LiFePO4 DIY options

[lfhoward]

I have been doing some in depth research on converting my trailer’s electrical system to LiFePO4 batteries. I’ve read/watched numerous threads/videos on the various options. Looks like I have 4 options:

1. Name brand 100 Ah cells (eg., BattleBorn) - plug and play, reliable, but too expensive for me ($900+)
2. High capacity cells from China (280 Ah) - risking bad cells, 2 month shipping ($500)
3. Medium capacity prismatic cells (25 Ah) from a local seller that tests them & stands behind them ($360 for 24)
4. High capacity (6Ah) cylindrical cells from the same local seller that I can make into a 150 Ah pack ($375 for 100)

Really I am looking at options 3 & 4. The question is whether I want to put together rectangular prismatic cells with bus bars or make a pack from cylindrical cells using nickel strips and a spot welder.

I could pick up 24 of these 25 Ah prismatic cells for $360 and make a 4s6p 150 Ah 12 volt pack.


Pros for prismatic cells:
- easier to assemble into packs, so can get done with the project sooner
- no fancy tools needed
- can make a 12 volt or 24 volt battery with them
Cons:
- prismatic cells can be subject to expansion, so need to build a box to compress the cells

Or I can pick up 100 (or 96) of these 6 Ah cylindrical cells and make a 4s25p 150 Ah (or 4s24p 144 Ah) 12 volt pack, similar to this:


Pros for cylindrical cells:
- more options for battery pack dimensions, making it potentially easier to fit
- don’t need compression
- less impact on the whole battery if one cell fails
- potentially more fun to build
Cons:
- Need to buy nickel strips and a spot welder (extra expense)
- more work and time to build

Of course once the packs are assembled they would need to be top balanced and capacity tested. I will need a BMS (battery management system) to be able to run a DIY battery (only option 1 above has a BMS built in).

Both options 3 & 4 would give me a 150 Ah pack with over 2000 charge cycles. The 150 Ah size is perfect for my needs (fridge, fan, Propex heater, computers & 200-300 watts of solar).

Which LiFePO4 option would you pick and why?

[saltydawg]

Order 8 of the 280ah batteries, do a load test on each one. Find the 4 that match the closest and sell the other 4 on ebay for a profit of 50-100 bucks.

or buy 8 of the 280 ah cells, if they all pass, assemble them with a bms into a complete battery and sell it.

Doing the pack compression is easy, just use plywood and cut it with handles and bolt together with all thread.

[lfhoward]

Actually, I just snagged 8 of these 78 Ah Lishen units about 5 minutes after they became available on http://www.batteryhookup.com/. Battery Hookup is less than an hour away from me so I can eliminate shipping from the cost.



This pack will provide my trailer with 156 Ah in a 12 volt configuration (4s2p). The terminal connections on these batteries look beefy as well, which is an advantage over many of the units available online.

Next up I need a good BMS with a low temperature disconnect.

[saltydawg]

The price on them is not horrible. I just looked looked on aliexpress and 100 ah 4 pack of batteries are about the same price or a little cheaper. But having a local place if one craps out is worth a few more bucks.


As for bms, before long someone is going to offer one with low temp cut off with recharge redirect for a heater. At least I hope they do, until then my thermostat, relay and bee hive heaters will have to do.

[lfhoward]

That should be the next big thing in BMS's! Wish someone will do that. Daly, the biggest manufacturer of BMS's in China, still doesn't have a low temperature disconnect on theirs.

I just ordered a 4S Smart BMS from Overkill Solar. The wait time for the backorder is at least 30 days, but it's worth waiting for a BMS that reliably works.
https://overkillsolar.com/product/bms-120a-4s-lifepo4/

[lfhoward]

@saltydawg, do you have a link to your bee hive heater & thermostat setup? How many amps does that use?

Being in PA, I will certainly be winter camping and will want to be able to charge my batteries when it is below freezing outside.

[featherliteCT1]

IMHO, the fact that the seller is so close to you is great!

[bdosborn]

I bought these to use for my LiFePo4 batteries:
Amazon Heater
I've got eight 200 a-hr cells and I'm planning on using 4 total, one pad fits nicely under two cells.There are a lot of heaters on Amazon and most of them get super hot (350F) so make sure you get the beehive heater, its gets about 150F.

I used this thermostat after playing with a few, there are a lot of junk thermostats on Amazon:
Amazon Thermostat

Bruce

[saltydawg]

@saltydawg, do you have a link to your bee hive heater & thermostat setup? How many amps does that use?

No I dont except a thread here somewhere. But I can explain it very easily.

