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2 x 6kWh Powerwalls Using 4p Cradles and No Solder
#1
Hi Everyone, Thought I would share my project with you.
I have also put a link in the youtube section for those who like visuals : http://secondlifestorage.com/viewtopic.php?f=10&t=165

I'm Building my powerwalls using the 4p cradles and 12mm copper pipe as busbars.  
Been running for 3-4 Months 250kWh+ output at my place.
About 5-6 Months at my mates place with a little more output than mine.

My mates setup is 4s96p x1 + 4s48p x1 (3v bus bar tie in, so its 4s144p)
1kW of solar panels, 1500w combi-plus CP-1500-122 inverter, xantrex c35 charge controller set to 16v
My setup is 4s48p x 3 (3v bus bar tie in, so its 4s144p)
1.5kW of solar panels, 1500w combi-plus CP-1500-122 inverter, xantrex c60 charge controller set to 16v

The only real shortcoming is the combi-plus inverters will only power on to a max of 16v
The unit can cope with 17.5, but safety margin means 16v is max, pity.  But 4v / cell is kind to them.

LVD is set to 12v so the cells dont go below 3v.  Bottom end balance down to 2.5v / cell.
No BMS on either rig, but we run meters across all the series so we can see balance at a glance.

Drop in replacement for our aging lead acid banks, and we are totally stoked at the performance and reliability.

I have to say first up that it all looks TOTALLY unsafe, No per cell fusing, wooden backboards, No BMS - its hectic.  
But a lot of time has gone into testing cells, balancing and ensuring that everything is under tiny charge input and discharge load.

My mates rig charges at ~20-40A the cells get 138-277mA each during the charge cycle.
My rig charges at ~35-70A and the cells get 243-486mA each during the charge cycle.
Discharge load of 1.5kW is about 100-120A depending on the OCV of the rig at the time, this is about 694-833mA per cell.

I have used cells of around 2500mAh, so they are rated for about 1200-1300mA charge and about 5000mA discharge.
All cells capacity tested by charging up and discharging at 1000mA, so real world performance is better than in testing.
 
We can pop individual cells out easily, and I am constantly monitoring everything for temp and smell (yes ...)

Its a work in progress, constantly trying to make it better and safer.
I went no solder and cradles as I wanted the ability to pop out a cell and replace it easily.
(not to mention I can't solder very well)

kind regards


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#2
Holy Shite Balls

That went nuclear quick...

http://forums.whirlpool.net.au/archive/2586675
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#3
Hi 3nergE,

I read your dayiry at whirpool forum and now I quoting you:

Initial results were surprising. My 800Ah lead acids performed about twice as well through the night and under heavy loads with the little 200cell 90Ah lithium bank jumper lead attached with no additional modifications. WOW.

So to clarify my untderstanding I want to know:

Do you have connected your Li-Ion battery parallel to the lead acid battery?
If yes, it means you have mixed both chemistry types: lead acid (plumbum) and Li-Ion to work them together?
Your obeservatoin was that lead acid even "performed about twice as well" assisted by Lithium?
Were there some other problems except the different levels of (chemistry) voltages?

I ask you about that experiment, because I have also a lead acid battery (310Ah/48V) from fork lifter and was thinking to mix both chimistry types but all of my mate "experts" were saying: "don't mix them".
If your expirience was positive, it encourages me to give also a try to "help up" my plumbum baby.

Thank you for answering!

BigBen
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#4
(12-22-2016, 03:58 AM)hbpowerwall Wrote: Holy Shite Balls

That went nuclear quick...

http://forums.whirlpool.net.au/archive/2586675

Indeed.  Few ppl got hot under the collar, a couple even got banned.  But overall a great discussion thread again.

Many chuckles to be had though.

A few stages there I felt like a public defendant.

(12-23-2016, 11:16 AM)BigBen Wrote: Hi 3nergE,

I read your dayiry at whirpool forum and now I quoting you:

Initial results were surprising. My 800Ah lead acids performed about twice as well through the night and under heavy loads with the little 200cell 90Ah lithium bank jumper lead attached with no additional modifications. WOW.

So to clarify my untderstanding I want to know:

Do you have connected your Li-Ion battery parallel to the lead acid battery?
If yes, it means you have mixed both chemistry types: lead acid (plumbum) and Li-Ion to work them together?
Your obeservatoin was that lead acid even "performed about twice as well" assisted by Lithium?
Were there some other problems except the different levels of (chemistry) voltages?

I ask you about that experiment, because I have also a lead acid battery (310Ah/48V) from fork lifter and was thinking to mix both chimistry types but all of my mate "experts" were saying: "don't mix them".
If your expirience was positive, it encourages me to give also a try to "help up" my plumbum baby.

