18650 DIY powerwall 48v

I use just 1.....
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and I don't use spacers (to keep packs apart) or washers (to keep bolts tight). The packs are pretty close side by side and the buss(s) 'could touch' but if they did, there's no issue since they're serialized anyway. Perfectly safe.

Powerwall is >5yrs old and no trouble with hotspots (or even warmth) or bolts loosening etc.
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OffGridInTheCity said:
I use just 1.....
View attachment 31545View attachment 31546
and I don't use spacers (to keep packs apart) or washers (to keep bolts tight). The packs are pretty close side by side and the buss(s) 'could touch' but if they did, there's no issue since they're serialized anyway. Perfectly safe.

Powerwall is >5yrs old and no trouble with hotspots (or even warmth) or bolts loosening etc.
View attachment 31547
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I love your pictures Offgridinthecity. 😊

Is it possible for me to make a 14S60P in parallell with 14S120P? Would it work ok together? Or do I have to make another 14S120P?
 
kje said:
I love your pictures Offgridinthecity. 😊

Is it possible for me to make a 14S60P in parallell with 14S120P? Would it work ok together? Or do I have to make another 14S120P?
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Short answer - yes it should work :)

Longer answer, there will be a disparity and depending on the level of load and low/hi operating voltage range there could be more or less stress which might eventually impact overall lifespan. But I don't understand how significantly - likely to be minor with moderate stress on the overall battery.

Maybe someone will answer in more detail as to what happens.
 
OffGridInTheCity said:
Short answer - yes it should work :)

Longer answer, there will be a disparity and depending on the level of load and low/hi operating voltage range there could be more or less stress which might eventually impact overall lifespan. But I don't understand how significantly - likely to be minor with moderate stress on the overall battery.

Maybe someone will answer in more detail as to what happens.
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Thank you Offgridinthecity. If I use 300mah pr cell of the 120P it's 600mah pr cell of the 60P?

Is there someone on the forum who has tried this?
 
kje said:
Thank you Offgridinthecity. If I use 300mah pr cell of the 120P it's 600mah pr cell of the 60P?
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If I'm understanding correctly, yes. You add up the individual mah/cell of each pack to get the total. If you have 60cells * 600mah each, that's 36,000mah or 36ah. If you do 120cells * 300mah each, that's also 36,000mah or 36ah. So the 60p and 120p packs would be well matched.

kje said:
Is there someone on the forum who has tried this?
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If what I wrote above is you're situation - then sure, I do this. Some of my packs have 120p and some have 88p but ALL packs have the same total of 260ah.
 
kje said:
I was thinking of using 120P 260ah together with 60P 130ah?
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OK, that's back to my original response. If you don't like the result, then later on make another set of 130ah packs and parallel them for a set of 260ah packs.
 
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What is acceptable voltage reading after resting 1 month at 3.7v?

My cellpack readings are between 3.69v - 3.60v after over 1 month. Except two packs with voltage reading at 3.52v and 3.58v.
 
kje said:
What is acceptable voltage reading after resting 1 month at 3.7v?

My cellpack readings are between 3.69v - 3.60v after over 1 month. Except two packs with voltage reading at 3.52v and 3.58v.
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If they started at exactly 3.700v rest voltage - then after after 4 weeks, 3.690 is OK but 3.6, 3.58, 3.52 indicate self-discharge in my opinion. You can confirm by waiting another 4 weeks and you should see something like 3.68v (OK) but 3.5v, 3.46v, and 3.36v respectively kind of thing - and the packs should be fixed if you want a trouble free battery.

Did you test for self-discharge of the individual cells before building them into packs?
 
OffGridInTheCity said:
If they started at exactly 3.700v rest voltage - then after after 4 weeks, 3.690 is OK but 3.6, 3.58, 3.52 indicate self-discharge in my opinion. You can confirm by waiting another 4 weeks and you should see something like 3.68v (OK) but 3.5v, 3.46v, and 3.36v respectively kind of thing - and the packs should be fixed if you want a trouble free battery.

Did you test for self-discharge of the individual cells before building them into packs?
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Yes I did the self-discharge test of the individual cells before building them into packs. The individual cells was resting between 3 months and one year. The lowest voltage reading on the individual cells I accepted was 4.09v. The majority was at 4.13v.

The cellpacks started at exactly 3.70v and was resting for over 1 month. The majority of the cellpacks is 3.69v, 3.66v and 3.64v.

But I was kind of disappointed to see a few cellpacks with numbers like 3.60v, 3.58v and 3.52v after just 1 month.

One observation: the cellpacks that have been used in service/cycled is holding 3.70v - 3.69v. They have been used in a 3s configuration to discharge and charge individual cellpacks with ICharger s6. Maybe the cellpacks with low resting voltage could benefit from some cycles as well?
 
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kje said:
Yes I did the self-discharge test of the individual cells before building them into packs. The individual cells was resting between 3 months and one year. The lowest voltage reading on the individual cells I accepted was 4.09v. The majority was at 4.13v.

The cellpacks started at exactly 3.70v and was resting for over 1 month. The majority of the cellpacks is 3.69v, 3.66v and 3.64v.
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This is normal.

kje said:
But I was kind of disappointed to see a few cellpacks with numbers like 3.60v, 3.58v and 3.52v after just 1 month.
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Since you did individual cell self-discharge, this is not what I would expect and hasn't been my experience.

Maybe something else is going on - you said something about cycling these packs but it wasn't clear to me what you're doing with these packs.
 
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