Build Battery Packs
Cells
- DIY500AMP.COM
- Order #1584 2025-09-25
- Ampace JP40 "LT Wrap" 21700 4000mah 70A Battery - Tabless Cell × 120
- Subtotal $474.00 Shipping $22.99 Total $496.99 USD
- Order #3924 2026-09-09
- Ampace JP40 "LT Wrap" 21700 4000mah 70A Battery - Tabless Cell × 1 $5.99
- FEB 21700 Battery Cell – 6500mAh 13A Ultra High Capacity Energy Cell × 30 $224.70
- Subtotal $230.69 Shipping $10.80 Total $241.49
Welder
- Heltec HT-SW02H
- Manual
- Order #114-4340207-9060214 2025-10-30
- Spot Welder & Milliohm Meter
- 42 KW 7000A Capacitor Energy Storage Pulse Welding Machine
- Subtotal $729.90 Tax: $43.79 Total: $773.69
Battery Case
- 15 cell m18 kit (8 batteries)
- $389.20
Cost
- Me: $497+$774+$390=$1660
- Milwaukee (with worse cells): $279*8=$2232
Balancer
- Balancer: 2A Active Balancer 2S–24S with Built-in Bluetooth RS485 and Temp Sensor for LiFePO4 Li-ion LTO 20V–100V Smart Equalizer Module (JK-DZ11-B2A24S)
- HD26 connectors: shipping
- male CN-DSUBHD26PN-000
- female CN-DSUBHD26SK-000
- 20 wire ribbon 28AWG
- 24x 21700 Sleds
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Balancer pinout:
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1 Cell 18
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2 Cell 19
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3 Cell 20
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4 Cell 21
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5 No connection
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6 No connection
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7 No connection
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8 Cell 24
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9 NEGATIVE
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10 Cell 9
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11 Cell 10
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12 Cell 11
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13 Cell 12
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14 Cell 13
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15 Cell 14
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16 Cell 15
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17 Cell 16
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18 Cell 17
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19 Cell 8
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20 Cell 7
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21 Cell 6
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22 Cell 5
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23 Cell 4
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24 Cell 3
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25 Cell 2
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26 Cell 1
Assembly
DIY Charger
Cell Information for Packs
| Parameter | Why It Matters | Target Variance |
|---|---|---|
| 1. Discharge Capacity ($\text{mAh}$ / $\text{Wh}$) | Sets the total energy reservoir. The weakest P-group determines when the entire pack's BMS cuts off. | $\le 1%$ variance across parallel groups |
| 2. Internal Resistance ($m\Omega$) | Governs voltage sag under load and heat generation. In parallel, low-IR cells do more work; in series, high-IR cells heat up faster. | $\le 5%$ variance across parallel groups |
| 3. Self-Discharge Rate ($\Delta V / \Delta t$) | Cells that bleed voltage while idle will constantly pull down their parallel group, overworking the BMS balance circuits. | Eliminate outliers (reject self-discharge $> 0.01\text{V}$ / week) |
| 4. Voltage Recovery Curve | How fast voltage bounces back after a load is removed. Indicates internal chemical health and degradation. | Reject cells that lag significantly behind the group recovery slope |
| 5. Thermal Delta under Load ($\Delta T$) | Temperature rise during a sustained high-current discharge. | Reject cells that run $> 5^\circ\text{C}$ hotter than the batch average |
Equipment for 21700 Cell Profiling
| Metric / Parameter | Primary Tool Recommendation | Primary Function |
|---|---|---|
| 1. Discharge Capacity ($\text{mAh}$ / $\text{Wh}$) | SkyRC MC3000 $\rightarrow$ BLE Wireless $\rightarrow$ ESP32 Dev Board $\rightarrow$ TTL UART $\rightarrow$ MAX3232 $\rightarrow$ RS-232 Wire $\rightarrow$ ZPE Console Server | Automated C–D–C (Charge-Discharge-Charge) cycling with custom voltage cutoffs ($2.5\text{V}$–$2.8\text{V}$). |
