Sold to the Powerwall idea !!

Hi folks,

I've been reading blogs, forums and watching YouTube video's for the last 5 months I guess. I've spent HOURS on the 'world wide web' gathering info and all sorts of info and ideas and I can say that I'm FINALLY HOOKED UP to the idea of my own powerwall.


I want my house still connected to the grid but I do NOT want my PV system connected to the grid,in Belgium you have to pay TOOOOOOO MUCH to have it connected to the grid (at least that's why I think).

So I want to start small and build up (main reason beingbudget :blush. I would like to hookup all the lights (all led-type HUE kind),fridge/freezer (new A+++ type 183kW/annum) and some electrics (RP3+, router)first (prox1kW/day) and see if I can get all this powered solo on PV + batteries. Because I want to build up gradually when budget allows me too, I want to start of correctly straight away so I don't waste money by buying the wrong stuff. That's where I can use the help and advice from the more experienced people here .

Goal is a 48V system, I would start off with 14s20 (Samsung INR18650-29E, 2900mAh, 8.25A discharge) so roughly a 3kW bank.
To charge: 6 x Boviet BVM6610M-300 solar panels comes at 1800 Wp.

Now what concerns the inverter, don't have PIP here in Belgium (I think) and import is too hight cost. I can find Volticon (UK) what seems to be a copy of the PIP. I see a lot of people here with the PIP 5048(some type) here. Don't even understand what difference intypes mean (MK, MS, GK, etc....). My question is, even if I only have like a small power input to start with, can I get a big inverter like that immediatly or not? :huh:
Also, do you think the type of batteries are suitable for powerwall ?

Thanks on the advice and the moment I'll start off, I will keep everything posted on here ofcourse.

Greetz from Belgium :shy:

Welcome the club

Starting small is a good plan, especially where budget is involved. 48V is also a good start as it gives you the best options to price.

Are you buying the Samsungs new, or repurposing recycled cells? If they are new, great, and they'll work just fine.

Going with 14s20p will put you at about 40A peak surge (you could actually go for 80A surge, but why stress the cells that hard if you don't have to)
I'm not familiar with Volticon. But there are others. AIMS makes a good inverter and there are a few supposed clones out there (is it clone if the same manufacturer produces the various brands with a different label?) But I don't know if that's available in your area.

Usually the Type (MK, MS, etc) is for the functionality, bells&whistles, surge ability, programability of the software, etc.

Hi Korishan,

The cells would be new indeed, I can get them for $1.67/cell which is not bad I think. I have to start with new ones as I have no flow (yet) of used cells. I just started my 'begging' round but found it's not that easy. Either they don't trust it or they smell 'money'. Guess everyone starts to see a 'new market' in used cells.

Could you explain me how you come to the 40A surge please? I don't quite understand that one. As far as I calculate, if I use a 5kW inverter, I would draw 5000/48 = 104A, which means 104/14 = about 7,5A per battery pack. Or am I wrong in this calculation and does it not work this way? I am a newbie after all

Yes, they do charge a lot to feed back into the grid... gonne be some changes next year tough, d'ont know if its gonne be for the better of worse, butthat is part of the problem overhere right?

Those PIP's are from MPP , they are sold under many different names, Voltron is just one of them. There is also Infini solar... these are noclones.
You can find them on Ebay, cheapest from the UK or Germany, i have got mine from Spain very cheap.
But do your homework before buying....

For new cells, Nkon.nl is the place to be.

Do not forget a BMS, it is a important part of any kind of DIY battery stystem.
Start with the forums FAQ if you not already did:https://secondlifestorage.com/t-Frequently-Asked-Questions-FAQ

Oh, and Welcome

Hi Wim,

Knowing our government, it won't be change for the better good. Also, I found out I have the most expensive rate = Gaselwest
I already know NKON.NL (Arne), that's where I get my batteries indeed
I didn't mention the BMS indeed but I think I would invest in Batrium, I know it's expensive but I've read enough about it to know it's good. Sometimes you have to spend some money on (good) things.

I didn't get an answer yet on the inverter. Is it ok to start with a big inverter straight away ? Will this not cause any problem?
Also, do you know how Korishan gets that 40A peak surge ? Where he get's that from ?

I thinks he is talking about the max A rate a 40p pack with your cellscan do, i think ... but ... yea who knows ... Maths ... not my thing ... let him explain it.

