Great output voltage than input voltage

Thread Starter

zemanekj

Joined Jan 31, 2019
58
Good afternoon/morning,

Is it possible to have an input voltage of 20 Volts into a circuit, and have the output be higher than 20 Volts? Such as in this diagram:

Here you see a DC Power source input 20 volts into the circuit.
That 20 volts powers a DC motor - which turns the shaft of the DC generator
The DC generator then produces DC electricity.
Thus, is it possible for that generator to produce a greater voltage than the 20 Volts put into the circuit?
Or am I correct in presuming that this is not possible?

Thank you - and let me know if you need any clarification.
 

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AlbertHall

Joined Jun 4, 2014
9,266
You can get a bigger output voltage than the input voltage by many means including the one you suggest but the output will be at a lower current than the input current and thus the output power will always be less than the input power - efficiency will always be less than 100%.
 

AnalogKid

Joined Aug 1, 2013
8,299
Is it possible to have an input voltage of 20 Volts into a circuit, and have the output be higher than 20 Volts?
Yes. It is called DC/DC conversion, and there are many ways to do this. Some work better than others depending on other parameters around the system: size, weight, cost, power level, environment. What you show is called a motor-generator set. These were very common in WWII planes and ships, doing things like converting 60 Hz AC power to 400 Hz AC power (and vice versa), and various forms of AC/DC and DC/DC conversion. As solid state devices became more reliable and able to handle higher power levels, the industry quickly shifted to switch-mode power supplies. A search for DC/DC or DC-DC converter will find thousands of components and thousands of circuits. Depending on the operating parameters, conversion efficiencies of greater than 95% are possible. An all solid-state circuit for your application is called a boost converter.

Note that those pesky laws of thermodynamics still apply to the total energy flow through the system. No matter what the techniques, voltages, and currents are, to get 100 W out of the output you must put more than 100 W into the input.

ak
 

BR-549

Joined Sep 22, 2013
4,938
You sure can. But there are easier ways. Just remember that you lose some power when you do it.

Your example is called a motor-generator, and has been used for many decades in different configurations.

Type in "motor generator set" on ebay. Motors are heavy. Instead, by switching or pulsing the DC current thru an inductor, we can hold the output voltage at almost any level.

A motor generator can also provide another function. It can change the number of phases of the power system. But with digital switching......that's done electronically now too.
 

crutschow

Joined Mar 14, 2008
24,306
You can increase voltage with a corresponding reduction in current, or you can increase current with a corresponding reduction in voltage, but, thanks to the conservation of energy theorem, you can't increase both at the same time, since that would increase the energy.
 

Papabravo

Joined Feb 24, 2006
12,878
The governing equation for the process is:

PO = ε*PI

PO = Output Power
PI = Input Power
ε = efficiency

For any given process, like the one you drew in your diagram, the efficiency can take any value in the range [0,...,1)
The notation for the range of ε means you can construct a process with zero efficiency in which there is no Output Power, and you can construct a process which approaches 1, in which all of the Input Power is available as Output Power. The catch is that you cannot get arbitrarily close to an ε of 1. Maybe the actual limit is 0.93 for the particular process you have chosen. The point is there will be some loss in ANY conversion process.
 

Thread Starter

zemanekj

Joined Jan 31, 2019
58
Thank you all for the responses! Here is my next question then (and if it's not clear please let me know)

If you have one wire and two power sources (such as in the picture) and both 1, and 2 produce the same amount of voltage/current I presume nothing would flow through the wire because of the opposing currents. However. if you make the voltage or current higher for, say, 2 then the electricity would flow from 2 to 1 correct?
 

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AlbertHall

Joined Jun 4, 2014
9,266
They will only oppose each other if the voltages are exactly equal, and then only if positive is connected positive and negative connected to negative - not the case in your diagram!
 

Thread Starter

zemanekj

Joined Jan 31, 2019
58
They will only oppose each other if the voltages are exactly equal, and then only if positive is connected positive and negative connected to negative - not the case in your diagram!
So to clarify whichever generator has the highest voltage wins and overpowers the opposing voltage?

Depending on the internal construction of the generators, yes. Also, not good.

ak
So to clarify whichever generator has the highest voltage wins and overpowers the opposing voltage? Let me know if you need me to clarify my question more.

The governing equation for the process is:

PO = ε*PI

PO = Output Power
PI = Input Power
ε = efficiency

For any given process, like the one you drew in your diagram, the efficiency can take any value in the range [0,...,1)
The notation for the range of ε means you can construct a process with zero efficiency in which there is no Output Power, and you can construct a process which approaches 1, in which all of the Input Power is available as Output Power. The catch is that you cannot get arbitrarily close to an ε of 1. Maybe the actual limit is 0.93 for the particular process you have chosen. The point is there will be some loss in ANY conversion process.
So what happens when you have two opposing currents in a single wire?

You sure can. But there are easier ways. Just remember that you lose some power when you do it.

Your example is called a motor-generator, and has been used for many decades in different configurations.

Type in "motor generator set" on ebay. Motors are heavy. Instead, by switching or pulsing the DC current thru an inductor, we can hold the output voltage at almost any level.

A motor generator can also provide another function. It can change the number of phases of the power system. But with digital switching......that's done electronically now too.
Thank you! That is very helpful. One more question - what happens when you have two opposing currents in a single wire? Let me know if this question seems redundant. Thank you again.
 
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sparky 1

Joined Nov 3, 2018
40
You are getting higher output voltage than input voltage.
I am sorry but it is very very common to find higher voltage in certain circuits.

Is it necessary to have more details of the circuit ?
Yes the current at the output together with voltage are interdependent.
I enjoy electrical equations and I appreciate people like Michael Faraday.

A fluid in a pipe of a given diameter is measured for it's pressure.
Another pipe having a much larger diameter is also measured.
Likewise taking into account the volume of fluid moving through either pipe
gives us us a relationship that works. What exactly goes on in some electrical
circuits cannot be observed completely in our present level of understanding.

We can rely on the equations and they are very accurate in a closed circuit.
In an open system just which details are needed is an ongoing study.
The discipline of quantitative representation in closed system does not
interfere much with research. The open system can use the classic equations as subroutines.
It has been proposed that hierarchy is incorrect. It is likely because we perceive the galaxy as
(Open system(closed system)) should this awareness be taught in electrical courses ?
 

WBahn

Joined Mar 31, 2012
25,223
Thank you! That is very helpful. One more question - what happens when you have two opposing currents in a single wire? Let me know if this question seems redundant. Thank you again.
The question is pretty much nonsensical. It's like saying what if I have two opposing water flows in the same hose. The flow of water will be the same throughout the hose and the direction will be determined by the pressure difference across the ends of the hose.

It should go without saying that I'm talking about an ideal, rigid hose completely filled with an incompressible fluid that is perfectly horizontal.
 
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