Bus Bars on LFP

[CaptainRivet]

Originally Posted by 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.

Agree graphite paste is really bad.
Simple leave terminals as well as busbars as is, use nothing.
As mentioned above the relation to each other is important and if done the same way in 95% you still figured the strongest and weakest cell, how far they are apart. That's your most valuable data and a 100Euro ZKE tester is all you need.

-- 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.

You need 6 threaded rods and 2 scrap pieces of wood and clamp 8 together. The threaded rods you need later anyhow for the final battery. That's what you work with, build one 1p8S battery At a time.

-- 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.

Make 1p8S battery put BMS on and charge with shorepower charger till cutoff. You need busbars and torque down properly, during that charge measure with finger and IR temp meter each connection. If they are even, nothing to do but if then check the busbar is even. In 95% the bar has a notch from drilling or stamping the hole. Sand that even and try again. The oxide layer on alu builds very quick so in 90% case you put paste over oxide and they do more harm then good. Use them very seldomly and only as kinda last resort. No-al-ox is the one that most use.
Now Let battery rest and now do top balance each cell individually with ZKE or a adjustable power supply. Now do a full cycle with the ZKE for every cell a curve.
Now build the 2nd 1p8S battery and use one BMS here and do the same procedure as above. Repeat.
now match the closest curve cells together into parallel packs. The weakest cells go into together into one pack and on 5th pack position in the middle of the battery.
By doing the capacity test you already top balanced them, not 100% but 99. The rest will the active balancer do when you charge them to 29.6V with 2h absorption for the first 2 weeks.
Then do stress test with 0.3C and 0.5C and use your finger tips and an IR temp gun measure every cell connection. Heat tells you what's going on between cells, nothing else works here. Only way.

Slamming together like with single cell batteries won't work here unless you a) have a very powerfull active balancer and you wanna keep your bank for 3 o 4 days above 3.4V cell voltage so they can really equalize. And even then you don't know if you mixed weakest and strongest cell together in one parallel pack as what you see as cell deviation between packs is not what it really is.
Only way to this 0.3 or 0.5C test as the strongest cell will be significantly colder then the weakest you put in the pack. 2 degrees is max acceptable, all more you have a problem.

[Loredo]

Thus far, I have not seen any corrosion nor can I measure it through changes in the IR. Keep in mind, I have not disturbed any connections inside the battery bank since I installed it. MAYBE, if I took the bus bars off I could see / know more but I'd do this only if I'd find a significant increase in IR without an apparent reason. Then I'd do it for sure. After two years, is it enough time for a final verdict? I don't know! That's another reason why I keep checking everything. Yet, like I said it's getting old to check stuff that just keeps working. Would I use that conductive paste again? Absolutley yes. The resistance difference in a connection with / without it is very measureable.



Accuracy? In electronics it's everything. The question though is, how tollerant are the LFP cells to over or under voltage? I mean to say, reading the data sheets for LFP cells, all say that max voltage is 3.65(00)V. How much higher can we go before we damage the cells? How "wrong" can my measuring equipment be before I mess up? One thing to consider is that normally readings are not off by a fixed amount but by a percentage. Means, if you read 1.1V instead of 1.0 then your reading is off by 10% not a 0.1V. In other words at two volts you'll not read 2.1 but 2.2.



Before I made the step with the big house bank, I purchased eight 50Ah (cheap) cells to play with and get a deeper insight into the LFP world. Out of stupidity I overcharged one cell to 3.7two-ishV. It bloated the cell within an hour. I did a capacity test on that bloated cell then. Less than 40% of original capacity was left. How much not-accuracy is still OK? For me, the least possible. If the MFR tells me 3.65V then that is has to be. As exactly as possible.



I have purchased three different BMS's. None of them gives exact voltage reading. Thus, my bank has no BMS other than my brain. OK, it's protected against over charge in several ways but if and when to balance the cells is manual, decided by myself.


Balancing, when? The decision I think depends upon the cells. Reputable reseller, grade A cells, all similar in IR and V when they arrive? Whenever one wants although I'd still do it before final installation. That's just my preference because I'd still want to beat the heck out of the battery before it goes into the boat. With grade B cells bought from china? Place your money either on red or balck...


