2 x in 1 box LifePO4 15S build with JK-B2A24S20P BMSs

[sunshine_eggo]

A benefit of a 15S setup is lower cost. It's minor but a benefit nonetheless that reflects that natural tension in building batteries: more batteries offer more capacity but cost more.

Lower total cost, but higher per unit energy cost. Since a 15S BMS costs the same as a 16S BMS (especially if a universal is chosen)...

15S + BMS is more $/kWh than 16S+BMS

15S yields less kWh/$

Do you want to save money or get more for your money? I'm in the latter camp.

Furthermore, the 15S will have a reduced cycle life due to higher current and greater DoD for a given application than 16S. Not a lot, but one can't argue the opposite. This further increases the cost of the 15S...

As for 16S better matching 48 volt operating ranges, it seems that 15S will work fine with currently available equipment and are a better match for legacy gear that was used with FLA batteries.

literally the opposite of what has been said/documented.

15S operates 4.5V below the low limit and 4.45V under high limit of FLA.
16s operates 2.5V outside the low limit and 0.8V under high limit of FLA.

Less voltage is outside of FLA range with 16s than 15S. Not sure how 15S is a "better match."

I'm not a proponent of one over the other but I believe it's important that people aren't given the impression that 15S can't be part of a highly functional 48 volt system.

I am a proponent of 16S. It's literally all upside for 16S. I don't believe I have presented anything that can be used to give an impression that 15S can't be as you state. It absolutely can. It's just always second choice.

16S has some advantages just as 48 volt has advantages over 24 volt (but the 16S advantages over 15S are much smaller compared to 48v v 24v).

If there are no existing restrictions, there is no technical reason to select 15S over 16S. There may be a financial reason, but if $150/battery is where one is trying to save money, the system margins are probably too tight.

Now... all of that said... if I had an option where 15S was 25% cheaper per kWh than 16S, sure. I'd probably go for it, but I would wrestle with the decision.

Back to the OP... they have no choice. I wouldn't consider mixing 15S/16S, nor would I scrap or replace a perfectly healthy 15S with 16S just on principle.

 

[jimf909]

@sunshine_eggo , thanks for the helpful response to my earlier question and other comments. You've covered the differences pretty well although I'll have to sketch out the comparison the FLA voltages to get my head around it.

 

[sunshine_eggo]

@sunshine_eggo , thanks for the helpful response to my earlier question and other comments. You've covered the differences pretty well although I'll have to sketch out the comparison the FLA voltages to get my head around it.

12V FLA cut off: 10.5V
12V charging: 14.8V (varies, some are lower and some are as high as 15.0V - Rolls Surrette)

4* 10.5V = 42V
4 * 14.8V = 59.2V

LFP:
Cut off: 2.5V
Charging: 3.65V

15S:
37.5V vs. 42V min (-4.5V)
54.75 vs. 59.2V (-4.45V)

16S:
40V vs. 42V (-2V)
58.4V vs. 59.2V (-0.8V)

I acknowledge that these are absolutes, and few will want to run any chemistry down to the extreme minimums; however, in an emergency, one might want to use every last electron.

 

[Steve_S]

And Steve, a 16S pack IS 51.2V not 48V as a 15S battery config.
Mkay?

Don't get SNARKY MKay ! We always refer to these are 48V systems regardless of 51.2V or not...
ALSO I am NOT some idiot NOOBY !
Charge Profiles, presets etc are designed for specific voltage curves 12V, 24V, 48V which is the common default industry standards.

YES a 15S will work BUT there will be side effects & issues as discovered by several others which can and sometime DO limit operations. I will not get into this Rabbit Hole again... it has been previously beaten to death.

