DIY Lithium Packs, Proposal and Discussion
- Thread starter luthj
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luthj
Engineer In Residence
This is a good option. Inexpensive, minimal external component count, mostly programmable via bluetooth. Decent history. Since it includes low temp disconnect, and high/low voltage disconnect, it serves all the basic BMS needs. Its only 120A continuous (needs a heat sink for that I think), but thats enough for many modest sized applications.
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Add it to the long unresolved questions list... Some say the only purpose they serve is to prevent mechanical stress on the terminals & controlling overcharge. Until I see real data over a long period I think the truth is somewhere in between.
No.
Allowing cells to swell past a tiny percent definitely reduces lifespan, delamination can quickly render a cell scrap.
Sure gentle C-rates, low temperatures, avoiding the shoulders
reduces the chances of swelling
but in a propulsion context it is pretty inevitable.
You did look at the vendor data right?
The big makers don't publish that stuff, all the buyers they care about have their own battery scientists on staff know this stuff already.
Allowing cells to swell past a tiny percent definitely reduces lifespan, delamination can quickly render a cell scrap.
Sure gentle C-rates, low temperatures, avoiding the shoulders
reduces the chances of swelling
but in a propulsion context it is pretty inevitable.
You did look at the vendor data right?
The big makers don't publish that stuff, all the buyers they care about have their own battery scientists on staff know this stuff already.
luthj
Engineer In Residence
Making some progress. Need to decide on how the cables will be routed, and If I want to put the main fuse inside the box. I think I will need to make some bus bars. They may need to accommodate some expansion, so I am not sure what I want to do. I could dig around for some that might work with my spacing. Another option is to get a bunch of thin copper cut and make stacked ones myself. Solid copper might be okay with the clamping fixture.
Hillbilly Heaven
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Georgia Copper
www.gacopper.com
luthj
Engineer In Residence
Georgia Copper
I was just looking at mcmaster carr and they carry 2/0 gauge braided strap which looks like the same product. I can solder a copper plate with hole, or crimp a pass through eyelet to terminate for each cell.
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luthj
Engineer In Residence
Okay, just ordered material for bus bars. Plan is to sandwich the copper braid between two pieces of 1" square copper 1/16" thick. Clamp it down, then solder the edges. Its going to be a challenge to keep the wicking down I think. After that I can drill them for bolts.
I am pretty close to ordering steel, I just need to figure out where my main fuse will go. I would like to put it in the battery box, but its pretty big. I have a height limit of around 11", any lower will hang below my hitch, and I don't want to catch it on departing some crappy road or ditch.
I am pretty close to ordering steel, I just need to figure out where my main fuse will go. I would like to put it in the battery box, but its pretty big. I have a height limit of around 11", any lower will hang below my hitch, and I don't want to catch it on departing some crappy road or ditch.
Nice! I just built mine up using fortune cells.
I’m currently waiting on the BMS from AliExpress. I went with this one for about half the price of this link.https://overkillsolar.com/product/bms-120a-4s-lifepo4/
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I’m currently waiting on the BMS from AliExpress. I went with this one for about half the price of this link.https://overkillsolar.com/product/bms-120a-4s-lifepo4/
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I am tempted to put something like this together myself, but I probably know just enough to be dangerous.
Have been looking at going renogy or BB.
If I did go this route I think I'd need 8 cells for 200ah and a quality BMS with temp cutoff, I am in the great white north. (I like the looks of the overkill solar one linked above).
I already have a victron 712 monitor but as far as I understand I'd need another monitor to manage individual cells and balance the pack properly. Is this correct?
I am not afraid of DIY stuff but with batteries I'd like to get it right the first time.
Hopefully not hijacking this thread, but it seemed relevant.
Have been looking at going renogy or BB.
If I did go this route I think I'd need 8 cells for 200ah and a quality BMS with temp cutoff, I am in the great white north. (I like the looks of the overkill solar one linked above).
I already have a victron 712 monitor but as far as I understand I'd need another monitor to manage individual cells and balance the pack properly. Is this correct?
I am not afraid of DIY stuff but with batteries I'd like to get it right the first time.
Hopefully not hijacking this thread, but it seemed relevant.
luthj
Engineer In Residence
A proper BMS performs the following:
The overkill solar BMS looks like it will perform these functions. Make note of the current limits.
Most BMS will need their settings programmed for the cells in question.
- Cell voltage monitoring
- Cell temperature monitoring
- Cell balancing (typically passive shunt type)
- Pack disconnect if the cell voltage or temp goes outside the accepted range
The overkill solar BMS looks like it will perform these functions. Make note of the current limits.
Most BMS will need their settings programmed for the cells in question.
Drop-ins already have an inaccessible BMS internal.
Really quite a different topic from this (IMO much better) more DIY "bare cells + containment + BMS" approach, posts on each type should really be kept in segregated threads.
Really quite a different topic from this (IMO much better) more DIY "bare cells + containment + BMS" approach, posts on each type should really be kept in segregated threads.
luthj
Engineer In Residence
Getting closer. Box has been enlarged to house the class T main fuse and BMS. For ease of assembly the BMS module mounts to the side of the pack. Its tight, but I should be able to route the 4/0 cables to the fuse block and negative terminal. I am using high strand count marine wire which helps, but I may need to bend some long lugs to the appropriate angle. I am not sure how I want to run the external BMS wiring. The shunt, programming, and relay wiring will need to exit the box. Probably the best option is to run is with the main cables, which will be about 7ft of run from the box to the electrical cabinet midship.
I realize they have their own BMS. I was pondering building my own system using the cells and BMS approach rather than the drop ins.