LiFePO4 DIY options

[lfhoward]

Bruce, thanks for that link! I’m going to read all I can about top balancing before attempting it, and I’m adding your blog post to the list. Overkill Solar (where I got my BMS) has good detailed instructions as well. Are there others you recommend I look up? Some YouTube personalities that do LiFePO4 I know of are: DavidPoz, Will Prowse, and Dan over at FreelyRoaming. Are there others I should look up?

[bdosborn]

This guy has the best DIY guide I've found for LiFePo4 batteries:

http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/

Here's another guide I like:

https://marinehowto.com/lifepo4-batteries-on-boats/

Bruce

[saltydawg]

Not saying about your purchase, but I am pretty sure when you order from aliexpress they come with buss bars. But would not bother me as a i have plenty of stuff to use as buss bars already. Heck I have some 1/4 thick copper buss bars for huge switch gear at my office.

[bdosborn]

I was buying copper off eBay for cheap to make bus bars but then this happened:



No more cheap copper on eBay.

Bruce

[Tom&Shelly]

I was buying copper off eBay for cheap to make bus bars but then this happened:



No more cheap copper on eBay.

Bruce

Feel like I "invested" in wood by over-buying a few years ago while building the teardrop. Hope you managed to find enough copper before the price went up!

Not sure what's driving copper prices, but wood may come back down as the market settles down after COVID.

In the 70's, as a teenager, I started collecting silver coins. Found my collection was eventually worth umpteen dollars more than I paid for it. Turns out my good friends, the Hunt brothers, were cornering the market in silver driving up the price. "Good on them!" I thought, until they gave it up and the price crashed.

Tom

[bdosborn]

Yup, I always buy more than I need to cover screw-ups so I had enough for the last battery.
Bruce

[lfhoward]

Copper bars arrived today! I got 2 of 24” long, 1/8” thick, 3/4” wide flat bar. That is enough to have some extra in case of screw ups. The Overkill BMS arrived today as well. I know they arrived from alerts on my phone, but not because I am actually there to look at them. When I get home I will have to check to see if I have enough ring terminals for the BMS’s balance leads. I know I don’t have M8 flange bolts. I need to check the depth of the terminal holes on the battery before I go and buy those.

[lfhoward]

Incremental progress.

I repaired a blown up 450 watt inverter I had accidentally crossed the contacts on a while ago. The sticker said: “Warning! Do not disassemble. No serviceable parts inside.”

Two 30 amp fuses later and some solder and we are back in business! The inverter is running the lamp in this photo from an old AGM battery I had on the shelf.



So the reason why I repaired the inverter is that the new LiFePO4 cells must be discharged fairly soon after doing a top balance. It is not good for them to sit at 100% charge, like we prefer with a lead acid battery. I want to be able to draw the new cells down and do a capacity test right after top balancing, and this inverter will connect them to a load.

These batteries can do a 2C discharge which would be 156 amps for 78 amp hour cells. A capacity test should be done at 0.2C, or 15.6 amps for this pack. I can easily run a 15.6 amp load from this inverter. Since my pack is a 2p4s arrangement, should I double the capacity test to 31.2 amps? That should make each parallel cell feel a 2c draw, correct?

[lfhoward]

Thinking about 2p4s battery arrangement.

Here is the arrangement I want to use in the trailer, that fits inside the compartment I want to use.


This way keeps the width to about 7” (8” available) and length to about 12 inches (14” available).


The other option would be 8 in a line, but the longer length (14”) wouldn’t allow me to build a box around them to maintain compression, as there is only 14” of room.


Thinking back to the first photo, the parallel pairs of batteries should be electrically isolated with a divider from other parallel pairs, as the metal under the blue wrap is continuous with battery +. I am thinking I will find some thin but tough plastic sheeting. The dividers cannot be very wide as I also need to fit side walls for compression and the total width cannot exceed 8”. That’s 1” total thickness for compression walls + dividers. I am thinking of using 3/8” plywood or maybe plate aluminum joined front to back with threaded rods and locking nuts, similar to this photo from nordkyndesign.com:

Click here to see image: http://nordkyndesign.com/wp-content/uploads/2016/06/LFP-200Ah-with-BMS-768x1024.jpg

I like how this box from marinehowto.com has a plexiglass top to prevent accidental short circuits if a tool gets dropped onto the battery. I can imagine mounting the BMS to a top like this also, since there is enough height in my compartment to allow for that.


Just thinking ahead. I want to make the box and have the dividers installed before cutting my copper strips to length for bus bars. Dividers will move the batteries apart meaning my bus bars will need to be slightly longer. I also need to source M8 flange bolts to connect to the battery terminals. Further, I need a shunt for the capacity test. Going Victron, I think. I will install it in the trailer later.

[tony.latham]

Thinking about battery arrangement.

This is a nice juicy thread. Something I may take on when my two-year-old AGM falters.

Keep the photos coming.

Tony

[saltydawg]

I personally like the first arraignment better, not for any reason but I think it would be more stable over the long, as its not as long.

Tony I looked up the battery you suggested on a facebook post. the price was around 270 bucks or so for most links. For less money with lithium these days you can diy a battery with more capacity. You do need to look in to lifepo4, but I suspect you 3 years from needing to do so.

[rjgimp]

I repaired a blown up 450 watt inverter I had accidentally crossed the contacts on a while ago. The sticker said: “Warning! Do not disassemble. No serviceable parts inside.”

Warning...? Yeah, kiss my....

LOL!!!! Well done. Nice when you can resurrect a useful item out of the scrap heap.

[tony.latham]

I personally like the first arraignment better, not for any reason but I think it would be more stable over the long, as its not as long.

Tony I looked up the battery you suggested on a facebook post. the price was around 270 bucks or so for most links. For less money with lithium these days you can diy a battery with more capacity. You do need to look in to lifepo4, but I suspect you 3 years from needing to do so.

It was $220 three years ago. I would still recommend a good AGM. I think DIYing a lithium is still a bit over the top for most folks.

Tony


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[lfhoward]

The lithium will be replacing three group 24 flooded lead acid batteries. They are marine deep cycle batteries, are only a year old, and there is nothing wrong with them other than they weigh 150 pounds and can’t perform as well as LiFePO4. I probably should be waiting a few years too but found a great deal from a local business. That and I love to tinker with tech stuff like this.

On the other hand, if anyone reading this thread wants a great deal on some nearly new FLA’s once I get the lithium installed, send me a PM. This also goes for the battery charger and solar charge controller that I’ll have to replace in order to charge the new lithium cells.

[bdosborn]

<snip> I think DIYing a lithium is still a bit over the top for most folks

Yeah, the learning curve is pretty steep and unless you like messing with electrical stuff, lead acid is the way to go for folks who just want to run some lights and a fan.

Bruce