| 2. Internal Resistance ($m\Omega$) | YAOREA YR1035+ $\rightarrow$ TTL to RS232 $\rightarrow$ console server | $1\text{kHz}$ AC 4-wire Kelvin resistance measurement, bypassing contact resistance noise. |
| 3. Self-Discharge ($\Delta V / \Delta t$) | Fluke 87V | High-resolution voltage tracking across a 7- to 14-day resting phase to catch micro-shorts. |
| 4. Voltage Recovery Curve | ZKETECH EBD-A20H $\rightarrow$ GX12-4pin Male Aviation Connector $\rightarrow$ ESP32 $\rightarrow$ TTL to RS232 $\rightarrow$ Console Server | High-rate real-time logging of voltage rebound immediately after removing discharge load. |
| 5. Thermal Delta ($\Delta T$) | K-Type Glass Bead Thermocouple $\rightarrow$ K Type Thermocouple Module $\rightarrow$ MAX31855 $\rightarrow$ ESP32 $\rightarrow$ MAX3232 | Direct surface temperature tracking during high-amp continuous discharge ($10\text{A}$–$20\text{A}$). |
- Device setup
- YAOREA YR1035+
- serial output mod
- Calibration setup:
| Component | Example Part / Model | Source | Est. Cost | Purpose / Function |
|---|---|---|---|---|
| 10mΩ Resistance Standard | Vishay / Dale WSL402610L00FEA or Ohmite FC4L110R010FER (10mΩ, 0.1%, 4-terminal) | DigiKey / Mouser | ~$4.00 | 20mΩ Range Calibration. Low AC inductance metal foil resistor for low-IR cell verification. |
| 100mΩ Resistance Standard | Vishay Y14880R10000B9R or Ohmite FC4L110R100FER (100mΩ, 0.1%, 4-terminal) | DigiKey / Mouser | ~$4.00 | 200mΩ Range Calibration. Calibration standard for higher-IR cells or module assemblies. |
| Breakout PCB / Terminal Board | Custom 4-wire SMD test PCB or generic SOP/SOT adapter board | OSH Park / Amazon | ~$3.00 | Holds the SMT sense resistors cleanly and exposes 4 isolated solder pads for Kelvin clips. |
| DC Voltage Reference Board | AD584LH / AD584KH Precision Voltage Module | eBay / AliExpress / Amazon | ~$15.00 | Voltage Calibration. Outputs 2.500V, 5.000V, 7.500V, and 10.000V with factory DMM calibration slip. |
| 4-Wire Kelvin Test Clips / Leads | High-quality gold-plated Kelvin clips | Amazon / eBay | ~$8.00 | Dedicated test harness to ensure zero contact resistance during calibration passes. |
Safety Equipment and PPE
| Equipment Category | Item | Function & Primary Hazard Mitigation | Essential Specifications |
|---|---|---|---|
| Personal Protection | Full-Face Shield | Face protection from molten nickel spatter during spot welding and high-current arc flashes. | ANSI Z87.1 rated, worn over safety glasses |
| Class 00 Insulated Gloves | Prevents shock and accidental short circuits across exposed high-voltage series strings. | Rated for 500V AC / 750V DC working voltage | |
| Multi-Gas/P100 Respirator | Respiratory protection against toxic HF (hydrofluoric acid) vapor and organic solvents during cell venting. | Organic Vapor / Acid Gas cartridge combination | |
| Bench Infrastructure | Flame-Retardant Silicone Mat | Heat protection for the workbench during soldering and short-circuit containment. | 500°C temperature rating |
| 1000V VDE Insulated Hand Tools | Prevents accidental cross-terminal shorts when tightening busbars or installing balance wires. | IEC 60900 certified cutters, pliers, and wrenches | |
| Kapton / Polyimide Tape | Electrical insulation across cell shoulders, nickel crossovers, and ungrounded sensor probes. | High dielectric strength, 260°C thermal limit | |
| Thermal Emergency | AVD / Lith-Ex Fire Extinguisher | Direct cooling and thermal insulation to interrupt thermal runaway propagation. | Aqueous Vermiculite Dispersion agent |
| High-Temp Battery Fire Blanket | Containment cover for active thermal events, containing flaming debris and smothering surface fires. | Heavyweight 100% woven high-silica fabric (1000°C+ rating) or 4–6 folded layers of heavy fiberglass | |
| Heavy Aramid / Welding Gauntlets | High-temperature hand protection to manually evacuate a venting/hot cell to an outdoor safe zone. | Split cowhide or Kevlar/Nomex lining | |
| Cell Storage | Vented Steel Ammo Cans | Physical containment for unstable, swollen, or quarantine cells. | Metal construction with rubber lid gasket removed |