What I'd NOT do is to allow a BMS to take care of the initial balancing. First of all, IF there's a cell with several AH more in it than the rest, how long does it take an likely passive BMS balance circuit to transfer those AH? Will it succeed at all? I think that top balancing the cells in parallel is the easiest way to KNOW (I can easily measure it) that the whole thing is balanced. Second, what if the BMS reads the voltage of by x%? What happens then? Hmmm, I've lost faith in relatively cheap equipment to be accurate enough. In fact, I'm still searching for a way to monitor the cell voltages without the Fluke. Thus far... no luck.



Good point about the compression of the cells! I SHOULD have compressed them before initial charge but also wanted to capacity test them individually. Which would've been even more difficult had I had to move a six pack instead of a single cell. Or, I should have discharged them completely, compress, and then re-charge them. Discharge / charge AND balance again 43KW of batteries takes "some" time. Here I played dumb & lazy. Then again, most say compression is adamant, some say no. Each of the two camps bring some valid points. Who's right? Maybe I've lost a few hundred charge cycles, the house bank will still be longer lived than myself anyway.



Helps?

[Loredo]

I forgot to mention one important thing! I do not have any solar on my boat, nor do I want to. That means, no charging of the batteries without my direct surveilance. Little detail but important to consider.

[Fuss]

If you are using grease, use any grease you like..some have very slight advantages, that’s all. They all do the same job, that is, reduce corrosion and increase dirt attraction.
Use Lewmar winch grease or battery pole grease, why would you use a controversial grease like graphite or copper. It just opens you up to uncertainty for corrosion….
The advantage that Loredo seeks, is that he never has to balance his cells.

[newhaul]

Originally Posted by Fuss

If you are using grease, use any grease you like..some have very slight advantages, that’s all. They all do the same job, that is, reduce corrosion and increase dirt attraction.
Use Lewmar winch grease or battery pole grease, why would you use a controversial grease like graphite or copper. It just opens you up to uncertainty for corrosion….
The advantage that Loredo seeks, is that he never has to balance his cells.

CRC 05046 Battery Terminal Protector spray a non grease spray corrosion inhibitor for batteries should work . Works great on car battery connections
And doesn't attract dirt. Not that there's much on a boat.

[Franziska]

Originally Posted by Fuss

If you are using grease, use any grease you like..some have very slight advantages, that’s all. They all do the same job, that is, reduce corrosion and increase dirt attraction.
Use Lewmar winch grease or battery pole grease, why would you use a controversial grease like graphite or copper. It just opens you up to uncertainty for corrosion….
The advantage that Loredo seeks, is that he never has to balance his cells.

We have aluminium bus bars and sanded the contact areas slightly before assembly. We do use a dielectric grease with aluminium in it. It seems to help.

[Fuss]

Originally Posted by Franziska

We have aluminium bus bars and sanded the contact areas slightly before assembly. We do use a dielectric grease with aluminium in it. It seems to help.

why bother, you used aluminum bus bars so you show you don’t care much and then overpaid for a special grease that does nothing extra.

[s/v Jedi]

For battery terminals my recommendations:

- use a purple 3M Scotchbrite metal prep pad to polish up the terminals and cable lugs contact surfaces.

- coat the contact surfaces with a good quality dielectric grease, I prefer this one because of its plastic spout: https://www.amazon.com/gp/product/B000CCIDAA

- assemble the terminal connections and use the torque as specified by the cell manufacturer or experts recommend as you research this for your type of cells.

- wipe away excess grease. The exposed metal parts of terminals and cable lugs need protection and I prefer to use the battery terminals protection spray that I apply in multiple thin coats. There’s also other options, like a conformal coating spray but it’s much more expensive and I don’t think it’s much better.
I use this one: https://www.amazon.com/CRC-05046-Bat.../dp/B000CIPUNC

[Franziska]

Originally Posted by Fuss

why bother, you used aluminum bus bars so you show you don’t care much and then overpaid for a special grease that does nothing extra.

We are actually very happy with our Aluminum bus bars.
The LiFePo4 is already working fine for three years in non stop use after ironing out a few installations issues.

As the cells have Aluminum terminals we felt no need to throw another material into the mix.

