Idiot's guide to a self build battery

[Joeboy]

I manually charged the car for an hour this morning at 3kWh, with the background load at that time the average was 3.45kWh as shown on the Goodwe Hybrid inverter graph.

Start soc was 79% & end soc was 54%. A 25% drop in soc. Allowing for the granularity on the chart with regard to 1% true value and also the sampling timing by the inverter I am quite happy with that result. 4x3.45kWh=13.8kWh and my stack began life with a max capacity of 14.4kWh. A minute after the test ended the soc was showing at 53% so that brings it even closer together.

Interested to see how it all performs next week when I get back. That same load test should draw the soc down by 12.39% once the build is complete.

[Kenny000666]

Hey guys

Very interesting read here, and sounds like a project to add to my 2023 roadmap haha assuming battery prices from China doesn’t go crazy next year.

Do you guys have a picture of how the final thing looks after connecting it up to the pylontechs and existing inverter?

Also do you know what kinda of protection you can get when ordering from China? I wonder if we can buy the items using a credit card or something, and have purchase protection? Super scared to fork out a large amount of cash for potentially fake batteries (so many you tube Vids of fake batteries from China)

[Joeboy]

Hey guys

Very interesting read here, and sounds like a project to add to my 2023 roadmap haha assuming battery prices from China doesn’t go crazy next year.

Do you guys have a picture of how the final thing looks after connecting it up to the pylontechs and existing inverter?

Also do you know what kinda of protection you can get when ordering from China? I wonder if we can buy the items using a credit card or something, and have purchase protection? Super scared to fork out a large amount of cash for potentially fake batteries (so many you tube Vids of fake batteries from China)

Will have photos when finished, Caesium has completed his. Buy from a recommended supplier. Caesium has one as do I. I will update once complete on capacity tests and full details on my supplier.

[Caesium]

I posted a picture in this thread somewhere I believe (you may have to go back a few pages!) but I'm reluctant to do it again as it's a bit embarrassingly untidy right now

I have another 16 cells on order and plan to basically start again and redo my existing DIY stack when they arrive, so I end up with two identical DIY stacks side by side in parallel (then junking all the Pylontechs and flying solo!).

I learned a lot with the first construction and will tweak a few things for the next one:

My first stack was 15S (to match Pylontechs) so they were clamped as 3x5S (like Joeboy plans to I believe) but ultimately I will have no such restriction (no Pylontechs) so my next ones will be 16S, which I can clamp as 2x8S, with all cells directly next to each other, making better use of the busbars they supply. That will eliminate my home-made inter-cell jumper cables entirely. (this paragraph may make more sense if you go find my pic then you'll see the physical layout I'm talking about)

I'll also lie them flat on the floor next to each other, instead of side-on stacked on top of each other. This may be marginally more risky when building the pack (that you can drop a metal spanner across some terminals) but this is mitigated with some common sense (don't use metal tools). It's also more convenient once its finished to put another sheet of ply over the top of the entire thing so they're completely hidden from view and protected from falling objects and I think it'll be easier to work on.

And finally I'll take a lot more care over cutting balancing/BMS cables to length and routing wires, because once you start just throwing things on its hard to recover from and ever make it neat

[Joeboy]

I posted a picture in this thread somewhere I believe (you may have to go back a few pages!) but I'm reluctant to do it again as it's a bit embarrassingly untidy right now

I have another 16 cells on order and plan to basically start again and redo my existing DIY stack when they arrive, so I end up with two identical DIY stacks side by side in parallel (then junking all the Pylontechs and flying solo!).

I learned a lot with the first construction and will tweak a few things for the next one:

My first stack was 15S (to match Pylontechs) so they were clamped as 3x5S (like Joeboy plans to I believe) but ultimately I will have no such restriction (no Pylontechs) so my next ones will be 16S, which I can clamp as 2x8S, with all cells directly next to each other, making better use of the busbars they supply. That will eliminate my home-made inter-cell jumper cables entirely. (this paragraph may make more sense if you go find my pic then you'll see the physical layout I'm talking about)

I'll also lie them flat on the floor instead of side-on, stacked on top of each other. This may be marginally more risky when building the pack (that you can drop a metal spanner across some terminals) but this is mitigated with some common sense (don't use metal tools). It's also more convenient once its finished to put another sheet of ply over the top of the entire thing so they're completely hidden from view and protected from falling objects.

