Bus Bars on LFP

[s/v Jedi]

Originally Posted by Loredo

You understand that capacity testing each single cell would take..well how long? 48 cells each roughly 900 Wh, 43KWh in all. Not to mention equalizing the whole thing then again then. No thanks, only if I'd have a serious problem which I otherwise could not explain.

For which reason would I want to do it? Sorry, when I charge the bank to 29.2V (Normally I stop @ 27.6V) and have a deviation of 0.0001V between the parallel cells, what should be wrong with this bank? What would make me want to investigate into ???...? The battery works like a charm as is.
Yes, I do have a thermal camera. Yes, I use it, no hot spots in the whole bank (bus-bars, cables, fuse...) pulling 300A out of it for an hour. Things get a bit warm but that's expected. I do not understand what would be so detrimental in parallel(ing) cells.

What I mean is to capacity test the whole assembled 24V battery. If the battery fails the capacity test, then first recharge the battery fully, then compare the eight 8P voltages to see if one or more indicate where the problem is located. Those 8P packs under suspicion need to be taken apart, then let the cells rest 4-6 hours, then measure each individual cell voltage which would show the weak cell.

After identifying the weak cell, it needs to be fully charged by itself. It would be great if its internal resistance can be determined at that time and compared to the other 7 cells of that 8P set. The parallel cells need to have the same internal resistance in order to equally share the load and stay in sync with each other during cycles.

If the complete 24V battery finishes the capacity test successfully, none of this is needed.

[Loredo]

CR,
sorry I have no desire to publish any pics of my installation. I didn't convert over to LFP to run a show or to show off. Not my way, I'm not lost deep enough in the social rabbit hole. If I can share some of my (technical) experience with those interested in the subject, great. If not, great also. I guess you need to understand how I describe what I did.


Jedi,
thanks for the advice but I have yet to understand where the desire to school me comes from. I have as much experience in electronics as you do. What you know, I know and vice versa. Over the past two years I have repeatedly tested the banks capacity. I've calibrated the BMV 712 repeatedly so that now it's almost 100% right. (Both discharging and charging.) I always end up in the same place, balance between the 6P cells within 0.0001V. Thus, I'd dare to say, parallel cells can do their thing nicely.

[CaptainRivet]

Originally Posted by Loredo

CR,
sorry I have no desire to publish any pics of my installation. I didn't convert over to LFP to run a show or to show off. Not my way, I'm not lost deep enough in the social rabbit hole. If I can share some of my (technical) experience with those interested in the subject, great. If not, great also. I guess you need to understand how I describe what I did.

Jedi,
thanks for the advice but I have yet to understand where the desire to school me comes from. I have as much experience in electronics as you do. What you know, I know and vice versa. Over the past two years I have repeatedly tested the banks capacity. I've calibrated the BMV 712 repeatedly so that now it's almost 100% right. (Both discharging and charging.) I always end up in the same place, balance between the 6P cells within 0.0001V. Thus, I'd dare to say, parallel cells can do their thing nicely.

I done multiple parallel cell banks since 20 years? Not a professional installer per se but was doing sound quality competition car stereo and even had a company that putting demo vehicles together for shows and product demonstrations. Just doing g it now from rum kitty as I have fun doing it.
Some banks i had to redo one or twice as a new issue showed up while doing my routine stress check tests after put together. So I know what to look for and how you figure you have a hidden problem or not. As stated multiple times parallel banks can and most do hidden problems and the more parallel the more is the likelihood you do.
How many did you build?
Just give you my experience for free as the earlier you detect or make sure all is really OK or ypu discover is not and can fix it the more you can rescue or avoid having a desaster. All data you gave are either not sensefull to detect if you have a problem or not the right way measured or are too good to be true. Also a 5p8s bank needs to be charged high to 3.55V as only there cells can really equalize and needs a long absorption with an active balancer to do thay as all is diveded by 5. The famous 13.8V or 27.2V is not the right target absorption voltage for multiple parallel cells banks.And 5p8S screams for issues, there are many reason from my experience I stop at 4P8S with Lifepo4. And that starts with different busbar length from cell 1 to cell 5 as I explained or the fact that >=4 cells can easliy cover up 1 bad or wrong connected cell so nothing shows except at the 0.3C or even 0.5 test with cell stud temps.
If you want you can send me the fotos via PM and I won't post them. Like this i see how it's build which is much easier then writing text.
And connect cells with a busbar have automatically all the same voltage if you measure.
Till know I see you still don't understand why and where you can have a hidden problem or the tests are too much effort for you. Well you have a 5p8S bank and therefor signed up for this and what jedi and I described with every cell a full capacity test with curves is the basic If your cells are fit enough for a 5p8s bank or not and also how you need to put them together.
Or well ignore it and you most likely will have a big problem sooner then later as 5p8s screams for it. And believe me I hate to be right but sadly often I am. Competition means you go at limits and above and discover a lot things eg a normal installer didn't and you really find out the weak spots as limits accelerate issues. And yes I paid my lessons too, ruined leads would fill containers, melted cables and also burned a complete car down.
So take advantage of that or not, your choice.

