure to be a lifetime of disappointment.

JoeHam said:

What Mom told you is true, you can’t believe everything you hear.

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Me in second grade - "Can I stay up late cause I heard Tommy say school is going to be cancelled tomorrow."
Mom - "You can't believe everything you hear."
I go to bed and think about that I just HEARD that I can't believe everything I HEAR. A life long struggle begins....

or perhaps more appropriate would be the quote below from Raising Arizona...

Parole Officer #1- Are you just tellin' us what we wanna hear?

HI - No, sir, no way.

Parole Officer #2 - Cos we just wanna hear the truth.

HI - Well, then l guess l am tellin' you what you wanna hear.

Parole Officer #1 - Boy, didn't we just tell you not to do that?

HI - Yes, sir.

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In reality, we are most vulnerable to deception when we are being told things that we want to hear. Salesmen count on it. It was questions about the claims of lithium battery vendors that brought me to the forum. So, thanks everyone, for telling me the truth even when its not what I want to hear.

hankcurt said:

Me in second grade - "Can I stay up late cause I heard Tommy say school is going to be cancelled tomorrow."
Mom - "You can't believe everything you hear."
I go to bed and think about that I just HEARD that I can't believe everything I HEAR. A life long struggle begins....

or perhaps more appropriate would be the quote below from Raising Arizona...


In reality, we are most vulnerable to deception when we are being told things that we want to hear. Salesmen count on it. It was questions about the claims of lithium battery vendors that brought me to the forum. So, thanks everyone, for telling me the truth even when its not what I want to hear.

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I try to make it clear when I pass on information that it is what I am being told by the supplier, and for some of it (like a 5 year warranty) that I personally wouldn't count on it.
But, being only human and sometimes trying to fit 20 hours of work into 12 hours, I may at times forget to do that.

JoeHam said:

However, a prudent and reasonable person knows you cannot trust everything a sales person half a world away tells you. Especially when the sales culture is known for creative adaptations of the truth in order to make a sale.

What Mom told you is true, you can’t believe everything you hear. If one does there is sure to be a lifetime of disappointment.

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I learned a lesson. The lesson is even when things are put in writing from ANY Chinese supplier they may not be telling the truth. I am old enough to know better. But hey....even with age I learn something new every day.

They didn't have to lie to me because I didn't ask any questions. I just ordered them.
Seems like we all got the same cells.
We probably could have got all 280Ah + if we paid extra.
Probably not worth the extra money though.

All cells are now charged. Here's where I'm at now (5 cells to be inserted into the "holes" in the bottom row). No fixture until I've decided this is what I want.



A preview of the wiring I previously mentioned:



The wires in the foreground form a balanced series connection. The posts in the background would have lugs on them for series connection to the adjacent groups of 4 cells. Lugs first, bus bars second.

To cut all those wires to the same length:



And you can see the hydraulic crimper on the right. This should make for reasonably similar resistance cables.
The rest of the lugs arrive tomorrow, but the wire doesn't arrive until next week, so I can't assemble the battery until then. But I can work with what I have, plus I can insert the molex connectors (forgot to take picture) into the BMS sense/balance leads.

That's a lot of cutting, stripping, and crimping batman!

BMS, breaker, etc, will be temporarily mounted somewhere on the right. In the final configuration, the first and last cells will have an additional mounting "plate" on the end for that equipment.

hrm.. another thread got me thinking ... why not turn the cells around and parallel them with wire (not enough room to create a flexible wire connection if the poles are on the same side) like so?



If I do that, then I could do spring-based compression fixture, 8 cells to a fixture, and reduce the number of anderson (and molex) connectors. I think I could still lift the ~95 pound group of 8 cells into the truck and then into the RV when that time comes.

So many things to try! haha. I only wish it didn't mean 64 wires and 128 hydraulic crimps... and what if I don't like it?