4 ms·

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire?

This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you? What exactly is magical about higher voltages that makes them suddenly able to carry more power across the exact same wire? I know you just said it's "lower amperage" but I don't understand how amperage can be the only thing dictating the required size of a wire.

hansvm 3y ago
A higher voltage system enables the same energy at a lower amperage, so constrained to wanting to do a particular thing (loud stereo, bright headlights, ...), higher voltages result in lower amperages. I'll opt to not try to explain that intuitively, hoping that somebody else chimes in. For the other half, "why do amps determine wire size?" Amps are coulombs per second -- how much electrical stuff moves through a cross section in a second. The amount of heat produced is directly proportional to amperage (every bit of movement has a chance to whack into something and produce heat, and more movement per second or more seconds generates more heat). Wire size is ultimately constrained by being able to release that heat while still acting like a wire (not melting, not sublimating, still conducting, not setting anything else on fire, ...). The amount of heat released is proportional to surface area (proportional to the square root of diameter, but that difference doesn't matter a ton right now), and the amount of heat produced is proportional to amperage and approximately nothing else. The point where those two terms are equal is the limit for the system (engineers add in huge safety factors to account for conduit and insulation and other imperfections), above which your wire melts and below which it behaves reasonably. Higher amperages require higher surface area to release the extra heat (so much higher thicknesses), so a given amount of power (stuff you want your electrical system to do) requires lower amps or thicker wires to work appropriately, because you can achieve the same power by increasing the voltage on the same amperage, thereby solving your power problems without extra heat.
- hansvm 3y ago
  Edit: Heat released is also proportional to the temperature differential between the wire and the outside world, as well as a constant associated with how well it's thermally insulated. The wire temperature rises till either some sort of breakdown occurs or that rate of heat release balances the rate of heat production. The spirit of that original comment is correct, but this feels like a nuance that might matter to somebody new to the topic.
kukkamario 3y ago
The power loss by the resistance scales in the square of the current and linearly to the resistance. So doubling voltage reduces resistance power loss to one quarter so you could lower wire size and increase its resistance to double and still resistance power loss would be halved
rcxdude 3y ago
What matters is energy but what's being carried by the wire is charge. A given amount of charge can have more or less energy, which is what voltage is. So if you give each unit of charge more energy then you can carry more power by only moving the same amount of charge. You get a similar thing in mechanical systems: a shaft is sized based on the maximum amount of torque it can withstand, but the amount of power going through it also depends on the RPM. More RPM = more power, for the same amount of torque, so if you are for some reason limited in the size of the shaft, you can use a gearing mechanism to rotate it faster and then gear down the other side and get more power through a smaller shaft. It's just that in mechanical systems gears are a lot less convenient than changing voltages is in electrical systems. (RPM and voltage are in fact related in EVs as well: generally speaking a higher voltage motor will be able to produce more power for the same amount of space and materials, but mostly by spinning faster, not producting more torque. You then need to gear it down to be practical in a car. But the trend is that things that make higher voltages and higher RPMs possible (the technology in transistors, insulation, bearings) are already cheap or getting cheaper, while things that make higher currents and torques possible (generally more raw material like copper and steel) are staying the same or getting more expensive. So EVs in general are pushing to higher voltages for lots of things)
kzrdude 3y ago
Just as further confirmation, remember that long distance power delivery uses high voltage, often measured in kilovolts. Because of reduced losses that way.
Sohcahtoa82 3y ago
Imagine you've got an object you want to move by shooting water at it from a hose. If the pressure coming from the hose is high, then you don't actually need a lot of water, and so you can use a narrow hose. On the other hand, if the pressure is low, you'll need to use a lot more water at once, so a wider hose. It's the same thing for electrical components. If you'll excuse the mixed analogy, if you need to push an object with 480 watts of water to get it to move the speed you want it to, you can either do it with 48 volts of pressure with a hose 10 amps wide, or do it with 12 volts of pressure 40 amps wide.

hansvm 3y ago

A higher voltage system enables the same energy at a lower amperage, so constrained to wanting to do a particular thing (loud stereo, bright headlights, ...), higher voltages result in lower amperages. I'll opt to not try to explain that intuitively, hoping that somebody else chimes in. For the other half, "why do amps determine wire size?" Amps are coulombs per second -- how much electrical stuff moves through a cross section in a second. The amount of heat produced is directly proportional to amperage (every bit of movement has a chance to whack into something and produce heat, and more movement per second or more seconds generates more heat). Wire size is ultimately constrained by being able to release that heat while still acting like a wire (not melting, not sublimating, still conducting, not setting anything else on fire, ...). The amount of heat released is proportional to surface area (proportional to the square root of diameter, but that difference doesn't matter a ton right now), and the amount of heat produced is proportional to amperage and approximately nothing else. The point where those two terms are equal is the limit for the system (engineers add in huge safety factors to account for conduit and insulation and other imperfections), above which your wire melts and below which it behaves reasonably. Higher amperages require higher surface area to release the extra heat (so much higher thicknesses), so a given amount of power (stuff you want your electrical system to do) requires lower amps or thicker wires to work appropriately, because you can achieve the same power by increasing the voltage on the same amperage, thereby solving your power problems without extra heat.

hansvm 3y ago
Edit: Heat released is also proportional to the temperature differential between the wire and the outside world, as well as a constant associated with how well it's thermally insulated. The wire temperature rises till either some sort of breakdown occurs or that rate of heat release balances the rate of heat production. The spirit of that original comment is correct, but this feels like a nuance that might matter to somebody new to the topic.

kukkamario 3y ago

The power loss by the resistance scales in the square of the current and linearly to the resistance. So doubling voltage reduces resistance power loss to one quarter so you could lower wire size and increase its resistance to double and still resistance power loss would be halved

rcxdude 3y ago

What matters is energy but what's being carried by the wire is charge. A given amount of charge can have more or less energy, which is what voltage is. So if you give each unit of charge more energy then you can carry more power by only moving the same amount of charge. You get a similar thing in mechanical systems: a shaft is sized based on the maximum amount of torque it can withstand, but the amount of power going through it also depends on the RPM. More RPM = more power, for the same amount of torque, so if you are for some reason limited in the size of the shaft, you can use a gearing mechanism to rotate it faster and then gear down the other side and get more power through a smaller shaft. It's just that in mechanical systems gears are a lot less convenient than changing voltages is in electrical systems. (RPM and voltage are in fact related in EVs as well: generally speaking a higher voltage motor will be able to produce more power for the same amount of space and materials, but mostly by spinning faster, not producting more torque. You then need to gear it down to be practical in a car. But the trend is that things that make higher voltages and higher RPMs possible (the technology in transistors, insulation, bearings) are already cheap or getting cheaper, while things that make higher currents and torques possible (generally more raw material like copper and steel) are staying the same or getting more expensive. So EVs in general are pushing to higher voltages for lots of things)

kzrdude 3y ago

Just as further confirmation, remember that long distance power delivery uses high voltage, often measured in kilovolts. Because of reduced losses that way.

Sohcahtoa82 3y ago

Imagine you've got an object you want to move by shooting water at it from a hose. If the pressure coming from the hose is high, then you don't actually need a lot of water, and so you can use a narrow hose. On the other hand, if the pressure is low, you'll need to use a lot more water at once, so a wider hose. It's the same thing for electrical components. If you'll excuse the mixed analogy, if you need to push an object with 480 watts of water to get it to move the speed you want it to, you can either do it with 48 volts of pressure with a hose 10 amps wide, or do it with 12 volts of pressure 40 amps wide.