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

JRG

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Dec 7, 2020
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76
Really nice battery build! Maybe you've already answered this, but with the solid buss bars and a set-up to allow expansion between the cells, isn't that an issue?
 

cinergi

1.21 Jigawatts
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Aug 9, 2020
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Really nice battery build! Maybe you've already answered this, but with the solid buss bars and a set-up to allow expansion between the cells, isn't that an issue?

That's the common theory here and what makes logical sense -- but my testing revealed 0.2mm or less movement between terminals between 10% and 100% SoC - so I decided solid bus bars are actually OK.
 

cinergi

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OK, I've started when damn well better be the final version of the battery 😂

Two separate packs of 16 cells (remember this is a 2p16s battery - so each pack is actually 2 in parallel, 8 in series). Sitting on top of the same plywood ends with angle bracket and rubber feet. I've added 1 more rubber foot to each end. Spanning the length is two 1"x2" t-slot aluminum. Surprisingly strong - I'm getting almost no flex with the 16 cells on top of it. Those will "float" on top of the angle bracket, allowing for the cells to "breathe".

I'll be using the same 1/4" by 1" solid copper bar between everything. 4-5 shaped pieces of 3/4" by 1/16" copper bar from the end cells to their endpoints (breaker, relay, and interconnect terminals).

I've moved up to 3/8" threaded rod and will use 6 per pack instead of 4. The threaded rod is also medium strength (70,000 PSI instead of 40,000). This should give me extremely high strength and consistency. As a result of going with 16s AND increasing from 4 to 6 rods, I've ordered new springs (due tomorrow).

I intend to drill & tap small holes into the bus bars and connect the BMS leads to that instead of using the cell terminal connections. This will keep everything else off the terminal -- that way a serrated nut will directly contact and dig into the bus bar and provide a nice durable vibration-resistant connection.

I've sacrificed the ability to move the pack (too heavy now) for less AC ripple. But since this is a much easier pack to build (mostly due to single 4-terminal bus bars for everything), I'm OK with that. I'll have to disassemble and reassemble one more time.

IMG_9230.JPG

IMG_9231.JPG

IMG_9232.JPG
 
Last edited:

bdbugbee

Solar Addict
Joined
Mar 26, 2020
Messages
118
OK, I've started when damn well better be the final version of the battery 😂

Two separate packs of 16 cells (remember this is a 2p16s battery - so each pack is actually 2 in parallel, 4 in series). Sitting on top of the same plywood ends with angle bracket and rubber feet. I've added 1 more rubber foot to each end. Spanning the length is two 1"x2" t-slot aluminum. Surprisingly strong - I'm getting almost no flex with the 16 cells on top of it. Those will "float" on top of the angle bracket, allowing for the cells to "breathe".

I'll be using the same 1/4" by 1" solid copper bar between everything. 4-5 shaped pieces of 3/4" by 1/16" copper bar from the end cells to their endpoints (breaker, relay, and interconnect terminals).

I've moved up to 3/8" threaded rod and will use 6 per pack instead of 4. The threaded rod is also medium strength (70,000 PSI instead of 40,000). This should give me extremely high strength and consistency. As a result of going with 16s AND increasing from 4 to 6 rods, I've ordered new springs (due tomorrow).

I intend to drill & tap small holes into the bus bars and connect the BMS leads to that instead of using the cell terminal connections. This will keep everything else off the terminal -- that way a serrated nut will directly contact and dig into the bus bar and provide a nice durable vibration-resistant connection.

I've sacrificed the ability to move the pack (too heavy now) for less AC ripple. But since this is a much easier pack to build (mostly due to single 4-terminal bus bars for everything), I'm OK with that. I'll have to disassemble and reassemble one more time.

Awesome! Are you planning to insulate the bottom of the cells from the aluminum rails when you install in your RV?
 

cinergi

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Awesome! Are you planning to insulate the bottom of the cells from the aluminum rails when you install in your RV?

Thanks!

Nope - the bottom of the cells have a pretty thick stuck-on layer just like the tops do ... and I need the cells to be able to freely slide around on the aluminum (extremely smooth) as they breathe, so I don't see any problems with e.g. abrasion.
 

Luthj

Photon Sorcerer
Joined
Jul 1, 2020
Messages
946
The bottom and top plastic caps are pretty high density. No worries about abrasion in a fixture like that.
 

cinergi

1.21 Jigawatts
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New springs arrived. Extra long so I maintain more consistent pressure and so I don’t have to torque them flat at 100%

my parts list is updated if you want the link / specs.

