Idiot's guide to a self build battery

[Joeboy]

All measured at 3.25V.

[Colin Deng]

Thank you Colin!

Thank you Joe for the feedback
Nice photo of the battery

Enjoy now

[Joeboy]

Thank you Colin!

Thank you Joe for the feedback
Nice photo of the battery

Enjoy now

They are in and equalising.

[Joeboy]

They are on! Another 14kWh storage for the secret list Nowty.



Sig updated.

[Joeboy]

Nice to see the soc climb rate on charge slow right down with the extra capacity. There's 0.85A difference in charging between old stack and new stack with 1.4kW incoming PV and no home demand. Will see if that difference narrows over next few days. I expect it will.

Old stack 4.35A


New stack 3.5A


This extra capacity will mellow me right out for any overnight charging. Should be able to negotiate a few solar speedbumps with this extra buffer.

[Andy]

Over in bridge of Don. Just got a call. The driver is dropping the pallet of batteries at mine right now. Come get them lads!

Ops. Sorry I couldn’t help. Damn work getting in the way again. I can’t believe how quickly you got them in. Fully primed and ready to go I guess. I am not

[Joeboy]

Over in bridge of Don. Just got a call. The driver is dropping the pallet of batteries at mine right now. Come get them lads!

Ops. Sorry I couldn’t help. Damn work getting in the way again. I can’t believe how quickly you got them in. Fully primed and ready to go I guess. I am not

I don't like to hang about! Having done it once before and the prep work already in place it was a doodle.

HWT heating through the night has brought stack down to 35% soc at start of today. Looking forward to seeing how it fills up.

A few cable ties to neaten balancing wires this morning and we are done. It was excellent to watch the balancer spring into life yesterday and start shunting power to the new stack. A decent DC clamp is a very handy tool indeed.



Edit- balancer is down to shifting 0.1A now. As the second new stack is further away in DC big cable length there may be more activity for longer periods as the balancer compensates for imbalance due to 1st stack dropping first and balancer shifts power from new stack back to old? That could be nonsense of course, we'll see.

[Joeboy]

I noticed last night that i was not getting above 96% SOC while we still had a little over 1kW PV incoming. I surmised that there was a lag between Pylontech data displayed and the charge state of the new third and furthest battery stack.

Had a look this morning at last nights data and we can clearly see where the 2 hour HWT programmed charge takes place 03.30 to 05.30 (orange neg downward spike being inverter lag on start up demand) and then with no PV generation or grid touch the battery SOC recovers from 50 to 60% SOC. After that the PV starts to kick in. I further surmise that my balancing board lifespan will be reduced and when it fails i'll replace with two units. For anyone going larger (Andy & Ian), be as close to mm precise as you can for your large dia cable lengths even if it means spare cable on the shortest run or go from a central tap and fan out. Just a thought.



I've been rather impressed with the extra capacity. On good days i'm chucking power hither & yon at EV's, HWT's etc knowing I have enough capacity to get through. Next good day (likely when i get back from Turkey) i'll monitor and see what 96% and above equates to in extra kWh's stored. So far I can see that the transfer speed between the Pylontechs and the EVE stacks is more than enough that the Victron PV charge controller hasn't shut its PV down. Although I do want to know a rough useable kWh figure for my own reference.

Fortunately we have had a few nice days since I hooked in the new storage capacity. I did find an upstairs SH which i'd inadvertently left on a scheduled charge. With that taken care of we are down to 1.5kWh bought from grid per day and that can all be laid at the feet of inverter lag coupled with my sailing too close to the wind of PV generation ceiling & Battery discharge rate combined.

If i can leave it alone more we'll be 0.5kWh or lower per day from grid.

[AlBargey]

.. It was excellent to watch the balancer spring into life yesterday and start shunting power to the new stack. A decent DC clamp is a very handy tool indeed.



Edit- balancer is down to shifting 0.1A now. As the second new stack is further away in DC big cable length there may be more activity for longer periods as the balancer compensates for imbalance due to 1st stack dropping first and balancer shifts power from new stack back to old? That could be nonsense of course, we'll see.

You got it all up and running quickly!

Did you consider running them as a separate battery with its own balancer and disconnector? If you prefer parallel, it's maybe not an ideal install with sharing extended balance leads and associated voltage drop if you can avoid it, maybe wire them like a single block. I do like the LED's though

Sorry if I've misunderstood the wiring!

Useful layouts for wiring parallel, adjust for 15S:









^ They're not mine, they're from a useful "LiFePO4 Cell Configurations" pdf in the resources of DIYSolar

[Joeboy]

Thanks for that Al, I am interested to see how it all settles down as its not been in quite a week yet. I set a 12A draw on the batteries to EV last night at and it pulled the stack down to 12% soc by early this morning. It did recover a little but not as extreme as the 10% gain a few days ago.

We'll leave it to do its thing while I'm away for a week then see what's sliding around in terms of power transfer in the balance wires. Thanks for the diagrams Al. I'll likely progress to two passive balance units in time. I will keep an eye on the single tiny yellow led on the balance board! The only sign of life without using a DC clamp.

Pure batteries running the show. I think we gained about 80 miles on the EV 0vernight. Interested to see what the stack recovers to today. Its already back up to 21%.