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)

Battery Connection

The first item on the agenda after the last post was to connect the batteries to the inverter. This was super simple. A couple of lugs later and voila done! The only issue I ran into was that the 35mm2 lugs I used would not fit through the cable glands properly. Lesson learned, terminate the cable after feeding through the cable gland. If you’re running a GW5048D-ES then it suggests 25mm2 cable which would probably fit with the lug through the gland, but I decided on a heavier gauge cable. Also, try and keep the cable run short to minimize any voltage loss on the cable. You can calculate this but at less than a meter, I assume the cable loss would be negligible.

Batrium CANbus to Inverter Connection

This had me stumped for a while, however, we eventually got through it. The GW5048D-ES came with a dedicated BMS cable. This cable at one end only had 3 pins terminated. After a bit of investigation, I found that the Blue pin = CAN-H, White/Blue = CAN-L, and the Orange is GND. In the image gallery below you can see the extract from the manual. Now I am no expert on the CANbus protocol but it seems that having a 120ohm resistor on each end is pretty important. The Batrium Watchmon 4 came with the resistor installed and I was able to find some clear instructions on the Batrium website for which pins to connect to.

At first, I did not connect the GND pin, It still seemed to work, however, I eventually connected it with no significant change in performance. Also of note is that I connected the BMS cable from the BMS port on the inverter to the CAN/H/L pins on the Watchmon. See the Gallery below for a few pics of connection.

(Almost) A complete Failure

After connecting the CANbus cabling, I attempted to configure the Batrium software to talk to the Inverter. As it turns out the only way I could get Batrium to talk to the inverter was in the integration settings in Batrium and select the “Project Lychee” integration. This integration mimics an LG RESU 6.4 battery. Thus on the Inverter and inside the PV Master App (Goodwe Configuration Tool) I had to select the LG RESU 6.4EX battery type. I was then able to confirm in Batrium that CAN comms were working. What you need to look for is that batrium transmits and receives.

Now that I had Batrium Communicating with the inverter, surely it would just be a few tweaks of Batrium?… How wrong I was. At first, all looked good, the charge cycle completed at the values I had set in Batrium and all was well. I started running into issues during the discharge cycle. The inverter could not make up its mind if it wanted to discharge or sit at idle. As you can see from the video below, keeping an eye on the “Shunt A” value. That is what is happening on the BMS shunt.

So where am I at now?

So after much back and forth with both the Batrium support team and Goodwe, no one can or wants to help me. I paid $85 for Batrium support in which they basically told me it was an inverter issue and Goodwe told me to use an approved battery. Boooo! So, for now, it looks like the remote integration is a no go. Not all is lost though, the inverter actually has a “self Define” battery option. This option is designed for Lead Acid batteries and has a few settings that can be configured. Such as Battery Capacity, Voltage Charge Target (56.7v in my case), Charge/Discharge Current (20A/20A to test.) and some SOC protect percentages. I have since been using these settings for a few days now with no issues. The inverter charges nicely and cuts of at set voltage. I am yet to run the battery down to test the SOC protect. That is next on my list.

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

Let us start with the BMS

As mentioned in other posts I ended up purchasing the Batrium Watchmon 4 14S kit with expansion board. At the time, this was the ‘bees-knees’ of Battery Management Systems. It comprises of the main and unit and the Longmons which attach to each cell pack. The longmons look after the voltage of each pack, basically it burns off excess power to keep each cell pack balanced with each other. The Longmons and Watchmon 4 kit is not an active balancing unit. More of a passive balancer. The Longmons also have a few other functions, such as temp monitoring and feeding of this information back to the Watchmon. See the latest Watchmon 5 for a more centralized approach to battery management.

I ended up finding a couple of clear front enclosures and mounted the BMS inside on some DIN rail. Originally I thought I would mount the gear on the same wall as the inverter, but after some thought and worry about running out of space, I decided on mounting on the cabinet itself. This part was probably the most complex of the build, but it’s pretty straight forward to follow once you have all the parts.

My Solar (Finally) Installed

After much procrastinating, I decided upon the Goodwe GW5048D-ES Inverter. It is a 5Kw Hybrid inverter and has a lot of the features I needed. The first being a 48v suitable charger for the batteries. The spec on the charger is up to 60v @ 100A charge/discharge. At 48v that is a lot of current. I think I’ll run it at 50A first. The other bonus to using this inverter is the ‘backup’ functionality. It has a built-in UPS type function in which it can switch to battery during a power outage. I’m not really sure I’ll be using this just yet, but other inverters require separate hardware to make this happen.

As for solar panels, I ended up getting a good deal on some 315w Link Energy panels. Now a lot of pros and cons going for a less than known brand, however, my main considerations were; They must be considered tier 1 panels, they must be on the CEC approved list and they must have a good warranty that can be executed directly in Australia. They seemed to tick all these boxes so I pulled the trigger. (Hopefully, this theory works for me, could come back to bite me.)

