Cmax cells

[Partlyshady]

Hello all!! In addition to being new here I'm posting a question for anyone who has information or guidance on this . I have a Cmax traction battery compromised of many 3.7volt 5 amp hour cells.
It is 7.6 k total and I'm looking for the best means necessary to get it to 48 volts (I purchased an 48v EG4 all in one inverter) was hoping to use these cells but not constricted
by them either.
Thank you! -John

 

[sunshine_eggo]

Energi or standard?

 

[Partlyshady]

I'm not sure .. most likely standard .
I haven't even tore the cells out yet.
I'm just going by other tear downs I've seen and from the top view they look like the same 3.7 5ah cells. I don't remember the count poss 80 in all.

 

[Partlyshady]

I'm not sure .. most likely standard .
I haven't even tore the cells out yet.
I'm just going by other tear downs I've seen and from the top view they look like the same 3.7 5ah cells. I don't remember the count poss 80 in all. Edit- 7.6 k is the Energi battery pack apparently

 

[sunshine_eggo]

I'm not sure .. most likely standard .
I haven't even tore the cells out yet.
I'm just going by other tear downs I've seen and from the top view they look like the same 3.7 5ah cells. I don't remember the count poss 80 in all.

The Energi is the plug-in with a ~20 mile range. Only the Energi has 7.6kwh of capacity. Yours is 1.4kWh

I have 7 of of the Energi packs and have been trying to build a battery for the better part of 3 years (14S2P). I'm about 80% finished with half of it (14S).

I wouldn't wish it on anybody let alone trying to do anything productive with the baby packs.

IMHO, abandon all efforts.

If I had known about LFP, I would have gone that route as I wouldn't have to deal with 588 cells. I would have spent about the same and been done 2.5 years ago.

 

[Partlyshady]

The Energi is the plug-in with a ~20 mile range. Only the Energi has 7.6kwh of capacity. Yours is 1.4kWh

I have 7 of of the Energi packs and have been trying to build a battery for the better part of 3 years (14S2P). I'm about 80% finished with half of it (14S).

I wouldn't wish it on anybody let alone trying to do anything productive with the baby packs.

IMHO, abandon all efforts.

If I had known about LFP, I would have gone that route as I wouldn't have to deal with 588 cells. I would have spent about the same and been done 2.5 years ago.

Well. As stated in my original post the pack is 7.6 k and is plated as such on the covers .
And I'm not stuck going this route just putting out feelers as to what's possible. I may just part the cells out in the end.

 

[sunshine_eggo]

Well. As stated in my original post the pack is 7.6 k and is plated as such on the covers .
And I'm not stuck going this route just putting out feelers as to what's possible. I may just part the cells out in the end.

Then it's an Energi pack. Should weigh around 200#.

4 modules, 21S
24Ah cells
Internally fused for 150A.

Baby pack:



Energi:

 

[Partlyshady]

Then it's an Energi pack. Should weigh around 200#.

4 modules, 21S
24Ah cells
Internally fused for 150A.

Baby pack:

View attachment 99509

Energi:

View attachment 99510

Yes, it's heavy all right! 24 ah cells huh? (I'm still waiting on the right spline socket for teardown to come in) you have 7 of these? I was hoping to get two but the other one got sent back to Ford . I built a small solar trailer ( my avatar) which uses 4 LA batteries and modified sine inverter with a dc alternator powered by predator engine, and 2 100 watt solar panels .
But I wanted to play with something bigger.

 

[sunshine_eggo]

Yes, it's heavy all right! 24 ah cells huh? (I'm still waiting on the right spline socket for teardown to come in) you have 7 of these? I was hoping to get two but the other one got sent back to Ford . I built a small solar trailer ( my avatar) which uses 4 LA batteries and modified sine inverter with a dc alternator powered by predator engine, and 2 100 watt solar panels .
But I wanted to play with something bigger.

