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# Powering a motor with 2 RF sources?

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#### zemanekj

##### New Member
Can one power a single motor with two different RF sources?

No.

what if the two difference source emit the same RF frequency to power a single electric motor?

It doesn't matter. It's too inefficient to be practical. Plus, the power levels required to drive even a tiny motor would be to even look in at, let alone be around.

And methinks enough RF power to run even the tiniest motor would bring you swiftly to the attention of the authorities, as an unlicensed broadcaster.

It doesn't matter. It's too inefficient to be practical. Plus, the power levels required to drive even a tiny motor would be to even look in at, let alone be around.

I'm not looking to do this practically. I'm a student and need help with a theoretical circuit I'm drawing.

And methinks enough RF power to run even the tiniest motor would bring you swiftly to the attention of the authorities, as an unlicensed broadcaster.

I'm not looking to do this practically. I'm a student and need help with a theoretical circuit I'm drawing.

I'm not looking to do this practically. I'm a student and need help with a theoretical circuit I'm drawing.
Generating RF to drive a motor is a seriously bad inefficient idea.

JimB

Generating RF to drive a motor is a seriously bad inefficient idea.

JimB

I know it's terribly inefficient, but as a student trying to design a theoretical circuit I'm just trying to see if it's possible, and maybe some of the reasons why, or why not - aside from that it's inefficient. Thanks!

I know it's terribly inefficient, but as a student trying to design a theoretical circuit I'm just trying to see if it's possible, and maybe some of the reasons why, or why not - aside from that it's inefficient. Thanks!
Well that really is the issue. Saying something is wildly inefficient is another way of saying something produces a lot heat and needs to be really massive (and expensive) for the tiny amounts of useful power you can get from it. In this case, there's also the safety issue because RF leaks and scatters everywhere and those power levels it's dangerous to be around.

Depends what you mean by Rf.
100mhz would be tricky to arrange, 100khz piece of cake.
This curio sits on my desk and qualifies as Rf powered, spot the coils, the base transmits at 150kc, the car has a receiver that powers the processor & lights.
The system works using a magnetic field not an electric field, I wonder if some of the above comments are thinking of the latter.

as a student trying to design a theoretical circuit I'm just trying to see if it's possible, and maybe some of the reasons why, or why not

OK, let us try and channel your thinking.

1 How much power does the motor require?
Without knowing this, all other considerations are moot.

2 What range do you anticipate between the RF transmitter and the RF receiver?
As mentioned else where, if you are relying on true electro-magnetic coupling, the inverse square law applies.
ie as you double the distance between tx and rx, so the received energy drops by a factor of four ( ie 2 squared).

If you are relying on magnetic coupling, you start to encounter an inverse cube law.

3 What frequency do you plan to use?
A higher frequency would allow the use of directional antennas, radiating the RF energy in the required direction. This would improve the range, but the inverse square law still applies.

Also don't forget that you cannot just park a great big transmitter on any frequency you like. You are likely to make the existing users of that frequency very angry.

4 While on the subject of frequency.
It is fairly easy to rectify RF power up to a few 10s of kilohertz, just use the same sort of diodes as used in switchmode power supplies.
But when you get into the MHz region, rectifying significant amounts of power becomes more difficult.
You my be able to use an active rectifier scheme...
Who knows. It all depends on the amount of power you need to rectify.

So, does that help with your theoretical study?

JimB

There was talk of parking a solar powered satellite in geo-synchronous orbit over an uninhabited region (The Sahara Desert comes to mind)
and using a MASER to send a microwave beam to a ground based receiver. This would be rectified and converted
to DC and ultimately to AC power.

Sure it's terribly inefficient, dangerous, and not something that would be easy to do.

But it is doable.

Many years ago, it was written about in a science fiction story.

For the life of me, I can't remember where.

Many years ago, it was written about in a science fiction story.

A great many SciFi stories utilise beamed wireless power, it's a common story line.

A classic example is Spacehounds of IPC by E.E. Doc Smith

A great many SciFi stories utilise beamed wireless power, it's a common story line.

A classic example is Spacehounds of IPC by E.E. Doc Smith
A more recent example is Xenosaga. It's used to broadcast power to all the mechas from their ship that carries them. They still get their ass whupped by ships that basically draw their power from higher spatial dimensions.

OK, let us try and channel your thinking.

1 How much power does the motor require?
Without knowing this, all other considerations are moot.

2 What range do you anticipate between the RF transmitter and the RF receiver?
As mentioned else where, if you are relying on true electro-magnetic coupling, the inverse square law applies.
ie as you double the distance between tx and rx, so the received energy drops by a factor of four ( ie 2 squared).

If you are relying on magnetic coupling, you start to encounter an inverse cube law.

3 What frequency do you plan to use?
A higher frequency would allow the use of directional antennas, radiating the RF energy in the required direction. This would improve the range, but the inverse square law still applies.

Also don't forget that you cannot just park a great big transmitter on any frequency you like. You are likely to make the existing users of that frequency very angry.

4 While on the subject of frequency.
It is fairly easy to rectify RF power up to a few 10s of kilohertz, just use the same sort of diodes as used in switchmode power supplies.
But when you get into the MHz region, rectifying significant amounts of power becomes more difficult.
You my be able to use an active rectifier scheme...
Who knows. It all depends on the amount of power you need to rectify.

So, does that help with your theoretical study?

JimB
Yes that helps a lot thank you!

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