For the inverter, it depends on your end goal, do you wanne be compleatly off grid ? The bigger the inverters are, the less efficient they become, kind of.
I mean, a inverter to big for your loads, will work fine, but less efficient due to higher idle losses.
But it is possible to "parrallel" connect multiple inverters (mpp), so you can always expand later, bit more expensive tough.

The cells are rated at 8.25A max. This is usually not a continuous until it's dead kind of thing. You have you 20p, so if we go with 2A for each cell, that'd be 40A.
The 80A surge was because you could pull 4A out of them for awhile without a significant decrease in capacity. Remember, the more Amps you pull from a cell, the lower the capacity.

So, at 2A, it might have 2200mAh, but at 8A it might only 1400mAh (numbers are for example only). Also, the higher the amp draw, the lower the life of the cell. Take all that into consideration, and we get 40A with 80A surge

Yes, the inverter maybe able to handle the higher amp, but until your packs are ready for it, don't try it. You could either cause wiring to melt, fuses to blow, or the inverter will go "Ok, I'm done" and power off.

Not sure where you are getting your cells from, but if you can buy the LiFePO4 from the same supplier without it breaking the bank, I'd recommend going with those. They are little more expensive, and you do need more cells to achieve the same kWh storage, but they can handle a lot more amps and full DoD better than LiCo (Lithium Cobalt)

Ahh, reread a portion of your previous. Series increases voltage, parallel increases amps/capacity. So it'd not be divided by 14. 104A / 20 cells = ~5A per cell

OK... I see where you got that number now but I don't know how I would get even to 2A per cell ? Or I'm missing something or making errors in my calculation but let's say that I hook up a load of 1000W on the inverter. That means I will draw, without the losses from the inverter intself, 1000W from the battery or 1000W/48V = 20,8A, correct? If I'm correct that means, in a 14s config, only about 1,5A per batterypack.
Am I calculating this correctly?

You keep trying to calculate the cells in series. This is a no no.

ONLY cells in parallel matter for amperage. So with 20 cells in parallel: 1000w/48V = 20.83A / 20 cells = 1.04A per cell.
Under a surge condition where the inverter pulls 2000W, then each cell will see 2.08A (or there abouts)

I think you need to revisit the FAQ https://secondlifestorage.com/t-Frequently-Asked-Questions-FAQ as it discusses the layout and how each section effects the capacity, voltage, amperage

Oooh.... OK, sorry to be the 'pain in the arse' but I think I got it now. I thought when it pulls 20amps it would be divided over the complete string of 14 packs but it doesn't, in fact, it pulls the 20A from all packs. So if I calculate current I only look at the cells in parallel. Idiot me, now I understand why people try to make 80p, 100p or even 120p. Trying to get the current per cell as low as possible.
On the positive side, I think I finally got this thru now. On the negative side, this means I better invest in double the batteries to start off with so I can make 14s40p instead. That means the current would be halved already and would improve my battery lifespan, right ?

Yes, the more cells in parallel, the lower the amp draw per cell, and the longer their life. Also, it makes it easier to lower the voltage cutoff points a bit and still maintain run time.
So, with 20p, you might need to run 4.2-3.2V, but with 40p, you can run 4.1-3.4V and still have good run time, if not longer even with the lower voltages.

As I'm calculating the necessary starting budget for my system, I came to the next question : "Would 7 panels of 300Wp each be sufficient enough to charge a 6kWh battery pack with a days yield?".
Are following calculations plausible ?
2100Wp * 0.8 (correction for winddirection) * 0.8 (losses in electrical circuit) = 1344Wh (might be a lot more during nice days but I want to calculate realistic numbers)
Let's say I have about 3hrs in a day I get this max and the rest (morning - late afternoons) I get 1/3 of that.
1344 * 3 + 448 * 4 = 5.824kWh
Does this look acceptable or do you think I will yield more or less with these 7 panels ?

Woeha.... finally a big boost for the project. I was having trouble finding 18650 cells. Today... I had to pick up my moms electric bike with my minivan and bring it to the repair shop (problem with motor). I rolled in the bike, told him what the problem was and then I just asked him: "You wouldn't have by any chance some used batteries lying around you want to get rid off?" He looks at me for a second and then goes like: "How many do you want?" Me... "Euhm... don't know, whatever you can spare.". "Pick your car and drive up to the backside of the building.... "



3 Big boxes FULL of battery packs, I think there's about 30 or 40 packs !!!
Started harvesting this morning so my 'cell count' goes up quickly now

By the way... how do I change the cellcount on my profile ?