Powerwall voltage

youlasty

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hey im gonna make my very first pack, 6s50p 3000wh mini powerwall and i have all the parts ready to buy but, i cant find an inverter which you can select the cutoff voltage in, one i found was for 21 volts cutoff voltage which means it will cutoff the cells at 3.5 volts but they arent near discharged at 3.5 volts, theyre disharged at 2.9 or 3 volts,

now i could just connect the inverter to the load in the solar charge controller but the solar charge controller only out puts 100 amps or so but id rather connect them to the battery itself so no voltage is changed as i dont think the solar charge controller can supply enough wattage, {2400w} is the max it can output but i need 3000 in my inverter. any help?
 

Redpacket

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youlasty said:
hey im gonna make my very first pack, 6s50p 3000wh mini powerwall and i have all the parts ready to buy but, i cant find an inverter which you can select the cutoff voltage in, one i found was for 21 volts cutoff voltage which means it will cutoff the cells at 3.5 volts but they arent near discharged at 3.5 volts, theyre disharged at 2.9 or 3 volts,

now i could just connect the inverter to the load in the solar charge controller but the solar charge controller only out puts 100 amps or so but id rather connect them to the battery itself so no voltage is changed as i dont think the solar charge controller can supply enough wattage, {2400w} is the max it can output but i need 3000 in my inverter. any help?

You can't run a typical non-grid tiedinverter directly off the solar controller. It'll be unstable at best.
Panels > solar controller > batteries > inverter > loads

re the voltages, you need to focus your efforts on the common inverter voltages of nominal 24V or nominal 48V.
24V = 7s with 18650 Li-ion cells, 48V = 14s

100A from the solar is going to stress a 50p battery, that's 2A/cell charge which is steep.
At 3kW, you want to be looking at a 48V system.
 

Sean

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youlasty said:
..... which means it will cutoff the cells at 3.5 volts but they arent near discharged at 3.5 volts, theyre disharged at 2.9 or 3 volts,

If you are able to, measure the capacity between 3.5v and 2.9v (or just look at some typical discharge curve graphs) - I suspect you'll then be amending your requirements such that your low cell disconnect voltage is nearer to 3.6v than 3v.
 

youlasty

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Redpacket said:
You can't run a typical non-grid tiedinverter directly off the solar controller. It'll be unstable at best.
Panels > solar controller > batteries > inverter > loads

re the voltages, you need to focus your efforts on the common inverter voltages of nominal 24V or nominal 48V.
24V = 7s with 18650 Li-ion cells, 48V = 14s

100A from the solar is going to stress a 50p battery, that's 2A/cell charge which is steep.
At 3kW, you want to be looking at a 48V system.
thanks ill do 7s, and ill connect the inverter directly to the battery, turns out, at 7s, batteries discharged are 21V! exactly what the inverter cutoff voltage is! gonna go with a 2000w inverter not 3000w as im not gonna be powering serious stuff
 

OffGridInTheCity

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As my system grew... I eventually took the step up to a Midnite Solar Classic Controller. More sophisticated controllers have auxiliary controls based on things such as battery voltage (or other controller parameters). I use this to turn the inverter on/off based on battery voltage - so I can affirmatively control the battery discharge depth. This lets me draw power in a middle range of battery bank voltage range in an effort to make battery last twice as long.
 

youlasty

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OffGridInTheCity said:
As my system grew... I eventually took the step up to a Midnite Solar Classic Controller. More sophisticated controllers have auxiliary controls based on things such as battery voltage (or other controller parameters). I use this to turn the inverter on/off based on battery voltage - so I can affirmatively control the battery discharge depth. This lets me draw power in a middle range of battery bank voltage range in an effort to make battery last twice as long.

ive decided on a 7s36p, 3016wh battery consisting of 252 18650s, and it will be 430amps of output, if i calculated right. but i dont think a wire that handles 430amps exists unless its a gigantor industrial wire thats negative10awg.. the dual xt90connectors would burn off. how do people use little xt60 connectors and 12awg wiresfor a monster powerwall battery?
 

daromer

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36cells of high Power cells can hand out many 100a but do you need thta? You design the Wire based on ur useage and same goes with the fuse.


And No.. noone uses xt 60 for that Power. Xt60 is max 60a continued.... ;)
 

youlasty

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daromer said:
36cells of high Power cells can hand out many 100a but do you need thta? You design the Wire based on ur useage and same goes with the fuse.


