Upgrading 15s Battery to 16s

[boarder2k7]

I just picked up two no name brand 15s server rack batteries as detailed here.

One of them (possibly both) needs a new BMS. I'm finding that options for 15s BMSes look relatively slim when thinking about overall features and compatibility with other packs in the future as most good server racks seem to be 16s setups. I really like the looks of the Overkill BMS but it is 16s only.

Is there any reason that I can't grab myself two new 100 Ah Eve cells, top balance the whole lot, and drop the Eve cells in line with the existing 15s setup to get a 16s that could use a better BMS?

I understand that the new cell would likely be a higher capacity than the rest of the pack that has had some cycling (unknown count) up until this point, but in my understanding as long as they are top balanced, I'll still be able to get the full capacity out of the original 15 cells. The new 16th will essentially not ever fully discharge.

Is this a viable course of action? Alternatively if someone could recommend a good 15s BMS that has decent communication protocols that I can hopefully monitor from Linux, that would also work.

Thanks in advance for any help. All the threads I found in my search were about putting 15s and 16s in parallel with each other, but no one seems to have touched on doing this.

 

[sunshine_eggo]

If it fits, you top balance, and you find a 16S BMS you like, I see no issue with it.

 

[justgary]

Several JBD models will do 15S. How much current do you need?

 

[HighTechLab]

I would contact Overkill solar about their BMSs. They are using JBD BMSs and those can usually be reprogrammed and wired accordingly for various configurations; typically 12S to 20S on the same PCB.

 

[LakeHouse]

I just picked up two no name brand 15s server rack batteries as detailed here.

One of them (possibly both) needs a new BMS. I'm finding that options for 15s BMSes look relatively slim when thinking about overall features and compatibility with other packs in the future as most good server racks seem to be 16s setups. I really like the looks of the Overkill BMS but it is 16s only.

Is there any reason that I can't grab myself two new 100 Ah Eve cells, top balance the whole lot, and drop the Eve cells in line with the existing 15s setup to get a 16s that could use a better BMS?

I understand that the new cell would likely be a higher capacity than the rest of the pack that has had some cycling (unknown count) up until this point, but in my understanding as long as they are top balanced, I'll still be able to get the full capacity out of the original 15 cells. The new 16th will essentially not ever fully discharge.

Is this a viable course of action? Alternatively if someone could recommend a good 15s BMS that has decent communication protocols that I can hopefully monitor from Linux, that would also work.

Thanks in advance for any help. All the threads I found in my search were about putting 15s and 16s in parallel with each other, but no one seems to have touched on doing this.

The JK BMS's work for a range of cell counts. Any of them that will do 16s will also work fine with 15s.
But your idea of adding an additional cell to get to 16s sounds like a better plan for future compatibility. And as long as the new cell has at least the same capacity of the old ones, it should integrate pretty seamlessly.
I would ignore any naysayers that will rant about 'matched and batched' cells being the only way to make anything work.

 

[boarder2k7]

I would contact Overkill solar about their BMSs. They are using JBD BMSs and those can usually be reprogrammed and wired accordingly for various configurations; typically 12S to 20S on the same PCB.

I did contact Overkill, they responded very quickly that it was 16s only so that's what I was basing it on.


Based on people's responses here I think I'm going to go ahead and order 2 Eve cells and upgrade to 16s. Seems like a better path forward and I'm glad at least a couple others agree.

 

[SparkyJJO]

Another vote (granted, from a nobody) for upgrading to 16s of possible. 15s as you said is not common and greatly limits your expansion options.

 

[Blakes]

Pardon my ignorance, what does 15s and 16s mean?

 

[boarder2k7]

Does anyone know of a way to buy only 2 Eve cells? I looked on their online store with the link in the battery thread and it looks like the minimum order is 4.



@Blakes it refers to the number of batteries in series. A nominally 48v pack can be made with either 15 or 16 cells, so 15s or 16s. You'll also see "p" used to indicate parallel arrangements in some circumstances so a "3s2p" pack might be used for example in an RC car and is 3 series 2 parallel.

 

[Blakes]

@Blakes it refers to the number of batteries in series. A nominally 48v pack can be made with either 15 or 16 cells, so 15s or 16s. You'll also see "p" used to indicate parallel arrangements in some circumstances so a "3s2p" pack might be used for example in an RC car and is 3 series 2 parallel.

ah now that makes sense. thanks. I have my Renogy 48v inverter set to 15s which is connected to 4 Chins 12.8v LFP. At 16s it seems to 'bounce' off the BMS when the batteries were full. I'll dig into this a bit. thanks again.

