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The Powershed
I'm very excited to share my project and document my progress. Anyway, I got involved with 18650's when I spec'd them for use in my Startup's line of IoT devices. I bought a few genuine ones, then when I need to source a large quantity, I reached out to a local computer recycler. We've reached an agreement and I get about 100 ish packs per week now for free. Most of those cells go towards our IoT efforts, but I took some and put them towards building a powerwall. I can only use cells 2500+mAh for my requirements for the IoT devices, meaning I have like 1500 passing cells that don't meet the threshold. 

I've tested something like 2000 cells now. With my 7 opus chargers, I can test 80 ish per day. They are being mounted on plywood and getting neatly cabled this weekend. 5/7 of them have the fan mod with an 80mm case fan. The bigger fan works great. I don't need to do any external cooling on them. 

One week's haul

Old opus setup

I've been putting together my packs with 2000-2300 mAh cells. The system is designed to be 7s 80p with a 40 amp draw. It became hbpowerwall style by accident. I wanted to limit my draw per cell to 0.5 A (hence the 80p) for longevity and the fact that these cells are repurposed laptop cells. My capacity should be around 4.5kWh. 

The cells are being made "Tesla style", cell level fusing on both sides with 1/8w resistor legs serving as the fuse. The bus bar is 6ga stranded bare copper wire with mechanical lugs screwed on for the series connection. 

I've soldered 6 of the packs completely now. I'll add pics later when I finish the seventh (The shop is a mess). 

These packs are going into my shed - 

I've got two 100w panels on it at the moment, but it will need more. Those panels are tied into an Epever Tracer 4215BN MPPT charge controller. There's a failing offgrid system in there that will be ripped out when the lithium batteries are ready. The lithium packs will be connected to an 800w Reliable Electric pure sine wave 24v inverter. That will be connected to a little subpanel converted to a main lug one to feed the shed. 

The loads in the shed are minimal. My idle load is 20-30w. The inverter powers the lights inside and outside of the shed, the ip surveillance cameras outside and the powerwall computer. There are outlets for intermittent small power tools and chargers inside. No - the camper trailer will not be plugged into this powerwall, at least not at the moment. It would be nice to get to that point one day though. 

The powerwall computer is connected to the charge controller. The epever has neat software that lets you monitor everything about the controller and set parameters. One day when I can afford a propper batrium setup, it will be connected to the computer.
gregoinc, wim, Korishan And 1 others like this post
So after the festivities of Thanksgiving yesterday I finished soldering all my packs. I've got the 260w weller solder gun and that thing stinks. I do not recommend. The trigger switch lit on fire when I was using it, so I had to jurry rig it to work. I went through 8 of their tips making these packs, which is crazy. Anyway, I got it done and put the packs in series yesterday night.

Here's the readings from my idst bg-8s while I was balancing them sitting on the bench. I didn't have an extra 8 pin jst connector so I soldered some dupont connectors from my arduino stuff to some wire to connect the packs to the balancer temporarily. 

Packs going up after I ripped out the old system and put up a sheet of plywood for the stuff to attach to. You can see the solar feed dangling there. 

The rough in and testing of the components working together. The batteries are sitting on a wooden shelf made from a piece of plywood strong-backed onto the wall. I think I'm going to try to cover the battery packs with a sheet of acrylic or something or maybe some foam insulation board to keep them warm in the winter. There's no climate control or insulation in the shed and it gets down to 10F or so in the winter here. 

The battery and solar have a 40 amp inline resettable fuse on them. I'm not sure I like those fuses. I may order a din rail and some nicer breakers. 

Close up of component wiring. I didn't realize I left my level on the charge controller lol. 

The wiring still looks like spaghetti and it's the first thing on my to do list to tidy up tomorrow. I've some cable staples and clamps I'm going to use and make things neat and tidy. 

All the wiring except for the balance leads is 4 awg stranded copper. If you notice, I took a slightly unique approach to my balance leads. Each balance lead on the battery is 18 awg copper running from the lugs on the battery to the terminal block under the charge controller. I wanted to be able to plug in my idst unit on demand without unplugging the bms. Since the amp hour rating is so large compared to the measly 100ma balancing current on that chinesium bms, I also wanted the flexibility to install a higher power balancer - if such a thing exists. A batrium setup is out of the budget now. 

By the time I finished this it was dark and there was no solar power to charge the pack. It's running at about a 30w idle load right now. We'll see what I see when I open the charge control monitoring tomorrow morning. I installed it at 5 at 29.4v, 6 hours later I'm seeing 29.13v. Compared to my gell batteries, this is a big improvement.
RikH, jdeadman, Korishan And 1 others like this post
Looking good Mate
Consider the low temp Problem. Going under 0 degrees C will half your power and half the cycles . If not worse.
0,8kWp in Test
4 kWh battery target
Ultra low cost
The low temps haven't been a problem so far and we've had temps down to 20F or -7C. I've seen typical drain and capacity under those conditions. I believe you that it will be a more of a problem when temps get down to -15C ish. I'm open to suggestions, but there isn't much I can do. If it becomes a big problem, I can make a cover out of some insulation board and put a little heating element inside to keep things a tad warmer. I'm not sure how I feel about that for safety reasons, but it's something to keep in mind. I've been following averagejoe's cold weather build and I'm patiently waiting for some results from him too.

Two weeks after initial installation, things are still working nicely. One thing is very clear though, I need a bigger solar array. It was pretty cloudy and rainy for 5 consecutive days so I turned on my charger for a while to keep things running.  My idle load is 30 watts, so I'm pulling a minimum of 0.7kwh per day. I think the lowest voltage I've seen so far is 24 ish volts, after that cloudy period, so I think that's pretty good with my solar array size. The winter sun is killing my solar output. 

Here's a slightly more cable managed picture that I forgot to post a while ago. BMS and balance leads got mounted and straightened out. The bg-8s is still kinda hanging there temporarily. 120v distribution still isn't done yet hence the power strip. After the pictures were taken, I reinforced the wooden shelf with some metal corner brackets that made everything much stiffer. 

The third inline fuse got installed to the solar feed - 

Powerwall computer got mounted on the wall with some aluminum U channel to slide it out easily. 

Got my battery testing station mounted up and looking significantly better. 

Just in time for another 100 packs to show up. (for free!) More to come this week too. 

Korishan likes this post
Looking good.

Just because the "ambient" temps are 20F/-7C, doesn't mean the cells themselves are that cold. If you are actively charging/discharging them, they may stay above 32F easily. Considering your powerwall sections above the inverter/chargers, the heat rising is probably helping to keep them warmer, too.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
Exactly, I have a battery temperature probe on the pack through the epever controller, so I always know what the cell temps are. I haven't seen it lower than 32F.

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