15S "working voltage range for LFP" = 45V to 51V
16S "working voltage range for LFP" = 49V to 54.4V
Working LFP Range = 3.000-3.400 Volts per cell.
Allowable LFP Range = 2.500-3.650 (the SAFE Voltage Range for the cells that does not cause harm)

Also:
15S (200AH) = 9600Wh
16S (200AH) = 10,200Wh

As for the Snark... you are on your own...
Some lessons can be expensive & painful. Lessons are standing by.

 

[jimf909]

12V FLA cut off: 10.5V
12V charging: 14.8V (varies, some are lower and some are as high as 15.0V - Rolls Surrette)

4* 10.5V = 42V
4 * 14.8V = 59.2V

LFP:
Cut off: 2.5V
Charging: 3.65V

15S:
37.5V vs. 42V min (-4.5V)
54.75 vs. 59.2V (-4.45V)

16S:
40V vs. 42V (-2V)
58.4V vs. 59.2V (-0.8V)

I acknowledge that these are absolutes, and few will want to run any chemistry down to the extreme minimums; however, in an emergency, one might want to use every last electron.

Thanks for walking through this information for me. Much appreciated!

 

[LydMekk]

 

[LydMekk]

More progress:

 

[LydMekk]

Why the vent holes with mosquito netting? Want to keep the batteries as cool as possible.
Very hot climate her in south Spain and living in the countryside so the occasional bug vanders around.
Don't want them in the battery ^^

 

[LydMekk]

Spacers in thin plastic between the cells:

 

[LydMekk]

Some more photos, Blue Sea 350A main row switches etc.:

 

[LydMekk]

 

[LydMekk]

Finished...in production - no issues. Installed a transparent plastic lid.
The red lights look cool ^^.
I know the fuse on the negative isn't really needed but it makes me sleep better at night...
The positive side has fuses inside the Victron box.









My only piece from Victron - Lynx Power-In busbar connecting old and new batteries.
So, a total of 1360ah should last some time before the upgrade ghost visits me again ^^...

 

[Steve_S]

Looks really good, I don't think you will have heat issues... The cells will warm up when charging but it isn't that much unless you are pushing 0.5C at each side...

I REALLY LIKE THIS ! Can you provide a link for it ?

 

[SparkyJJO]

@Steve_S it looks similar to this

https://a.co/d/9D3NNDW

 

[LydMekk]

Block cable splitter

That one has some brittle plastic, 3-4 single units where destroyed during first install. I would try another brand if I were you.
There is several alternatives on Amazon with similar config.
It helped me make the battery sensor leads long in a "professional" way due to me wanting the form factor of the cells long and in one row per battery and the JK BMSs on the shelf at one end.
I used ferrules (small ones) at one end of the cables to the plug into this. I think there is a picture here showing the ferrules.

 

[LydMekk]

Yeah it stays very cool which was the intent. Resting temps are 22-23C in the cells and 26C in the JK BMSs.
Only charging with 40ish amps per battery as I have 6 and the total adds up.
Also, wanting to keep things cool and the lifetime longer I don't see the need to charge any faster.
My total pack is charged to full at around 14:00 each day.

 

[jimf909]

Nice work on the assembly! Have you combined your original 15S batteries with these 16S batteries and if so, will charge to the 15S profile? Thanks.

 

[LydMekk]

Yes. 4 old, 2 new. The new ones are 280ah's (old ones 200ah each) and therefore it is like adding 3 more of the old ones in regards to capacity. I have 2 pcs. more of the EVE 280K cells as a reserve or if in the future I will transition to 16S configs.

Charging with 3.55 per cell x 15 pcs = 53.25V
Float with 3,45 x 15 pcs = 51.75V

 

[LydMekk]

Some useful links to products:

https://www.amazon.es/gp/product/B0BFKFQVR5/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

https://www.amazon.es/gp/product/B097M2RD4M/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

https://www.amazon.es/gp/product/B000MMC914/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1

https://www.amazon.es/gp/product/B00ORVVKDE/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

You should find the same stuff on amazon.com in the US.
My links is from the EU.

But, they market the same products on all amazon's.