[Fuss]

Originally Posted by Loredo

CR,
sorry I have no desire to publish any pics of my installation. I didn't convert over to LFP to run a show or to show off. Not my way, I'm not lost deep enough in the social rabbit hole. If I can share some of my (technical) experience with those interested in the subject, great. If not, great also. I guess you need to understand how I describe what I did.

What .. no pics!!!! but we need them, we do, we really need them!!!
We are so very clever, probably the most intelligent lithium installers in the world. we will diligently analyse them and give even better advice than we already do.
Speaking for myself, I have created the lightest 3kwh battery in the world, i know I know, i’ve said this several times before… but I do like the sound of it.

[CaptainRivet]

Originally Posted by Fuss

What .. no pics!!!! but we need them, we do, we really need them!!!
We are so very clever, probably the most intelligent lithium installers in the world. we will diligently analyse them and give even better advice than we already do.
Speaking for myself, I have created the lightest 3kwh battery in the world, i know I know, i’ve said this several times before… but I do like the sound of it.

Need to proof that and Who needs that?
Either my 27kg light Tohatsu MB 9.8 hp 2-stroke on the UL340 Highfield for longer distance, high load or big chop and for short and calm either human powered Kajak or Sup.
Electro unless it's the wynns jetpowered expensive as hell dingy the 9.8hp gets you with a UL340 where no comparable e-outboard gets you and for all else human powered as we move to less anyhow....

[Fuss]

Originally Posted by CaptainRivet

Need to proof that and Who needs that?
Either my 27kg light Tohatsu MB 9.8 hp 2-stroke on the UL340 Highfield for longer distance, high load or big chop and for short and calm either human powered Kajak or Sup.
Electro unless it's the wynns jetpowered expensive as hell dingy the 9.8hp gets you with a UL340 where no comparable e-outboard gets you and for all else human powered as we move to less anyhow....

hmm, it’s so depressing , there I was thinking that I was the best… and now i’m just ordinary . Surely this can’t be right that i’m just ordinary…life is so unfair sometimes, perhaps sailorboy1 and boatman61 can give me some support??

[CaptainRivet]

Originally Posted by Fuss

hmm, it’s so depressing , there I was thinking that I was the best… and now i’m just ordinary . Surely this can’t be right that i’m just ordinary…life is so unfair sometimes, perhaps sailorboy1 and boatman61 can give me some support??

Ooh let's give you a big hug. Not reason to be depressed, life is good and most are out of the hamster wheel...
No competition here who is the best, we all just enjoying our boating passion.
Do what makes you happy...

[s/v Jedi]

Originally Posted by Loredo

Jedi,
thanks for the advice but I have yet to understand where the desire to school me comes from. I have as much experience in electronics as you do. What you know, I know and vice versa. Over the past two years I have repeatedly tested the banks capacity. I've calibrated the BMV 712 repeatedly so that now it's almost 100% right. (Both discharging and charging.) I always end up in the same place, balance between the 6P cells within 0.0001V. Thus, I'd dare to say, parallel cells can do their thing nicely.

Not sure where this aggressive response comes from? I was simply answering your question. If you ask, I try to answer thinking this is a positive thing to do

You asked if I knew how much work it is to do capacity testing for each individual cell, so I explained that this wasn’t what I tried to say, followed by different wording to show what I did mean.

So once again I am flabbergasted by the weird attacks on me for trying to help people.

[CaptainRivet]

Originally Posted by s/v Jedi

Not sure where this aggressive response comes from? I was simply answering your question. If you ask, I try to answer thinking this is a positive thing to do

You asked if I knew how much work it is to do capacity testing for each individual cell, so I explained that this wasn’t what I tried to say, followed by different wording to show what I did mean.

So once again I am flabbergasted by the weird attacks on me for trying to help people.

Well no pictures, doesn't wanna accept what we try to tell and explain him, doesn't wanna take action as too much effort...
I know 99.9% how this install look and what desaster we will see in the pics...another poster who just wanna have a sign-off that all is perfect he has done. Wasted time...
And then we get attacked we are influencer because that all that's left.
And when we tell these posters the real truth then we get punshied by the mods not being nice...