And finally I'll take a lot more care over cutting balancing/BMS cables to length and routing wires, because once you start just throwing things on its hard to recover from and ever make it neat

Glad your adventure is continuing Caesium! All sounds great. I see the logic in moving past the Pylontechs and building your own full system. Looking forward to the photos, post build/tidy of course.

I am home on Wednesday so should have it together by the weekend, SWMBO worklist allowing! I'll post a few photos too.

[Stinsy]

I too am following this thread closely.

Here is my plan:
- Buy 15x LF280k batteries.
- Sell 2x of my 5x Pylontech batteries (I want to keep 3x to retain BMS comms and max inverter power).
- Fit a 15S balancer and parallel up the new batteries with the Pylontechs.

This would leave me with c. 20kWh of battery storage. This is plenty given that I can only charge c. 13kWh in the 4hr cheap period.

Money is tight right now as I’m waiting for my BEV to be delivered and I have a rental property with a tantalisingly small mortgage outstanding, currently on the SVR, so every spare penny is going towards paying the mortgage off. So deffo a plan for 2023.

[Caesium]

Here is my plan:
- Buy 15x LF280k batteries.
- Sell 2x of my 5x Pylontech batteries (I want to keep 3x to retain BMS comms and max inverter power).
- Fit a 15S balancer and parallel up the new batteries with the Pylontechs.

Solid plan Stinsy. That is exactly my situation at the moment; the 3 batteries keep 75A flowing in and out of the batteries which is the max the Luxpower inverter can do.

After losing my remaining Pylontechs I'm planning to use a JK BMS to monitor cell voltages and provide cutoffs (temperature, pack voltage, etc).

There's also the possibility to take the data the JK BMS spits out and munge it into Pylontech-compatible data using an ESP32 or a Pi or something, but maybe that's a project for another day

[Joeboy]

Here is my plan:
- Buy 15x LF280k batteries.
- Sell 2x of my 5x Pylontech batteries (I want to keep 3x to retain BMS comms and max inverter power).
- Fit a 15S balancer and parallel up the new batteries with the Pylontechs.

Solid plan Stinsy. That is exactly my situation at the moment; the 3 batteries keep 75A flowing in and out of the batteries which is the max the Luxpower inverter can do.

After losing my remaining Pylontechs I'm planning to use a JK BMS to monitor cell voltages and provide cutoffs (temperature, pack voltage, etc).

There's also the possibility to take the data the JK BMS spits out and munge it into Pylontech-compatible data using an ESP32 or a Pi or something, but maybe that's a project for another day

Caesium,
No duty charges on yours? I ask as its quite a large variable on the cost per kWh comparison of LF280k's v's Pylontechs.I might go this route myself and offload my original two US2000's and keep the four newest units. Would be nice to step up to a further set of 15 LF320k's and cap my personal madness. (For a moment).

[Caesium]

No duty charges on yours? I ask as its quite a large variable on the cost per kWh comparison of LF280k's v's Pylontechs.I might go this route myself and offload my original two US2000's and keep the four newest units. Would be nice to step up to a further set of 15 LF320k's and cap my personal madness. (For a moment).

Nope, I was pleasantly surprised! I did see that a few of the alibaba listings had suggestions like import duty paid but I wasn't sure whether to believe it.. perhaps they're telling the truth

I'll report back on whether the second batch gets the same treatment

[Joeboy]

No duty charges on yours? I ask as its quite a large variable on the cost per kWh comparison of LF280k's v's Pylontechs.I might go this route myself and offload my original two US2000's and keep the four newest units. Would be nice to step up to a further set of 15 LF320k's and cap my personal madness. (For a moment).

Nope, I was pleasantly surprised! I did see that a few of the alibaba listings had suggestions like import duty paid but I wasn't sure whether to believe it.. perhaps they're telling the truth

I'll report back on whether the second batch gets the same treatment

I was presented with the same scenario, may fortune shine on your second venture!