18567E35-71AC-48AF-8BFB-0CB70F0BDF45.jpeg
 

uberpixel

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Jun 14, 2020
Messages
50
I repaired one of my cell's threads:
Great video! Thanks for putting this together. This could be very helpful in the repair of the crooked threads in my recently acquired Lishen 272ah cells. [thread link]

It would appear that you didn't break the tang off of the helicoil after it was inserted - was that to avoid damaging the terminal? Seems like you'd gain another thread of engagement, but maybe not worth the risk? Am I correct in the assumption that you didn't break it?

-uberpixel
 

cinergi

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Great video! Thanks for putting this together. This could be very helpful in the repair of the crooked threads in my recently acquired Lishen 272ah cells. [thread link]

It would appear that you didn't break the tang off of the helicoil after it was inserted - was that to avoid damaging the terminal? Seems like you'd gain another thread of engagement, but maybe not worth the risk? Am I correct in the assumption that you didn't break it?

-uberpixel

I didn't break it off. I was being lazy. I'll try to break it off and see what the difference is.
 

cinergi

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I assembled the top row into it's new 16-cell compression pack with the new springs and rods. The bus bars no longer fit by a significant margin even after putting them back under compression. Removing them from the compression at 100% SoC was a bad idea. I'll have to discharge using flexible bus bars and then retry the solid bars.

I screwed up 6 of the threaded rods and need to buy 6 more. *sigh*

IMG_9238.JPG
 

uberpixel

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Jun 14, 2020
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50
I didn't break it off. I was being lazy. I'll try to break it off and see what the difference is.
I guess if you’re getting adequate torque maybe no need to poke the bear? Those short helicoils look like they could do the trick for my repair without too much grief. Just not sure if the M7 tap will be large enough to cut away and correct the off axis direction that my holes were tapped.

Let us know if you try breaking tangs off and how it goes.

-uberpixel
 

cinergi

1.21 Jigawatts
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I guess if you’re getting adequate torque maybe no need to poke the bear? Those short helicoils look like they could do the trick for my repair without too much grief. Just not sure if the M7 tap will be large enough to cut away and correct the off axis direction that my holes were tapped.

Let us know if you try breaking tangs off and how it goes.

-uberpixel

Yeah I forgot to mention - I don't know if drilling M7 will let you straighten the hole *if* it's a crooked hole. Maybe the threads are just crooked?

I'll go break off a tang tonight and report back.
 

cinergi

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Let us know if you try breaking tangs off and how it goes.

I don't have any tangs apparently. I'm not sure if I broke them off during installation by twisting the installation tool hard or if they got sort of shoved out of the way with the beveled edge of the stud. I'm getting 4.5 - 5 turns.
 

uberpixel

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I don't have any tangs apparently. I'm not sure if I broke them off during installation by twisting the installation tool hard or if they got sort of shoved out of the way with the beveled edge of the stud. I'm getting 4.5 - 5 turns.
Well, that explains why I didn’t see any in the bottom of the hole when I paused your video. I must have watched that part 5 times to figure out what you did.

I think the intention is that you hit the tang with a punch and then remove it from the bottom of the hole. Without knowing how much precious aluminum is left at the bottom of the hole that part scares me. There’s a video online of a guy just bending the tang back and forth with a small screwdriver. Maybe it’s unnecessary?

I guess for now it will just have to be the mystery of the missing tangs.

-uberpixel
 

cinergi

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Well, that explains why I didn’t see any in the bottom of the hole when I paused your video. I must have watched that part 5 times to figure out what you did.

I think the intention is that you hit the tang with a punch and then remove it from the bottom of the hole. Without knowing how much precious aluminum is left at the bottom of the hole that part scares me. There’s a video online of a guy just bending the tang back and forth with a small screwdriver. Maybe it’s unnecessary?

I guess for now it will just have to be the mystery of the missing tangs.

-uberpixel

yeah if I still had a tang, I would have moved it back and forth. They're notched so they're relatively easy to break off.
 

cinergi

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Some progress on the build ... The compression fixtures are done & tuned. The end boards with equipment are basically done. I need to receive the 3/4" x 1/8" copper so I can connect the battery terminals to the relay and breaker and also make the connection between the breaker and the positive battery terminal. I've installed the new 3 amp ceramic high AIC fuse and the terminal blocks which will allow me to run that positive line up to the BMS and relay area. The Ethernet jack is installed and wired to the CANBUS (this is how the Victron's connect to the CANBUS). I've played around with bending 3/4" x 1/16" copper and that's easy ... hoping the 1/8" isn't too bad (plus I have a cheap bending tool).