A quick mention of the cable tray and gantry into the shed

It seems a lot of people don’t exactly get their inverters installed in a small shed. I had to be confident I could keep the space cool and that I could get all associated cabling in the shed safely and be accessible to the battery cabinet. I ran some 75mm cable tray down a concrete wall and around into the shed. I then installed a large box to act like a gland. This should allow for future expansion and putting the Xmas lights in/out as required. I also installed a couple of runs of cat5 and got the sprinkler controller/cable to come in as well. I will be covering the cable tray with some cream-colored sheet metal. I am yet to get this priced up.

Trip Shunt Install

The ZJ Beny Trip Shunt I also installed in a similar fashion to the BMS. Its a tight fit, but with some carefully placed glands I can get the 35mm2 cable in/out. (I may need to drill them out for the lug thou!) The trip shunt is controlled directly from a relay on the Watchmon 4 expansion board. I have installed a Meanwell DC-DC power supply to feed 24vdc to the trip shunt (Via the relay). When the Watchmon activates the relay because of a ‘critical fault’ it will activate the trip and cause the ZJ Beny breaker to be turned off. It was interesting to note that during my testing, I was required to turn the 24vdc power off first before I could reset the unit. This kind of made sense, but took me a little while to figure it out.

Battery Mounting in the Cabinet

If you have been following along in the last post, you would have seen that I tried to build some funky perspex holders for the cell packs. I ended up throwing this idea out and going with something a little bit more simple. I ended up using the laser cutter and

router to make a permanent shelf with side protection. The 6mm acrylic base was routed to seat 7 cells and the 3mm acrylic used to slot into the base as side protection. I glued all these parts together using acrylic glue and it seems to be very solid. This approach means that I can disconnect a battery and just slide it straight out to work on it. I won’t have to mess around taking apart the last design.

So what now?

Well apart from finishing the wiring in the BMS enclosure and running the battery cable to the inverter, I need to start looking at how the Batrium BMS interacts with the CANbus. I’ll get back to you soon with how the connection went!

A couple of pics from progress thus far!

If you missed the first parts of the build.

Part 1 – Recycling batteries
Part 2 – Building Packs
Part 3 – Fusing and cell protection

Saying that, it is not all ‘doom and gloom’, I have managed to make some progress on other fronts. The first is the cabinet shelves. I have managed to rig up some V-slot ally that I had lying around for shelves and was still able to use my vertical mounts on them. I also started work on some pack side protection and Longmon mounts. More info below!
EDIT: and yes I know the fuse wire is doubled up, It is easier to work with a continuous length. I am yet to trim them up.

Fusing – Let us have a quick chat about the path I took.

Very early on I decided to spot weld fuse wire on both the positive and negative sides of each individual cell. My reasoning behind this was that the cells are from unknown batches and even though I tested each cell individually I still did not trust each cell. It would have been a different story if I did not get the batteries from recycled laptop packs. The fuse copper wire I decided upon was around the 32AWG mark and is tinned with copper. This wire gave me about a 2amp draw before blowing. If an individual cell pulls 2 amp then I’m in a LOT of trouble anyhow.

It was pretty clear from the start that I needed to practice the spot welds. I grabbed a pack of 20 discharged batteries and went to town. The biggest thing I will say is that you do not need a lot of power when spot welding 32AWG tinned copper wire. I left the spot welder on 2 pulses and only put the power up to 5 or 6 on the dial. The other technique that needs practice is the positioning of the welder tips. You can either put both tips on the wire and weld or put one tip on the wire and one on the battery surface. Either or, does not really matter, however, I did notice at higher powers the welding tips would arc a lot more if putting both tips on the wire. You will find that the wire will break at the weld if under stress. Thus having two welds on the wire doesn’t really matter.

Cabinet Layout

My initial intent was to have the battery packs laid out vertically. I felt this was much easier on the eyes and for maintenance easier to get in and out. However, with the size of the cabinets and my battery pack sizes, I was not left for much room if I was to put two banks in. The cabinet was deep enough to run them horizontally and as it turns out uses the space much better. I still have a ton of room for more banks when/if required. Saying that I doubt I will be spot welding more packs any time soon. I still used the vertical mounts but laid them down and mounted to the V-slot. This will stop the packs moving if for some reason we have an earthquake or someone runs into the cabinet.

Cell pack side protection

This is a work in progress. Have you heard of the saying ‘Keep it simple stupid’? well, in this case, I am aiming VERY high and already feel that I will be coming back down to earth quicker than expected. Not only am I trying to protect the fusing on the side of the packs, but, I have also decided to incorporate the following items: Voltmeter, Cell Pack Labelling, Some Vents and a Longmon (BMS). I’ve decided to use 3mm clear acrylic and make a hybrid type case. I have attached a design file. It may change once I do the laser cutting. You will have to wait until part 4 to see how it turns out.

