10kWh LifePO4 DIY Battery Addition..... Here is my write up.

championc · 05-09-2022 6:37pm

@S' looking good 👍

SD_DRACULA · 05-09-2022 8:58pm

https://www.boards.ie/discussion/comment/119575695#Comment_119575695

If it's from the inverter to the BMS/isolator (like your diagram), you can also use pylontech cable kit and snip one end and put whatever lugs you need on it. Or maybe it has the lugs on one end anyway don't recall, had to snip them to put them into the 125a mcb.

Maybe add another one of those marine switches on the negative to tidy things up and have only one cable going to the inverter?

slave1 · 06-09-2022 8:38am

Is it possible to purchase the "insert" to battery (opposite end of the lug) for Puredrive/Pylontech and just crimp your own cables to custom length?

SD_DRACULA · 06-09-2022 9:32am

https://www.boards.ie/discussion/comment/119577711#Comment_119577711

Not worth it, those round plugs for the battery connectors are not cheap (cost more than the ready made cables) and require special crimper too.

I picked up a pylon cable pack from midsummer for around 30 ish.

slave1 · 06-09-2022 9:55am

€30 is decent, the reason I asked is because I was gifted a dryness set for my DIY battery pack and snipped off the "connector" end, at the end of the day a crimp and not propriety (crimp) in nature

randombar · 08-09-2022 8:41am

Hi Lads, does anyone know what the approximate losses in this set up are?

10kwh LifePo + Seplos + Sofar

graememk · 08-09-2022 9:12am

https://www.boards.ie/discussion/comment/119588170#Comment_119588170

20% power measured in and out, via a ct

slave1 · 08-09-2022 10:31am

Which is why we encourage self consumption there and then as much as possible and also discourage batteries to charge an EV as there are further ~8%-10% there

randombar · 08-09-2022 10:47am

https://www.boards.ie/discussion/comment/119588612#Comment_119588612

Yes, plus it's good to know when calculating the energy savings for overnight charging. It's not nightsaver vs daytime it's really nightsaver + 20% vs daytime

graememk · 08-09-2022 11:12am

https://www.boards.ie/discussion/comment/119588696#Comment_119588696

What I've found is it's mostly on charging eg 15% on charge, 5% on discharge but I don't have hard numbers for that

I'd say in the summer, discharge the battery into a car, if your on a day night as your export isn't measured anyway

DC999 · 08-09-2022 11:18am

So that setup means you've around 20% less capacity in the battery basically (than what went into it). Am not being critical. Good for me to know when looking at battery options. All batteries have losses of course.

unkel · 08-09-2022 11:26am

https://www.boards.ie/discussion/comment/119588852#Comment_119588852

No, you get about 20% less coming out of the battery than you put into it (@graememk and others have measured this). But you have also got losses even before putting it into the battery

The whole process: PV from your panels -> PV inverter converts to AC (10% loss). AC inverter (like Sofar ME3000SP) converts to DC for batteries (10% loss). Then AC inverter converts DC from batteries to AC for your house (10% loss). So overall 30% or so loss. This is less in a hybrid inverter as DC is stored directly and only once converted to AC for your house so only 10% loss in total

randombar · 08-09-2022 11:34am

https://www.boards.ie/discussion/comment/119588898#Comment_119588898

I'm just working out how much I save per day charging on the nightsaver so not working with Panel -> inverter losses. PV has paid for itself already I'd say.

I'd say saving maybe 0.75 and 1.00 a day.

unkel · 08-09-2022 11:55am

In my own case: 20kWh (usable) battery, day rate 27.43c incl VAT, night rate 7.90c incl VAT

So savings per month:

30 days * 20kWh * (0.2743-0.079) * 80% efficiency = nearly €100 per month saved by peak shifting...

Paid €2300 for the battery a few months ago, so you can see it will pay for itself very quickly indeed. And of course taking electricity from the grid at night when it is mostly green (from wind) and using it when it is in high demand and mostly made from burning fossil fuels during the day is a very important consideration too.

randombar · 08-09-2022 12:10pm

https://www.boards.ie/discussion/comment/119589051#Comment_119589051

You are using 20kWh * 0.8 (16kwh) of electricity from 8am to midnight??

unkel · 08-09-2022 12:14pm

Yes I'd empty the battery alright every day in winter and then some. Busy 5 person household, working from home, I use almost zero fossil fuels. Heat the house with electricity, have 3 electric vehicles. Heat the water with electricity. Have a large solar thermal and very large solar PV setup too.

slave1 · 08-09-2022 2:09pm

Apart from EVs, I'll be able to run the home for three days with my battery backup, that's immersion, oven etc, everything (just not oven+immersion at the same time).