 

[boarder2k7]

Looks like $90 each is about the best I can do from this ebay seller in the US. They seem to have decent reviews even though they're a newer seller.

DIY 100 Ah 3.2V LiFePO4 Lithium Iron Phosphate EVE Cells - 3.2V, 12.8V | eBay

Saving a Bank compared to buying a high capacity LiFePO4 battery. This batch of EVE's is great, and will last you DECADES with proper care. We are proud to always bring you Fresh, Matched, Grade A LFP cells for your battery building needs.

www.ebay.com

That puts me at $180 more batteries plus about $300 for 2 BMSs, bringing my total cost for two rack batteries to $880, so a bit better than half price. Maybe I'll use cheaper BMSs though to save some off that.

Edit: These Daly BMSs look like they might be okay
https://a.co/d/284maTj

 

[HighTechLab]

Daly BMSs are a great way to burn down your house. I don't recommend touching them with a mile-long stick from personal experience.

 

[boarder2k7]

Daly BMSs are a great way to burn down your house. I don't recommend touching them with a mile-long stick from personal experience.

Wow, that's a strong opinion!

What would you recommend? I know that the Overkill BMS is well regarded but I was hoping to avoid that price tag.

 

[Partimewages]

Cheap = destruction!

 

[HighTechLab]

I've heard good thinks about JK BMS...but no personal experience. Might be worth looking into.

 

[Robbert]

Looking at your other post, where you show your battery, I think you can do what you want.

It seems that all busbars are welded, so fitting it in could be a challenge. On the negative side, you might be able to remove the foam and add a cell, but you will need to do some rewiring. If there is space, it should not be too difficult. Only a new longer negative wire to the negative pole and a flexible busbar from negative cell 1 (that will become 2) to positive new cell.

As for the bms. Maybe you can access the current bms with pc software. If it is a seplos (clone), you might be able to use the current bms, change the settings and only get a new harness for the cell-wires

 

[chrisski]

I wonder if 15S LiFePO4 is common.

At first I thought the 15S might be a different chemistry, but they look like LiFePO4.

 

[sunshine_eggo]

Looks like $90 each is about the best I can do from this ebay seller in the US. They seem to have decent reviews even though they're a newer seller.

DIY 100 Ah 3.2V LiFePO4 Lithium Iron Phosphate EVE Cells - 3.2V, 12.8V | eBay

Saving a Bank compared to buying a high capacity LiFePO4 battery. This batch of EVE's is great, and will last you DECADES with proper care. We are proud to always bring you Fresh, Matched, Grade A LFP cells for your battery building needs.

www.ebay.com

EVE LF105 Grade A Cells - 3.2V LiFePO4 105Ah Battery

Shop the brand new EVE LF105 Grade A Cells - 105Ah LiFePO4 Battery for reliable and long-lasting power. Available now with fast shipping. Order today!

www.18650batterystore.com

New EVE 3.2v 105ah Lifepo4 Prismatic Cell LF105

These batteries are brand new and grade A. Every battery tested above 109ah. Here is the testing data for every cell in this listing. Xlsx datasheet download click HERE. You can match the cells to the datasheet testing with the serial number on each cell. You can download and open this file in...

batteryhookup.com

That puts me at $180 more batteries plus about $300 for 2 BMSs, bringing my total cost for two rack batteries to $880, so a bit better than half price. Maybe I'll use cheaper BMSs though to save some off that.

Edit: These Daly BMSs look like they might be okay
https://a.co/d/284maTj

Screw DALY. IMHO, there are more problems report

 

[sunshine_eggo]

I wonder if 15S LiFePO4 is common.

At first I thought the 15S might be a different chemistry, but they look like LiFePO4.

some manufacturers went 15S for the explicit 48V nominal where 16S works better for the operating lead-acid range of most 48V systems. Pylontech seems to be one of the first.

 

[boarder2k7]

Thanks all.

@Robbert my plan is to add the battery to the front left spot in my picture there, on the negative end as you mentioned. As I'm already replacing the damaged BMS I figure they might as well match so I'm not going to get in to reprogramming the cheapo one that's in there.

@chrisski It seems to me that 15s is common in the dirt cheap batteries. Saves them a little money and is still nominally 48 volts. The advice on the forum is of course not to parallel 15s and 16s batteries as the voltage is different.

@sunshine_eggo Thanks for those links! The first one looks like 16 cell minimum, but the second appears to sell individually with quite reasonable shipping. I'll place an order later. Taking the couple notes here on not using Daly, I won't. What would you recommend? JK or Overkill seem to be the top choices I'm seeing currently.