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I currently have a variable DC power supply, a cheapo china one 0-30v 0-5A that can be constant current or constant voltage. It's helped me a lot until my recent project where I need 12v at 30A. A brand-name variable power supply of this capability costs $250-$600 and I'm just a poor college student.

The Question:

If I bought a $40 12v 40A power supply from Amazon or ebay or whatever, could a DC motor controller (PWM type) make that into variable voltage from 0-12V? Obviously there'd be no current readout or constant current capability, but I don't really need that for this project.

The DC motor controller: http://www.ebay.com/itm/10-50V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V-48V-2000W-MAX-/370962506627?hash=item565f16a383:g:LusAAOxyFjNSORPa

Power Supply: http://www.amazon.com/uxcell%C2%AE-100-220VAC-12VDC-Switching-Supply/dp/B00H8W6GKQ/ref=sr_1_1?rps=1&ie=UTF8&qid=1456433505&sr=8-1&keywords=12v+40a&refinements=p_85%3A2470955011

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  • \$\begingroup\$ Related Question: If that same 40A power supply were to be attached to a load that demands 30A instantaneously, how horribly would that go and what would be a better way? \$\endgroup\$ Commented Feb 25, 2016 at 22:46

2 Answers 2

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A PWM speed controller varies motor speed by turning the power on and off rapidly with a variable on/off ratio. The output will be a series of 12V pulses, not a smooth DC voltage proportional to the pot position.

It is OK for brushed DC motors (obviously!), resistive loads such as a heating element or incandescent light bulb, and other devices that can handle PWM (eg. LED strip, Peltier cooler). It will not work properly with devices that need smooth DC power.

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  • \$\begingroup\$ I was gonna use it with a Peltier cooler so that's actually good news. Could I use some sort of capacitor based filter if I ever did need it for less than 12V? Also, do you know the answer to my comment I posted on the OP? Instantaneous 30A from a 40A rated power supply? \$\endgroup\$ Commented Feb 26, 2016 at 0:24
  • \$\begingroup\$ Do not use a capacitor filter - it will raise the voltage to 12V and negate the action of the speed controller. Resistive devices respond to rms voltage which doesn't have to be smooth. If the load wants to draw 30A at 12V then that's what it will draw. Just because the PSU is capable of 40A doesn't make the load draw that much. \$\endgroup\$ Commented Feb 26, 2016 at 5:29
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It should work fine, pretty low risk. At most you may need an electrolytic capacitor on the 12V between the two devices. Can the voltage regulate with a step in voltage? The 12V will dip and the amount depends on how well it was designed. You cannot tell from the information provided.

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