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Why DC May Replace AC (2019)

electricalindustry.ca

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Re: Why DC May Replace AC (2019)

#11

Post by castratikron »

nickff wrote: post #8
sabareesh wrote: post #7

Pretty much all device in a household can function using only DC and now we can also generate DC directly DC at home, thanks to Solar. So we can cut the losses switching to AC and DC.

Counter-example: Motors consume >= 25% of all electrical power, and the majority of household and industrial motors are AC. Think air conditioners, fans, compressors, etc.

Question is whether those devices would be better off using brushless DC or some other DC motor? Tesla uses a switched reluctance motor (basically stepper motor) instead of induction motor on their low end vehicles for example.

Re: Why DC May Replace AC (2019)

#12

Post by WorldMaker »

sabareesh wrote: post #6
wbsss4412 wrote: post #5

Earlier quoted context omitted.

Same reason why it didn’t win out 100 years ago. It isn’t as efficient.

I don't think it is efficiency, we had no way to step up and step down DC as we can do AC

Yup, transistors especially have given us major breakthroughs in the ability to step up/step down DC.

Also, there have been huge breakthroughs in High-Voltage DC: https://en.wikipedia.org/wiki/High-voltage_direct_current

At certain huge (grid) scales they have found that AC and DC swap "efficiencies" again and we're increasingly starting to see current flows as DC-AC-DC "sandwiches" with DC used by the majority of consumer electronics and DC used for extremely high scale grid transport, and AC still useful in the mid-range transport.

Re: Why DC May Replace AC (2019)

#13

Post by vegetablepotpie »

sabareesh wrote: post #6
wbsss4412 wrote: post #5

Earlier quoted context omitted.

Same reason why it didn’t win out 100 years ago. It isn’t as efficient.

I don't think it is efficiency, we had no way to step up and step down DC as we can do AC

Yes, this is true. To step up/down AC voltages, you only need a transformer, a pair of coiled wire. This is very simple tech.

To step up/down DC. There are ways to do it with solid state electronics. One of the ways I’ve seen is to transform the dc to ac internally, change the voltage, and convert and output DC.

Re: Why DC May Replace AC (2019)

#14

Post by WorldMaker »

castratikron wrote: post #11
nickff wrote: post #8

Earlier quoted context omitted.

Counter-example: Motors consume >= 25% of all electrical power, and the majority of household and industrial motors are AC. Think air conditioners, fans, compressors, etc.

Question is whether those devices would be better off using brushless DC or some other DC motor? Tesla uses a switched reluctance motor (basically stepper motor) instead of induction motor on their low end vehicles for example.

Just about every electric vehicle at this point uses DC induction motors. Many support AC fast charging with various sorts of battery hacks, but Lithium Ion batteries are kind of inherently DC when it comes to applying power to the motors. At this point DC motors generally seem to out-class their AC counterparts other than the efficiency of using the same current as walled outlets in homes.

The article puts it this way in a bullet point toward the top:

> DC motors and appliances have higher efficiency and power to size characteristics.

Re: Why DC May Replace AC (2019)

#15

Post by kevin_thibedeau »

castratikron wrote: post #11
nickff wrote: post #8

Earlier quoted context omitted.

Counter-example: Motors consume >= 25% of all electrical power, and the majority of household and industrial motors are AC. Think air conditioners, fans, compressors, etc.

Question is whether those devices would be better off using brushless DC or some other DC motor? Tesla uses a switched reluctance motor (basically stepper motor) instead of induction motor on their low end vehicles for example.

No. AC motors are more reliable simply by having fewer parts that can fail.

Re: Why DC May Replace AC (2019)

#16

Post by Youden »

The author seems very confused about whether they're talking about the grid or devices.

"DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant.

"DC motors and appliances have higher efficiency and power to size characteristics." -> Brushed DC motors aren't efficient, just cheap. Brushless DC motors actually require a separate circuit to turn DC into something resembling a sinusoidal current (i.e. AC).

"DC is inherently compatible with renewable sources of energy such as solar and wind." -> solar generates DC but wind generates AC.

"requiring storage (batteries)" -> chemical batteries require DC but other forms of storage like dams require AC to drive motors or turbines.

"Most energy storage technologies are DC-based" -> at a local level (mobile phones, cordless power tools), sure. At a grid level, we're often talking about hydro.

"Electronic equipment operates on DC power." -> equipment that deals with computation. Electric fans, washing machines and many industrial consumers of electricity use AC. Plus, the existing grids and existing generation infrastructure are built on AC.

Re: Why DC May Replace AC (2019)

#17

Post by seanalltogether »

AC is still way better for power transmission, and I don't mean giant power lines spanning from one city to another, I mean from the curb to your home, or within the walls of your home. Electroboom has a video on this topic https://www.youtube.com/watch?v=S7C5sSde9e4 and its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous, and if its not high voltage, you're just losing too much power to resistance.

Re: Why DC May Replace AC (2019)

#18

Post by InTheArena »

I keep wondering if there might be some value in a derivative high-efficiently USB-C PD standard (since distance, and other factors come in) for whole house. IE, could you add DC power via USB connections to a bunch of different devices with a high-efficiency power supply for all of the different connections, rather then having low-efficiency power supplies in lots of other devices?

Re: Why DC May Replace AC (2019)

#19

Post by jbay808 »

Youden wrote: post #16

The author seems very confused about whether they're talking about the grid or devices. "DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant. "DC motors and appliances have higher efficiency and power to size characteristics." -> B…

In terms of motors, yes -- virtually all motors need to provide AC to the coils to run, so DC motors need to use an inverter.

But increasingly these days, even AC motors are being run from variable-frequency drives, in order to squeeze out a bit more efficiency, because the savings from better matching the load more than makes up for the losses in the drive. Many jurisdictions are starting to incentivize or require VFDs for HVAC applications. And typically the first thing the VFD does is rectify the AC input to DC.

Re: Why DC May Replace AC (2019)

#20

Post by watermelon0 »

kevin_thibedeau wrote: post #15
castratikron wrote: post #11

Earlier quoted context omitted.

Question is whether those devices would be better off using brushless DC or some other DC motor? Tesla uses a switched reluctance motor (basically stepper motor) instead of induction motor on their low end vehicles for example.

No. AC motors are more reliable simply by having fewer parts that can fail.

I thought newer devices (washing machines, ACs, etc.) mostly used brushless DC / ECM motors, since they are more efficient and quieter?

They do need controllers that use AC, so I don't think that existing devices would work on DC.

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