Woody
Solar Enthusiast
My DIY LiFePO4 Battery Build Experience - Part 1
Summary: Was is worth it…yes from a learning experience but no because I thought I only would have to assemble and go. Who knew I had to become a battery manufacture? I just wanted affordable high capacity batteries.
=====================================================================
Background:
Around the fall of 2020 I started my search once again for a battery for emergency backup system. I always like the amount of available energy big Flooded Lead Acid (FLA) forklift battery could provide, and the used market wasn’t too bad on these reconditioned batteries. Used forklift batteries was the way to go over the years if you had the means to move them about. However, the price was still rather high for a battery that would be left in a standby state. As times were becoming more dynamic and unstable, it was time to start looking again for something. In reviewing the available FLA batteries there was a couple ways to go. Banked style where the cells are contained in a steel bin and all connected or modular aka single cell that you have to connect together. I favored the single cell approach since you could move one piece at a time verse one massive battery. Price was rather high for the available amp hours. In my searches, going back a little over a year ago is when I found online these amazing videos talking about LiFePO4 batteries. There was this very excited guy talking about solar energy, his experience with it, and more. Yeah it was Will! Will’s videos on LiFePO4 batteries got me very interested in them. Seemed oh so easy to do it yourself that after a few months I decided to try to assemble one. After all I’m an EE doing solar for ages and I have the fabrication equipment and skills, so piece of cake.
Here’s what I’ve built.
Build 1: (12v 4S) 200Ahr LiFePO4 cells, 4 of them, purchased online via a dealer who had stock in the USA and would deliver in a few days. Big dollars for get these batteries NOW vs pay and hope the came in from China. The batteries that came were very nice. Had the laser welded bolt stud for attaching the cable. Ordered the BMS Will’s recommended via OBS. This was a 12v setup so a simple 4S configuration. --- Overkill BMS 120Amp
Build 2: (24v 2P8S) 280Ahr LiFePO4 cells, 16 of them, purchased online via AliExpress. Boy that was a big concern. Big dollars to me and I hoped and prayed all would go ok. After a long wait, the shipment did finally arrived. The protracted shipping time was not the seller’s issue but huge backlog in shipments going across the ocean. --- Overkill similar BMS Only 60amp but will use the BMS as a battery monitor and as a controller to enable/disable a power feed to the inverter via solid state relays.
Build 3: (12v 4S) 100Ahr LiFePO4 cells, 4 cells, purchased via AliExpress. Another 12v battery system --- Overkill similar BMS 120Amp
Build 4: (12v 4S) 200Ahr LiFePO4 cells, 4 cells, purchased via AliExpress. Another 12v battery system --- Overkill similar BMS 120Amp
Additional Tools/Materials:
For all the equipment and tools that I already had, I still need additional items to support these builds including:
Lastly, I had to purchase a new LiFePo4 capable shore power chargers (PD9180ALV) and MPPT chargers. The older ones I have are all for lead acid. The only item that I choose not purchase to support the build process that many do, was an active or passive loads for capacity testing device. I choose not to perform discrete load/capacity testing on the cells. This process would require more of my time and money that I just didn’t want to consume.
DIY Battery Build Issues/Considerations:
Studs/Bolts/Nuts and Stripping:
Terminal holes on the 280Ahr cells were not drilled perpendicular. I had to customize bending each stud for holes. Then I used Loctite to secure the studs to the cell terminals. The bus bars that I fabricated have a center terminal stud so that I could tighten sensors/cables to it and not touch the nuts attached to the cell’s terminal studs again. The idea was to reduce the amount of tightening and loosening of the connections/nut at the cell terminals.
Cell Insulation:
To insulate between cells or is the blue plastic covering enough? I followed the suggestion of another DIY forum member who recommended the thin Dollar Store plastic cutting board as an affordable way to add additional electrical isolation between the cells.
Battery Box HVAC?
Do you include a heating pad and controls with cells or keep the battery in a heated environment? How about cooling if located in a high temperature location? I skipped all of this and will keep them in an temperature controlled space instead.
To Compression or Not To Compress, That tis the question:
I choose to use Kapton tape the cells together and then structural constrain them to keep them from moving about. So, the cells are constrained but no additional compression applied.
Bus Bars:
Copper or Aluminum, Rigid or Flex – I went with solid copper bus bars but time will tell if I should have used flexible cable instead. This cell bloating is a concern since this can cause a lot of stress on the terminal studs when using solid bus bars. Properly managing the charge/discharge process along with a conservative depth of charge / discharge (10-20% off low/max values) should help reduce any bloating and extend battery life.