A 12 volt thermostat that can handle iirc 10 amps pass thru. It has 12 volt in, 12 volt out with a temp sensor. the out side goes to two 12volt 12 watt bee hive heater pads and a 12 volt 30 amp relay. The relay has on the common and NC terminal my charger out put. There is a switch that powers the thermostat, so turn the switch on it powers the thermostat. If the temp is below 37 degrees it turns on the output which powers the heater pads and activates the relay and shuts it off at around 43 degrees, which interrupts the charger output to the battery. Total cost like 30 bucks., actual load for the pads is about 2 amp per hour. From my testing when the battery was about 25 degrees it took about 90 mins to reach 43 degrees. so a total of 3-4 amps left in the battery needed to warm them. It is self controlling, when its cold I can just turn on the switch and it does the rest sense it shuts off the heaters at non freezing temps I could leave it on all the time. I have the temp sensor between my batteries.

I also have it after the shunt so my power monitor does see it, so while it does run off the batteries when cold it still gives me an accurate SOC.

BTW i am about 1.5 hours from you zip 21158

edit bruce is using the same pads I am, and I think he is using them from my suggestion

[lfhoward]

Just want to say I haven’t forgotten about this thread. Right now I’m waiting on shipping. The following is coming this week:
- 156 Ah of LiFePO4 cells (to pick up)
- 1/8” x 3/4” copper stock for bus bars
- Overkill 120 A 4s BMS
- Benchtop power supply for top balancing

I’ll post photos of the batteries when I get them, and of the top balancing process.
I still need to get a shunt and battery monitor to be able to run a capacity test. Also, a charger that can charge Lithium would be nice, although I should be able to charge my pack on the workbench with the power supply & BMS.

[saltydawg]

Just want to say I haven’t forgotten about this thread. Right now I’m waiting on shipping. The following is coming this week:
- 156 Ah of LiFePO4 cells (to pick up)
- 1/8” x 3/4” copper stock for bus bars
- Overkill 120 A 4s BMS
- Benchtop power supply for top balancing

I’ll post photos of the batteries when I get them, and of the top balancing process.
I still need to get a shunt and battery monitor to be able to run a capacity test. Also, a charger that can charge Lithium would be nice, although I should be able to charge my pack on the workbench with the power supply & BMS.

Once you get it charged, bring it buy here. We can easily hook it to my trailer do a load test. It has a shunt and we can control the test with any from 1 to 100 amps. I have a enough charging abilities to put about 30 amps an hour back in to it.

[bdosborn]

You definitely want as large a charger as you can get when top balancing. Putting eight 78 a-hr cells in parallel is 624 a-hrs @ 3.2 v nominal. I started top balancing my cells with a 5 amp charger and after a week it still wasn't charged. I bought an iCharger x6, much faster charging at 30A.I plan to use it as a DC-DC charger to charge the LiFePo4 battery off my alternator.

Bruce

[lfhoward]

Thank you Scott & Bruce for the load test offer and top balancing advice, respectively!

Scott, you really aren’t that far away in 21158. I am sometimes in the Catoctin Mountain area for my work, not far at all. And Bruce, I got an adjustable 10 amp / 30 volt dc power supply that just arrived today. That should charge the cells in less than a week at 3.2 volts. But, I could risk it and fast charge at 13.something for a while at 12 volts with the batteries in 4s2p configuration, then put them back into 8p and finish them off at 3.2 volts. With 8 cells I could even go for 10 amps at 24 volts, even more juice. BatteryHookup says they ship batteries at 30% charge level, so there would be a buffer in there where I could maybe fast charge safely. BUT, I don’t want to over charge any of the cells and kill them before I even have a chance to use them.

[bdosborn]

That's a nice feature with the iCharger, it has a cell monitor and will stop charging when any cell gets to 3.60V so you don' t have to worry about overcharging. It will charge at any voltage (1S-8S) and will take any DC voltage input up to 30V, its super flexible. I charged a set of four new cells in series up using my Iota 12V charger; I was adding another 360A-hr to an existing battery. Then once both batteries were charged I put them all in parallel and top balanced them. I don't think it works as well with that method as the cells went out of balance after a couple of charge/discharge cycles. I ended up discharging them to 50% and top balancing all over again, with all the cells in parallel. I top balanced my newest 400a-hr battery with all the cells in parallel initially and it's stayed in amazing balance, ~1mv, through a couple of full discharges. After the first top balance I let them sit for an hour and top balance again. Repeat till they stay above 3.5V. https://www.saildivefish.ca/lifepo4-batteries-part-four-top-balancing-pack/

The awesome state of balance for the new cells might be because of how I top balanced it or might be the BMS I'm using (http://www.electrodacus.com/). Or it might be I got lucky with the cells, who knows?

Bruce

[lfhoward]

I picked up the batteries today at Battery Hookup!

This will give you an idea of how small they are in comparison to the three Group 24 lead acid batteries I currently run:

Vs.


I checked before leaving, and yes, all 8 cells were in the box.


On the workbench! So excited. Every single one measured exactly 3.28 volts.


I have a work trip tomorrow so I won’t be able to mess around with these for several days. But the bus bars aren’t here yet anyway, so we have to wait!