By Michael O. Smathers
Updated March 24, 2022
Adding a second DC power supply in parallel is a common technique to boost the available current for experimental circuits. In a parallel arrangement, each supply contributes to the load, effectively sharing the current and extending runtime. For example, a 60 Ah battery powering a 1 A load would last 60 hours; two identical batteries in parallel would sustain the same load for 120 hours because each delivers 0.5 A.
Use insulated alligator clips to attach the positive and negative terminals of the first 9‑V battery to the corresponding contacts on the load. Leave the second lead open until the second battery is in place.
Cut and strip a length of insulated copper wire as needed to reach the first battery.
Place the second battery next to the first and join their positive terminals with a short length of wire or a dedicated terminal block.
Repeat the connection for the negative terminals, ensuring both ends are secure and insulated.
Reconnect the previously disconnected lead to the load, closing the parallel loop. Verify that all connections are tight and insulated.
Parallel wiring is a straightforward method to double the current capacity of a DC circuit; the same principle applies to more complex setups.
Verify that both batteries are identical in voltage, age, and health. Avoid using leaky or damaged cells, and handle alligator clips by the insulated part to prevent accidental short circuits.
