Expanding 24V 8s to 16s - Howto

[AlexanderKristiansen]

I have 8x3,2V LifePo4 202Ah cells in a 24V configuration and an Overkill BMS.

I'm planning to buy 8 new cells and expanding from 8 to 16. My "old" cells are under a year old with few cycles.

As I understand it I have two options. either 8 cells in parallel with 8 others. But then I will need 2 BMS's.

The other option is to put all 16 cells in a 24-volt configuration with only one BMS.

Can anyone help me with this? And please explain it very simply. Illustrations are highly appreciated!

I understand you put two and two cells together in series. But I don't understand how and where I will connect the balance leads...And should I put a new and old cell together or new+new and ol+old?

Is the easy or is there an easy way to screw this up?

 

[Bob B]

If you download this document in resources, the options you are considering will be on pages 5 and 6.

I would probably try a 2P8S configuration, but most people will probably recommend the 8S2P method.

If the cells are too mismatched and the 2P8S doesn't work out, you could always buy a 2nd BMS and reconfigure later.

Capacity testing and matching may be the key to getting it right.

Cell Configurations for 12V 24V and 48V LiFePo4 Batteries

This short deck shows 1P and 2P cell configurations for 12V, 24V & 48V LiFePO4 batteries. To get the deck, click on the orange button at the top of this page. Note: Reviews, Comments and corrections are welcome Document Revision History...

diysolarforum.com

 

[AlexanderKristiansen]

This document?

 

[Bob B]

I forgot to put it in initially and edited in the link when I realized I forgot it .... there will be an option to download.

 

[AlexanderKristiansen]

I forgot to put it in initially and edited in the link when I realized I forgot it .... there will be an option to download.

Thanks a lot, @Bob B Are the lines between the poles bus bars? And how do you connect the balance leads?

 

[Bob B]

Do you have a question about a specific layout?

 

[AlexanderKristiansen]

Yes, example C on page 6.

 

[Bob B]

Looks to me like it would be like this.

 

[AlexanderKristiansen]

That's great, thanks a lot! But really important that this is correct, can anyone else give their opinion on this?

Someone mentioned also that I would need a more powerful BMS. I have the Overkill 100Ah BMS and the output power of the inverter is 1200W, surge capacity 2400W. But the only thing that changes when I go from 8 to 16 cells is the capacity of the pack, @Bob B ?

@BarkingSpider @Hedges @Ampster @Gazoo

 

[Bob B]

If you will have the same load you will have all along .... you don't need more amps if what you have now is working fine.

.... and also tag @FilterGuy who put together the resource.

 

[AlexanderKristiansen]

If you will have the same load you will have all along .... you don't need more amps if what you have now is working fine.

.... and also tag @FilterGuy who put together the resource.

Thanks @Bob B! Waiting for some confirmation from @FilterGuy regarding the placing of the balance leads

 

[Supervstech]

I have 8x3,2V LifePo4 202Ah cells in a 24V configuration and an Overkill BMS.

I'm planning to buy 8 new cells and expanding from 8 to 16. My "old" cells are under a year old with few cycles.

As I understand it I have two options. either 8 cells in parallel with 8 others. But then I will need 2 BMS's.

The other option is to put all 16 cells in a 24-volt configuration with only one BMS.

Can anyone help me with this? And please explain it very simply. Illustrations are highly appreciated!

I understand you put two and two cells together in series. But I don't understand how and where I will connect the balance leads...And should I put a new and old cell together or new+new and ol+old?

Is the easy or is there an easy way to screw this up?

Just an FYI for you and any novices reading your post...

16S would be 48V
Your post states putting two cells in series to double the Ah, that would be incorrect, you meant in parallel.

 

[AlexanderKristiansen]

Just an FYI for you and any novices reading your post...

16S would be 48V
Your post states putting two cells in series to double the Ah, that would be incorrect, you meant in parallel.

Yes, of course, @Supervstech its 2x8s in parallel or 8s2p as I now have learned? Anyway, I am still definitely talking about 24V.

What do you think about the wiring of the balance leads, @Supervstech does this look correct to you?

 

[FilterGuy]

Thanks @Bob B! Waiting for some confirmation from @FilterGuy regarding the placing of the balance leads

Sorry AlexanderKristiansen. I am out of town an not following the forum very closely.

The image @BobB looks correct... but it does not show the most negative harness wire.



I agree that if the Wattage load you are putting on the battery currently is not changing and the current BMS is handling everything. You should not need a new BMS.

If the new cells are the same AH as the old.... I would go ahead and put them all in one battery as shown above. In fact, I would mix them like this:


Be sure to top balance them all before you put them together.


If the cells are a different AH rating you may want to make two separate batteries with two separate BMSs. Mixing separate sized cells or batteries is not ideal, but should work OK.

 

[AlexanderKristiansen]

Sorry AlexanderKristiansen. I am out of town an not following the forum very closely.

The image @BobB looks correct... but it does not show the most negative harness wire.



I agree that if the Wattage load you are putting on the battery currently is not changing and the current BMS is handling everything. You should not need a new BMS.

If the new cells are the same AH as the old.... I would go ahead and put them all in one battery as shown above. In fact, I would mix them like this:

View attachment 47037
Be sure to top balance them all before you put them together.


If the cells are a different AH rating you may want to make two separate batteries with two separate BMSs. Mixing separate sized cells or batteries is not ideal, but should work OK.

Thanks for the advice, @FilterGuy The cells are identical, 202Ah. I will of course top balance all 16 of them and I pair new and old.

I just assumed cell nr. 1 is the most negative and nr. 8 is positive, as I have now on my 8S setup.

Regarding the bus bars. There is no way to mess this up? I mean seriously with a short? Is it correct if I assume that the only way to short in this example is if positive and negative are connected on one cell, or if the positive and negative are connected on the pack (1and 8). Any other combo will not result in a short?

 

[Bob B]

There are always a lot of ways to mess up .... and there are a number of ways shorting to another cell would create fireworks .... just gotta be careful and insulate your tools the best you can.
These cells have a LOT of energy .... always wear safety glasses when working on the pack. Don't work on the pack when you are tired or when your attention is split.

Gotta have a lot of respect for the pack, but not be afraid to the point of being nervous ..... just make a plan for what you are going to do and proceed carefully and with your full attention.