This is the variable up to 5V & 40A charger. I don't know of other ways maybe some other guys can step in & comment but I don't know another way to top balance without this equipment. 

I have 30V 10A DC variable source.. its a switching mode power supply .. that shouldn't be a problem?

What voltage should I set on the charger ?

Should I compress the cells before charging/balancing ? I'm afraid that the cells will swell up while balancing on the charger .. on the other side, if I compress them I would like to arrange the electrodes in alternate positions, so that I can connect them with busbars in series afterwards..  then I can't use the same busbars to connect them in parallel for balancing.. what should I do ?

Edited January 11, 20251 yr by Skipbidipop

So you need to decide whether you subscribe to compression or not. Me personally I don't subscribe to it. I can't convince you, it's a personal choice, do the research & do what is comfortable for you. 

Setup the cells in a long parallel stack using the busbars, set your charger to 3.60V & set 10A. Some guys go as high as 3.65V personally I don't think it's necessary, 3.6V is as good as it gets for me. 

When the charger reaches 0A you know your cells are all top balanced. Now you can begin your battery assembly starting with good knowledge that they are all at the same SOC. 

Now 10A over a stacked Parallel set of 15 or 16 cells can take a long time to charge. Because that's 100ah x 16 or 15 cells so you might need to let this charge a good few days depending on the individual SoCs. Also make sure you place you charger + & - on opposite ends of the parallel stack, so that energy is traveling directly through the entire bank, not via individual cell transfer. 

Your 10A charger can take long & that is why I prefer the 40A charger it just goes 4 times faster & can also give me cycle data on the cell, but what you have there will definitely be good enough to do the job. 

Enjoy the build if it's your first time: be careful it's becomes addictive !!

1 hour ago, Steve87 said:

Also make sure you place you charger + & - on opposite ends of the parallel stack, so that energy is traveling directly through the entire bank, not via individual cell transfer.

ok.. this is a good idea.. I wouldn't think of that myself.. I know of this but always forget .. thanks

 

1 hour ago, Steve87 said:

So you need to decide whether you subscribe to compression or not. Me personally I don't subscribe to it. I can't convince you, it's a personal choice, do the research & do what is comfortable for you.

why don't you compress your cells ? I thought it would give you more life out of your battery, stop the delamination, etc.. I thought this was standard practice

So, I should not expect swelling if I just charge-balance them without compressing? I can compress them later?

___

1 hour ago, Steve87 said:

Enjoy the build if it's your first time: be careful it's becomes addictive !!

 yes, my first build with lifepo4.. only lead-acid before this .. I can already see it is addictive 😅🤣 and quite fun.. only if shipping was faster

Keep us posted, there are quite few guys battery building & some guys that will add some great value. The first time you connect the battery & it produces power, that rewarding feeling is what is addictive. 

16 hours ago, Steve87 said:

This is the variable up to 5V & 40A charger. I don't know of other ways maybe some other guys can step in & comment but I don't know another way to top balance without this equipment. 

I love your rig!!! capacity test most probably just as important as top balancing to exactly know where you at and swop out the weaker cells cool very cool 😎 

If i grow up i would love one😝

Edited January 12, 20251 yr by TaliaB

10 hours ago, Skipbidipop said:

why don't you compress your cells ? I thought it would give you more life out of your battery, stop the delamination, etc.. I thought this was standard practice

So, I should not expect swelling if I just charge-balance them without compressing? I can compress them later?

Have a look at this video from Andy regarding cell compression.

 

thanks.. I've seen this video yesterday.. and a later video from Andy, also about compression.. basically, he still argues that compression is not needed due to cell's calendar ageing will happen well before you reach cycle damage... but, he also said that it does increase cycle life nevertheless.. it's just that most people will not be able to use it .. as I understand this.. what compression also does is it squeezes out the gasses that form in first couple of cycles.. and thus prevents this kind of damage.. if you miss it from the start, then compression will not help you at all

here is the video

as I think my cells are indeed grade A and were not charged or cycled in factory, it might be worth compressing them .. just because I might by cycling my batteries more than normal users

___

here is the spec/datasheet of my cells: REPT CB56-100Ah 产品规格书.pdf

there is no spec for torquing the screw nuts on the terminals or compression.. what do you recommend ?

just a quick note,browsed through fast,did not see it specifically mentioned(except for !datasheet! for batteries-you can see it there)

DO NOT CHARGE UNDER 0 C (degrees)

sorry for the bold letters

as pylontech has it,i think full 0.5C till 10Celsius and gradually lowers charge to 0 at 0 Celsius,bms should have the settings and when you connect bms to inverter(hopefully you can),it will inform inverter(charger) what it can push/pull

set it conservatively to prolnong cell life (no long times at 3.6V definitely,LFP really hates high voltage,low voltages under 2.8V hates a bit too)..

but watch andy's videos,he has a lot of usefull info...

k.

