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What is negative DC voltage?

U

upriverpaddler

[H]ard|Gawd
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Jun 11, 2004
Messages
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I have a proximity sensor. It requires a supply of negative 24vdc. The output variable is -0.2vdc to -19vdc.

What is negative vdc. Can I just reverse the polarity of 24vdc? Power to COM and neutral to power?
 
from what I remember form my EE classes, if we needed -5V, we'd set "ground" to be at +5V. At 0V, you have apparent -5V and at -10V you'd have +5V.
 
Well voltage is simply potential difference so it's treated as a difference. If you have one wire with the potential of 5 volts above ground, and you have another wire that's at ground, then the current flowing from one to the other is 5 volts.

If you have a wire at +5 above ground and one at -5 volts below ground then the current between them would be 10 volts.

To put it simply, it's a reference to ground. If you connect a wire to ground and current flows TO the ground, then it's positive. If current instead flows FROM the ground, then it would be negative I believe. Correct me if I'm wrong though because all I know about electronics is self-taught from books.

Also to note: Make sure your power supply actually says minus 0.2vdc and minus 19vdc. Take a careful look and make sure it's not ~ which simply means "Around 0.2vdc or Around 19vdc"
 
Your replies gave me just enough courage to go ahead and hook it up to +12vdc backwards and everything worked ok. Thanks.
 
Hooking it up 'backwards' works fine, unless you are dealing with a multiple output power supply, in which case grounding any of the positive leads may lead to disaster, and/or the signal potential may be at odds with other equipment.
 
MjrStryker said:
Also to note: Make sure your power supply actually says minus 0.2vdc and minus 19vdc. Take a careful look and make sure it's not ~ which simply means "Around 0.2vdc or Around 19vdc"
Click to expand...
I think you'll find that's the symbol for AC, seen against the input voltage (eg, 230V ~ 50Hz 95mA on my router's plug-top transformer) and on the output of AC-AC adaptors (9V ~ 1A on the same device - this router has rectifier, smoothing and regulation built-in).

DC is represented by an equals sign '=' with the bottom line dashed.
 
negative voltage is the same as positive voltage.. it's just voltage LOL!!

the negative or possitve part just comes from how you reference the voltage to a ground node..
 
RancidWAnnaRIot said:
negative voltage is the same as positive voltage.. it's just voltage LOL!!

the negative or possitve part just comes from how you reference the voltage to a ground node..
Click to expand...

I don't understand why that is funny. For those of us without EE degrees, the bottom line answer was...

Yes, reverse the polarity on +24vdc and you get -24vdc.
 
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