Introduction: 24V Mini PowerWall Using 6S Lithium-ion 18650 Cells

By www.vu3pyn.com
About: A hobbyist who loves to explore new technology & a proud HAM Radio Operator with call - VU3PYN

Here you will realize how you can build a 24v Mini Powerwall using 6S Lithium-Ion Cells.

This build includes,

  1. Wire Fuse Protection for each cell.
  2. Battery protection against Over Charge, Over Discharge protection using BMS.
  3. Cell Balancing with retrofit 6S balancer.

Step 1: Building Materials Required

  1. 18650 Cell Holder (4 Cell holder Block) - 12 No
  2. 22cm x 9cm PCB General Purpose PCB - 6 No
  3. 6S BMS with Over Charge/Discharge Protection(With Cell Balancing preferable) - 1No
  4. 6S Cell Balancer(If the balancing feature is not part of BMS) - 1No
  5. Fuse Wire 5A Tinned Copper Wire.(lesser than the individual cell 'C' ratings)
  6. Copper Rod to act as Bus Bar.
  7. Silicon wire 16 AWG
  8. XT60 Connectors
  9. Heat Shrink Sleeve
  10. Insulating Sheet
  11. Circuit Breaker (Optional)
  12. Fuse 10A (Rating shall be based on Load and Battery capability)Fuse Holder

Step 2: Tool Required

  1. Soldering Iron - capable of heating above 300 degree
  2. Soldering consumables
  3. Drilling Machine
  4. Glue - To stick the insulation sheet
  5. Measuring Tape/Instrument
  6. Wire cutter/ Stipper
  7. Knife
  8. Digital Multimeter

Step 3: Placing the Cell Holder to PCB

Place the 18650 cells holder to PCB by drilling holes to the PCB. Repeat the same to fit in 2 holder in a PCB on six sets.

Step 4: Connect the Copper Rod

Once the Battery Holders are placed to the PCB use the Copper rod and solder them as shown in the picture.

Step 5: Soldering Wire Fuse

One of the side of 18650 holder shall be soldered together with copper rod and the other side shall be fused with the tinned copper wire to the copper rod as shown in the picture.

Step 6: Making the 6S Connection

Mark the Positive (+) and Negative (-) sides of each PCB with a Marker on both sides of the PCB.

Connect each PCB to the other one as shown in the diagram/pictures.

Tip: Make sure the terminals of each boards are at opposite side, if one terminal is at the top then the other terminal should be at the bottom, By doing so the current shall evenly flow across all cells.

Step 7: Soldering the Terminals

Solder the Silicon wire as shown in the picture, use any clamp to hold the silicon wire tight to the PCB. This helps in making fine soldering joints.

Step 8: Check the Connections

Once the 18650 Battery holders were soldered to the PCB cross check the connection, to make sure there are no short / open circuit.

Step 9: Insulating the Conductive Side of the PCB

This is one of the important stages, make sure the conductive sides of the PCB's are insulated properly to avoid any accidental short circuit.

I my case i have used Class B insulation sheet which is really good against conduction.

Step 10: Connecting BMS

Here comes the electronics integration part:

As shown in the figure solder the XT60 pigtail to the 6S BMS and connect the Sense wire to B-, B1, B2, B3, B4, B5 & B+. Make sure the connection are properly made to avoid battery shorts which may result in safety hazards.

Hence proper connections and insulation are very much important.

Step 11: Connecting 6S Balancer

As illustrated in the diagram proceed connecting the wires to the 6S Balancer. Make sure you use a wire that is capable of carrying 1A current. This Balancer acts as a Top Balancer, means it start doing its balancing job only when any of the six branches reaches 4.2V.

Step 12: Insulating Connectors and Sense Wires

On all my steps explained, you would have seen me emphasising on insulation because it is very much important. Zero Tolerance toward shorts as it will create safety hazard.

Step 13: Testing

Its time to test the build.

  1. Take six cells in hand
  2. Check if the cells are healthy and at the same voltage
  3. Connect one by one to the holders.
  4. Check the voltage as shown in the image. you may use a digital voltmeter or a Cell meter as shown in the picture

Step 14: Safety Tips:

  1. Use a fuse in Series with any of the battery terminal.(Shown in image)
  2. Use a circuit breaker in series to isolate the battery pack / Powerwall when not in use.(Shown in image)
  3. Select the right wire fuse which is soldered to one side of the cells(Step-5). "Faster it Blow, Safer it is"
  4. Select the rite 18650 cells for your use, either use a new one or test each cell before use.

"Stay Safe and Keep Creating"

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Caution: Do Not Try this at home if you are unaware of the Risks involved with Lithium Ion Batteries.