This is 13 of 14 modules for 48V:



Just disassembling them is a bear. They don't want to go back together. A friend built a fixture for his project, and I bought it from him. I still have two packs to break down and 14 modules to disassemble/assemble. I flipped them around to the same polarity and have 1/4" x 1" Al bar as bus bars:




With 84 cells you have great 7S and 14S options for 24 and 48V, respectively.

48V would be 6P14S. 24V would be 12P7S. You'd need to split them across modules to get there. I was hung up on this for the longest time trying to get 5 packs/20 modules to work out. Then I said "eff it!" and bought two more, so I have a total of 28 modules, hence 14S2P.

Invested in a Batrium WM5 and MM8 to maximize the financial pain and complexity.

 

[Partlyshady]

...... I'm looking for the info on a bms, I won't lie I get lost in the terms . Can two or more 24 ah battery be out into parallel then series? Putting a monitor from bms on each parallel ,"cell" group? Or point me to a good tutorial. I really appreciate your time.

 

[sunshine_eggo]

...... I'm looking for the info on a bms, I won't lie I get lost in the terms . Can two or more 24 ah battery be out into parallel then series? Putting a monitor from bms on each parallel ,"cell" group? Or point me to a good tutorial. I really appreciate your time.

Yes.

The module above is a 21P (21 cells in parallel) "cell". I have 14 21P modules that I will place in series for a 48V system. Each module will have one BMS sense lead for monitoring that cell voltage.

Aside from the physical nightmare of disassembling them, flipping them around and reassembling them, it's pretty simple.

It's somewhat common for folks to use 2X 6S Tesla modules for a 12S/"48V" battery. You could do this and not have to split "cells" across modules if you're looking for a 48V system.

You could do 7P3S per module and then series each of the modules. You'd have a total operating voltage range of 36-50.4V. Realistically, for cycle life/longevity considerations, you'd want to limit it to 42-48.6V.

Here's a long ago "proof of concept" 24V arrangement (yes. Pure shit workmanship) with only the top "layer" of modules used:



I have noted 12P Cells 1, 2 and 3. The little black boxes are active balancers because I didn't have a BMS. Cells are joined with Nickel plated Prius bus bars in a very haphazard way (it's what I had). You can see the red and black "bridging" wires connecting the 9P cells in module one with the 3P cells in module two.

You can also see by the color of the terminals where I swapped them around.

 

[Partlyshady]

Cool setup, I'm not one to judge I often do things half ass or thrown together just to make sure it works.
Whose BMS would you go with ?
If you wanted to keep it simple?

 

[sunshine_eggo]

Cool setup, I'm not one to judge I often do things half ass or thrown together just to make sure it works.

Yeah. That's how I do things until they threaten to become permanent after a couple years. FWIW, I only used the battery like that a couple times because I didn't want it to run unmanaged, and those bus bars are pretty thin. I bought a 8 Trojan T-1275 golf cart batteries for $500 for a 4S2P bank. Unfortunately, those worked well enough to make the battery build far less urgent.

Whose BMS would you go with ?
If you wanted to keep it simple?

Depends on your need. If you can live with 100A, JBD. I bought a "backup" 14S JBD just in case I couldn't get the Batrium working.

 

[lakehead7]

...... I'm looking for the info on a bms, I won't lie I get lost in the terms . Can two or more 24 ah battery be out into parallel then series? Putting a monitor from bms on each parallel ,"cell" group? Or point me to a good tutorial. I really appreciate your time.

I'm looking at building a 24 volt battery out of each rack of 21 cells my thought is to do three in parallel and seven groups of these three in series for the battery but I'm curious how I could put a bms on that? This is my first build and I'm unsure about the BMS wiring if you can do series and parallel connections with a BMS onto each cell or would I just put a sense wire on each Parallel Group I've been pondering this one for over a year now help

 

[sunshine_eggo]

I'm looking at building a 24 volt battery out of each rack of 21 cells my thought is to do three in parallel and seven groups of these three in series for the battery but I'm curious how I could put a bms on that? This is my first build and I'm unsure about the BMS wiring if you can do series and parallel connections with a BMS onto each cell or would I just put a sense wire on each Parallel Group I've been pondering this one for over a year now help

The parallel cells are essentially a single cell, so you'd hook the BMS sense leads accordingly. See if this helps:



Red lines are drawn every three cells to separate the "cells".
The thick black lines are where there is a break in the bus bar separating the cells
The circles are the primary (-) and (+) terminals.
Arrows indicate the locations where sense leads would be attached and correspond to the BMS sense leads in the image.