Thank you for answering!

BigBen

Hi Ben,

Originally I did have my lithium bank (200 cells) connected to the aging lead acid bank.
The lead acid bank was only good for about 1-2kWh of power overnight, and the lithium did indeed add another kWh of runtime.

Mixing chemistry is really a dance of mixing charging voltages, currents and High and Low voltage limits.

Some things to watch out for are:

LVD - lithium needs to stay above 3v per cell ideally, so going lower than 12v isnt a great idea.
HVD - lithium can in theory (4s) go as high as 16.8v and lead acid shouldnt be taken above 15v

Charge rate, not to exceed 0.5C on a lithium cell (half the amps in of the actual capacity ie 2500mah cell, 1250mah charge rate)

OCV fully charge of lead acid 12v is about 12.6v / 13.8v float
OCV fully charge Lithium 14.8v (4s - 4x3.7v) no float

So to summarize the preamble, adding a lithium rig to your lead acid may indeed increase the capacity, but there are definitely considerations, first and formost, the lithium is not going to get to a full charge and capacity will suffer, secondly, lead acid will not be fully discharge and will not give you full capacity.  Lastly, the lithium cells are (at 4s) going to remain at a higher voltage and therefore try to float the lead acid rig up to 14.8 most of the time, this can lead to electrolyte usage in the lead acids.

My results were good as I draw large loads, and had an isolation switch between banks.
I would charge both banks up in parallel during the day, draw my large dinner time loads with both banks, then let it run overnight as the lithium ocv would be lower and not try to charge the lead acid too much overnight, this lead to overnight runtime increases and power first thing in the morning before the sun hit the solar.

So if your lead acid bank is aging, low capacity from its original state, then yes, adding lithium to supplement will work.

Personally, I switched over to all lithium pretty quick as I had the cells and things were a lot better that way.

With an idolator between the two banks, I think you could get the best of both worlds, just be carefull of your charge rates, high and low end voltages and you should be fine.

kind regards
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#5
At least you educated some people (at least one person) on that forum! I guess that is how we have to do it!? One convert at a time. Smile

Here is a quote:
"When I first started reading this thread I thought "how the hell is this safe with no BMS. How do you work around individual cell under/over voltage in each 4S string!?!?!", but then I watched your youtube videos and realized when you have 48/96-odd cells in parallel, they are going to do a pretty damn good job keeping themselves regulated in each parallel bank. I'd image even if a few individual cells aren't too happy, the rest of the bank will keep them in line, at least enough so the don't over-discharge and puff.

Also, I'd like to add that 18650 failure, although definitely a thing, is nothing like a big LiPo pack or a phone battery failure. These little buggers have a lot stronger case, and have built-in over pressure relief valves at the top. So more likely to pop-and-hiss than to burst into flames. And even that only really happens on physical cell damage (unlikely in a static setup like on a wall), or on over-voltage which wouldn't happen in a setup like this were you're not charging to a full 16.8v. Overall I'm very impressed and it has caused me to rethink some things about these packs."

Come chat with us! http://chat.diypw.com/
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#6
(12-28-2016, 01:17 PM)Elwood Wrote: At least you educated some people (at least one person) on that forum! I guess that is how we have to do it!? One convert at a time. Smile

Here is a quote:
"When I first started reading this thread I thought "how the hell is this safe with no BMS. How do you work around individual cell under/over voltage in each 4S string!?!?!", but then I watched your youtube videos and realized when you have 48/96-odd cells in parallel, they are going to do a pretty damn good job keeping themselves regulated in each parallel bank. I'd image even if a few individual cells aren't too happy, the rest of the bank will keep them in line, at least enough so the don't over-discharge and puff.

Also, I'd like to add that 18650 failure, although definitely a thing, is nothing like a big LiPo pack or a phone battery failure. These little buggers have a lot stronger case, and have built-in over pressure relief valves at the top. So more likely to pop-and-hiss than to burst into flames. And even that only really happens on physical cell damage (unlikely in a static setup like on a wall), or on over-voltage which wouldn't happen in a setup like this were you're not charging to a full 16.8v. Overall I'm very impressed and it has caused me to rethink some things about these packs."

Thanks Elwood, Ive tirelessly tried to help educate people without soapboxing my background but instead trying to demonstrate stuff.

Cell failure is nearly universally a tinny and cute 'tink' sound as it goes open circuit.

Shorted cells get about 100mAh of charge overall and barely get warm. 
I hesitate to post my footage of such things as I dont want people to get a false sense of security,
and I like the work people such as pete and mike do with fusing and safety.  Even if its at huge risk to their own health.

I plan on showing induced failure in the future on my channel just as a FUD counterpoint.  Just dont want to fan the flames atm.

kind regards
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