When I left you in Part 5 of the Powerwall series, I said I was done. That was the case, I don’t think I will ever be done. Part 6 is a testament to all the bits and pieces I have done since to get a fully configured Powerwall that I am happy with.

Batrium and Goodwe CANbus Communications Issue

In Part 5, I mentioned and had a video of the problem I was having with the CANbus comms link between the battery management system (BMS) and the inverter. In a nutshell, during discharge, I was seeing the inverter constantly stop discharging from the battery. It stopped discharging then started at random intervals. Now, I spent a lot of time trying to fault find this. I even went to the extent of sniffing the Batrium CANbus comms and learning and converting the outputs so I could see if that was the problem. As it turns out, it was not the CAN comms causing these symptoms.

After two months of trying different settings and combinations on both the Batrium BMS and the Goodwe Inverter, I finally contacted Goodwe again and asked if I could purchase a new Goodwe ‘GM1000’ Smart Meter. The support guys here in Australia sent me one out straight away via TNT Express without charge. It’s kinda like they knew it could have a fault. No questions asked…(Thanks Goodwe!) I was very skeptical that this would fix the issue. However, I did get my electrician over and we installed the new one. Low and behold the inverter could now track the battery usage better and no dropouts on the DC battery side at all! If only I had tried this first!

A battery Upgrade

As it turns out, the 9-10 kW 18650 pack I spent so much time on is not enough to give me coverage throughout the afternoon and the night. I went very conservative with my usable battery voltages and on average my battery was reaching its bottom voltage around 3 or 4 am. I was ok with that at first as the power usage between then and when the solar kicks in were minimal. However, as luck would have it, an opportunity presented itself and I was able to get a hold of 16 x LifePo4 prismatic cells. These suckers are around the 400Ah mark in capacity and were used in a trial bus project which by all reports did not progress past a trial. Not only was the added capacity what I needed, but the LifePo4 chemistry is much safer than the 18650 lithium cells currently in service.

Bus Bars

With new cells come new busbars. I wish it had been this easy from the start. Measure the distance between the lugs, cut and drill some super thick copper and voila, bus bars for days! If only it were that simple, hey! As it turns out, these cells actually swell slightly, and having a solid bus bar can cause issues at the lugs. It is suggested that you use some kind of flexible busbar so that when the cells swell slightly, the pressure is not on the terminal. I am yet to source some flexible links.

Done? Probably not…

So what do you think? after all that I don’t think I’ll ever actually be done with this Powerwall build, however with the fixes and additions, I am hoping that it is more peace of mind and only periodic maintenance. Onto bigger and better projects now. Bring on the Electric vehicle build!

If you missed the first parts of the build.

Part 1 – Recycling batteries
Part 2 – Building Packs
Part 3 – Fusing and cell protection
Part 4 – That’s a wrap
Part 5 – Finally Finished (Kinda)

After a small bit of research, I stumbled across two resources that have become staples in my DIY Powerwall diet. Those are the Second Life Storage forum and the HBpowerwall Youtube channel, run by Peter Matthews. Using these two resources you can find out just about everything you need to know about building your own power-wall. Check out the links. Also, check out my journey below.

First Steps – Find Laptop Packs, Pull them apart…

Some of the DIY’ers find this step one of the most difficult. Finding laptop battery packs to recycle the 18650 cells can be tricky. I approached a few battery stores and computer stores but most seemed disinterested in selling me the old packs. I am not sure if it’s a health and safety thing, or they get more recycling them. However, after finding the right people through a few Facebook groups I was able to get a steady supply of laptop batteries through an IT recycler. At first, I purchased 20Kgs of batteries not knowing what I would get. But then went on to purchase 30kgs, 40kg and most recently 60kgs. The break-down of how many usable cells I actually got from these old laptop batteries is below.

Everyone has their own method for pulling apart the laptop packs, however, I will say that safety is paramount here. The last thing you want to do is slice yourself open on the nickel strip or even worse short/explode a cell or two. (Saying that, it’s pretty hard to do this unless you’re super careless.)

I would suggest purchasing the following items:

• Vice Grips
• Sharp Small Side Cutters
• Gloves
• Eye protection

The end state of pulling the laptop batteries apart is to get the singular 18650 batteries out. Once we have them out and ready to go we can begin to analyze them to see if they are suitable for our power wall. Noting that these batteries did come from old laptop batteries we really do not know what state they are in, we must ‘process’ the cells to determine the capacity of every cell. Also, try and detect the bad from the good cells.

Step two – process a heap of cells

Once you have started your journey to building a DIY power wall, you will no doubt need to process bulk cells to weed out the good from the bad. There are many ways to achieve this outcome, however, I will give you a rundown on how I am doing it. (And a basic guide to the budget required for processing.) This part is easily the most tedious part of the build. For example, if you decide you would like a 48v 10-12kwh power wall then you are looking at requiring 1400 cells at a minimum. 1400 may not sound like many, however, after weeding out the bad cells, you soon find that it does take time.

The process that I follow to process cells is as follows. First I will check the voltage of each cell. If a cell pulled directly from a laptop pack is at 2V then it will go into the pile to be charged/discharged via the charging wall. If the cell is below two volts then I will put the cell into another pile which will require a specific charger to get them back to health (If they can be revived?)

For the cells that pass the 2 volt test, they will then be placed into the cell holders attached to the TP-4056 chargers. These small lithium specific chargers are very cheap and an ideal way to bring any old batteries up to full charge. You can pick these up from eBay very cheap in packs of 10-20. I went with 20.

Once the cells are charged to maximum voltage, the cells are then cycled into the Opus chargers for a discharge test. This is will give us the remaining capacity of the cells. Basically, it ensures that the cell is at 4.20v, discharges the battery to 3 volt, records the capacity in milliampere-hours (mAh), then charges the battery back up to 4.20v ready for the next test.

Once we know the remaining capacity of a cell, we then write it on the side of the cell for future reference and we also notate the current-voltage of the cell at the time. The cells are then placed into tubs grouped by capacity and left to sit for a minimum of one week. The reason for this is that we want to identify any cells that can not hold their voltage. These are known as ‘Self Dischargers’ we do not want a cell in our packs that cannot hold a charge/voltage. This can have significant effects on our packs once built.

Step three – prepare processed cells for packs

It will depend on a lot of factors on how you will proceed with building your packs. Each choice will have pros and cons. Go with the method that best suits your cell count and abilities. At present, I have not 100% decided on the method I am going to use, however, I am re-wrapping the vast majority of my cells first. Once I have 1400 quality cells, I will then arrange them into 14 packs of 100 cells. (14S100P) This will give me a 48v nominal power-wall around the 10-12kWh.

So where am I at right now? Well, I have processed approximately 60Kgs of recycled laptop batteries. I set my limits for the cells to go into my wall at 2000mAh. I currently have 4 packs with 100 cells in each pack. If I lower my standards to 1800mAh I could probably have a 5th pack built, but for now, I plan to stick to the magic 2000mAh for my wall.

• Cell pack builds (Once I decide which method to use)
• Some tips and tricks for better pack build.
• Solar/Inverter installation and connection to battery packs.
• cost/cell breakdown
• Anything else I can think of that may be relevant! (Let me know in the comments what you want to know?!)

What to skip forward in the series? check out the other parts of the build!

Part 2 – Building Packs
Part 3 – Fusing and cell protection
Part 4 – Solar/Inverter Install and BMS
Part 5 – Thats a wrap….Kinda