 

18 hours ago, Skipbidipop said:

there is no spec for torquing the screw nuts on the terminals or compression

You can use an online calculator to find the clamping force (Bolt Torque, Axial Clamp Force, Bolt Diameter Calculator)

That will tell you that 4 x 8mm screws tightened to a torque of 1.2Nm will generate about 3000N (about 300kg force)

Edited January 13, 20251 yr by Calvin

14 hours ago, korenchkin said:

DO NOT CHARGE UNDER 0 C (degrees)

yes, thank you.. I think we talked about this in the beginning of this thread

14 hours ago, korenchkin said:

bms should have the settings and when you connect bms to inverter(hopefully you can),it will inform inverter(charger) what it can push/pull

set it conservatively to prolnong cell life (no long times at 3.6V definitely,LFP really hates high voltage,low voltages under 2.8V hates a bit too)..

My BMS can't be connected to my inverter as it doesn't have rs485.. only UART(TTL 5V I guess) and bluetooth.. That's why I said I plan to make a converter for this.. because those BMSs are really cheap and good.. InverterBMS from the same manufacturer is about 150% more expensive

I hope I can set the BMS over bluetooth to not charge under or around 0°C.. it does have 2 external temp sensors after all

_____

6 hours ago, Calvin said:

You can use an online calculator to find the clamping force (Bolt Torque, Axial Clamp Force, Bolt Diameter Calculator)

That will tell you that 4 x 8mm screws tightened to a torque of 1.2Nm will generate about 3000N (about 300kg force)

Thanks.. good idea.. almost any problem has an online calculator solution 😅 ..one just has to remember to search for it

So, I put in 4mm as bolt major diameter and 750N of force because it's 1/4 of 3000N = 300Kg and I will have 4 threaded bars... and I get 600Nmm = 0.6Nm for torque

Does this make sense ? 1/4 for each threaded bar ? Is my bar too thin? 4mm for 75Kg ?

18 minutes ago, Skipbidipop said:

Does this make sense ? 1/4 for each threaded bar ?

Yes.

18 minutes ago, Skipbidipop said:

Is my bar too thin? 4mm for 75Kg ?

You would be using about 50% of the yield strength of the rod (assuming grade 3.6 steel), so in theory it would be (just) OK.  However, depending on the length of the rod, it will twist significantly as you tighten it.  I would recommend an 8mm rod.

Another useful calculator: Torque and Preload Calculator | Bossard South Africa

 

I have assembled the battery, but didn't torque it down yet.. as you can see I have subscribed to compressing after all

I used 8mm plexiglass on top and bottom sides ..and some aluminum profiles (painted white in the photos), to compress the battery.. and 2 sheets of cardboard (~1mm) between every cell.

I had to make some space between the two rows because the busbars don't fit on terminals if they are together.. I think this is actually good because I think I need to add 2 more threaded screw bars in between the 2 rows because when I started to tighten the nuts there was some bending in the aluminum profiles and the plexiglass.. I used straightedge to check as I was tightening.. is this OK?

Here are some pictures:

Also.. I don't know what torque to use on the terminals.. I've found spec for compression in datasheet(1500-5000Nm) but nothing for terminals.. is 5Nm enough?

Edited January 14, 20251 yr by Skipbidipop

I bought a torque wrench today.. but I just realized how little torque is actually needed for 3000N of force.. spread out on 4 bolts.. one can easily over tighten it just with a hand screwdriver.. and I now have a wrench used for tightening car wheels and such😅 .. minimal torque setting is 28 Nm 😅

Couple of posts ago we calculated it needs to be just 0.6 Nm for 4x 4mm bolts.. now I have 6 bolts, that is 0.4 Nm.. is this correct ?

It doesn't make much sense to me.. that is only 0.04kg=40g on 1m .. one can easily tighten this with fingers.. am I supposed to divide 3000N by 6, for six bolts ,,or each bolt must press with 3000N ? 40g is 2 packs of cigarettes 🤔???

Edited January 15, 20251 yr by Skipbidipop

I have finally connected the charger..

