4s4p LiFePO4 Build Log

ed209

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Joined
Nov 27, 2019
Messages
29
Finally ready to build a battery! Will document my progress here over the next couple months. Please let me know if this is not an appropriate place to do so.

Battery Build Diagram v3.png

Major Parts list:
Modular toolchest (DeWalt at top of list, rated for heavier weights)
SAB 3.2v 55ah 176wh 60280 cells in 4p4s (2816 wh) (https://batteryhookup.com/products/8x-new-sab-3-2v-55ah-176wh-60280-cells)
150a BMS with bluetooth (https://www.aliexpress.com/item/1005001633527595.html)
6061 aluminum plate connectors (fabricated from scrap)
3d printed polyurethane (TPU) support bumpers
Samlex PST-1500
Renogy DCC50S
Anderson SB120 connectors
4ga wiring throughout

Application:
Secondary battery for my Chevy Volt (Gen 1) and portable for other uses/vehicles
Learning for future BAB (big-ass battery) for a home

Notes:
I've never ordered a part from China. This one looks like the same manufacturer as what Overkillsolar uses. Since I have to wait for backlog shipping anyway, I opted for this one.

Outstanding Questions:
Q: Is coating all terminals with dielectric grease the standard procedure? With proper torquing aftwards.
A: will be using Noalox for the cell bus bars with regular torque checks for the first couple weeks. Dielectric grease (Super Lube) on the rest.
 
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ed209

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Nov 27, 2019
Messages
29
Oops... there's a time limit on post editing. More info here: https://diysolarforum.com/threads/edit-post-time-limits.112/

I got half of my cells so far. The other half is taking a scenic tour across America, apparently. Speaking of FedEx, the Renogy warehouse is about 10 miles from where I live in California, yet my DCC50S went out to Louisiana first, 1600 mi away. Logistics™

The cells I received so far also have (stainless steel?) nuts, which was an nice bonus. They seem OEM, so if the other shipment also have nuts, I will be returning the lug nuts I purchased. Turned out that automotive lug nuts have the same threading as these cells (M12-1.25), and they were far cheaper than anything else I could find.

Current status: top balancing the cells. It will be a few weeks before my BMS arrives so I'm passively balancing my cells for now. I have an old hobby charger that amazingly has LiFePO4 battery settings, so I will use that to do my final balance.

Since I'll be using aluminum plate for the final configuration, I needed a cheap way to connect my cells for balancing.

Enter 18 gauge copper hanging wire. Only cost $6 for 25 feet at the local store, and after carefully measuring all the voltages and double checking my math, they worked just fine. I also wouldn't do this will small cells... in this case the terminals are almost 1 ft apart.

I found the cells were tested by Batteryhookup in batches of 4, with matching voltages in each. One set was about 3.28v, the other 3.22v. They seemed close enough™ in voltage, so I first paralleled each set, then used 2 connecting wires to link the two sets together. At max, there were about 4.5 amps going through the pair of wires, not even enough to get them warm. I wore my safety glasses just in case!

passive balancing.png
Again, this is just a temporary solution to perform the balancing.

added washer.png
I had to use a flat washer because there's a bit at the bottom of the terminal with no threading.


Renogy unit seems really solid. I like how all the screws had flat washers and split washers attached, instead of relying on the plasticity of the plastic to hold things in place. I'll open it up later and post some pictures. (attached)
Update: Everything looks really, really good in the Renogy unit, no complaints!

BMS update: looks like I ordered the same BMS as used in this SOK knockoff:
 

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ed209

New Member
Joined
Nov 27, 2019
Messages
29
It was truly sad times when the box I chose did not fit all 8 in a row.

fitment.jpg


After reviewing many options, I've decided to keep the box for now. Other suitable options were either too expensive or not strong enough to carry the batteries. If I can find a good used pelican case I may change it up and go for that instead.

