Wolf's PowIRwall

>1.71% Solar/Victron + Victron/Battery 2.17% + Inverter 9.36% = 13.24%

- 1.71% Solar/Victron: This loss is converting PV input to charging current? Interesting. The Midnite Classic spec sheet says "98%" typical system - so that's perfectly normal sounding.
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- Victron/Battery 2.17%: This loss is between power going into the battery and coming out? I've been thinking that lithium-ion charge/discharge should be more at 1%? What do you think about this?


>We shall round it out to 15% losses in which case the system is ≈85% efficient as previous preliminary calculations seemed to indicate.
I'm happy with that!
I know what you mean, but then I look at my 2020 yearly total of 18,000kwh from panels but only 15,000 consumed. That's 3,000kwh that I'm 'loosing' and my SOCD starts rearing its head. Breathe.... Breathe.... Breathe (deeply)... :)
 
I did similar calculations-tests but only using Iotawatt and the chargecontrollers info and the same inverters. I got 85% to 87%. Not bad for these cheap inverters and outback charge controller
 
OffGridInTheCity said:
- Victron/Battery 2.17%: This loss is between power going into the battery and coming out? I've been thinking that lithium-ion charge/discharge should be more at 1%? What do you think about this?
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No that's a completely different calculation. What I am doing is taking the Victron output wattage subtracting the Inverter use wattage and then comparing that calculation to the Batrium shunt input to the batteries. That the difference between the calculations of 3 readings is only 2.17% is just icing on the cake. All 3 readings are calculated from 3 separate sensors (Victron, Inverter, Batrium) and for all of them to agree within 2% is better than the margin for error that I anticipated. It might as well be 0.
For me to figure out the charge/discharge efficiency of the battery pack I need to do some more math. Darn you, you ,you slave driver.😒


OffGridInTheCity said:
........................... but then I look at my 2020 yearly total of 18,000kwh from panels but only 15,000 consumed. That's 3,000kwh that I'm 'loosing' and my SOCD starts rearing its head. Breathe.... Breathe.... Breathe (deeply)... :)
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Ha ha well with those numbers you are still at 83.3% efficient. Just be glad you don't work for the power company. I imagen from power generation to actual outlet their losses are far greater than ours and they still make millions. Just think of the losses from miles and miles of transmission lines and all of a sudden your efficiency becomes quite good. There you go you can breath.🤯

In my opinion the home independent solar/wind/hydro generation owner is the most efficient use of power generation.
I don't think solar/wind farms are the answer. Think about those losses going through the grid that we (well not all of us) subsidize.
Decentralization i.e. independent producers of their own power is the answer. With the grid serving as a backup not as the primary source.
OK off of the soapbox.
Wolf
 
Small confirmation of the accuracy of the calculations as it is night and I am now running 100% on batteries.
The negative values are from the Batrium sensors which correlate to the Inverter sensors.
It's nice to have something work out and be so visual. Given that in this case 2 separate sensors calculate the same results within a very narrow margin.
Wolf
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Wolf said:
So I couldn't let it go I was on a roll mathematically speaking.
Here is my method of calculating the Solar to battery efficiency.
First of Victrons MPPT controllers are awesome giving me the numbers to work with.
So first calculate the actual watts the panels produce going into the Victrons which gives me total watts produced by just the panels
In this case 2864.12W.
Then calculate total Victron output.
In this case 2790.69W
Which gives us an efficiency through the Victrons of ≈0.974 or 97.4%
View attachment 24410
OK next we take the Victron total wattage output, subtract the inverter wattage draw and we get what is left over to charge the batteries.
In this case total Victron Watts is 2805.47 minus Inverter Watts 365.22 equals 2440.25 Watts that should be going to the Batrium shunt.
The Batrium shunt is claiming 2371.28 Watts so we calculate again and the results are 0.971 or 97.1%
View attachment 24412



Once the calculations are condensed the results are as such on an
ever changing basis but the numbers hover in the 96% to 98% range.
View attachment 24413
So if my math and methods are correct. from solar panels to the household plug my losses are ≈13.24%
1.71% Solar/Victron + Victron/Battery 2.17% + Inverter 9.36% = 13.24%
We shall round it out to 15% losses in which case the system is ≈85% efficient as previous preliminary calculations seemed to indicate.
I'm happy with that!
Wolf
View attachment 24415
Click to expand...
This is great..! Gets my creative juices flowing to tweak my own grafana dashboard..
 
Awesome use of "The Maths"
 
Battery #3 update.
So all the bus bars are done on battery #3 and all have been tested.
If there is one reason I use the excel based repackr is that the results are just stellar. I don't care how anyone decides to build their packs but I for one will continue to use this marvelous tool to Ah balance my packs.
The proof is in the pudding as they say.
All packs charged with an iCharger X6 to 4.2V . Regen discharged at 30A to 3.0V. To come up with a difference of 0.91Ah between the high and low pack is my idea of a perfectly balanced battery. Can't wait to install it into the battery box. Summer is coming and charging is commencing.
Wolf
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That is great! show what attention to detail can acheive. Although for less detail orientated individuals like me a result like that would be an accident. I like that you have detailed the procedures you go though when constructing a battery.

later floyd
 
>with a difference of 0.91Ah between the high and low pack
I think that's pretty darn good. Based on cell adding I've done to bring individual packs up, about 10% of my packs (out of 84) were in the 6% (15.6ah) lower than the majority / other 90%. 1 was over 10% off and I don't know why - but adding cells brought it up to the rest and its been OK.

I don't read much where folks adjust the packs of their powerwalls once they put them online - seems like it would be more common for 18650 / second-hand cell builds to have some packs needing attention.
 
