Idiot's guide to a self build battery

[Joeboy]

After much thinking on this I am very close to having a crack at expanding my current 6 pylontech US2000 (plus & B) battery storage system.

The sketchy plan is to buy 15 of 3.2v lifepo4 prismatic batteries from Shenzhen and hook em up as a 48V (15x3.2) 200Ah stack expansion.

To be clear, I have never attempted anything like this and in my innocence thought that I could simply T off the top and bottom of the current stack and have dumb storage capacity off to one side controlled through the Pylontechs BMS.

Turns out that won't do and I need a control/balancing board. It took me a moment to realise that the power I wanted to T into was uncontrolled from the hybrid inverter pre Pylontech BMS.

So far I have a quote for the cells, busbars & bolts incl shipping at a little under £1,200. No vat or import duty applied but at least it will spread the load a little by separating the payments out. I have no clue on balancing boards but would like to find the closest to plug n play with good control over the stack extension and lcd display showing voltage and SOC. If anyone knows of such, please weigh in.

Photos to follow of work site on my return to UK. Looking to order end Sept for a mid Nov delivery.

All advice much .

[Stinsy]

You should seriously consider investing in a set of VDE sockets/spanners. Great care needs to be applied if using ordinary metal tools because risk of causing a short is very high.

You don’t need a full function BMS because the Pylontechs talking to the inverter does the heavy lifting with charge/discharge voltages, etc.. But you do need a 15s balancer.

The only other thing to add is that you’re supposed to tape the batteries together very tightly because they benefit from mechanical force preventing them from swelling.

[Joeboy]

First change is that the 200Ah won't do the job. Don't have DOD I am looking to match in the Pylontechs.
Now looking at Eve LF280 batteries 3.2V 280Ah capacity across the stack and a 90% DOD at 6,000 cycle lifespan.

Cost is 1,998 US dollars incl shipping and excluding tax/vat. £1,638 for (280x48/1000)= 13.44kWh pack size. So maybe £2.5k all in incl govt cut boards, cables/crimps & isolators?

[Joeboy]

You should seriously consider investing in a set of VDE sockets/spanners. Great care needs to be applied if using ordinary metal tools because risk of causing a short is very high.

You don’t need a full function BMS because the Pylontechs talking to the inverter does the heavy lifting with charge/discharge voltages, etc.. But you do need a 15s balancer.

The only other thing to add is that you’re supposed to tape the batteries together very tightly because they benefit from mechanical force preventing them from swelling.

Cheers Stinsy, are you saying that powerflow from the hybrid inverter is already being regulated by the inverter due to info sent back from the pylontechs?

I am thinking of 3 banks of 5 and building aluminium end caps while clamping with stainless steel threaded rod and nuts. BOOM, there goes the budget!

[Caesium]

Can't offer much useful advice I'm afraid as I'm in much the same boat as you with just a stack of 6 Pylontechs at the moment, but just wanted to say hugely interested in following progress as I'd like to investigate doing something similar.

So please do let us know how this goes. Subscribed

Edit: this BMS seems pretty well-featured? https://www.ebay.co.uk/itm/154950958354 - bluetooth module for seeing individual cell voltages and some pretty whopping charge/discharge capabilities.

[Stinsy]

Cheers Stinsy, are you saying that powerflow from the hybrid inverter is already being regulated by the inverter due to info sent back from the pylontechs?

I am thinking of 3 banks of 5 and building aluminium end caps while clamping with stainless steel threaded rod and nuts. BOOM, there goes the budget!

Correct. The Pylontechs signal to the inverter when to start/stop charging due to SoC, charge/discharge current will be no problem because the max your inverter can apply is way below what the batteries can take/deliver. And the Pylontechs will signal the inverter if they want to slow down charging/discharging for whatever reason.

Your only problem is that batteries in series strings are not identical. Over time one can become progressively higher than the others and move out of spec, even though overall the string voltage is within spec. This can damage that battery. (The same if one is low). A “balancer” takes a teeny bit of power from the highest battery and puts it in the lowest one to keep them all exactly the same (cruder balancers just draw off power from the highest through a resistor).

You can spend £200+ on a full-function BMS if you like but a £50 balancer is all you need.

[Joeboy]

Cheers Stinsy, are you saying that powerflow from the hybrid inverter is already being regulated by the inverter due to info sent back from the pylontechs?

I am thinking of 3 banks of 5 and building aluminium end caps while clamping with stainless steel threaded rod and nuts. BOOM, there goes the budget!

Correct. The Pylontechs signal to the inverter when to start/stop charging due to SoC, charge/discharge current will be no problem because the max your inverter can apply is way below what the batteries can take/deliver.

Your only problem is that batteries in series strings are not identical. Over time one can become progressively higher than the others and move out of spec, even though overall the string voltage is within spec. This can damage that battery. (The same if one is low). A “balancer” takes a teeny bit of power from the highest battery and puts it in the lowest one to keep them all exactly the same (cruder balancers just draw off power from the highest through a resistor.

You can spend £200+ on a full-function BMS if you like but a £50 balancer is all you need.

Cool, any direction to a good un? (He hoped,)

[Joeboy]

Well, being a child of shockingly poor impulse control I am placing a 20% deposit today on the LF280's. Balance to be paid on 19th Sept when order will be made for a mid Nov delivery.

I will then plagiarise Nowty's system to an outrageous level! (If he let's me).

[Caesium]

Did you order from ali or a local supplier, do you mind me asking? I was pricing up on ali and got to pretty much the same costs as you.

Some local sellers on ebay obviously have their outrageous markup.

Wondered if there was a safer UK supplier you know of?

[Joeboy]

Did you order from ali or a local supplier, do you mind me asking? I was pricing up on ali and got to pretty much the same costs as you.

Some local sellers on ebay obviously have their outrageous markup.

Wondered if there was a safer UK supplier you know of?

I am ordering directly from a Shenzhen company of good reputation. On my hunt I quickly realised that the upside.to a few quid spared is minimal compared to empty shells with only concrete and a wired in small cap battery. Will share company details once they come through for me. So far, very professional.