LiFePO4 DIY options

[lfhoward]

Thanks Bruce for the encouragement that swapping cells can help. So far so good. At the 60% charge mark and only 0-1 milliamps delta. Of course the rubber hits the road during the free fall at the end, so we will wait and see.



I have one of these in the trailer that will get first dibs at any short:

DB Link ANL150 150 Amp ANL Fuse https://www.amazon.com/dp/B000P0UBPO/ref=cm_sw_r_cp_api_glt_fabc_15N1R8HWKJ9B1JPQ5H72

I sure hope I never drop a wrench or a screwdriver across the terminals. Shudder to think.

[lfhoward]

Second capacity test results:



Switching the cells did the trick. I was able to pull 154.7 Ah this time, (+1.4 compared to last night), not even taking into account that the cells started at 3.55 volts today instead of 3.65 volts like yesterday. I think I probably pulled full capacity.

It’s interesting that this time block #2 was the best, whereas last night it was the worst. I think I have one fantastic cell there, the one I moved. Block #3, last night’s best, became average. Block #1 tripped the low voltage cutoff this time. Delta was much smaller, 0.202 instead of 0.368, indicating less difference between 2p blocks. I don’t think there are any “bad” cells that need to be returned.

I think this is the last capacity test I’ll run for a good while. Taking the cells down to 2.5 volts can be hard on them. I’ll set my BMV to use a discharge floor of 10% (it will show me 0% remaining when the battery has 10% left in real life) and I'll set the MPPT charger’s absorption voltage to 4.10 (slightly lower than the default of 4.20) to increase my battery’s life span. I don’t think I will come close to needing all 156 amp hours with the camping I do, even if it rains for a week straight and solar is minimal.

Does anyone have any other tips for Victron or BMS settings with battery longevity in mind? Or are there tech questions I can answer about this LiFePO4 unit? Thanks for following!

[saltydawg]

The spread does look better, also dont forget that even just a simple thing like not being consistent on torque on the terminal screws or a bur from drilling the holes in the buss bars can throw it off.

But other wise looks good.

I would still not charge it up, take the pack apart and let it rest for a few hours and check each cell voltage. That might give you a better idea if one cell is much better or worse.

[lfhoward]

For people who want to see this battery system installed on my camping trailer, here is the link to the relevant page on my build thread so you can continue to follow along:

http://www.tnttt.com/viewtopic.php?f=50&t=62581&p=1279497#p1279497

I also want to take the important bits from this thread and distill them down to an easy to follow “recipe” of sorts for folks who want to know how to build one of these. Once that thread exists, I’ll put a link to it here.

http://www.tnttt.com/viewtopic.php?f=30&t=74022

I am also happy to continue interacting here about battery related questions and ideas, so this thread doesn’t have to stop. Feel free to carry on!

Cheers,
Lauren

[lfhoward]

The spread does look better, also dont forget that even just a simple thing like not being consistent on torque on the terminal screws or a bur from drilling the holes in the buss bars can throw it off.

But other wise looks good.

I would still not charge it up, take the pack apart and let it rest for a few hours and check each cell voltage. That might give you a better idea if one cell is much better or worse.

Thanks!

That’s a good point about the bus bars torque. I have two bolts in the center of the pack that only thread into the battery maybe 3/16 of an inch because they secure two stacked bus bars (between block #2 and #3). I didn’t torque them very tightly because I was worried about stripping them. I’ll see if I can find some longer M8 flange bolts that aren’t too long.

Sorry I missed that last part and charged the battery up immediately after the capacity test! But I am really sure the cells are dialed in well. Maybe I could eke out another amp hour or so by swapping a cell from block #1 but I’m not sure it is worth the time. I’m very happy with it and it will suit my needs both for camping and for my forest ecology field research. Very excited to get it installed in the trailer next!

[lfhoward]

I got the beehive battery heaters wired up today and tested them out. I stuck the thermostat sensor in a glass of ice water and just as it hit the threshold temperature, the Inkbird thermostat clicked on the heating pads. According to my BMV they drew about 30 watts of power together (I have two). Currently I have the following settings programmed in but am open to discussion on making them better:

Inkbird thermostat:
- turns the beehive battery heaters on at 37°F (3°C) and off at 40°F (4°C)

Victron MPPT charge controller:
- won’t charge below 36°F (2°C)

Overkill BMS:
- won’t allow charging below 34°F (1°C)

I like having redundancy in safety measures, so if the heater doesn’t turn on the charge controller stops charging. If the charge controller charges inappropriately, the BMS should shut it down. Battery damage would occur if charging below 32°F (0°C).

[lfhoward]

My lead acid batteries and chargers are in the for sale section in case anyone wants them.

http://www.tnttt.com/viewtopic.php?f=18&t=73937

[lfhoward]

Battery is installed in my trailer and is on line!





Details can be found here:
http://www.tnttt.com/viewtopic.php?f=50&t=62581&p=1279497#p1279497

[lfhoward]

If you want to see my How-To thread that distills all of this information down, click here:

http://www.tnttt.com/viewtopic.php?f=30&t=74022

[shannonswyatt]

Seems funny now reading about making your own batteries now that the price of LifePO4 batteries has dropped so much in such a short period of time. I'm wondering how much lower the prices can go for these batteries. Maybe I shouldn't throw out that little Microwave :-)

[bdosborn]

DIY with prismatic cells is still cheaper than drop-in replacements, take about a half to a third as much space and you get to pick a good BMS. I can get 280 a-hr Eve cells for $600 ($2.14/a-hr). The cheapest battery I could find on Amazon is $319 for 100 a-hrs ($3.19/a-hr). So unless the drop-ins get a lot cheaper and smaller I'm still going DIY when my battery dies.
Bruce
P.S. CALB just released a new 280 a-hr cell that is rated at 9,000 cycles.

[TimC]

I have to agree with you Bruce...

My first prismatic cell build is a 48V 150 aHr bank using new 75 aHr Eve cells I put into service two weeks ago. I spent $1906 (shipped and taxed) for 32 75aHr cells and all the materials to build the two 75 aHr batteries paralleled to get 150 aHr.

To make an "almost" apples to apples comparison, with those 32 cells and two additional BMS at a significant savings on each 4S BMS I could have built four 12v 150 aHr batteries (2S4P). With the less expensive 4S BMS that's less than $476 each.

I wouldn't consider my builds the quality of Battleborn, but just for kicks and giggles lets assume they are close in quality. 75 aHr Battleborn LiFePo4 are currently priced at $725 (Plus sales tax of $39.88, shipped free) each and you'd need two to make 150 aHr coming to a grand total of $1530 for one 150 aHr 12v battery bank. Not only a considerable savings but a fun project.

[John61CT]

Buying raw cells and (maybe) wiring a BMS is not "DIY building" a battery.

Drop-ins are crazy expensive and the cells of unknown quality, no communications with the outside no visibility of balancing issues, on and in, an obviously inferior solution just preying on ignorance and fear.

[tony.latham]

Buying raw cells and (maybe) wiring a BMS is not "DIY building" a battery.

John:

When are you going to build something and share it with us? As in a DIY project. Something like a camper.

Tony

[TimC]

Buying raw cells and (maybe) wiring a BMS is not "DIY building" a battery...

Nonsense... everything I read about DIY LiFePo4 describes it as such. I didn't know there were rules for describing DIY building a battery. With that rule in place there is no such thing as DIY anything. Mother nature made the wood to build the trees y'all. Please people, stop calling your teardrop a DIY project because you didn't make the tree or plywood, foam, fasteners, etc. You are misrepresenting your efforts!