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New power wall Mures
#1
I've started building a new power wall 14s20p as proof of concept and then plan is to expand it to 14s40p/14s60p.

PV array contains 22 Canadian Solar 285W, Sunny Boy 5000 on grid inverter, ~5 kw installed power.
My plan is to use Sofar ME3000SP, so nothing will be changed on existing grid, just plugin new inverter, clamps and battery.
All cells will be packed 20p (4x5) with 2A glass fuse on each cell, bus will be coper 6mm. I don't plan using packets bigger than 20p as I can upgrade when I get a batch of 280 tested cells.
Bus between strings will be from aluminium 2x30mm.
Fuse of 60Amps to the inverter.
Cells are only from laptops, over 35 different models, planning to keep only cells with capacity over 1900.
Until now over 300cells, nominal capacity average 2338, tested capacity average 2174, ~20 tested.

My inspiration was from this link: a2delectronics.ca/2018/06/22/2-4kwh_diy_powerwall/

Does anyone used ME3000SP until now with with home made battery?

RikH likes this post
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#2
I think you should rethink your 60A battery / inverter fuse. The cell level fuses will start breaking at just 40A (in practice probably somewhat higher). So if something goes wrong somewhere, you'll be looking to replace at least 20x 2A cell fuses, if not more. I'd replace the 60A fuse with a 25A~35A breaker, so that it will trip long before the cell fuses start popping.
Solexx X likes this post
Modular PowerShelf using 3D printed packs.  30kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#3
(12-07-2018, 12:33 AM)ajw22 Wrote: I think you should rethink your 60A battery / inverter fuse.  The cell level fuses will start breaking at just 40A (in practice probably somewhat higher).  So if something goes wrong somewhere, you'll be looking to replace at least 20x 2A cell fuses, if not more.  I'd replace the 60A fuse with a 25A~35A breaker, so that it will trip long before the cell fuses start popping.

So true! He could be blowing every fuse at 60amps and more that 4 amps possible per cell.
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#4
In my opinion you should opt for a max current of each cell to about 400- 500 ma by nominal power
On one side for the urge of use the cells as long as possible.
On the other side if you go for say .4a and the average cell is 2.4Ah in you pack in theory you would have a runtime of about 6 hours
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#5
On second thought... What I posted before holds true only if all the cells have the same capacity.

It gets a bit more complicated with mixed cells. Suppose one pack consists of 5x 1000mAh, 10x 2000mAh, 5x 3000mAh cells (thus average is 2000mAh), and you try to draw just 35 Amps. The current does not split evenly between the cells. The 1000 cells will supply only about* 0.875A, the 2000 cells about* 1.75A, and the 3000 cells about* 2.625A. The 2A fuse on one of the 3000 cells will probably pop within minutes. Now 35Amps has to be split by 19 cells, and the fuse on the next 3000 cell will pop... it'll be a accelerating chain reaction of fuses popping, probably on all the packs at the same time. Now, that's a video I'd pay to watch ;-)

*"about": internal resistance of the cells come into play as well, so the calculation gets even more complicated. Best to stick with very conservative current draw vs fuse size and/or use reasonably closely matched cells.
Modular PowerShelf using 3D printed packs.  30kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#6
In his drawing there are two packs of 20 parallel so that makes 40 cells p. With 2A fuses (Yes I know, on averag..) that must be enough. But because of this unequality it would indeed be better to lower this 60A fuse to what ajw22 advised.
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#7
(12-07-2018, 01:30 PM)RikH Wrote: In his drawing there are two packs of 20 parallel so that makes 40 cells p. With 2A fuses (Yes I know, on averag..) that must be enough. But because of this unequality it would indeed be better to lower this 60A fuse to what ajw22 advised.

Hello everyone, I didn't expect to get so many replies Smile. Thank you for feedback!

You all are right,  I'll lower the fuse to 20-25Amps with 14s40p, as I add more cells 14x20 or 14x10 I'll change the fuse, so keep maximum 10-12A for each 14x20 cells.
On inverter specs I found a settings to limit charge/discharge power and voltate, so I can match power wall capacity. Drain would be limited by setting, so should be pretty safe.

As bms I've ordered this one: https://www.aliexpress.com/item/58-8V-14S-Bluetooth-BMS

Sorting cells is a really slow process Sad, I'll have to buy 1-2 more opus for testing.
For charging I have 18 x TP4056 and 2 sources 5V 8A + sockets, so opus is just for discharge/test.

Right now I have ~300 cells, 140cells tested with average 1850mAh, after testing all cells I'll drop those under 1800mAh or use them for something else.

I just wait a new lot of 100 laptop batteries, over holidays I hope to sort them out to hit 14s40p on middle of January.

Also the updated diagram to reflect battery fuse options:


Have a nice weekend!
Korishan likes this post
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#8
Without having read all.

If you plan on 1A max current on cell level thats also the max current you NEED to have tested them at!

The cell fuses should then be arount 5A. That value is not to protect against max current from the system but for a fail on cell short level! If you got 20p you got 19 cells that easily can give 5-10A each and thats ALOT. No need to have to low cell level fuses!

The fuse to the battery pack is what limit for a dead short and should be at at the highest level the charger or user will pull. If thats 20A you should set the fuse at that. Of course all other components need to cope with it.

I always recommend to have cell level fuses above the max total current because otherwise you just screw it up.

and ONCE AGAIN the burst current that people tests is not what you should go by. Thats the instant burst. A fuse made of 1A max then you should NEVER go above that because that just causes voltage drop and losses.

Personally if max current could be 1A on cells i would NEVER go below 2a fuses. its not needed. Yes if you want extra protection its fine but you also create issues long run.

Good work
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#9
Speaking from experience, you'll want to put in at least 1 battery disconnect breaker (ie. with a lever, not a fuse). Most inverters/chargers have a big capacitor that will suck current as the battery is first connected. In my case with a similar setup, I could not slide in the fuse properly as the inrush current sparked like mad and welded the fuse connector.

For my next project, I will be using 1 40A main battery disconnect breaker, as well as 20A breakers for each battery bank. That way, I can (dis)connect battery banks safely and spark free.
Modular PowerShelf using 3D printed packs.  30kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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#10
(12-15-2018, 11:29 AM)ajw22 Wrote: Speaking from experience, you'll want to put in at least 1 battery disconnect breaker (ie. with a lever, not a fuse).  Most inverters/chargers have a big capacitor that will suck current as the battery is first connected.  In my case with a similar setup, I could not slide in the fuse properly as the inrush current sparked like mad and welded the fuse connector.

For my next project, I will be using 1 40A main battery disconnect breaker, as well as 20A breakers for each battery bank.  That way, I can (dis)connect battery banks safely and spark free.

The inrush current issue is solved by using pre charge, that's a fairly basic requirement when using large inverters and chargers.
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