[GordMay]

Originally Posted by CaptainRivet

...
And when we tell these posters the real truth then we get punshied by the mods not being nice...

We can disagree, without being disagreeable; and whenever you do disagree, you can settle it, with a staring contest.
Then, you’ll see eye to eye.

[newhaul]

Originally Posted by CaptainRivet

We when we tell these posters the real truth then we get punshied by the mods not being nice...

It's not what you say to them it's how you say it

BTDT have the strikes to prove it .
Things have become more politically correct now .

[Dennisb2]

For a low resistance connector bond a 3/8” dia stud properly torque is required to a freshly abraded surface. Also do not exceed 2 cable connectors per stud. For a long term low resistance bond the contact fay surfaces need to be sealed with a dielectric grease or paste. The 3/8 size is important for the large cables with high current loads.
The blue sea systems has copper with 4 and 8 studs which I have used with success on my boat.

[Loredo]

I'm about 99.5% sure that one makes or brakes a DIY (single) cell based LFP battery bank at the very beginning, during assembly. Good & sound practice is needed to A) perfectly balance the single cells to 3.65V before connecting them in series B) avoid any high(er) resistance connections anywhere. Where anywhere means between the single cells all the way up to the distribution panel. Another essential part of the assembly process is of course having the adequate instrumentation's for the job. Most important to me was a multi meter able to reliably read voltage down to 0.0001V. If you do your homework, here, the only answer without costing a leg and an arm is Fluke. Most do not realize that their testing equipment is "way" off from reality. Before I went (finally!) with the fluke I purchased three, progressively more expensive, multi meters... until I gave up and went with the Fluke. One of the cheap ones was off one tenths of a volt... With LFP absolute voltage precision is needed. Can't read 3.65V instead it's 3.7. Once it's possible to reliably -really- verify voltage and compare that with the readings from cheaper equipment...Holy cow! That's a whole other story. Let me just say, don't trust a BMS's reading too much...



So I wanted to build a 6 cells in parallel & then 8 of them in series to get a "24V" battery.

What I did when I received the EVE LF280K grade A cells.
1) Test & document voltage and internal resistance (IR) of each cell.

2) Select the single cells to get eight-6P packs as close as possible in IR.
3) After having cleaned the poles, charge each single cell to 3.65V (CC-->CV) and capacity test them. All cells tested @ 290AH +/- 1%. Percentage deviation I considered due to the test equipment tolerance. Essentially, the cells are perfectly matched. Recharge every cell to 3.4500V exactly.
A beast of a job in reality useless but hey, at least now I knew.

4) Start to build the 6P cells. Assemble the cells into packs of six applying requested clamping force (Well more or less; good enough.). Clean and polish (down to 200 grid) each pole and bus bar (Flexible multi-layer copper). Apply Prussian blue, check for perfect contact surface flatness (correct if needed). Clean off PP then apply graphite based conductive paste to every contact surface. Cell to buss bar, bus bar to bolts... torque the bus bar to 3Nm onto cell 1 in the "six pack". Check cell IR at the end of the bus bars. If not happy with result, take apart check, correct, retry until deemed OK. Proceed to cell 2 then 3 and so on. Once done with all six cells, re-torque all bolts to 4Nm. Repeat all this another 7 times to get all 8 six packs done. Compare IR readings of the eight six packs, eventually correct if any discrepancies surface. Luck got it, there were none.
5) Connect all six packs in parallel and charge to 3.6500V exactly. That has taken a long time. I charged 48 cells in parallel with 5A to allow them to absorb as much energy / as slowly as practical. Once charge current went down to 0.1A, disconnect charger and let them sit for another 10 days to let them equalize.
6) Now I have eight 6P packs ending each with a + and - bus bar. To connect them in series I used tinned copper bus bars (120mm equivalent), all cut to the exact same length, drilled the holes for the bolts in the exact same location. Exactly in the center of each I drilled a hole and threaded for a 4mm bolt for the BMS / balancing wires. These wires, I first crimped and THEN soldered a 4mm ring to, then protected with heat shrink.
7) Assemble the bank like as if it was installed in the boat to test-check-test-check...whatever could come to my mind. One of the tests I'm very glad I did was to loosen the bolts (to just 2Nm) of one cell in one 6P pack to simulate an "increased resistance" situation. With low amps nothing could be seen, if memory serves me right, starting @ +/- 20A load on the bank there was a voltage "sag" on that six pack that was very noticeable. Somewhere around 10-20mV. Re-torque the cell's bolts and the sag was gone. Now it's clear to me how/what to check and keep an eye on.