[Fuss]

Originally Posted by Franziska

We are actually very happy with our Aluminum bus bars.
The LiFePo4 is already working fine for three years in non stop use after ironing out a few installations issues.

As the cells have Aluminum terminals we felt no need to throw another material into the mix.

all true but if you used the standard no aluminum ones then , without sanding and using special grease you would still be better off as well as the standard ones costing less. copper is used for a reason.

[Franziska]

Originally Posted by Fuss

all true but if you used the standard no aluminum ones then , without sanding and using special grease you would still be better off as well as the standard ones costing less. copper is used for a reason.

Regarding costing less, ours came for free from a scrapyard. We could not use the standard ones because of the footprint onto which the battery had to fit.

[Loredo]

Then more I use the LFP, then more I read how others assemble and use it, then more I'm led to believe* that at the end of the story the whole LFP thing is much more robust than what we all think it is. With grease; works. No grease; also. Bus bars of all kinds and makes, works. With passive balancer; works. Active balancer; also. And so on... I think* if the cells are a reasonable match in the battery pack, it just works.
Like the lead-acid technology, as long as you don't do anything real stupid, works. As most often, there's more than just one way to skin a cat. Let's start another thread. Who has had a catastrophic failure with LFP? My guess* not too many if any.

*believe, think, guess = worth nothing. Know is the only real thing. How do I know? It has to be observeable, precisely measureable, repeatable.

[s/v Jedi]

Originally Posted by Loredo

Then more I use the LFP, then more I read how others assemble and use it, then more I'm led to believe* that at the end of the story the whole LFP thing is much more robust than what we all think it is. With grease; works. No grease; also. Bus bars of all kinds and makes, works. With passive balancer; works. Active balancer; also. And so on... I think* if the cells are a reasonable match in the battery pack, it just works.
Like the lead-acid technology, as long as you don't do anything real stupid, works. As most often, there's more than just one way to skin a cat. Let's start another thread. Who has had a catastrophic failure with LFP? My guess* not too many if any.

*believe, think, guess = worth nothing. Know is the only real thing. How do I know? It has to be observeable, precisely measureable, repeatable.

The cheap EVE cells have had lots of problems, with second hand, rejected etc. cells with a new wrapper being offered as new and orders filled with cells with wildly differing internal resistance. Much of the cautionary comments incl. mine are based on that.

But maybe things have improved and you can now buy really good cells from the same production run and everything is fine. The problem is knowing this for sure.

[Fuss]

Originally Posted by Loredo

Then more I use the LFP, then more I read how others assemble and use it, then more I'm led to believe* that at the end of the story the whole LFP thing is much more robust than what we all think it is. With grease; works. No grease; also. Bus bars of all kinds and makes, works. With passive balancer; works. Active balancer; also. And so on... I think* if the cells are a reasonable match in the battery pack, it just works.
Like the lead-acid technology, as long as you don't do anything real stupid, works. As most often, there's more than just one way to skin a cat. Let's start another thread. Who has had a catastrophic failure with LFP? My guess* not too many if any.

*believe, think, guess = worth nothing. Know is the only real thing. How do I know? It has to be observeable, precisely measureable, repeatable.

Good points , Catastrophic failure ... I have asked this question before on this forum, answer, no-one.

[Fuss]

Originally Posted by s/v Jedi

The cheap EVE cells have had lots of problems, with second hand, rejected etc. cells with a new wrapper being offered as new and orders filled with cells with wildly differing internal resistance. Much of the cautionary comments incl. mine are based on that.

But maybe things have improved and you can now buy really good cells from the same production run and everything is fine. The problem is knowing this for sure.

Mine are not installed and tested to the level of Loredo, however, I put a lot of effort into bus bar installation and cabling.
They are now 2 year old A grade Eve from Holland, never get balanced by the BMS, some get used far outside the discharge spec of 0.5c and show no signs of swelling at all.
I imagine that when you buy A grade from a reputable company, then they are A grade....else all would hear about it right??

I wonder why this thread is so interested in bus bars when the quality of the cells is so important. If you want to install 24v straight then just use the standard ones, if in box form then you need one of the flexible, over to the other row of 4 ones.