Idiot's guide to a self build battery

[Joeboy]

Deposit placed! Game on!

[Stinsy]

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

This is what you’re after:

https://www.ebay.co.uk/itm/144493487942

Available from all the usual places (eBay, Amazon, Ali) it comes down to a price/shipping time trade off.

[Caesium]

Might be getting ahead a little bit here, but have you thought about how you'll hook these up? My 6-stack has a spare positive terminal on the top battery, and a spare negative terminal on the bottom battery. Inverter connects negative on the top battery and positive on the bottom battery. I suspect this is a fairly common setup as it's the recommended way.

So if I were to do this, most likely I'd get myself another set of long Pylontech cables (they already have a lug on one end) then use those spare terminals to go to this new chain. This would mean the new pack is connected across the entire existing stack and also more or less directly to the inverter.. does that make sense and sound sane?

[Joeboy]

Might be getting ahead a little bit here, but have you thought about how you'll hook these up? My 6-stack has a spare positive terminal on the top battery, and a spare negative terminal on the bottom battery. Inverter connects negative on the top battery and positive on the bottom battery. I suspect this is a fairly common setup as it's the recommended way.

So if I were to do this, most likely I'd get myself another set of long Pylontech cables (they already have a lug on one end) then use those spare terminals to go to this new chain. This would mean the new pack is connected across the entire existing stack and also more or less directly to the inverter.. does that make sense and sound sane?

That is the plan, I already use those spare ports to tap into an emergency 2kW 240V inverter so will add a couple of busbars to allow me to tap into pylontech stack, inverter and new LF280 stack.

[Joeboy]

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

This is what you’re after:

https://www.ebay.co.uk/itm/144493487942

Available from all the usual places (eBay, Amazon, Ali) it comes down to a price/shipping time trade off.

Thank you Stinsy, I will look into that. Just getting my head around the charge discharge parameters for both batteries.
Pylontech us2000's operate between 45 to 53.5v according to the manual.

That's 3v to 3.56v range per unit in the 15 batteries within the pylontech unit.

The LF280's range is 2.5v to 3.65v so I am never going to be troubling the LF's in the charging cycle but will lose some of that stated 280Ah capacity. Once I am home and rebalanced the pylontech stack I will take readings at either end of the Pylontechs range to confirm and go from there.

If the 280Ah stated is full capacity I wonder if that capacity is 0-100% and 10% is already not accessible due to dod protection? Anyone know the answer?

If that's the case then 280Ah becomes 252Ah useable across a stated 1.15v range. Of that 1.15v range in the LF280's I am restricted to 0.56v due to the Pylontechs 3V Bottom end.

Hmmn, if all that us true then
252/115x56= 122Ah useable
If on the other hand the full 280Ah is available then
280/115x56= 136.34Ah useable

I don't think the above is true as tech sheet states that battery should be kept above 2.9V at all time so the charge/discharge window isn't as broad as I first thought so potential losses won't be crazy bad. Interesting though?

[Caesium]

That's 3v to 3.56v range per unit in the 15 batteries within the pylontech unit.

It will also depend on your inverter how hard these get pushed. My Luxpower 3600ACS only charges my stack to about 52.2v (it's setup for Pylontech batteries, so I'm trusting it to do the right thing..) and this works out to 3.48v per cell, which I can verify as I have serial hooked up to my Pylontech master to get the cell voltages every minute.

I'm not overly concerned about the loss of top-end charge as I gather there's rapidly diminishing returns above 3.45v for lifepo4.

[Joeboy]

That's 3v to 3.56v range per unit in the 15 batteries within the pylontech unit.

It will also depend on your inverter how hard these get pushed. My Luxpower 3600ACS only charges my stack to about 52.2v (it's setup for Pylontech batteries, so I'm trusting it to do the right thing..) and this works out to 3.48v per cell, which I can verify as I have serial hooked up to my Pylontech master to get the cell voltages every minute.

I'm not overly concerned about the loss of top-end charge as I gather there's rapidly diminishing returns above 3.45v for lifepo4.

Once it's all in and running I will do some real world after dark fixed tests charging the EV. I will know off of the Hybrid inverter SOC % and the EV charger total kWh's consumed roughly what I am playing with.
https://www.evlithium.com/hot-lithium-b ... ttery.html

[Oldgreybeard]

My experience with LiFePO4 battery packs has been that there is almost nothing to be gained by discharging them below 3V per cell and the same for charging them to anything over about 3.6V per cell. The shape of the capacity curve is such that almost all of the capacity is available between 3V and 3.6V and testing seems to show that battery life is enhanced by stopping them going outside those limits.

Interesting that raw cell prices are so reasonable when compared to buying packs. Looking at the price of Pylontech packs at the moment makes me glad I decided to bite the bullet and by six US3000Cs last year. At the time I was convinced I'd gone way OTT, and would never need 21kWh of capacity, but I'm now really glad I made that decision. The only issue with having lots of capacity is being able to get enough charge.

I really need to look at adding some more panels to catch the early morning sun, as our 6kW system doesn't really start to get going until late in the morning, as it faces more or less SW. Ideally I want a mounting system that fits to a wall and forms a cantilevered covered walkway from our back door to the place where we stow the bins. That way the panels can do two jobs and deliver some morning generation and provide shelter when we need to go out to the bins when it's raining. I haven't been able to find an off-the-shelf panel mounting system that can do this. Probably need to get something fabricated to do the job. I could get about six 330W panels along that wall, but would also need a couple of panel-sized sheets of glass for the bit that runs past a window.

[Caesium]

I've been eyeing up these LF280's all morning (trying to convince myself not to buy some) and I've noticed they don't seem very heavy. The datasheet reckons they're 5.4kg each, so 15 of them to make 13kWh is only 81kg.

My 14.4kWh stack of 6 pylons is about double that.. 24kg * 6 = 144kg.

I'm wondering why the huge discrepancy, are the Pylons mostly just metal casing or what?

Did you get the K variant by the way Joeboy? https://energiepanda.com/the-difference ... 0n-lf280k/ I also see there's grade A and grade B.. the latter saves a bit of money but at the cost of only being around 90% capacity of grade A.

Decisions decisions!

[Joeboy]

I've been eyeing up these LF280's all morning (trying to convince myself not to buy some) and I've noticed they don't seem very heavy. The datasheet reckons they're 5.4kg each, so 15 of them to make 13kWh is only 81kg.

My 14.4kWh stack of 6 pylons is about double that.. 24kg * 6 = 144kg.

I'm wondering why the huge discrepancy, are the Pylons mostly just metal casing or what?

Did you get the K variant by the way Joeboy? https://energiepanda.com/the-difference ... 0n-lf280k/ I also see there's grade A and grade B.. the latter saves a bit of money but at the cost of only being around 90% capacity of grade A.

Decisions decisions!

K variant brand new and grade A. The per unit bare price was
US 108 per unit.

Interesting article Caesium, I had no idea!