well looks like AI just told me how too do so does this sound and look correct
Combining lithium polymer (LiPo) batteries to achieve a higher capacity (mAh) and specific voltage (22.2V, 6S) while maintaining a single balance port is a complex task that requires careful consideration of electrical principles, safety, and compatibility. Since you’re working with your 1/7 Big Rock 6S monster truck, which runs on a 6S (22.2V nominal) system, I’ll break this down step-by-step based on what you’ve provided: two 3S 5000mAh packs and one 6S 5000mAh pack. Your goal is to create a single 6S 15000mAh pack with one balance port. Let’s dive in.
### Understanding Your Batteries
- **2x 3S packs**: Each is 11.1V (nominal), 5000mAh, 150C (claimed), 55.5Wh. These are 3-cell packs, meaning 3 cells in series (3S).
- **1x 6S pack**: 22.2V (nominal), 5000mAh, 111Wh. This is a 6-cell pack, meaning 6 cells in series (6S).
- **Goal**: A single 6S (22.2V) pack with 15000mAh capacity and one balance port.
To achieve this, you need to:
1. Convert the two 3S packs into a single 6S 5000mAh pack by connecting them in series.
2. Combine this resulting 6S 5000mAh pack with your existing 6S 5000mAh pack in parallel to increase capacity to 15000mAh (while keeping voltage at 22.2V).
3. Rewire the balance leads to create a single 6S balance port.
### Step 1: Combine 2x 3S into 1x 6S (Series Connection)
- **Series connection increases voltage**: Connecting two 3S (11.1V) packs in series gives you 6S (22.2V). The capacity remains 5000mAh because series connections add voltage, not capacity.
- **How to do it**:
- Identify the main power leads on each 3S pack: positive (red) and negative (black).
- Connect the negative lead of the first 3S pack to the positive lead of the second 3S pack. This junction is the “middle” of your new 6S pack.
- The free positive lead from the first pack becomes the positive of your new 6S pack, and the free negative lead from the second pack becomes the negative.
- **Balance leads**: A 3S balance connector has 4 wires (1 ground + 3 cell taps). For two 3S packs:
- Pack 1: Wires are Ground, Cell 1, Cell 2, Cell 3.
- Pack 2: Wires are Ground, Cell 1, Cell 2, Cell 3.
- To make a 6S balance connector (7 wires: 1 ground + 6 cell taps):
- Ground of Pack 1 is the ground of the new 6S pack.
- Cell 1, Cell 2, Cell 3 of Pack 1 become Cell 1, Cell 2, Cell 3 of the 6S pack.
- Ground of Pack 2 (connected to Cell 3 of Pack 1 via the main leads) becomes Cell 3.
- Cell 1, Cell 2, Cell 3 of Pack 2 become Cell 4, Cell 5, Cell 6 of the 6S pack.
- Splice these into a single 7-pin balance connector (e.g., a 6S JST-XH connector).
- **Result**: A single 6S (22.2V), 5000mAh pack with one balance port.
### Step 2: Combine 2x 6S Packs into 1x 6S 15000mAh (Parallel Connection)
- **Parallel connection increases capacity**: You now have two 6S 5000mAh packs (the one you just made and your original 6S pack). Connecting them in parallel keeps the voltage at 22.2V but adds capacity: 5000mAh + 5000mAh + 5000mAh (from your original intent) = 15000mAh.
- **How to do it**:
- Ensure both 6S packs are at the same voltage (within 0.1V per cell) before connecting. Charge or discharge them individually to match voltages using a charger with a balance function.
- Connect the positive leads of both 6S packs together and the negative leads together. Use heavy-gauge wire (e.g., 10AWG) and a high-current connector (e.g.,
XT90 or EC5) to handle the combined current (150C * 15Ah = 2250A peak, though realistic draw will be lower).
- **Balance leads**: Each 6S pack has a 7-pin balance connector. To combine into one:
- Connect the ground wires together.
- Connect each corresponding cell tap (Cell 1 to Cell 1, Cell 2 to Cell 2, etc.) between the two packs.
- Splice these into a single 7-pin 6S balance connector.
- **Result**: A single 6S (22.2V), 15000mAh pack with one balance port.
### Important Considerations
1. **Cell Matching**: All cells (across the two 3S packs and the 6S pack) should ideally be the same brand, capacity, and age for consistent performance. Mismatched cells can lead to uneven discharge or charging, risking damage or fire.
2. **C-Rating**: Your packs are rated 150C, but as you noted, these claims are often exaggerated. In parallel, the effective C-rating may not scale perfectly, but total current capability increases (e.g., two 5000mAh 150C packs in parallel theoretically deliver 1500A combined). Check your truck’s ESC and motor max current draw (likely 100-200A) to ensure compatibility.
3. **Safety**: LiPo batteries are volatile. Use a fireproof bag during charging/testing, monitor temperatures, and double-check connections with a multimeter before use.
4. **Charging**: With a single balance port, charge as a 6S pack at 1C (15A max, though 5-10A is safer with most chargers). Ensure your charger supports 6S and has enough power (e.g., 22.2V * 15A = 333W minimum).
5. **Physical Setup**: Secure the packs together (e.g., with straps or a custom tray) to fit your Big Rock’s battery compartment.
### Alternative Approach
If rewiring balance leads feels daunting, you could:
- Use a parallel harness for the two 6S packs (after converting the 3S packs to 6S) and keep separate balance ports. Charge them individually or with a parallel charging board. This avoids soldering but sacrifices the “single unit” goal.
### Testing Runtime
- **Single System**: With 15000mAh at 22.2V (333Wh), runtime depends on your truck’s power draw. At 100A average (typical for a 6S monster truck bashing), you’d get ~9 minutes (15000mAh / 100A = 0.15h). Real-world runtime varies with throttle use and terrain.
- **Split vs. Single**: Test your stock 6S 5000mAh alone (111Wh) vs. the combined 15000mAh (333Wh). The single setup should triple runtime if draw remains constant.
### Final Thoughts
This is doable but requires soldering skills, patience, and safety precautions. If you’re unsure about rewiring balance leads, consult an RC hobby shop or electrician familiar with LiPo packs. Let me know if you need help with specific wiring diagrams or troubleshooting! How’s the Big Rock been treating you otherwise?
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