Idiot's guide to a self build battery

[Joeboy]

todo list..

• order 16 LF280K and assorted bits-n-bobs
• build 15S DIY stack to sit parallel to Pylontechs
• sell 3/6 Pylontech to fund this habit
• order 16 more LF280K
• build a second 15S stack in paralle
• sell remaining Pylontechs
• reconfigure both DIY stacks to be 16S
• spend years messing with smart BMS systems

yes I ordered more The Pylontechs sold for silly money, more than I paid for them. £900 a pop, so £5400 total potentially once they're all sold, which I'm replacing with £4000 worth of LF280Ks. That takes me from 14.4kWh to around 28kWh and puts a grand back in my pocket. Though some of that is being eaten by balancers and odds-n-sods.

Once I have no Pylontechs left I'm planning to rebuild both stacks to 16S, as I'll have no other 15S to be in parallel with. I'm not envisioning any problems with this. The LXP inverter reckons it can supply charge up to 60v and by that point I'll have far more capacity than I know what to do with (with no panels yet and only 5h of 3.6kW charge capability, I can only refill 18kWh of it a night anyway) so I'll set the charge voltage quite low, probably 54.4v (3.4*16). This should give the cells a nice easy life and not max then out to 100% every night. I can tweak up the voltage marginally if I ever do empty them.

Good for you, no half measures!
At my end DPD system now recognising the shipping number but not yet in their system. A step forward from previous no know No. £900 a pop is excellent .

[Joeboy]

DPD system now recognises the parcel number and knows its a four parcel consignment. Its not been handed to them yet so must be clearing customs, good to know though! That was a long silence...

[Joeboy]

Woohoo, DPD delivering the batteries on Tuesday the 25th Oct! I'm in Turkey until the 2nd Nov!

Not bad though that will be 30 days door to door.

[Joeboy]

They're here, hooray!

[MrPablo]

I've been following the DIY battery builds with quite some interest, especially with current Pylontech prices.

I do quite like the fact that Pylontech (and other batteries) expose BMS data to the inverter and user. Has anyone looked into using a BMS that uses an inverter compatible protocol?
I have seen Seplos mentioned in other forums, but need to do more research.

[Joeboy]

I've been following the DIY battery builds with quite some interest, especially with current Pylontech prices.

I do quite like the fact that Pylontech (and other batteries) expose BMS data to the inverter and user. Has anyone looked into using a BMS that uses an inverter compatible protocol?
I have seen Seplos mentioned in other forums, but need to do more research.

What are you looking to do? Add to an existing system or build from scratch? I'm not certain what you mean by inverter compatible protocol, Certainly the data from the Pylontechs can be seen and used. There are a lot of Chinese standalone bms modules out there too if you are looking to self build a battery pack. I only know them as seen them on other forums while finding info for this build. No hands on experience though.

[Caesium]

I do quite like the fact that Pylontech (and other batteries) expose BMS data to the inverter and user. Has anyone looked into using a BMS that uses an inverter compatible protocol?
I have seen Seplos mentioned in other forums, but need to do more research.

Seplos can directly talk Pylontech protocol so this would be a one-step solution and if I understand correctly would directly plug into any inverter that also talks Pylontech, almost a drop-in replacement. But I think they're expensive and I've also read the balancing current is pretty paltry so you may want a separate active balancer if going that route.

I did briefly look into it and have decided not to bother for now. Ultimately I realised I'm not actually that bothered about the inverter knowing every last detail about my batteries; but thats mainly because I prefer my data in Grafana and I can get that via other means.

I'm currently fiddling with a JK BMS; this has bluetooth so you can see individual cell voltages on your phone, and also an RS485 (actually, it's UART TTL but lets not get into those details for now) so I have it hooked up via USB and I can read the individual cell voltages for punting over to Influx/Grafana etc. There's already a few python scripts floating about that can do it - mpp-solar (search github) has it built in.

The JK BMS can cut off charging in the event of cell overvoltage, overtemp, etc etc, so I'm not really that bothered about letting the inverter control it, which would be the main advantage of feeding all the data back to the inverter. And as I graph everything myself, I'm not bothered about sending it all back to the Luxpower portal either.

[Joeboy]

Thinking about capacity testing once built. The easiest way I can see without buying test gear is to force charge the batteries in the Go Faster window pre build. Note the soc percentage at the end of the charge on the Goodwe hybrid unit and then charge EV for two hours. Note the percentage drop.

Then repeat the test on the built unit and hopefully see a massive difference. That should work.

[Joeboy]

Current stack is 300Ah at 48v 14.4kWh.
41.6% loss of SOC expected over two hours drawn at 13A 230v

Extended stack is 580Ah at 48v 27.84kWh.
21.55% loss of SOC expected over two hours drawn at 13A 230v.

There will be losses and fridge freezers kicking in and out too so the figures in reality wont be perfect. Will try and run test both times at a roughly even beginning SOC of below 88%.

I'll leave this here for posterity and see where we are in the morning. Test No1 tonight.

I will also take stack start/stop voltages when possible but unlikely to be getting up at 02.30 & 04.40.

[Lincs Robert]

This is a very interesting thread.

If I currently have two stacks of five Pylons (dual ACS3600 config for 7kW of throughput), I’m guessing I’d need 2 x 15 of these? I have 24kWh of capacity at the moment, how much could I end up with?

Will there be an overall “guide” or some documentation available at the end? Please?

Keep up the good work

Rob