I have compressed it by feel with hand.. and I'm done with compressing.. as many say it is not worth the effort.. If I ever build another battery I will just compress by feel again

I returned the big torque wrench and bought a smaller one, for bicycles.. still not low enough torque range.. this one is 2-20Nm +-4%.. but at least I can torque down the terminals and busbars now 😁

I connected all cells in parallel with household installation wire.. solid core, I think 2.5mm.. no wires are touching each other.. and the charger poles are on the opposite sides as you suggested

And from the start it was about 3A only.. my shitty TEMU voltage source came with very bad wires.. there is around 0.12V on each wire.. so the actual voltage applied to the battery is only around 3.3V.. it will go up as current gets lower.. I hope this will be OK.. I don't think I can damage the battery this way.. I don't want to increase the voltage on the charger to compensate for drop in wires

__

edit:

I realize now how stupidly long it would take to charge the battery at 10W.. I'm thinking 20 days or so.. I'm in search for better wires right now

__

2nd edit:

new wires.. charging at 8A now

Edited January 15, 20251 yr by Skipbidipop

Still charging around 8A.. this will take days.. 🤢 .. I'm thinking again about connecting the cells in series(with or without BMS ?), charging it with a solar inverter-charger(5.5kW) over the grid, to almost full.. and then again connecting it parallel like it is now, and charge/balance to full.

Also, in last few weeks I started working on quite a few Li-ion packs.. for scooters and bicycles .. so I may invest in a charger/load tester like Steve87 has.. or something similar.. I found one in EU for around 275€ with shipping .. still seems a bit expensive, but even on aliexpress I can't find it cheaper.. I think this one is a pretty good one.. 40A, PC software, etc

https://batteryfinds.com/product/zketech-ebc-a40l-large-current-lithium-battery-capacity-tester/

Can somebody recommend something else? Preferably cheaper

___

I bought cheap plastic box with a lid.. and lined it with fire retardant styrofoam.. this should help contain some heath during winter so it doesn't go under 0 deg C ..in summer, I can always take the battery out.

side panels are shorter because compression fixture can't fit otherwise

__

Also, I made a simple 3D printed brackets for mounting the BMS:

here is the file.. it's a spinoff of another bracket uploaded on thingaverse

JBD_BMS_Bracket.stl

 

Edited January 16, 20251 yr by Skipbidipop

Hy all.. I have connected the battery to the inverter.. And I have a problem 

12 hours ago, Skipbidipop said:

Hy all.. I have connected the battery to the inverter.. And I have a problem 

If you can, connect a load just to cell #16 and consume some of its energy so it Voltage comes down to 3.4V or even just below 3.4V to 3.35V, then it'll be a lot closer to its fellow cells... then you can try charge the pack and let the BMS do some balancing, although, a JK BMS with 2A active balancing would probably have been a better choice...

Ok.. I will try that .. Now the cells are all at different voltage because I used them during the night and early morning..I have no power here other than this

But the cells were at the same voltage before the first charge.. within 1mV..so I don't know how it will help 

6 minutes ago, Skipbidipop said:

Ok.. I will try that .. Now the cells are all at different voltage because I used them during the night and early morning..I have no power here other than this

But the cells were at the same voltage before the first charge.. within 1mV..so I don't know how it will help 

The voltages of the cells only vary at high and low voltage. Ie high or low SOC. Look up the charge curve online.

Edited January 19, 20251 yr by Tinbum

It won't charge.. I guess because of the 8th and 9th cell are below 2.7V

Edited January 19, 20251 yr by Skipbidipop

27 minutes ago, Skipbidipop said:

It won't charge.. I guess because of the 8th and 9th cell are below 2.7V

Your cell SOC's are all over the place you must top balance them. Your bms will never balance them as they are too far out.

4 hours ago, Skipbidipop said:

With your cells all over the place it might help to charge the lower cells from the high cells by connecting all of them in parallel to assist with balancing. I know you without power but at least try it for a few hours.

Thank you all for help.. I'm home now, and took the battery with me.. looks like I'll have to use lead-acid for few more weeks there .. good thinking for not taking those 200kg batteries out of the basement because my back would say "no" if I had to carry them down there again 🤣

They have been balancing (passive I guess, through the BMS) whole day today, while I was reconnecting my lead-acid back and traveling home.. and they are a bit closer to each other now.. when the BMS stops charging I will connect them in parallel again and top balance with my slow charger

I'm charging now with 20A.. Should I go higher?

So, should I go to 3.6 or 3.625, 3.65V ?