18Kwh - 12v off grid Powerwall

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jestronix

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Nov 7, 2017
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Hi all,

Finally starting my journey into a DIY powerwall. This will be intended for off grid solar with fairly small loads from two 700w inverters. Panels are 14 x 190w

This is a low cost build intended for maybe 5kwh per day use , giving a few days power on dark rainy days. I'm not going 48v or even 24v as I already have two high quality synergex inverters. All lights and pumpsare12v etc. so really no need to spend up as their are no huge loads.

Regulators are 30a MPPT epsolar units that I can program the output voltages to fit lithium ranges. I'll be running four of them, I have two already and know they work together well.

Basically a standard high efficiencyfridge , lights and a 42" LCD TV, pump etc is all I'll be running.

It will be a 3s x720p so all up 18 x 120cellpacks. Housed in a half height server rack.

I will be monitoring the pack voltages using a sitmon PacketFlux unit, which I can graph and calculate usages , state of charge etc, also each pack voltage, with App/Smsalerting through PRTG. I can also control relays based on heat and voltage etc. great product that I've used before. Cheap too.

Finally tested cells allloaded into my first pack tonight. Waiting on my glass fuses to arrive and will hunt down some bus wire ::) Now the real labor begins ::( hey it's a hobbby right ?

image_cwabfw.jpg
 

Korishan

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How come you went with 3s instead of 4s? That doesn't leave you with much run time
 

jestronix

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Nov 7, 2017
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Korishan said:
How come you went with 3s instead of 4s? That doesn't leave you with much run time

I looked at discharge graphs on low drawper cell, max my cells will see is 300mA . If you check out the amount from 4.1 down to 3.5v on these loads it looks like I'll get more. The drop off from 3.5 down is quicker. What do u think ? I'm still leaning on 3s but ..... I'm open to suggestions:)
 

daromer

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Oct 8, 2016
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i think you are correct jestronix. At such low current the 3s would work fine and 4s you will loose on top end.
Just make sure to reduce the voltage drop due to resistance as much as you can. Otherwise you will end up with cut off to early
 

jestronix

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Nov 7, 2017
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Just did a cell count, make this 20kwh ! Found one of my laptop packed had shorted on a bad cell, it melted the nickel buswire, acted like a big fuse. Anyway I'll see you in 6650 solder joints later ! Oh man what am I in for :)
 

Learjet

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Aug 30, 2017
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jestronix said:
Just did a cell count, make this 20kwh ! Found one of my laptop packed had shorted on a bad cell, it melted the nickel buswire, acted like a big fuse. Anyway I'll see you in 6650 solder joints later ! Oh man what am I in for :)

I wonder how many soldering irons you'll go through? Good luck.
 

daromer

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I would guess 0.5 soldering iron max! :) I have done 10000 points atleast with mine and its still on same bare copper tip :p
 

jestronix

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Nov 7, 2017
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[quote pid='20595' dateline='1512098759']

image_vtedrs.jpg


Picked up an 80w iron today, perfect temp for a quick solder that sticks and doesn't heatthe cells up much at all. Slowly presoldering the packs. I'm in a bit of a rhythm now, 12 cells a day slow as it might sound adds up pretty quick when it comes to then soldering the packs, sneaks up on you. I'm in no major rush to do all 26 packs, as soon as I build 3 packs I can hook the solar up for low load and charge testing :)
[/quote]
 

jestronix

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Nov 7, 2017
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I've backed down to 80p packs, one reason being the rigidity of the 100p packs is not the best, as in there is far more flex than the 80p. Second is the weight makes 100p heavier meaning my digits are putting more pressure in cells and fuse wire etc. third they fit in those HP holders :)
 

Korishan

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@jestronix: You don't need to post multiple threads for the same project. You could of asked your wiring question here as it directly pertains to your build. Makes it easier to follow your build ;)
 

jestronix

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Nov 7, 2017
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Korishan said:
@jestronix: You don't need to post multiple threads for the same project. You could of asked your wiring question here as it directly pertains to your build. Makes it easier to follow your build ;)

Hi Korishan , good idea , wasn't sure if the wiring question was a general, but ur right it's this build. :)


Well I just soldered 80 glass axial fuses and man it just about killed me compared to fuse wire! With fuse wire you can just keep the wire going and use your thumbnail to go pretty quick. But the glass fuses like average joes packs, is hard work. Your having to line things up and fiddle.

I'm not sure I'm going to continue with glass fuses ! That was easily three times the work.
 

Mark Kennard

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Nov 9, 2017
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Hi. Im not one to talk but with that many solder joints in front of you my advise is to set up a fume extract. All that flux and lead cant be good for you.
When I prepare my cells for soldering I never totally remove the spot welded tabs, this way you do not need to heat up the battery when attaching wires as the tabs are easier to solder to than directly to the battery posts.

Good luck.

Mark
 

jestronix

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Nov 7, 2017
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MarkKennard said:
Hi. Im not one to talk but with that many solder joints in front of you my advise is to set up a fume extract. All that flux and lead cant be good for you.
When I prepare my cells for soldering I never totally remove the spot welded tabs, this way you do not need to heat up the battery when attaching wires as the tabs are easier to solder to than directly to the battery posts.

Good luck.

Mark

My soldering efforts are done outside ::) with a big fan on, fumes are pushed aside.
 

Wattsup

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Feb 19, 2017
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Nice 12v build there. I have a bit of a soft spot for 12v ;)

Which cells are you using, are they recycled...all the same or random cells?
 

jestronix

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Nov 7, 2017
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Wattsup said:
Nice 12v build there. I have a bit of a soft spot for 12v ;)

Which cells are you using, are they recycled...all the same or random cells?

Thanks , yes these are all the same cells, the Sanyo heaters. So far about 15% or so are heaters. They are all used cells. Yes 12v is great for small builds ::)

As a kid we lived too far from the power lines and lived purely off two 40w panels, we had halogen lights (no leds back in the 80s). I'm amazed how well we did, a small tv, stereo, lights and even a water pump. Living off almost half a kilowatt a day, it blow me away today when we chew 20kWh a day. In reality we had a gas fridge and solar hot water, so maybe we were more like 10kw a day :)
 

jestronix

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Nov 7, 2017
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Testing begins ::) some tidying of cables to be done, this is just my test rig with low current draw and a max 30amp on these packs.



image_fyrawe.jpg



image_ppdbwq.jpg


90 amp XT connectors ::) doubled for 180 amp constant which these packs won't go near :)
 

Korishan

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Lookin nice!! Ohhh, but OCD kicking in, you need to the move red cell slightly to the left, it's outta of alignment :p
 

jestronix

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Nov 7, 2017
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Yeh glad they'll all be hidden when I finish, otherwise I'd be out there all day lining them up!
 

Wattsup

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Looking really good man.

What make/ modelare those charge controllers?
 
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