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I am replacing a DC power supply used in a lab experiment. We need to be able to choose a positive or negative current. Bipolar power supplies in our power range (around 1 kW) are expensive, so I am planning to buy two separate units: a unipolar supply, and another unit that will allow us to switch between the two polarities.

What is the name of that second component? Can I reasonably expect to get both from the same supplier?

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    \$\begingroup\$ A Switch? A Relay controlled by something else? \$\endgroup\$ – R Drast Jan 19 '16 at 11:00
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    \$\begingroup\$ Why are you replacing the power supply when, on the face of it, you can reverse the output power supply connections with a dual pole change over switch? \$\endgroup\$ – Andy aka Jan 19 '16 at 11:02
  • \$\begingroup\$ @Andyaka Because there's money in the budget? \$\endgroup\$ – Spehro Pefhany Jan 19 '16 at 12:59
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    \$\begingroup\$ @SpehroPefhany are you possibly saying that fiscal surplus and common-sense are related like frequency and wavelength? \$\endgroup\$ – Andy aka Jan 19 '16 at 13:03
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    \$\begingroup\$ No, I'm just having a little giggle with Spehro. Ignore my ramblings on this occasion. \$\endgroup\$ – Andy aka Jan 19 '16 at 13:20
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A DPDT (double-pole double-throw) switch or relay can be used to reverse polarity. In some circumstances an H-bridge can be used.

Note that if your supply has one side (perhaps the negative) grounded it may not be useful to reverse the polarity since that side will remain grounded.

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That device is called a switch. Just use a rated DPDT switch to switch the two leads of your supply...

Example of switch connection http://rollertrol.com/images/schematics/switches/DC-motor-reversing-switch-schematic-wiring-diagram-285x275.jpg

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It's called an H bridge. But at that power you're going to have to build your own from discrete components. I recommend using either 1 DPDT relay or 2 SPDT relays to construct it.

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