And No.. noone uses xt 60 for that Power. Xt60 is max 60a continued.... ;)

all cells will have to output 10 amps continious which theyre capable of.
10amps x 36 cells = 360 amps output x 7s = 2520watts output
 

Wolf

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youlasty said:
ive decided on a 7s36p, 3016wh battery consisting of 252 18650s, and it will be 430amps of output, if i calculated right. but i dont think a wire that handles 430amps exists unless its a gigantor industrial wire thats negative10awg.. the dual xt90connectors would burn off. how do people use little xt60 connectors and 12awg wiresfor a monster powerwall battery?

First of if you are only using 36 cells in parallel to get 430A you need to pull 12A from each cell.
A 3016Wh battery at 24V has 125.66Ah available.
That would still mean you are pulling 3.42Amps from each cell.

So I am confused here. I mean the average standard discharge of a 18650 is ~1A with potential busts into the 5 to 10 Amp range.
at a standard discharge of 1A a 3000mAh battery would last you 3hrs and a 7s36p pack would deliver 36A for 3 hrs.
A mind blistering draw of 5 amps per cell would give you 180 Amps for 0.6 hrs.
So I'm not sure where you get the 430Amps from.
Even if so 430A X 24V = 10320W WOW :exclamation:

Wolf
 

Korishan

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@youlasty: What inverter are you looking at using?

Even if a battery is "capable" of delivering 480A, you won't be drawing that continuously, unless you're welding or something extreme like that. Even an inverter rated 5000W with 10,000W surge @ 24VDC is going to pull 208A with 416A surge, and that's under full load. Running a 15000BTU window A/C unit or 4000W water heater off this thing?
 

Wolf

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youlasty said:
all cells will have to output 10 amps continious which theyre capable of.
10amps x 36 cells = 360 amps output x 7s = 2520watts output

10A per cell is 16.62 minutes of power from this 7s36p battery. Now that's what I call a power wall :p

Wolf
 

Redpacket

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So the OP mentioned 2kW draw & a 7s, "24V" system.
So at 2kW with say 90% inverter efficiency, that's 2000W/24V/0.9 = ~92.6A at full load.
So to keep the cell draw reasonable, say 0.5A/cell, that means 92.6A/0.5A/cell = a 7s/186p battery.
With this, under best conditions, you'd get approx 6hrs at full load for good 3000mAhr cells.

With the above, the cable sizing for the battery to inverter & DC breaker/fusing would need to be rated 100A or so continuous.
 

youlasty

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Korishan said:
@youlasty: What inverter are you looking at using?

Even if a battery is "capable" of delivering 480A, you won't be drawing that continuously, unless you're welding or something extreme like that. Even an inverter rated 5000W with 10,000W surge @ 24VDC is going to pull 208A with 416A surge, and that's under full load. Running a 15000BTU window A/C unit or 4000W water heater off this thing?

an edecoa 3000w inverter, with all my batteries at 10a continious it will be 10amps x 45 cells in paralell x 7s = 3150watts so it will power the inverter continious and it will shut off auto when batteries are at 21v {3v each cell}

so it will be 450 amps by 1s, 45p
my cells will be rated todo 10amps continious per individual cell
unless im seriously bad at maths, 3000w can power a heater, microwave and fridge
 

Wolf

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youlasty said:
an edecoa 3000w inverter, with all my batteries at 10a continious it will be 10amps x 45 cells in paralell x 7s = 3150watts so it will power the inverter continious and it will shut off auto when batteries are at 21v {3v each cell}

so it will be 450 amps by 1s, 45p
my cells will be rated todo 10amps continious per individual cell
unless im seriously bad at maths, 3000w can power a heater, microwave and fridge

A 3000W inverter at 24V will draw 125A.

You moved from 7s36p to 1s45p? I think you mean 7s45p? Right?

Your 3000W inverter even at surge ( excerpt from spec sheet)
  • POWER?Output Continuous Power: 3000w. Output Peak Power (<10ms): 6000w. DC working voltage: 21-28V. Modified Wave Type.
6000W for less than 10ms (that's not good) draws a max of 250 amps.

So in essence your now upgraded to a7s45p battery (with 3000mah cells I am guessing)
3Ah per cell X 45 =135Ah. Whichwould last at max output of 3000W continuous for about 1.08hrs in a perfect world.
I personally don't think you will be using the fridge ,microwave, heater (well maybe the heater if you are at the north pole, but then why the refrigerator??) 100% of the time so your battery should last longer.

Just because you have 450A available does not mean you are going to use it If you are using 450 Amps at 24 volts that is 10800W.
If you need that much wattage you need a bigger inverter.