8) Once done with my testing, re-connect all eight 6P packs in parallel one more time and get 'em up to 3.6500V exactly. (Fast version with 40A and 1 A final cutoff.

9) Re-torque all bolts on the cells to 5Nm.


All the above took about three months

10) Installation in the boat. Prior to installation I re-torqued all bolts one last time to 7Nm. Once installed, check, check ,check keep an eye on everything for two years...for nothing. It's getting old to keep checking just to never see the slightest problem. Cells in parallel, if done right, work flawless.


Said that, tone it down a notch or two or several more. See, I've wasted much more time on the keyboard than I'd like to do. For what? Convince you that I might know a thing or two? Pics? C'mon... Everything I've described is nothing more than good practice. I'm sure you're really nice guys, just a bit too convinced that your way is the only one. NOT.

[sailingharry]

Loredo,


A couple comments/questions if I may.


-- I was under the impression that graphite based grease was pretty bad on bimetal corrosion. Are you still happy with that?


-- You made a big point about accuracy. I have no doubt that a Fluke is more accurate than a $10 cheapo. But it makes me wonder. Is accuracy all that important -- or is precision what really matters? If a cheapo can read to .001V, but be off by .05V, is that OK? Yes, 3.65 could be 3.7, but if all the cells read 3.651, and every time you put the volt meter on they ready 3.651, does it matter that they are all really 3.701? As long as you are in the area where the voltage curve is steep, they are all "full" to the same level. The key, I would think, in top balancing is to get them all to the same charge level, and what that level is doesn't matter much. Of course, they must be accurate enough to not cause damage, so the 0.1V you mention is probably unacceptable.



-- I have been pondering top balancing in parallel prior to assembly. My understanding is that compression is needed FROM THE FIRST CHARGE. This is a conundrum. Unless you build a box with compression, you can't top balance. You could build the final box, put them in as final, but not bus them together and simply wire as required -- the whole top balance effort is rather low current and wire size/termination quality is pretty insignificant.


-- With my comment on balancing, I'm pondering an alternative approach. Build the entire bank and install it with charge as delivered. Fire up the charging sources and let it rip under the BMS. My build will hopefully be done and "mostly" installed by February, and our season doesn't start until April or even May. It will sit on shore power for a few months. The BMS will balance, even slowly, and all cells will sit in a static condition at 100% SOC (+/-), so they will totally equalize. In an odd way, this would UNDO all the efforts of a pre-installation top balance, since any errors in the BMS readings/logic would cause it to adjust any condition to its idea of balanced. I recognize that if the cells are way out of balance to begin with, it may take some manual intervention -- directly charging a low cell pack, or directly discharging a high cell pack -- to help out the slow movement of the BMS balancer.

[CaptainRivet]

Originally Posted by Loredo

I'm about 99.5% sure that one makes or brakes a DIY (single) cell based LFP battery bank at the very beginning, during assembly. Good & sound practice is needed to A) perfectly balance the single cells to 3.65V before connecting them in series B) avoid any high(er) resistance connections anywhere. Where anywhere means between the single cells all the way up to the distribution panel. Another essential part of the assembly process is of course having the adequate instrumentation's for the job. Most important to me was a multi meter able to reliably read voltage down to 0.0001V. If you do your homework, here, the only answer without costing a leg and an arm is Fluke. Most do not realize that their testing equipment is "way" off from reality. Before I went (finally!) with the fluke I purchased three, progressively more expensive, multi meters... until I gave up and went with the Fluke. One of the cheap ones was off one tenths of a volt... With LFP absolute voltage precision is needed. Can't read 3.65V instead it's 3.7. Once it's possible to reliably -really- verify voltage and compare that with the readings from cheaper equipment...Holy cow! That's a whole other story. Let me just say, don't trust a BMS's reading too much...



So I wanted to build a 6 cells in parallel & then 8 of them in series to get a "24V" battery.

What I did when I received the EVE LF280K grade A cells.
1) Test & document voltage and internal resistance (IR) of each cell.

2) Select the single cells to get eight-6P packs as close as possible in IR.
3) After having cleaned the poles, charge each single cell to 3.65V (CC-->CV) and capacity test them. All cells tested @ 290AH +/- 1%. Percentage deviation I considered due to the test equipment tolerance. Essentially, the cells are perfectly matched. Recharge every cell to 3.4500V exactly.
A beast of a job in reality useless but hey, at least now I knew.

