Solutions to reduce start-up currents from multiple DC motors
There are a couple simple ways of doing this. The most straightforward is to slowly ramp up the voltage from zero instead of applying 12V all at once; this "spreads out" your inrush pulse and makes it a lower current for a longer time.



If your power supply is fixed, however, one simple option is shown below:







simulate this circuit &ndash; Schematic created using CircuitLab

There's a resistor to limit the current, along with a relay to short the resistor out when the motor is up to speed. This is similar to ramping up the voltage, as the resistor's resistance will reduce the voltage across the motor by an amount proportional to the motor current, and then the relay pulls the voltage the rest of the way up. The relay can also be any other type of switch that works for the currents and voltages needed; a MOSFET would be a perfectly acceptable choice as the application is DC.



You can also get what's called an inrush current limiter, which is simply a thermistor with a negative temperature coefficient. As current passes through the ICL, it heats up and its resistance drops, eventually balancing out with the motor current. You can also use an ICL in conjunction with a relay as above, which helps reduce the power lost in the ICL.



Note that relays used in this way do not necessarily need to be rated to break the full motor current. If you can ensure that the relays do not open while the motors are still spinning, you can use cheaper relays.