# Parallel motors on the same output

Am I getting motors correct? I'm building a third party psu for a slot car race track. Obviously easy bit is transforming 240Vac down to 12Vdc. But I am unsure how thiswill react with my motor. THe motor is rated as 12Vdc at 0.42A. Am I correct in thinking that if the motor is corrected in series with rheostat (as thus to adjust the Volts suppled to the motor) it will slow down? Or will it for some reason decide to take even more than 0.42A

CHeeers Motor in question http://www.pendleslotracing.co.uk/scaleauto-short-can-motor-30000rpm-sc-0005.html

Also, the main issue. I've got two tracks which essentially act as uninsulated wires. On each loop the respective Rheostat will of course cause a Volt drop and therefore less p=iv into the M1. But conservation of enerhgy,that v drop will now of course go into M2. How can I make it so that the motors are independentanly speed controlled? I've heard of pwm or something but that is out of bounds.

• PWM is basically turning on and off really fast, but make it so the on to off ratio changes according to speed. Like ON for 0.5 milliseconds and OFF for 0.5 milliseconds and repeat this makes it go half speed. ON for 0.75 milliseconds and OFF for 0.25 milliseconds makes it go 3/4 speed. Although that is recommended, how about replacing the potentiometer with a MOSFET and connect the gate to a potentiometer acting as a voltage divider? – Bradman175 May 3 '16 at 23:57
• Motors will not like PWM directly since they are intensely inductive - i have the welded-shut 30A relays (on a 1A motor field) to prove it. You will want to add some snubbing to that PWM output so it becomes effectively a variable voltage DC-DC converter. – Harper - Reinstate Monica May 4 '16 at 0:06
• Thanks guys, we haven't learnt of pwm yet, (Only know it from pc heatsink fank) Is there a way I could split the DC output into 2 different circuits? such that R wil control their own M independently? – Iain May 4 '16 at 0:46
• @Harper relays won't work with PWM. You'd use a MOSFET, transistor or an optocoupler connected to a TRIAC. – Bradman175 May 4 '16 at 3:21
• I mentioned relays only as a cautionary tale as to how much inductive kick a motor has. – Harper - Reinstate Monica May 4 '16 at 3:24