Wolf
 

youlasty

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yeah i moved to 7s45p for a total of 315 2250mah cells, resulting in 2.976kwh --> 3kwh

so that means, this battery outputs 3000w for an hour to the inverter which changes that 3000w to ac so it can power 3000w worth of appliances for an hour in a perfect world? or if a ps4 uses up 300wh then this mini powerwall of mine can keep a ps4 turned on for 10 hours?

when i make this first build then how do i add capacity to my profile
 

Wolf

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youlasty said:
yeah i moved to 7s45p for a total of 315 2250mah cells, resulting in 3kwh

so that means, this battery outputs 3000w for an hour to the inverter which changes that 3000w to ac so it can power 3000w worth of appliances for an hour in a perfect world? or if a ps4 uses up 300wh then this mini powerwall of mine can keep a ps4 turned on for 10 hours?

OK the dynamics have changed again.
Will you make up your mind or mine. :p

7s45p with 2250mAh cells is 101.25Ah Calculation goes as follows 45 cells in parallel times2.25Ah=101.25Ah.
101.25Ah at 24V = 2430Wh (2.43kWh) not 3kWh
Not including your Inverter loss you can play your 300W PS4 for 8.1hrs 300W X8.1hrs =2430Whs.


Wolf
 

youlasty

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Wolf said:
youlasty said:
yeah i moved to 7s45p for a total of 315 2250mah cells, resulting in 3kwh

so that means, this battery outputs 3000w for an hour to the inverter which changes that 3000w to ac so it can power 3000w worth of appliances for an hour in a perfect world? or if a ps4 uses up 300wh then this mini powerwall of mine can keep a ps4 turned on for 10 hours?

OK the dynamics have changed again.
Will you make up your mind or mine. :p

7s45p with 2250mAh cells is 101.25Ah Calculation goes as follows 45 cells in parallel times2.25Ah=101.25Ah.
101.25Ah at 24V = 2430Wh (2.43kWh) not 3kWh
Not including your Inverter loss you can play your 300W PS4 for 8.1hrs 300W X8.1hrs =2430Whs.


Wolf

wait but2.25 x 4.2 x 315 = 3000watts, enough to power the inverter

2.25= battery Ah, 4.2 is the max volts and 315 is the number of cells resulting in 3000w?

oh i think i get it, the batteries must supply 3000w of power even right when theyre gonna die. so 3000w+ at 3.1 volts or something. i guess ill just buy more cells.. this project is gonna cost alot. still worth it

wait mabye ill just use a 2000w inverter because even when the cells are about to die they output 2100watts and 3000w fully charged but would that not blow up the inverter

2000w isnt enough for my air heater tho :{, ugh not like it matters anyway
 

daromer

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No. Total capacity is based on nominal voltage. To be fair use 3.65v. then add 20% losses and you get ur total available energy and time it can run. This though Will be a 100% dod (depth of discharge) bad in real world this isnt usefulle. Perhaps 60% is better :)

Also the load on the cells isnt larger than the device hooked in. IF you have a tv using 100w then att the battery perhaps 150w. 100+20 +30 where 20 is. The losses and 30 is the Idle draw in the inverter
 

Wolf

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youlasty said:
wait but2.25 x 4.2 x 315 = 3000watts, enough to power the inverter
2.25= battery Ah, 4.2 is the max volts and 315 is the number of cells resulting in 3000w?

Yes at full load but are you running the Inverter at full load all the time? It may only need to supply 300W if all you are doing is playing on your PS4.

oh i think i get it, the batteries must supply 3000w of power even right when theyre gonna die. so 3000w+ at 3.1 volts or something. i guess ill just buy more cells.. this project is gonna cost alot. still worth it


wait mabye ill just use a 2000w inverter because even when the cells are about to die they output 2100watts and 3000w fully charged but would that not blow up the inverter
2000w isnt enough for my air heater tho :{, ugh not like it matters anyway

LOL you got way too many gears whirring in your head.

A 18650 cell will yes charge to 4.2v and usually the low Vcutout is ~3V. Once you put a load on a cell the V will drop to ~4.05V and will supply whatever amperage you demand of it till ~3V. So the cell will supply 2250mAh whetheryou draw 500mA or 2250mA. If you draw 500mA from the cell it will discharge in about 4.5 hrs if you draw 1000mA (or 1A ) it will discharge in 2.25 hrs. Your usable voltage range is really ~4V to ~3V were the battery will supply your amperage requests.
Once the cell hits its cutoff voltage the current supplied drops off rapidly. See chart below.
This is just an example of a cell which happens to be aLG 18650HE2 but all Li-ion 18650 cells work the same. Just different cutoff voltages depending on manufacturer and cell chemistries.

image_ntvecq.jpg


Another thought is a BMS for your 7s45p pack. You will have to find a BMS that will handle the amperage you are requesting and also have a shunt trip or some cut off when the pack voltage is ~21V. Also when recharging you will need to be able to balance the pack and have an upper limit cutoff so you don't overcharge the battery.

Wolf
 
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