4 ms·
How exactly do you define a negative voltage unless you are using some other voltage as a reference?
by firebat45 3y ago
How exactly do you define a negative voltage unless you are using some other voltage as a reference?
- dragontamer 3y agoLabel the power pin+ GND and the power pin- becomes -48V Voltages are all relative. It's like saying 'How do you get a height difference of 10 feet by digging?' Well, you dig and then label the initial level as +10 feet, and redefine the bottom of your hole to be ground.
- Kirby64 3y agoNo. In telco, the -48V is referenced against ground, like the physical ground. If you're isolated, you can do this. but they would still need to be referencing the 'ground' to something ... likely the negative side of the main battery pack. The reason why -48V is used is because it is provided as a bias voltage to give wiring cathodic protection, to prevent corrosion of telecom infrastructure. If you used 48V, it would not work. You need a negative voltage referenced against ground.
- applied_heat 3y agoGround positive terminal of battery string instead of grounding negative terminal. I see this more often on European stuff
- bluGill 3y agoGenerally with respect to ground. There are many good reasons to connect your power system to ground and so this is commonly done. (there are pros and cons to connecting to ground, but it gets complex fast)
- myself248 3y agoIt is with respect to ground, the positive pole of the battery is connected to ground. The telegraph system figured this out very quickly. Most water in nature has at least a bit of salt in it, which is present as positive sodium ions and negative chloride ions. By making the outdoor wiring negative with respect to ground, the chloride ions are repelled, and such wires corrode much more slowly than those that're positive with respect to ground. Since most of the telegraph network, later the telephone network, is outdoors, this is a pretty big deal.
- thebruce87m 3y ago> that’re First time I’ve ever seen this typed
- hinkley 3y agoWhat’re you talking about?
- denysvitali 3y agoI guess he refers to the shortening of "that are" into that're
- DennisP 3y agoI think you're missing your parent's joke.
- denysvitali 3y agoNow I see it, thanks :-)
- magicalhippo 3y agoIt's a matter of perspective. You tie one of the leads to earth (literally grounding it)[1], leaving the other non-grounded. Depending on if you tie the negative or the positive lead to ground, you get 48V or -48V with respect to ground. As long as the potential between the most positive lead and the least positive lead is 48V, the circuit itself doesn't care. As mentioned here[2], the reason for grounding the positive lead is to prevent galvanic corrosion[3] destroying the buried copper. [1]: https://www.bicsi.org/docs/default-source/conference-presentations/2017-mea-uae/grounding-and-bonding.pdf https://www.bicsi.org/docs/default-source/conference-present... [2]: https://www.poweringthenetwork.com/uncategorized/negative-48-volt-power-what-why-and-how/ https://www.poweringthenetwork.com/uncategorized/negative-48... [3]: https://en.wikipedia.org/wiki/Galvanic_corrosion https://en.wikipedia.org/wiki/Galvanic_corrosion
- hinkley 3y agoApparently in cars it’s weirder. Wire it one way and the wiring corrodes. Go the other way and the body corrodes.
- bloggie 3y agoVoltage is a measure of charge difference so there must always be a reference, usually the reference is 0 V.