I'm using a symmetrical design for the bus bar plates. They will serve multiple functions: carry current, separate the batteries, and secure them in the box. I originally though of using two layers of heavy rubber mats: one solid, and one slotted to fit the bus bars and hold them in place. But, those things are expensive and I'm already over budget. I might end up just printing some thick TPU "socks" and utilize some floor mat scrap I have.

Since I had time while the second set of batteries were touring the country, I printed some bus bars to mock the setup.

mock1.jpg
Full pack of 16 batteries. Suckers are heavy.

mock2.jpg
Staggered to reduce width.

mock3.jpg
A spacer will be printed (in ASA) to keep this area separated. About 2mm clearance between batteries.

The new set also included nuts, but this time most of them were aluminum. I should still have enough room to include the split lock washer, but no flat washer.

Finally, since I'm going through all this trouble with the batteries, I'm adding a 1/4" clear acrylic panel to go on top. I got a cheap hanging sneeze guard that will be cut to fit. There's a good chance I will also use the acrylic to mount the circuit breakers, to avoid more (if any) holes in the box itself. If I keep it.
 

ed209

New Member
Joined
Nov 27, 2019
Messages
29
Changed the box. Instead of the rolling toolbox, I'm going to use the DeWalt Toughsystem 2.0 Large Tool Box. The huge rolling box was awesome but it was just too big with too much wasted space. And the more stuff I crammed into it, the more structural support issues I was encountering.

I went with the modular system in the first place to avoid this issue. So, going back to the original design, and adding the open tote box from the original Toughsystem series to hold the inverter and other miscellaneous. I had to order the tote, so we'll see if the dimensions are accurate and there's not too much inside geometry to fit the Samlex.

The bad part of the new box is it's slightly too short, depthwise, to lay the cells in my original configuration. I didn't realize the rolling box was actually larger, and I admit to several minutes of panic and regretting the entire project. Then, after some experimenting with a sideways configuration I realized it not all was lost. Stacked 4 high and adding some space, it will stay just below the lip of the box.

Current status:
- now passively balancing of all 16 cells.
- The BMS has passed US customs and should arrive soon.
- rearranging cells and components to fit in the new box. It's going to be a tight fit but I think I have a design that works, as well as hole placement for external connectors. Still deciding whether to arrange cells in alignment or staggered to slightly lower the height, since I now have the room -- though I can also utilize the lid for stability. If the acrylic plate is good quality it might be usable as structural support and electrical isolators.
- Also don't know how hot the Renogy unit will get at full 50 amps (or the BMS at full load, for that matter). I have contingency for adding a fan and vents.


left.pngright.png
 
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ed209

New Member
Joined
Nov 27, 2019
Messages
29
3D print gallery time!
- SB120 panel adapter custom fit for the box
- aluminum plate templates for tracing cut lines (half height since my printer is small)
- cell end cap cover while cleaning the terminals. Some of them are grimy and could use a brushing.

Also discovered that most of my plate is 3/16", not 1/4". Quite happy with that: less weight, easier to cut and drill (since I've only got hand tools).
 

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ed209

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Joined
Nov 27, 2019
Messages
29
BMS finally arrived! Took one week to arrive after clearing US customs.

It seemed well-wrapped and packaged, though the box is a bit mashed on one side.

BMS comes with:
2x temperature probes (glued in, they really don't want you to remove them!)
Balance leads, about 23" long
- with ring terminals and screws. Ring terminals have a large crimp point so will crimp+solder them.
Decent instructions, all things considered
Terminal connectors are M5-0.8 threading

Also got the bluetooth module which is in a clear shrink-wrapped sleeve.

Planning on mounting it with some old computer fasteners which fit perfectly (6-32 thread I believe). Using motherboard standoffs and some old heatsink shoulder screws (need to find some small washers).

I won't be able to test it until later this week when I finish up the bus bars. Which are currently the ugliest hunks of metal ever created. In retrospect I should have bought a month at the local maker shop.
 