EDIT: 13/06/19 – Just in case anyone wanted to know how the first cut of the side protection covers came out. Check out the gallery below. It still requires some adjustments. I feel as if it has been over-engineered. But I will not really know until I try to mount the packs properly. Stay tuned.

Still to come:

• Finish Fusing
• Install Cable tray
• Gland for Shed
• Solar Install
• Watchmon install
• CB and Trip Install
• A lot!

If you missed Parts 1 and 2 of the DIY Powerwall. Here are some direct links:

Part 1 – Recycling batteries
Part 2 – Building Packs
Part 4 – Solar/Inverter Install and BMS

The Shed – No chance am I putting this build inside the house!

Having a suitable location for your power wall is probably one of the largest considerations of the whole build. As mentioned earlier, if lithium batteries are not treated correctly it could end up in a molten mess and no matter how many fire extinguishers you have, the lithium battery fire will consume everything in its path. If you do not believe me, check out some of the videos on youtube! My build takes us out to the shed of course. The shed is not far enough away from my house for my liking, but have to work with what I have. I was able to pick up this nice B&R electrical cabinet for $150. These cabinets are very sturdy and made of steel. The orange powder coasting was not by choice, but for the price, who am I to complain. The cabinet is large enough to fit my first 14S100P setup, with room to double it at a later date. (Top and Bottom) I am also looking to get some airflow top to bottom in the cabinet at some stage.

I went ahead and mounted some structural pine to the wall. My plan is to now use some slotted C-Channel to mount the inverter and components to the wall. This will allow me to conceal some of the cabling, whilst maintaining the structural integrity of the ply and wall. I’m yet to decide if I should paint the ply?.see what happens. I also need to look at cable management, and how/where to mount all the other associated equipment.

Insulation?? As we are working from a common garden shed, I had to insulate the roof of the shed. It was getting WAY too hot inside to house all these components. I ended up purchasing some foam foilboard from the local hardware store and mounted a small 200mm solar vent. It seems to keep the temperature steady. Even on 40deg C days, it seems ok inside. I do plan to hook up some temp sensors into the future. Also some more ventilation. Bring in the cool air from the bottom, vent out the top.

Sorting and Stacking Packs

From what I have read, sorting your cells into equal packs can be crucial to the whole setup. The aim is to have the same (or very similar) capacity in each pack. But how do we do that? well, there are a couple of methods. The first and possibly most accurate is using some online software called ‘rePackr’ which is located here. With this tool, the idea is you enter in the capacity of every single 18650 you have and it tells you which pack to put them in. Pretty much sorts them out so that each pack is as close to the same as possible. The downside is that you need to type in or cut and paste in the value of every cell. When your wall contains over 1400 batteries this can become a PITA.

The method I chose to use was a bit more archaic but has been proven to get the job done. I sorted all the batteries out into groups of 50mAh. For example, the cells that are at a capacity of 2050mAh to 2100mAh would all be grouped together. I did this across the whole range of my cells. I think I ended up with 20 groups of cells. From here it was then pretty easy to take one from each group and fill the packs so that they were somewhat evenly mixed. The proof will be in the pack testing. Only then will I know how close I got.

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.

Battery Management and Safety

ok, so we have our packs now and we need a few additional bits of hardware to make sure out battery packs are as safe as we can make them. The first item used is a Battery Management System (BMS). The BMS we chose was the Batrium Watchmon setup. This seems to be the go-to BMS for DIY type powerwalls at the moment. They seem to be doing a fair bit of development on the hardware and software which is always good. If you want to check out more of their items head over to the website here. In a nutshell, the Batrium BMS controls the charge states and the balancing of the packs. It is important to control this as we do not want to over/under charge the batteries and we also want each pack to drain and recharge in a balanced fashion.

The BMS works by connecting ‘Longmons’ to each pack. These are small bits of hardware which link each pack together and provide the feedback to the Watchmon controller. The Longmons are the workers and do the balancing, monitor temps and a few other cool bits and pieces. The BMS, with the help of some relays, can also be used to trigger a shunt trip. The Shunt trip will basically cut off any use of the batteries during a fault state. For example, if the temp rises past a set parameter, the BMS can trigger the trip and all use of the batteries will be cut. This is just one of the safety features which I intend to implement.

In line with the circuit breaker, we also have some large fuse(s). These 160A HRC type fuses in a disconnect/isolator will also be used. At $12 per fuse and $50 for the holder, you can never have too much circuit protection. So not only will each of the individual batteries be fused, but the entire pack will also be covered.

So that’s it for part 2! What’s next:

• Bus Bars on packs.
• Cabinet Install
• Solar Install
• Lots of wiring up!

Want to skip Back or Forward? Check out the other parts.

Part 1 – Recycling batteries
Part 3 – Fusing and cell protection
Part 4 – Solar/Inverter Install and BMS

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