Can you actually reverse the polarity?

I accidentally reversed the polarity when charging my car battery and blew it up. Is there anything you can reverse the polarity on?

Sure. Light bulbs, for instance, don’t care which way the current flows. I’m not sure what you’re specifically asking here.

And what’s this doing in Cafe Society?

Single phase motors turn the same way regardless of how the hot and neutral are connected.

(You reverse by altering the configuration of the winding connections)
Heating elements don’t care about polarity.

Moved Cafe Society --> General Questions.

I’m guessing it had something to do with “reverse the polarity” being a standard techno-babble plot resolution device, i.e. the bad guy’s lightning machine is running wild and will destroy the earth unless the hero can brave the hazards and, under the advice of his science-nerd sidekick, enter the machine and flip the “reverse polarity” switch, after which everything will be okay again.
It’s only a guess, though. That is one seriously unclear OP.

I’m not sure I understand the question, but most male plugs on power cords have one blade larger than the other, so that you are connecting the hot lead to the hot terminal when you plug it in. That of course assumes that the house is wired properly and that somebody didn’t connect an outlet backwards. It’s not a huge issue in normal homes (although you can get zapped from things like sinks, faucets, etc from improper grounding issues), but in mobile homes it can cause problems by sending stray voltage to the skin of the trailer.

Overseas, Americans commonly use autotransformers for their US appliances. Polarity is critical in this case, as reversed polarity can send 220v to the shell of the transformer, creating a potential shock hazard in anything connected to that transformer. It will also make short work of any electronics connected to it (my workers fried 15-20 motherboards in the Embassy in Bamako by inattention to consistency in wiring).


I hooked the battery charger up backwards on my rig a while back. Got lucky, the charger was really old and it died before it hurt the vehicle.

And when I say died, be thinking of a Viking funeral pyre.

I am a fire alarm technician. Almost all of the stuff I work on is 24vdc. Most control and power devices will not survive polarity reversal. Some indicating devices, such as horn/strobes, are actually tripped into their alarm state by reversing the polarity of the circuit.

What about a warp drive, as long as you route the output through the deflector dish?

The flux capacitor won’t allow you to do that.

Have you tried switching the flux capacitor to manual override and swapping neutral and ground?

Yeah, and of course the Romulan cloaking device that Spock ripped out. It took Scotty a while figure out the correct wiring on that thing. Good thing the Romulan’s used the same power requirements as the Federation.

One of my favorite SDMB posts ever was someone saying that he plugged a lamp in backwards, and it started emitting antiphotons.

For AC (e.g., things plugged into a wall socket) the device will work just fine plugged in either way, but many plugs have asymmetric prongs as a safety feature: If your house and lamp are wired properly, then the exposed part of the light socket will be the neutral (which under ordinary circumstances will probably not hurt you if you touch it), while the more dangerous hot contact will be down in the bottom of the socket, where it’s harder to accidentally touch it.

For DC, most things other than heating elements and incandescent light bulbs (which are really just heating elements themselves) will depend on the polarity being correct. Many things, though, will have a rectifier built in so that, no matter how it’s connected, the current will be turned around the right way before reaching the guts of the device.

DC motors will just spin in the opposite direction. Whether that’s useful or not depends on the application.

We need a courageous moderator to go into the OP’s post and reverse its polarity! Then it will all make sense.

Heh. They weren’t wrong, either.

A peltier device (aka a thermo-electric cooler) is a semi-conductor thingy that works like a bunch of itty bitty heat pumps. They were originally developed for use in space satellites. These days you see them in everything from portable cigarette lighter powered drink coolers to CPU coolers inside of computers.

If you run power through a peltier device, one side gets hot and the other side gets cold (though if you don’t remove the heat from the hot side somehow overall the thing will eventually overheat and fail). If you reverse the polarity, the hot side gets cold and the cold side gets hot.

Peltiers are also reversible in the sense that if you apply power they make a heat differential, but they also work the other way. If you apply a heat differential to them, they can generate power.

Peltiers aren’t very efficient, but they are small and have no moving parts which makes them kinda cool and useful.

The neutron flow!

It depends on what you want to reverse the polarity of. Any old shmuck can wire a plug backwards, but you need an academic degree higher than a master’s if you want to reverse the polarity of the neutron flow.

ETA: Damn! Ninja’d!

Most DC devices are specifically “DC” one way. (As mentioned above, some motors don’t care). Most AC - computers or other electrnics, convert AC to DC internally, so don’t care. Battery devices do care.

A battery is an electro-chemical device; electricty (charging) creates a chemical reaction, and using the battery 9discharging) creates a different electrochemical reaction. You mess with chemicals at your peril!

Most DC devices are electronics - basically, diodes and transistors. A transistor is a form of diode where the input is regulated by a third connection. Electrolytic capacitors, similarly, are polarized - one connector is designated positive. Diodes do not work well backwards. Overpower them with reverse voltage and you could damage them. Electronics, unlike motors, does not work “backwards”. Most electronics is tolerant enough of simple reverse voltage that it should survive, for example, putting batteries in backward. Of course, feed enough voltage/amps into anything and it will fail a smoke test - correct polarity, reverse, or AC.