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I'm trying to convert +/-12VDC to +/-24VDC to power a DC motor in both directions. I've tried using a step-up converter like this one, but when I feed it -12VDC, it doesn't output anything. Is there an electrical component that will output +24VDC when fed +12VDC and output -24VDC when fed -12VDC? Total noob here just trying to motorize a skylight with a chain actuator, so please excuse my limited understanding.

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I don't think you need a negative supply - just use a double-pole relay to reverse the polarity.

schematic

simulate this circuit – Schematic created using CircuitLab

You probably need a center-off switch to allow you to stop the motor wherever you want - or a separate off/on switch.

(You probably killed the DC-DC converter when you connected it with the wrong polarity.)

EDIT due to OP's comment that the controller outputs +12V or -12V...

schematic

simulate this circuit

When the controller outputs +12V, the upper relay will operate. When it outputs -12V, the lower relay will operate.

EDIT 2 Changed the upper relay to DPDT to prevent short circuits should both relays somehow become operated at the same time.

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    \$\begingroup\$ @Numbr The suggestion is to use a relay, not a manual switch. \$\endgroup\$ – user1850479 Jul 2 at 3:27
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    \$\begingroup\$ @Numbr: I was thinking switch, but wrote relay when I did the first schematic. The second schematic with two relays should work, if I understand your requirements. \$\endgroup\$ – Peter Bennett Jul 2 at 5:17
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    \$\begingroup\$ Better hope the timing works out well on the relays so they don't short the 24V supply momentarily. Also I think if the control signal is suddenly removed the coil current may circulate through both relays. \$\endgroup\$ – user253751 Jul 2 at 10:50
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    \$\begingroup\$ @Mast: I have shown two, double pole relays \$\endgroup\$ – Peter Bennett Jul 2 at 15:35
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    \$\begingroup\$ @Numbr: You only need a single 24 volt supply. The upper relay connects that supply to the motor with one polarity. The lower relay connects the supply to the motor with the opposite polarity. \$\endgroup\$ – Peter Bennett Jul 2 at 15:42

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