Hey PF, first time here, I have a problem I can't seem to solve! Any help is appreciated. I am using some DC motors with peristaltic pump heads to pump water (picture). I was having issues so I've broken my circuit down to the bare basics: 1) 12V regulated power supply 2) 12V motor 3) free-wheel diode That's all that's plugged in, the power pack is connected directly to the motor. The voltage measured across the power pack is 12V open circuit. For each motor I add (in parallel) the voltage measured at the power pack drops by 0.2-0.5V. I've measured (with a multimeter in current mode) 450mA being drawn by the motors. I've tried 2 power packs, a 12V 1.5A, and a 12V 5A, both regulated. Interestingly, while each pump dropped the voltage by 0.2V on the 1.5A supply, they dropped it by 0.5V on the 5A supply. The issue is that I need to control an accurate amount of water flow, which needs a consistent voltage regardless of the number of pumps used at any time. Other searching has returned that maybe the backEMF of the motors is to blame, but I'm at a loss how to solve this.