I'll get the system back online with dissected CALB bus bars so that the cells can do their initial compression. This certainly begs the question -- what do I do if I have to service the battery and decompress? The permanent bus bars don't fit after they expand. I'll discharge to 20% before I head to KS to pick up the RV and we'll see if I can get the system back together with the rigid bars. I hope so!

Negative battery side with BMS, ethernet, and terminal block for incoming positive juice:
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Back of that board - the Gigavac MX14 arrived and sips power exactly to its specs! I love the 1/4" x 1" bus bar between the relay and the negative battery bulkhead terminal - lined up perfectly.
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Positive board with circuit breaker, ceramic 3a fuse, and positive bulkhead terminal:
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Front of that board (breaker not screwed in yet):
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I really need a jigsaw! Dremel kinda-sorta did the trick with that square hole and a saw blade.

If you're paying close attention, you'll see that I'm mounting the breaker differently than I have before which I needed to do in order to make working with the bus bars easier and to give me enough room for everything (especially the bulkhead terminal).
 

cinergi

1.21 Jigawatts
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Got the battery back up and running using temporary broken down CALB bus bars and temporary 1/16" copper bars to the end boards and interconnects. I am very surprised at how much power I can pull through this system (the CALB bus bars are 0.5mm by 22mm, plus the 1/16" x 3/4" bus bars and the 1 gauge wire for the interconnect.. The system remains cold at 3500 watts and the bus bar feeding the relay gets +15F at 5500 watts. Really makes me wonder how much bus bar I actually need. Anyway, doing a standard discharge so the cells will all compress ... I'm seriously debating just using the CALB bus bars now.

I realized today that the outer boards are going to be subject to the changes in compression -- meaning the bus bar connecting the terminals to the outer board needs to flex a little. I took measurements at 100% SoC and will check at 10% to see how much I need to compensate for. Either that or lightly spring mount those, too.

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Here's the BMS / negative board:

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Front side of both end boards

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The other end - interconnects

IMG_9254.JPG
 

cinergi

1.21 Jigawatts
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Aug 9, 2020
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With the battery at 4% I disconnected everything and put the massive rigid bus bars back in place. I finished fabricating the rest of the rigid bus bars and put the battery back together. The voltage variation in the AC ripple of the battery is massively better -- each cell varies 1mv instead of 30. Yeah, so I'll be sticking with my rigid bus bars.
I cranked 140 amps of charge into this and those silly little 1/16" x 3/4" bus bars only got to 90F (up from about 60F). I think 1 piece of the 1/8" x 3/4" I'm waiting on for my final version is more than sufficient! If 1/16" x 3/4" can sustain 8kW then I really don't need anything bigger.
Even that 1 gauge interconnect wire got only a little warm.

Loving the MX14. It only gets luke-warm.
 

cinergi

1.21 Jigawatts
Joined
Aug 9, 2020
Messages
1,166
I spent a few hours replacing the skimpy 1/16" x 3/4" bar with 1/8" x 3/4" ... and spent some time getting some nice bends. I also decided I should use the tinned 1/4" x 1" to join the "end" cells before connecting this -- both to match up the resistance of all my bus bars better and to prevent direct copper on aluminum.

This one was the worst -- the shape is to accommodate the expansion/contraction of the fixture and I wanted the bar to come up from the bottom of the relay so that I had access to the bolt:

IMG_9257.JPG

I used this cheap bender to make those bends. It doesn't make the best bends but it's a lot better than I could do without it.

Here's that bar installed (and you can see it sitting on top of the 1/4" x 1" bar):

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More pictures:

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Charging at 8kW ... those bus bars didn't get the slightest warm. The AC ripple of the battery is very very low (I can no longer measure it on my DMM). My per-cell delta-V at 140 amps of charging is ~30mv. All the cells are within 1mv while resting. Amazing sauce.

All that's left for me to do now is heat shrink the bars and do some cable management. I'm waiting for stuff to arrive before I can do that. But in the meantime, I'm just continuing to cycle the pack daily and I've got 400 of ground mount solar deployed to exercise that, too.

I'm getting close to the point where I can do a video series of the entire process.
 
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