I'll need a changeover switch first but for the time being will go with dedicated sockets fed from EPS of inverter, the need might never arise so why plough funds into it

mrohare · 08-09-2022 9:36pm

Any last minute tips???

2 of my 4 boxes of cells arrived today, hopefully other 2 very soon. I have (near enough) all the other parts waiting - including ME3000SP.

how long should it take to top balance the 16 in parallel? should I just do the 8 for now and then the 2nd 8 seperately?

I have bought a capcity tester - should I capacity test each cell seperately or in groups. i.e. if 1 group is low then just test those 4 seperatly.

after capacity test, how long will the 2nd top-balance take?

for anyone who has already done this, are there any mistakes you made, or anything you have discovered that is worth giving me a heads up on?

Thanks.

munsterfan2 · 08-09-2022 9:45pm

I would fully charge a single cell, then test it with the discharge tester while charging the next cell. It will take a number of days to work through the cells. If any of the cells arent capacity lodge complaint with aliexpress / paypal ASAP. There are time limits on these. Dont bother trying to interact with OYear, they will only look to delay you.

slave1 · 08-09-2022 9:53pm

8 top balancing at a time, low amps first then higher, I assume you have a BMS in your setup that can manage 16 batteries, this means you don’t have to be 100% with the top balancing

slave1 · 08-09-2022 9:55pm

Wrap your wrench in electrical tape as much as possible, you don’t want to drop it and short a battery

electricus · 10-09-2022 10:27am

What BMS and inverter would you recommend for a smaller power backup pack based on 8S CALB cells? Ideally the pack will be (semi) portable with built in sockets.

Apologies if this is the wrong thread – I don’t have solar or an inverter so not looking to build anything as big as discussed here (as much as I’d like to!)

championc · 10-09-2022 12:28pm

You can't have 8s - the voltage will be too small. These inverters expect 48v

electricus · 10-09-2022 1:50pm

https://www.boards.ie/discussion/comment/119599407#Comment_119599407

Thanks, that's what I thought. I'll need a 24v inverter and a BMS that will work with it. I should probably start a new thread somewhere but asking in case anyone has tried it.

unkel · 10-09-2022 5:12pm

If it's a backup pack just for very occasional (emergency) use, would you not consider those all-in-one packs? They have everything built in, a charger for charging them up, an inverter for powering your applicances with 3 pin sockets, usb sockets, some even have inputs for PV.

This thread is more about large home attached power walls that are cycled every day and see some real heavy duty use.

electricus · 10-09-2022 5:30pm

https://www.boards.ie/discussion/comment/119600423#Comment_119600423

I looked at the backup packs but it looks like I could potentially get a much better battery for less if I built myself. I know its more trouble but hopefully this experiment will better prepare me for a future solar install (if I get get a bigger south facing roof!).

Anyway, I'll stop polluting this very informative thread.

unkel · 10-09-2022 6:46pm

https://www.boards.ie/discussion/comment/119600477#Comment_119600477

Any reason it has to be a 24V pack? Would need 8 CALBS and that's going to be heavy. I would just buy 4 CALBS for a 12V pack, use the busbars that come with them and buy a decent quality sine wave inverter. Tape it all together. Don't bother with BMS if you are only ever going to use it occasionally. After use just check the 4 cells individually and charge up the ones that are lower, and then just store. Rinse & repeat.

graememk · 10-09-2022 7:57pm

Something along these lines? What sort of power do you need?

https://youtu.be/XFn1j1mq1U8

electricus · 10-09-2022 8:38pm

https://www.boards.ie/discussion/comment/119600760#Comment_119600760

Very true, 50kg is heavier than I thought. I was thinking of a pack I could charge on night rate and use during the day for washer, dryer, air fryer etc. and also in case of power cuts as I work from home. Not sure how long I'd keep that up without grid tie in, so a smaller battery makes more sense if its not powering the whole house. Think I'll keep go with a BMS though to extend battery life and avoid problems.

https://www.boards.ie/discussion/comment/119600979#Comment_119600979

Thanks, looks interesting! Thinking about it, a 4 cell 12v setup will give me about 2kWh (80%) which should be enough, for now at least.

unkel · 10-09-2022 9:33pm

https://www.boards.ie/discussion/comment/119601139#Comment_119601139

How would you charge it up and use it during the day for washer, etc.? By micro managing the lot? Hey it's after midnight, I better plug it in to charge it? Hey the battery is full, I'd better buy a €1000 pure sine wave 2kW inverter so I can run my dryer off it? 😂

You get the picture? You either want a cheap and cheerful all in one for emergencies like I suggested above, or you want a grid tie system. There really is nothing in between that is a good solution for anything.

10kWh LifePO4 DIY Battery Addition..... Here is my write up.

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