Summary: Was is worth it…yes from a learning experience but no because I thought I only would have to assemble and go. Who knew I had to become a battery manufacture? I just wanted affordable high capacity batteries.
=====================================================================
Background:
Around the fall of 2020 I started my search once again for a battery for emergency backup system. I always like the amount of available energy big Flooded Lead Acid (FLA) forklift battery could provide, and the used market wasn’t too bad on these reconditioned batteries. Used forklift batteries was the way to go over the years if you had the means to move them about. However, the price was still rather high for a battery that would be left in a standby state. As times were becoming more dynamic and unstable, it was time to start looking again for something. In reviewing the available FLA batteries there was a couple ways to go. Banked style where the cells are contained in a steel bin and all connected or modular aka single cell that you have to connect together. I favored the single cell approach since you could move one piece at a time verse one massive battery. Price was rather high for the available amp hours. In my searches, going back a little over a year ago is when I found online these amazing videos talking about LiFePO4 batteries. There was this very excited guy talking about solar energy, his experience with it, and more. Yeah it was Will! Will’s videos on LiFePO4 batteries got me very interested in them. Seemed oh so easy to do it yourself that after a few months I decided to try to assemble one. After all I’m an EE doing solar for ages and I have the fabrication equipment and skills, so piece of cake.
Here’s what I’ve built.
Build 1: (12v 4S) 200Ahr LiFePO4 cells, 4 of them, purchased online via a dealer who had stock in the USA and would deliver in a few days. Big dollars for get these batteries NOW vs pay and hope the came in from China. The batteries that came were very nice. Had the laser welded bolt stud for attaching the cable. Ordered the BMS Will’s recommended via OBS. This was a 12v setup so a simple 4S configuration. --- Overkill BMS 120Amp
Build 2: (24v 2P8S) 280Ahr LiFePO4 cells, 16 of them, purchased online via AliExpress. Boy that was a big concern. Big dollars to me and I hoped and prayed all would go ok. After a long wait, the shipment did finally arrived. The protracted shipping time was not the seller’s issue but huge backlog in shipments going across the ocean. --- Overkill similar BMS Only 60amp but will use the BMS as a battery monitor and as a controller to enable/disable a power feed to the inverter via solid state relays.
Build 3: (12v 4S) 100Ahr LiFePO4 cells, 4 cells, purchased via AliExpress. Another 12v battery system --- Overkill similar BMS 120Amp
Build 4: (12v 4S) 200Ahr LiFePO4 cells, 4 cells, purchased via AliExpress. Another 12v battery system --- Overkill similar BMS 120Amp
Additional Tools/Materials:
For all the equipment and tools that I already had, I still need additional items to support these builds including:
- Kapton and Double Stick Tape
- 4 wire voltage / internal resistance meter YR 1035+
- Bench Power Supply (old ones couldn’t support the high current low voltage)
- Copper bus bar & Cables (needed more not enough on hand)
- 6mm Stainless nuts, washers, studs, … (Nothing this small s had to order)
- Clamp on DC amp meter (old ones OK but wanted a better one) UNI-T UT210D
- Cables/Lugs/Heat Shrink (Needed more that what I had already)
- Fuses / Breakers / Switches (Needed more than what I had already)
- Panel Volt/Amp/WattHr Display
- Plastic cutting boards
DIY Battery Build Issues/Considerations:
Studs/Bolts/Nuts and Stripping:
Terminal holes on the 280Ahr cells were not drilled perpendicular. I had to customize bending each stud for holes. Then I used Loctite to secure the studs to the cell terminals. The bus bars that I fabricated have a center terminal stud so that I could tighten sensors/cables to it and not touch the nuts attached to the cell’s terminal studs again. The idea was to reduce the amount of tightening and loosening of the connections/nut at the cell terminals.
Cell Insulation:
To insulate between cells or is the blue plastic covering enough? I followed the suggestion of another DIY forum member who recommended the thin Dollar Store plastic cutting board as an affordable way to add additional electrical isolation between the cells.
Battery Box HVAC?
Do you include a heating pad and controls with cells or keep the battery in a heated environment? How about cooling if located in a high temperature location? I skipped all of this and will keep them in an temperature controlled space instead.
To Compression or Not To Compress, That tis the question:
I choose to use Kapton tape the cells together and then structural constrain them to keep them from moving about. So, the cells are constrained but no additional compression applied.
Bus Bars:
Copper or Aluminum, Rigid or Flex – I went with solid copper bus bars but time will tell if I should have used flexible cable instead. This cell bloating is a concern since this can cause a lot of stress on the terminal studs when using solid bus bars. Properly managing the charge/discharge process along with a conservative depth of charge / discharge (10-20% off low/max values) should help reduce any bloating and extend battery life.