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tlag95

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Jun 30, 2021
Messages
3
Impressive detailed updates! I'm sure there are plenty of us following your project and looking forward to the final build. I know I am considering a build with those cells as well so really appreciate your efforts documenting everything for the rest of us!
 

ed209

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Joined
Nov 27, 2019
Messages
29
Test fitting bus bars ...we have 12 volts!

Need to make a bunch of tweaks, though I wish it were feasable to remake them. Main fix is they are too high by a few millimeters because I failed to notice the lid has a part that's much lower than the rest.

Also quickly coming to a design crossroads: continue with stealth anderson ports on the sides, or feed the wires through the front, making the connectors visible? The latter has so many usability advantages and solves many of my design problems but doesn't look as good... dangit.
 

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ed209

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Joined
Nov 27, 2019
Messages
29
Lesson of the day: do NOT buy this kind of breaker!
do not buy this.jpg
During charge testing, this mf-er caused such a headache.


EDIT: your mileage may vary but my experience was not good. Sketchy connection and breaks way under rated amps. I'm replacing it with a standard breaker from a recommended seller.


In other news, everything works! Including charging once I figured out the above breaker was junk.
- BMS - It works and seems extremely efficient. Tested light loads up to 50 amps with barely any heat.
- Dug out the trusty Hakko station to attach the leads for the balancing cables. I did a modified crimp, flood-filled the crevice with solder, and poked in the tinned wire. The included ring terminals were aluminum but my leaded flux solder worked just fine. One terminal had to be enlarged with a step drill bit, and since they only provided 4, I reused a damaged copper ring terminal for my last lead.
- Bluetooth works great with both the iOS and Android apps. I used Overkillsolar's Android version because it has more features and is free. Link: https://overkillsolar.com/support-downloads/
- charging - Renogy unit is rated for 50 amps, measured at 48. It gets uncomfortably hot without active cooling. In the spec sheet it's rated at up to 80C with reduced amperage at 60C. This is really high tolerance so I might be able to avoid cutting an external vent with 60+ lbs of battery as a thermal soak. There's also the option to open the lid -- though that's only when the vehicle is stationary.

Security of bluetooth
While connected, the bluetooth module will not accept another connection. It's surprisingly stable and persistent, but there are no security protocols (pairing) in place. This also means if I'm not connected, anyone could modify settings. Admittedly, the chance is low that someone will walk around some campground looking for BMSes to sabotage. I'm going to install a switch just in case.
 

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ed209

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Nov 27, 2019
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Tangent.

Here's where my scrap aluminum came from. Around 8 years ago I made a computer case based on a micro ATX form factor. It was completely impractical and the cooling sucked, but it worked and I was proud of it.

I figured I'd share since only a few people have ever seen it. Some day I'll remake it for a mini ITX or NUC.
 

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Draconius

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Joined
Mar 23, 2021
Messages
92
Lesson of the day: do NOT buy this kind of breaker!
View attachment 60430
During charge testing, this mf-er caused such a headache.



In other news, everything works! Including charging once I figured out the above breaker was junk.
- BMS - It works and seems extremely efficient. Tested light loads up to 50 amps with barely any heat.
- Dug out the trusty Hakko station to attach the leads for the balancing cables. I did a modified crimp, flood-filled the crevice with solder, and poked in the tinned wire. The included ring terminals were aluminum but my leaded flux solder worked just fine. One terminal had to be enlarged with a step drill bit, and since they only provided 4, I reused a damaged copper ring terminal for my last lead.
- Bluetooth works great with both the iOS and Android apps. I used Overkillsolar's Android version because it has more features and is free. Link: https://overkillsolar.com/support-downloads/
- charging - Renogy unit is rated for 50 amps, measured at 48. It gets uncomfortably hot without active cooling. In the spec sheet it's rated at up to 80C with reduced amperage at 60C. This is really high tolerance so I might be able to avoid cutting an external vent with 60+ lbs of battery as a thermal soak. There's also the option to open the lid -- though that's only when the vehicle is stationary.

