When making DIY battery packs, a spot welder is often needed to attach nickel strips to cells. But can we replace a commercial spot welder with a simple 12V battery? Is it really possible? In this post, we’ll explore the theory, test conditions, and real-world applications to find out.     How Spot Welding Works and What It Requires Spot welding fuses a nickel strip to a battery cell by passing high current for a very short time, generating enough heat to bond them. The core requirements are: High current output: More than 50A in a short pulse Short contact time: Ideally 0.1 to 0.3 seconds Proper conductors: Thick copper wires or silicone cables are necessary While a 12V sealed lead-acid battery isn't optimized for high current bursts, it may still be suitable for small-scale tasks like welding just a few cells.     What Makes 12V Batteries Viable for Spot Welding? Sealed Lead Acid (SLA) batteries have higher inte...

When a battery pack shows 0V across its P+ and P− terminals despite having good cell voltage, it's possible the discharge MOSFET is disabled due to protection lockout. In such cases, temporarily bypassing the MOSFET can help "wake up" the BMS.     1. Why Bypassing the Discharge FET Works The discharge MOSFET controls current flow to external loads. If the BMS controller detects a fault (e.g., undervoltage), it shuts off the gate signal, keeping the FET off and output voltage at 0V. A brief manual connection between P− and B− can restore normal state. P−: BMS output ground controlled by discharge FET B−: Main battery ground connected to cell negative terminal P+: Positive terminal (usually directly connected to B+)     2. Step-by-Step Bypass Test Set your multimeter to DC voltage mode. Measure voltage across P+ and P−. If 0V, proceed to the next step. Using an insulated wire or test lead, briefly connect P− t...