How would I go about building a 204.8 LFP battery pack?

[Supervstech]

Ok, so I came into possession of a trip lite 5KW ups system… 240V no neutral. I’m contemplating using it for my shop, but… it uses SIXTEEN 12Ah lead acid batteries in series…

So… I would need to build a 64S LFP… I don’t think 12V batteries can be put in series that high… most only have a 60V tolerance on the fets… maybe I could use 4 48v BMS in series, but I don’t know the voltage limit on them, and getting in contact with someone that would know seems doubtful…

Anyone know a way? Or am I stuck with lead acid?

 

[Mcgivor]

Use 60 LFP cells of desired capacity in series with a 60S BMS ?

 

[toms]

The biggest hurdle is charging the battery, putting the pack together is straightforward - line up the cells in series and use a Batrium BMS.

 

[Bob B]

I think there is a DIY BMS that is scalable ..... but I wouldn't want to be working around that high of DC voltage.

 

[Lt.Dan]

The Orion BMS goes up to 72 cells. But like @Bob B said, that high of DC voltage is down right scary. There is a lot of people who refuse to build 48v batteries because they are scared of 48v, let alone 200v DC.

 

[toms]

For sure you will want to keep your wits about yourself!

 

[Mcgivor]

The biggest hurdle is charging the battery, putting the pack together is straightforward - line up the cells in series and use a Batrium BMS.

The UPS would have a charger, assuming maximum charging voltage is 230.4V (14.4 per 12V nominal ) that would be slightly high for 60 cells, 67 cells using 230.4V would charge to a maximum 3.44 volts per cell.

 

[toms]

As long as the BMS can control the charge parameters and disconnects that would be fine.

 

[Supervstech]

I calculated 64S… no? Four LFP per 12V module… at 3.2V per cell nominal, that would be 204.8V
Anyway, I work with 300VDC all the time. I am EXCEEDINGLY careful around inverter drive minisplits and variable speed compressors…
If I build it, I will post up pictures on here.

I will research the Batrium setup… it sounds expensive though.

If anyone knows if 48V BMS sets can be connected in series that would be another option.

 

[Ampster]

If anyone knows if 48V BMS sets can be connected in series that would be another option.

They can be connected in series but there is no way that I know of to have any consistent voltage between groups. The result will be suboptimal. Your practical options are BMSs with an EV heritage which are accustomed to higher voltage and larger strings. Those typically use a contactor instead of FETs. Orion is one of the better known brands.

 

[Supervstech]

So… pricy…
Ok. I will consider the options. I may just stick with SLA for now.

Next will come the difficulty of solar charging. I’m highly doubting I can get a basic mppt at that voltage… I may charge the system off of a 48V inverter charger… hmmm… sounds counterproductive…

 

[Ampster]

So… pricy

Either way you look at it, a 200 volt pack is going to be pricey. I have not done the math but the cost and reliability of one good Orion or any of the other available options coupled with the efficiency of a Lithium pack has to compare favorably with the cost of a high voltage Pb pack when you are talking about 200 volt packs. Take a look on some DIY EV conversion sites and you won't see anyone trying to do a 200 volt Pb pack.
Charging from solar is a whole other issue that would be expensive.

 

[Mcgivor]

The existing AC chrged could be fed after the rectification with 240 VDC from the PV, there would need to be some form of regulation to avoid over voltage conditions.

Working with oddball equipment can be challenging due to lack of off the shelf components, there is always a solution with perseverance, there are BMS's available at lower costs, Shenzhen Battery Bodyguard may be able to help in that department, I've also seen some on Aliexpress which can support higher cell strings.

 

[cass3825]

Before you throw in the towel and stick with SLA, take a look at Stuart Pittaway’s DIYBMS.

 

[Supervstech]

Oh, by no means am I quitting, I am just contemplating all options for this beast I got. I may refurb it and put it up for sale… they go pricy on eBay… I got it free…