Security of bluetooth
While connected, the bluetooth module will not accept another connection. It's surprisingly stable and persistent, but there are no security protocols (pairing) in place. This also means if I'm not connected, anyone could modify settings. Admittedly, the chance is low that someone will walk around some campground looking for BMSes to sabotage. I'm going to install a switch just in case.
Why the hate on that breaker? I've got a 40a and 50a in my van.

One note...the OverkillBMS app (3.1.2026) doesn't have the ability to unlock the BMS in the event of protection. Only way out is to unlink, install 3015 version, link, hit the big unlock button, unlink, uninstall 3015 and then install 3026
 

Supervstech

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Why the hate on that breaker? I've got a 40a and 50a in my van.

One note...the OverkillBMS app (3.1.2026) doesn't have the ability to unlock the BMS in the event of protection. Only way out is to unlink, install 3015 version, link, hit the big unlock button, unlink, uninstall 3015 and then install 3026
For the simple reason they are totally unreliable. If they are passing current, they likely are never going to trip… if they are not passing current, they likely will never hold the rated value.
ditch them and get a quality buss brand. Or build a din rail and install rated dc breakers.
 

ed209

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Nov 27, 2019
Messages
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Why the hate on that breaker? I've got a 40a and 50a in my van.

One note...the OverkillBMS app (3.1.2026) doesn't have the ability to unlock the BMS in the event of protection. Only way out is to unlink, install 3015 version, link, hit the big unlock button, unlink, uninstall 3015 and then install 3026

I will add a note. The particular brand I got kept tripping at <50 amps, and would randomly disconnect while the switch was still engaged. On inspection I noticed some play in the connection barrels as well. Caused me a lot of grief while troubleshooting in a hot garage.

Thanks for the info about OverkillBMS app. It still doesn't guard against external connections which I want to avoid.
 

ed209

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Nov 27, 2019
Messages
29
For the simple reason they are totally unreliable. If they are passing current, they likely are never going to trip… if they are not passing current, they likely will never hold the rated value.
ditch them and get a quality buss brand. Or build a din rail and install rated dc breakers.
Yep, got it on a whim, while my other breaker is the recommended "T Tocas". New one is on order!
 

Draconius

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Mar 23, 2021
Messages
92
For the simple reason they are totally unreliable. If they are passing current, they likely are never going to trip… if they are not passing current, they likely will never hold the rated value.
ditch them and get a quality buss brand. Or build a din rail and install rated dc breakers.
Why won't they trip? Isn't that their purpose?
 

ed209

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Nov 27, 2019
Messages
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Top balancing cells with my little hobby charger. I can't get it to push more than 3 amps so this is going to take a while (I forgot to fully charge it while assembled). Since it's an actual charger and not a power supply, I do feel comfortable letting it run all night unattended... famous last words, perhaps.

Sliced ~5 mm off the bottom of each bus bar, for fitment. Some regret for not going with a staggered arrangement.

Started printing TPU "socks" for the bus bars. 3mm walls with 100% infill.

Also ordered an active balancer for maintenance without disassembly, if needed.
https://www.aliexpress.com/item/1005002617607510.html
I discovered that a switch can be added to one of the popular 5A active balancers, by desoldering the "run" terminals (credit to the fantastic Off-Grid Garage YouTube channel)
 

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ed209

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Nov 27, 2019
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Fun fact: my charger's time and mAh readings top out at 65535 (2^16 including 0)

Time gets stuck at 92:15 which is 1000 minutes (rollover) + 92 minutes + 15 seconds = 65535 seconds
 

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Sophie_Electrix

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Aug 2, 2021
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Thank you for sharing all the details of your project. I'm thinking about buying the same batteries but like you've already said, finding a big enough tool box / container is a problem.
 

tim0shel

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Jan 27, 2020
Messages
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Those breakers are something else I have been looking at some that I would like to connect between my inverter and MRBF fuse. Want it mainly for the compact size of having a disconnect.
 
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