DIY 12V Prismatic Lithium Battery

[1der]

Thanks Tim. I have been watching Will's videos for a few years now. Incredible resource he has created.

[Scalf77]

Originally Posted by Flux

AGM and LI are pretty different. I am not sure if AGM sufferes a voltage sag during heavy discharge. I don't think that is the case with LI. They have very different SOC profiles. LI is very flat in comparison. An LIFEPO4 at 12V is actually at 9% SOC. So my settings to to stop discharge there are to protect the bottom end and get more cycles.


on the SOK, if you look at their website and go to the 200AH model, they have a video with Will Prowse. Will is the guy owns diysolarforum and writes many of the how to's. I think he reviews that SOK. If he says it is decent, I would take his word for it.


Many off brands have entered the market. Without cracking the case and looking inside it would be real hard to know what you are getting and what the BMS is etc. I like the cases SOK uses. Watch that review.

AGM batteries will suffer from Peukert’s Law while discharging heavy loads, Li does not suffer the same.

Both systems will still see some voltage drop based on your wire size and length.

-greg

[posplayr]

Originally Posted by Scalf77

AGM batteries will suffer from Peukert’s Law while discharging heavy loads, Li does not suffer the same.

Both systems will still see some voltage drop based on your wire size and length.

-greg

I agree, but excuse me if I add a little clarification.

The original point was about voltage sag at high discharge rates. The ideal battery voltage model has an internal resistance (IR) parameter that is relatively much higher for LA vs LiFePO4 and most all Li.

LA IR varies with SOC but is generally above 20 mOhms(see link below). In contrast, LiFePO4 IR is typically sub 1 mOhms (EVE 280 Amp-Hr are typically 0.13 mOhms).

This is really what makes LI dangerous because whereas LA is somewhat sell limiting with >20 mOhms (it is still can act like a welder) the resistance of LI is 1/100th of that. The short itself is the only thing to limit the current.

https://batteryuniversity.com/articl...ct-performance


>>>AGM and LI are pretty different. I am not sure if AGM sufferes a voltage sag during heavy discharge. I don't think that is the case with LI.

So I think what is going to be easy to observe is that for LA the voltage drops at for example an inverter is going to be a combination of the LA internal resistance and the cable losses regardless of capacity or changes in capacity (e.g. Peukert's Effect).

For LiFePO4 the discharge is characteristically very flat with SOC but in addition, the internal resistance is probably < 1/100 of LA so the voltage drops are going to largely only those of the cables and connections.

[posplayr]

Originally Posted by Flux

I will say here that I most likely did not save any money over a packaged Li battery, but I learned a ton and that is worth it to me. I bought a decent Victron smart charger and a bench power supply, so that put me over. But I now have a true 120AH cell that will run a long long time.

The same conclusion here. If you only need 100-200 Amp-hr buy a completed battery. Of course, if you plan on building a larger 30 Kwatt battery bank as well a small 4S battery is a good starting point.

For mobile applications the various requirements for shock isolation, environmental temperature controls, controlled compression, fire resistance, and compliance due to swelling all turn into a bit of a design challenge. However, if you go to a commercial solution much of this is not even addressed. So going off the shelf in and of itself would seem to be a bit of a long-term gamble.

I'm planning to try to address most of this to the extent feasible for a 200 amp-Hr 4S2P pack. The 30KW pack is not mobile and therefore less stringent with some level of ambient environmental controls.

[225]

Originally Posted by Flux

Would like to see your setup when you install it. My DALY BMS is working pretty great. I know some had trouble with them. Mine seems just fine and the Bluetooth range is excellent. I guess if you hook them to a computer you can also define Depth of Charge curves for more accurate capacity readings. I am just using the cheap Amazon shunt and meter.

I'm going to use a Victron Multiplus 3000, Victron MPPT, Victron Lynx Distributor, etc....

The BMS does all the charging management, but I will program the Multiplus or course. I'll have 800w of solar and 1120ah. And a small 2000w generator.

[Flux]

Thanks for everyone chiming in and sharing their knowledge on this.


To 225's point. Yes, I highly suggest making sure all your chargers etc are in line with the BMS. Redundancy is key!


I am sure that if you got an off the shelf unit from a reputable company they would share the BMS settings with you, or at least they should.

[Flux]

These 100 AH cylindrical cells caught my eye:


https://www.alibaba.com/product-deta...101742197.html


Another seller:


https://www.alibaba.com/product-deta...5eb0b4901FobAr


Compression is already taken care of with these. I just think about the form factor possibilities. They are a bit smaller than three beer cans stacked up. You could create batteries that are super thin and tuck into walls etc.



Reviews seem decent thus far:


https://diysolarforum.com/threads/cy...s-100ah.22958/

[HIGHCOUNTRYMIKE]

My head is still spinning (no not from the HERRADURA).
I am so happy with my 2003 SMB (WEST).
I have the standard house battery. yes I have replaced it several times the last being Rock Springs, WY (Battery Solutions). I paid $440 for the same battery I paid $675 for in Los Angeles.
I have never had an issue with my standard system. It sounds like people are spending more time in their van than outside. I live out side and eat and sleep inside. I use my house lights, frig is running and listen to "old time radio" then off to bed.
I will disclose that I'm not an electrical geek.......I like that my lights work, frig runs and I can listen to my radio.
I may suffer from the old age syndrome: "if it ant broke don't fix it"
HighCountry 2003 E350 EB SMB 4X4 7.3 +290,000