Idiot's guide to a self build battery

[Joeboy]

Caesium,
I clicked through on aliexpress to the buckboard but as I am in Turkey it's showing me the Turkish language version! A neat wee bit kit. Does it operate on 220V ac incoming? If so, that is a neat wee variable solution.

https://m.tr.aliexpress.com/item/400123 ... c2turMsite

[Caesium]

Caesium,
I clicked through on aliexpress to the buckboard but as I am in Turkey it's showing me the Turkish language version! A neat wee bit kit. Does it operate on 220V ac incoming? If so, that is a neat wee variable solution.

https://m.tr.aliexpress.com/item/400123 ... c2turMsite

No, it's a DC-DC converter so you'll need a good beefy DC power source. Looks like it operates from 0-55V input so in theory you could use your existing Pylontech stack to power it

I have a 12V/33A power supply here that I'll probably use for it.

[Joeboy]

Caesium,
I clicked through on aliexpress to the buckboard but as I am in Turkey it's showing me the Turkish language version! A neat wee bit kit. Does it operate on 220V ac incoming? If so, that is a neat wee variable solution.

https://m.tr.aliexpress.com/item/400123 ... c2turMsite

No, it's a DC-DC converter so you'll need a good beefy DC power source. Looks like it operates from 0-55V input so in theory you could use your existing Pylontech stack to power it

I have a 12V/33A power supply here that I'll probably use for it.

Great idea, I have the exposed threads on the 2kW inverter posts. Could easy make up a couple of short cable runs with eyes on the end, nut them up and Croc clip'd leads on the output side for simplicity...

I am enjoying this, forcing my mind down non natural paths. SWMBO will rib me for this. Sitting in the garage with my multi meter, Tom Good jumper and a cup of tea watching my batteries charge

All kidding aside, that would be a great first test, moving power from the Pylontechs to the LF280's in a low load controlled manner, nice one!

[Bugtownboy]

If you get a WBS in the garage, Joe, you can alternate between the battery charging and being mesmerised by the flames.

Another kettle for the stove and yer self sufficient.

Even though I haven’t a clue what you guys are talking about, it’s interesting how this thread develops and evolves.

A very functional forum, methinks

[Joeboy]

If you get a WBS in the garage, Joe, you can alternate between the battery charging and being mesmerised by the flames.

Another kettle for the stove and yer self sufficient.

Even though I haven’t a clue what you guys are talking about, it’s interesting how this thread develops and evolves.

A very functional forum, methinks

Thank you btb, one to ponder! I have bought myself Caesium's earlier linked dc-dc converter and will equalise the new battery stack before stretching its legs into a top balance at 3.65v per battery module. I'll do that just for the craick and to transfer over the slowly, slowly catchy monkey philosophy of newly run in mechanical things. It will as I think top balancing is aimed at maximise the new stacks storage potential. Can't do any harm. That will be 54.75v which is overvoltage in comparison to the Pylontechs. I guess I could run the pylontechs down a bit and 180 the dc-dc buckboard to bring the LF280's back down while topping off the Pylontechs. Once that was done and both banks closely matched, throw in the Frankenstein breaker to make the parallel connection then add the LF280 balance board and wiring. Something like that...

£1,687- 15 of LF280K (A) batteries incl del, bus bars n bolts
£60.72 - 1 of 15s 5A balance board.
£60 framework and bolts
£20 DC-DC variable 20A buckboard (battery charger)

£1,828 total

[Joeboy]

Thinking about fuse sizes for the Frankenstein cut out. The most Ah I will see in normal circumstances is a combination of the goodwe inverter feed to the pylontechs coupled with the max incoming power from the Victron system.

Not the best at this but I think that would be
Goodwe battery charging system 3.8kW @ 48V
Victron PV charging system 5 kW @ 48V
Rounding those figures up to 9kW I come to a figure at 48V of 187.5A.
I have no idea how to then split the figure or even if I should. as X amount of that potential is flowing into the Pylontechs and won't make it to the LF280's but the potential is still there?
Should I just go with the closest fuse rating above the 187.5A or am I missing something? I am tempted to half it and go with 100A fuse as the incoming power will split, it would then stay in the realm of normal pricing. Stepping up to 200A and beyond fuses and carriers becomes quite pricey! Nonetheless I want to do it properly.

The max load drawn by the goodwe hybrid inverter is around 83A. I am managing to convince myself that 100A fuse will do it, anyone spotting a glaring omission in my logic, bear in mind the name of the thread!

[Stinsy]

I wouldn’t sweat the “top balancing”. When you get them they should be very close indeed. Paralleling them up and leaving them overnight will even out any small differences, the balancers will do the rest. If you’d bought a load of used batteries from different sources then you’d want to get them close before you parallel them because the current could flow from the highest to lowest quicker than you’d like.

The same is true when connecting the new string of 15 to the existing stack. Try to get them within 0.1V of eachother. They’ll “self balance” there is no problem there, they just might do it too fast if there is too big a difference (eg over 1V). Another solution would be to use a high power resistor when initially connecting the new string to the existing.

[Caesium]

Cheers Stinsy. There's a striking difference of opinions between forums - another one I'm reading (should I name it/link it or no?) has a few posters saying that basically top-balancing is the most crucial part and you're opening yourself up to a world of problems if you don't. I did wonder if it was a little overkill and even the process for doing it was unnecessarily complex (charge to 3.45v until 0A, then charge to 3.55v until 0A, then charge to 3.65v until 0A). I don't get why that's not the same as just setting a power supply to 3.65v and leaving it. Perhaps so the batteries don't spend too long at 3.65v if you forget about it for a few days? I think I'd be checking it every 10 minutes

So just check the cell voltages and ensure they're all within a couple of mV of each other before paralleling up or you may get some pretty nasty sparks? I guess LifePO4 have some pretty big SOC differences over quite a small voltage range so this initial balancing is the part thats worrying me most.

[Stinsy]

People will over complicate anything! And you have to make your own judgment as to which bits of advice you heed and which bits you ignore.

The batteries should be extremely close from the factory. If you like you can parallel the highest to lowest through a resistor (eg a 100W 1Ω resistor) then measure the voltage across the resistor and wait for 0V (or close to it).

However the important point is: to charge a battery you need to apply a higher voltage across it. Eg to charge a Lead Acid 12V battery to 12.8V you typically put 13.8V across the terminals. The charging regime you described misses this important point.

[Joeboy]

People will over complicate anything! And you have to make your own judgment as to which bits of advice you heed and which bits you ignore.

The batteries should be extremely close from the factory. If you like you can parallel the highest to lowest through a resistor (eg a 100W 1Ω resistor) then measure the voltage across the resistor and wait for 0V (or close to it).

However the important point is: to charge a battery you need to apply a higher voltage across it. Eg to charge a Lead Acid 12V battery to 12.8V you typically put 13.8V across the terminals. The charging regime you described misses this important point.

Agreed on the overvoltage potential mistake. As the top end of the LF280's is beyond the realm of the Pylontechs I will get them up to 3.6v+ a wee bit and hold for a while. Purely to allow a new made thing the chance to bed in slowly at max 20A, can check for hotspots etc. Plus I like the idea of playing about with this wee variable buckboard. I'm not going to get caught up in an endless cycle of infitesimal adjustments. As you say, that's the balance boards job.