Idiot's guide to a self build battery

[Oldgreybeard]

One tip I can give is to try and document everything, using language that a complete fuckwit will understand. I've gradually been doing this, I'm probably about half way done. I bought some clear, wall-mount, document holders (these: https://www.ebay.co.uk/itm/225079994231 ) and have screwed them to walls adjacent to bits of kit. In them I've put all the manuals, inside PVC wallets, plus printed out copies of the settings I've used, any quirks I've found when setting kit up, wiring and plumbing drawings, etc. My hope is that someone could some along and understand what I've done and why.

In the case of things like out well pump system and filtration, I've written step by step guides to swapping the pump out if it fails, how to isolate, drain and check the pre-charge in the main accumulator, the settings for the filtration backwash etc, so hopefully ant plumber can see how to service the system if need be.

It's still a work in progress, I need to document the electrical installation and EPS system, and the heat pump programming. I'll also need to do the same when the new PV system is up and running, with it's G100 relay box to ensure export cannot exceed 6kW.

[Stinsy]

I see, is this a big problem or disadvantage compared with having a data connection to the inverter?

One big advantage of the Pylontech-inverter data interface is the SoC percentage. In summer I set my inverter to charge the batteries to 50% in the cheap period. Most of the time I get enough sola that the batteries are already over 50% and no charging takes place. However if we have several dull days and/or I use more energy than usual, it automatically charges a bit.

This automation cannot be achieved without BMS interface.

I’ve heard of 3rd party BMSs that mimic the Pylontech interface. I don’t know any more than they exist and are less than perfect. However if the tech evolves then this would be a perfect solution.

[Caesium]

I like the box and the way that you cut the sides short so that the screws can compress the cells!

Yeah it really is that simple It doesn't bother me that the edges don't touch, gives me a lot more wiggle room for compression. They're not super tight, just enough to hold everything together and not let it move.

I assume you're planning on building a lid for the battery box? You need to reduce the chances of any unfortunate sequence of events that ends with a spanner or other metal object falling across the terminals of the cells.

Definitely. Next job, it'll just be a sheet of ply sat on the top. I'm KISS for this build!

A solution for your BMS interrupting current flow is to have it control a relay. 200A 48V relays are common enough (Eg: https://www.amazon.co.uk/Current-Starte ... B07NY8Z3BP).

Will check this out thanks Not sure how I'd integrate it though, the BMS sort of assumes the main contacts are inline with the negative terminal. This is how it measures charge/discharge current and hence works out SOC by coulomb counting I think, so I might lose that if I take it out of series with the main current. Will have a ponder on it!

[Stig]

It turns out Alipay uses your Alibaba account not your Aliexpress account (who knew they were different) and mine has been locked for inactivity. Took a fair while to fight through the automated responses in the chat clients (I had to create a new account as you need a working account to talk to them on chat, which if I had I would not need to talk to them).

https://dilbert.com/strip/2022-12-04

[Tinbum]

I do love the self build stuff though, it's fun. I woke up in the early hours the other night and found my batteries weren't charging. For some reason my Arduino wasn't accepting or sending mqqt messages so no message had been sent saying the grid was now connected.

A little bit of added flow in Node red and Alexa will now announce at 00.35 if it thinks the grid hasn't connected.

[Stinsy]

A solution for your BMS interrupting current flow is to have it control a relay. 200A 48V relays are common enough (Eg: https://www.amazon.co.uk/Current-Starte ... B07NY8Z3BP).

Will check this out thanks Not sure how I'd integrate it though, the BMS sort of assumes the main contacts are inline with the negative terminal. This is how it measures charge/discharge current and hence works out SOC by coulomb counting I think, so I might lose that if I take it out of series with the main current. Will have a ponder on it!

The implementations I've seen where a lower-power BMS controls a bigger load/charging current via a relay all involve BMSs that aren't as smart as yours.

[MrPablo]

I see, is this a big problem or disadvantage compared with having a data connection to the inverter?

One big advantage of the Pylontech-inverter data interface is the SoC percentage. In summer I set my inverter to charge the batteries to 50% in the cheap period. Most of the time I get enough sola that the batteries are already over 50% and no charging takes place. However if we have several dull days and/or I use more energy than usual, it automatically charges a bit.

This automation cannot be achieved without BMS interface.

I’ve heard of 3rd party BMSs that mimic the Pylontech interface. I don’t know any more than they exist and are less than perfect. However if the tech evolves then this would be a perfect solution.

There's a project I've been following on github (JK-BMS-CAN) that 'translates' JK BMS comms to pylontech or goodwe protocol RS485, which can then be interfaced with the inverter.
If you happen to have home assistant in play, you can apparently control some of the BMS functions also.
If I do decide to try the homebrew battery approach then I plan to utilise this.

[Kenny000666]

Hey guys,
Happy new year!
Batteries I ordered in November arrived slightly earlier (1 week) than I had expected! 50 days from order (44 days from dispatch) to my house. So time to begin my project of building my enclosure and connecting up.

Question for those who hooked up to pylontechs.
My plan was to
1) disconnect the pylons from the inverter
2) connect the EVEs + JK BMS in parallel to the pylons
3) do the standard procedure of allowing the 2 packs to balance
4) once balanced close the disconnector and have almost 20kwh of storage

Am I missing a step 1.1) to balance the EVEs first? I think Joe and Caesium you both had an active balancer and balanced the cells first right? I need to check, but I think Deriy balanced and checked the cells before dispatch, so hopefully voltages should be super close still.

[Tinbum]

Thats great news, perhaps now I have more confidence to take the plunge.

[Fintray]

Don't forget the pics of the build.