HOW TO BUILD A LiFePo4 SOLAR BATTERY FROM SCRATCH.


This battery is non-combustible, cheap, lasts a really long time, has a great discharge/charge rate, works with standard 12/24 volt equipment and more! Probably the easiest way to get started with DIY lithium batteries.

12v Battery


24v Battery

24v Battery

There are 6 crucial things that you  need if you plan to use a custom-built lithium iron phosphate battery:

There are 6 crucial things that you  need if you plan to use a custom-built lithium iron phosphate battery:

  1. Low-Temperature Cut-off or Heating System: Lithium batteries can NOT be charged when the internal cell temperature is below 0 degrees Celsius. If it is charged below this temperature, it will be permanently damaged and will be unsafe to charge. Try to find a solar charge controller with low-temperature cut-off, or build your own thermostat controlled heater pad to keep the battery warm. I am keeping my battery in my living area so it stays nice and warm during the winter. The easiest way to build a low temp cut off is to buy the Victron charge controller mentioned in the parts list of this page, and buy the battery temperature sensor from Victron. It costs a little bit, but it takes seconds to program and anyone can do it. This is the best way for a beginner to do this!
  2. MPPT Charge Controller Capable of Charge Profile Editing: Each lithium battery will require a different max charge voltage. For a 4 or 8 cell LiFePo4 battery (12v/24v) with new healthy cells, we can use the standard “sealed lead acid” setting on our solar charge controller. This will prevent charging over 14.4-14.6 volts and works great. If you want added protection, and increased longevity, charge to 13.3 volts, and set the float to 13.2 volts. (more information on this at the bottom of the page)
  3. Over-Discharge Protection System: If you over-discharge a lithium battery, it will change the chemistry of the battery and permanently damage it, and it will be unsafe to charge again. To ensure that this never happens, the battery should be able to disconnect itself from loads of your system if it is discharged too low. You can build your own relay system, or simply buy a “Victron Battery Protect” (click here) and program the low voltage disconnect for your battery (more on this soon). 
  4. High-Temperature Protection: If your system will be in a high-temperature environment, or discharging at high c ratings that it’s not designed for, you will need a battery cell cooling system. For solar power systems, lithium batteries rarely need a cooling system. So typically, this is not a big deal at all. But you can add a battery cooling system if you wish.
  5. Bottom Balancing the Cells: This is REQUIRED when first building a LiFePO4 battery. And it is very easy to do. Slowly discharge the cells to 5-10%  capacity while watching the balance of the cells. When the battery is nearly depleted, balance the cells. Then charge it back up again.  Discharge again and watch the balance of the cells. If they are bottom balanced properly, they should be nearly the same voltage when nearly depleted. This will ensure that none of the cells will dip to too low of a voltage when the battery is discharged. 
    Bottom balancing is recommended for solar because you want your SOC to float around 50%.  If you have a small battery, mismatched/used cells, chargers that only charge to 14.5 volts (and cannot be edited), you should top balance. More on this at the bottom of the page (or watch this video)
  6. Intermittent Cell Balancing: This may or may not apply to you. If you are charging and discharging from 100% to 0% at high c ratings, your cells will go out of balance over time and you will need to balance them. Most lifepo4 packs used for solar will not go out of balance, but it is wise to check the balance every couple of months. Lately, I have grown to love “active cell balancers” with my lifepo4 packs. They are super cheap (under $20), and if your packs ever do go out of balance, an active balancer will balance the cells extremely fast. Great insurance to have one! Takes seconds to install and you just leave it on your pack and forget it.

You can use a dedicated BMS for your LiFePO4 battery to manage various safety features, but you don’t need one. You can build safety protection features as you please. Also, understand that many BMS available online are cheaply made and will fail before the battery does. Many EV/marine forums people agree that a BMS is more of a liability than a benefit unless you spend the big bucks. High-quality BMS are so expensive that you are better off buying a drop-in lead-acid replacement lifepo4 as the battle is born, that has an actual warranty and will last for ages (click here to learn more). If you are trying to build a super-cheap battery with good LiFePO4 cells, and you follow the instructions on this page and add the most basic safety features, you won’t need a BMS.

PSC SOLAR LTD

PSC INDUSTRIES LIMITED is a Solar Electricity and Renewable energy total Solutions Manufacturer located in Lagos, Nigeria. We provide Cost-competitive, Environmental friendly, high quality and innovative Solar/renewable energy products including but not limited to Solar PV Panels, Inverters, Solar Charge Controllers, Solar Streetlights and Deep Cycle Batteries.

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