You would need to disassemble each module and flip the appropriate cells around or use cross cables.

 

[lakehead7]

Would you run these batteries without a bms? What BMS would you choose?

 

[Delmar]

I bought a 8 Trojan T-1275 golf cart batteries for $500 for a 4S2P bank. Unfortunately, those worked well enough to make the battery build far less urgent.

My used 48V golf cart came with six Trojan T-875 unknown age batteries. My plan is to replace with LiPo when they die, however they are still going strong.

Thanks for the info on the how difficult the Cmax cells are to reconfigure. I will probably go Nissan Leaf since they are easier to build by a novice.

 

[sunshine_eggo]

Would you run these batteries without a bms? What BMS would you choose?

FUCK NO!

Now, be honest... I actually did run a 24V system for a short period with no BMS; however, I capacity tested all cells, balanced all the cells to 4.05V, installed active balancers and kept the charge voltage to 27.4V (3.92V/cell - 75% SoC), and only ran it for a short while watching it like a hawk.

Would I do that again? Yes, but only for temporary/experimentation purposes.

I'm using Batrium. It's the most luscious headache I've ever had, and they charge a premium for the honor of causing me pain. If 100A is enough, I'd just go with a 7S JBD. You can probably find them in higher currents.

If you have the four modules (one pack), and they're all out of one car, and they are all sitting at ±.01V of each other, they are likely all the same capacity.

Before I continue, this test was purely for proof of concept AND it utilized only things I had on-hand, spare wire, ring terminals, bus bars, etc. It fails every "best practice" on the planet concerning building lithium batteries. I knew the risks, and I took precautions, I KNEW they were all the same capacity and internal resistance, and I can't tell you how many times I was out there measuring all 7 cells with a voltmeter just to make sure!

AND, this was about making it work fast with what I had on hand... not neat or pretty. It was in operation for maybe 4 days total.

For my initial test battery (I had 20 modules, used 4) I rearranged the cells in the modules in a 12P7S format. This required me to split each "cell" across packs.

Each NMC cell is around 20Ah if in decent shape. New is 25Ah.

CX = Cell 1, 2, 3, etc.
YP = # of NMC cells in parallel

Module 1: C1-12P, C2-9P
Module 2: C2-3P, C3-12P, C4-6P
Module 3: C4-6P, C5-12P, C6-3P
Module 4: C6-9P, C7-12P

I connected each module in series with 8awg superworm wire good for > 70A

On the right side of the pack, I have drawn red lines indicating where the cell "breaks" are and circled the terminals where one crossover wire is evident.

The little black boxes are active balancers that are supposed to keep adjacent cell voltages within .02V of each other.

This would be an option for you if you want a larger, 240Ah battery with a single BMS rather than 4 smaller batteries, each with its own BMS.

I know I've said it before, but I'll say it again, if I had to do it all over, I would have gone with LFP. It would have cost the same as 7 Energi packs, and I would have been done two years ago.

 

[sunshine_eggo]

My used 48V golf cart came with six Trojan T-875 unknown age batteries. My plan is to replace with LiPo when they die, however they are still going strong.

Thanks for the info on the how difficult the Cmax cells are to reconfigure. I will probably go Nissan Leaf since they are easier to build by a novice.

I had access to lower-than-market cost on most these. Even with the costs of > 100' of aluminum bus bar fabrication (1176 holes total) and the Batrium BMS, I'm sitting at about $165/kWh.

I don't want to think about the labor cost...

 

[lakehead7]

The energy pack was given to me so I'll be out time and the cost of the bmss which appears to be about 100 bucks each. Thank you very much for all the info