4) Start to build the 6P cells. Assemble the cells into packs of six applying requested clamping force (Well more or less; good enough.). Clean and polish (down to 200 grid) each pole and bus bar (Flexible multi-layer copper). Apply Prussian blue, check for perfect contact surface flatness (correct if needed). Clean off PP then apply graphite based conductive paste to every contact surface. Cell to buss bar, bus bar to bolts... torque the bus bar to 3Nm onto cell 1 in the "six pack". Check cell IR at the end of the bus bars. If not happy with result, take apart check, correct, retry until deemed OK. Proceed to cell 2 then 3 and so on. Once done with all six cells, re-torque all bolts to 4Nm. Repeat all this another 7 times to get all 8 six packs done. Compare IR readings of the eight six packs, eventually correct if any discrepancies surface. Luck got it, there were none.
5) Connect all six packs in parallel and charge to 3.6500V exactly. That has taken a long time. I charged 48 cells in parallel with 5A to allow them to absorb as much energy / as slowly as practical. Once charge current went down to 0.1A, disconnect charger and let them sit for another 10 days to let them equalize.
6) Now I have eight 6P packs ending each with a + and - bus bar. To connect them in series I used tinned copper bus bars (120mm equivalent), all cut to the exact same length, drilled the holes for the bolts in the exact same location. Exactly in the center of each I drilled a hole and threaded for a 4mm bolt for the BMS / balancing wires. These wires, I first crimped and THEN soldered a 4mm ring to, then protected with heat shrink.
7) Assemble the bank like as if it was installed in the boat to test-check-test-check...whatever could come to my mind. One of the tests I'm very glad I did was to loosen the bolts (to just 2Nm) of one cell in one 6P pack to simulate an "increased resistance" situation. With low amps nothing could be seen, if memory serves me right, starting @ +/- 20A load on the bank there was a voltage "sag" on that six pack that was very noticeable. Somewhere around 10-20mV. Re-torque the cell's bolts and the sag was gone. Now it's clear to me how/what to check and keep an eye on.

8) Once done with my testing, re-connect all eight 6P packs in parallel one more time and get 'em up to 3.6500V exactly. (Fast version with 40A and 1 A final cutoff.

9) Re-torque all bolts on the cells to 5Nm.


All the above took about three months

10) Installation in the boat. Prior to installation I re-torqued all bolts one last time to 7Nm. Once installed, check, check ,check keep an eye on everything for two years...for nothing. It's getting old to keep checking just to never see the slightest problem. Cells in parallel, if done right, work flawless.


Said that, tone it down a notch or two or several more. See, I've wasted much more time on the keyboard than I'd like to do. For what? Convince you that I might know a thing or two? Pics? C'mon... Everything I've described is nothing more than good practice. I'm sure you're really nice guys, just a bit too convinced that your way is the only one. NOT.

You done a lot things right which as you said yourself is good practice.
Too much measuring is just asking for too much garbage data as we talk here in the millohm and voltage range.
For measuring I take the ZKE tester and always make full curves, it tells you all you need to know for below 100Euro. No expensive fluke needed, good to have for other needs. What's important is the relation and deviations between the cells, not the total values. And if the equipment is not precise but you done it all the same way then you measured in 95% all the same way wrong, so it's only a total shift to left or right or higher or lower.
But the relations is still correct and that's what you need to build the right packs together. That's the most valuable information from all your time consuming testing and you called it measurement error and ignored it.
But all that is only 60%. The other 40% is an absolutely symmetrical design, how you connect positive and terminal, which shape, the more in parallel the more you get into clamping issues over time....

3 or 4 years ago parallel banks were in favor when you done it right and invested in one good BMS. The mosfet and most consumer BMS were crap.

But now a 100A JK that works really well and does communication is 60 Euro with an active balancer.
So building 1p4S or 8S or 16S and paralleling is much less trouble, in the end cost the same as a proper multiple cell parallel bank. Plus its safer for the normal user as you see every fault right away and not covered up by parallel cells.
And you can simply switch one off and take it out while the system is running. Thanks to active balancer I don't even top balance them anymore individually. Just match them roughly with the data I got delivered clamp 4 or 8 cells quickly together with 6 rods and 2 scrap pieces wood and put multi shorecharger on and boost them full with 120A. Then reduce current with 14.4V absorption and 2h time and recharge at 13.6V and keep them a day like that. Jk perfectly does top balance and then I see the cell deviations, then connect to boats main power, reset the BMV712 and turnoff charge sources and use till it switches off. BmV Tells me capacity and then recharge with the 100A which is 0.3C. Hardly ever use anything else then 300AH cells. That tells me again charge capacity and I see the top balance and total deviation. Only if a cell is now behaving suspicious I take it out and test with ZKE. If multiple batteries and there is significant deviation in capacity or devation I know just dismantle and group the strongest into one battery and weakest into one to minimize deviation in the battery.
Simple, efficent and quick.