OffGridInTheCity said:
I don't read much where folks adjust the packs of their powerwalls once they put them online - seems like it would be more common for 18650 / second-hand cell builds to have some packs needing attention.
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Yea I don't either. I'm just wondering if they let the BMS take care of it? Or they use them for a while and go with the new craze LiFePO4?
I do know. I do know that @ajw22 does do some maintenance every so often on his packs as he mentions having to replace a cell every so often. My packs don't lend themselves to that very easily. So I want them to be as good as possible to begin with.
I'm still dedicated to Li-ion 18650 and as long as they are available will be using them. I have 1 more battery to build and will have maxed my storage out at 56 packs. I may at some point replace my "Frankenstein" battery but for now it's working just fine and on May 18 it will have its 1 year anniversary. Who knows I may become more obsessed and build another battery box and add another 4 batteries. Problem is I won't have the solar to charge all that and there does come a point of diminishing returns. I am now getting nervous of what I am going to do once I finish the 4th battery. Well I guess I will cross that bridge when I get there.
Wolf
 
OffGridInTheCity said:
I don't read much where folks adjust the packs of their powerwalls once they put them online - seems like it would be more common for 18650 / second-hand cell builds to have some packs needing attention.
Click to expand...

Wolf said:
@ajw22 does do some maintenance every so often on his packs as he mentions having to replace a cell every so often.
Click to expand...

My main source of 18650 cells is from workhorse ebikes - none of those posh medical packs. So I had to settle for a much more lax cell quality criteria, thus I built my system with regular cell replacements in mind.
I keep a close look at the voltage graph of all the packs, and about once a month I inspect the ones that have drifted.
By looking at how the voltage drifts over time, I can deduce if I have a self-discharging cell, or the pack has lost capacity unusually fast.

In case of SD, just a visual inspection usually finds a cell that's corroded on the positive side. If I don't find any, and the voltage drift isn't too bad, I just give it a charge and take another look the next time around. If the SD is bad, I disconnect the fuses and the hunt begins.

If it's capacity degradation, it's often a broken fuse. If not, I replace a low capacity cell (got a few 1200mAh cells in each pack for this purpose) with a 2500mAh cell to balance out the capacities of all the packs.

I now have a little over 10,000 cells, and on average I have a replacement rate of maybe 5~10cells/month.

Key to my maintenance system working well are:
* Pack voltage monitoring and logging
* Low balancing current that doesn't mask bad cells
* Small 108p packs for quick pinpointing of problem cells
* Packs designed for easy replacement of cells
 
ajw22 said:
My main source of 18650 cells is from workhorse ebikes - none of those posh medical packs.
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Was that a dig? ;) Not at me anyway as I really haven't used medical packs other than some of my cells in the frankenstein battery which is a combination of mostly laptop batteries. As you know 6228 tested cells and 1120 made the grade. What's that? 17% success rate?
My cells for Battery #2, #3, and the upcoming #4 all came from e-bikes or scooters. Much better success rate.


ajw22 said:
Key to my maintenance system working well are:
* Pack voltage monitoring and logging
* Low balancing current that doesn't mask bad cells
* Small 108p packs for quick pinpointing of problem cells
* Packs designed for easy replacement of cells
Click to expand...
Yes indeed monitoring and logging is very important!
Fortunately I don't have to balance very often. As this is my first winter with these packs, it does appear after a winter of low charging when spring arrives and proper charging begins, I noticed a small pack imbalance and some top end balancing was required. Once that operation was completed, may take a day or 2, (done quite automatically by the batrium) further balancing does not seem to be required, as so far all my packs have since then evened out to within ≈0.02 when coming to a full charge and when discharging to <3.7v getting a max deviation of ≈0.07v.
Smaller packs are definitely the way to go. If you need more capacity add another row of packs. Also if you need to take a battery off line to service a pack you still have another one or more to fall back on.
My pack design unfortunately does not offer easy cell replacement thus I have to make sure the pack is balanced to start with as I don't get a second or third chance. So far I haven't needed to do that and hope that my building technique and cell choosing criteria will prove to be a relative maintenance free venture. We will see. So far Battery #1 (Frankenstein) has been trouble free and as I add more capacity to the battery as a whole each cell will be stressed less and less and with my max load on the battery of ≈60A. Once I have all 4 batteries installed, it will be 15A per battery which translates to ≈ 0.187A or 187mA per cell. Quite gentile.
Time will tell but so far things are looking good.

Wolf

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Small Update;
Battery #3 is almost top balanced just another evening and all packs will be at 3.95V ± 0.03V. Once that is done the Lexan sides and Longmons will be installed and into the battery box it will go.
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Battery #4 cell testing has begun and I will be picking out the best 1120 cells out of ≈1500 LG M26 cells.
Using the Megacell chargers that I have dialed in and they seem to be working ok.
20210409_224456.jpg
Wolf
 
Update:
Lexan sides have been installed on all packs and waiting for longmons to be mounted then the packs will be ready to be made into the 3rd battery and will join the other 2.

Wolf
20210503_064241.jpg
 
Alright 3rd battery installed and working.
Its starting to look like a real powerwall.
Batrium is happy and all longmons reporting in.
Does look like I may have to top balance a couple of packs as I didn't really have them perfectly equalized.
We will see how things go tonight and tomorrow. Still not bad 0.05v diff between low and high.
Wolf
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Very nice! I notice the 'dip' in the blue piano keys (as my wife calls them) on the right hand end. Sometimes the Batrium display makes it look a little worse than it is... but in my experience, 4mv is perfectly operational. :)
 
I would say all within 20-50mV is more than fine for most cases :)
To me the Longmons itself arent that precse that you can get 4mV. If you add a voltmeter on top it often differ more :D

Good work!
 
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