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No one is talking about using the original vehicles BMS, they are only suitable for the EV parameters.

Chopping up salvaged auto packs then re-assembing into small lower voltage blocks is what you apparently don't realize you're talking about.

And doing that requires a much more stringent custom BMS in any case, and that's a much greater challenge than the simple LVD / OVD needed to protect standard prismatics.

The main point is, these non-LFP chemistries are inherently more dangerous.

The biggest buyers of LFP prismatics are military, in use cases much bouncier than civilian EVs.

China is irrelevant, it is the brand and sales channel that needs to be trustworthy.

I don't see that in most eBay sellers and junkyards myself.
Absolute NONSENSE
BMS's cause battery fires - most failures have been caused by the BMS partially discharging one cell

- without a BMS as long as you know that no cells have failed you are much safer than with some shoddy non OEM BMS

And yes I do know about
"Chopping up salvaged auto packs then re-assembling into small lower voltage blocks "
As I have a lower voltage pack in my car

The FACTS

Prismatic LFP have a much much higher failure rate than OEM cells - almost everybody who has used them has experienced at least one cell failure

NON OEM BMS's - have a similar high failure rate

OEM cells have a very low failure rate AND if you don't have a stupid BMS unbalancing them they won't go out of balance!

Battery fires are caused when a cell fails completely and you then charge the battery to the normal voltage - leading to n overcharge

If you have a BattBridge it will give warning if a cell has failed - that is all that you need to avoid problem
 

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Discussion Starter · #22 ·
Whoa, apparently I'm not subscribed to my own thread. I definitely am going to keep the packs at 48 volts and while i considered that most loads would be 12 volts I'm actually in a position where the entire interior of my motorhome is being rebuilt so i can install whatever size loads I can find. 48 volt seems to make the most sense currently for inverters and a DC mini split as well as not having to chop up the modules. For the things i can't find in 48 volts I'll weigh my options between running something off the inverter or using a DC to DC converter. Specifically the fridge is what my biggest question is. Thanks for the info everyone!
 

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If the fridge is the typical newer multi way the 12v load is only an amp or so for controls.

Fwiw I have an old 3 way in the casita that draws 40 amps but it runs while driving down the road. It's a rare beastie and when if fails.......
 

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Discussion Starter · #24 ·
If the fridge is the typical newer multi way the 12v load is only an amp or so for controls.

Fwiw I have an old 3 way in the casita that draws 40 amps but it runs while driving down the road. It's a rare beastie and when if fails.......
I am currently renovating the motorhome and when I put a refrigerator back in I would like to upgrade. The old 3 way I have has seen better days so I was contemplating a DC unit that I could swap between the RV and the Boat. Something like a whynter portable Fridge. They have dual zone models that are top loading that seem pretty efficient! I eat mostly food prepared from fresh ingredients or dry ingredients and my residential fridge is mostly empty so I don't need a lot of space.
 

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Concerning the BMS on separated modules, there are 3 bus bars running along the top of the modules that are inside the black plastic module cover.

If the connecting welded tabs from, say, a 48v module are severed, what about the busbars as interacting with the BMS, if one is implemented ? They are very difficult to cut without shorting to adjacent bus bars. Will connecting to the busbars that are NOT severed, cause problems with BMS or how to monitor the individual 4 cell, 16V modules if the busbars are still interconnected ? Looks to me like a 45V to module will interfere with the 4-16V module readings ?

I am referring to pre 2017 batteries. The 2017's look to be easier to cut the bars, using moderate care. The busbars are exposed and not covered as much as the older models.
 

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I have parts of 2--2013 Volt batteries. I managed to cut 2 sets of 3 cells off one end of a module to make a 20S battery for my motorcycle. I was extremely careful and found NO bars in the black plastic cells cover.

However, there is a video on Youtube, where someone used his milling machine to cut cell groups away from a module, and you can clearly see 3 copper bars (solid wires) inside that black cells cover. I have looked very carefully and never found anywhere that BMS/balance wires were connected to cell groups ? I figured they HAD to be inside that cover as the youtube shows.

There are several comments on threads to be extremely careful separating cell groups because of these balance bars ?

Maybe I'm delusional ?? I'm preparing to create several 7 cell groups for my 28V house battery bank, so, I am really interested in what I explained is true or not and if those bars do exist, how that would affect the battery I am going to construct.
 
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