Resonance in motors

[mbrownn]

The things I leave out are the things I don't know I would be interested to know more. Of course I have my objective which is what I tailor my posts towards.

I pulled apart a motor from a cheap RC helicopter to find a nice pair of neo magnets and a core-less rotor, unfortunately they don't make this type of motor in big sizes

I would also be interested in the relationship of iron saturation and its effects as I know almost nothing about it although I plan NOT to saturate the coils or cores.

Thanks to Steven Jones I will be able to carry out tests in the near future which I will post on this site which we all may learn from. Strangely I have found little on the internet that is relevant to what I am doing other than PWM and motors. As they do not exploit the recycling of energy in the same way the motor characteristics may be different.

Opposing magnetic fields have interesting effects on oscillations as do compensation coils in combination wound universal motors so there will be interesting things to find when when I get the thing built. Someone posted a link to a youtube video recently showing such an effect, It caused an amplification of the oscillation If this only causes higher voltage and reduces current it will be of little use but if it can cause higher current regardless of voltage it will be a benefit to motor power.

I always say, keep firing questions and opposing views as this makes me think about what is happening from a different angle and then I learn more.

What is your device that you are working on? you are probably aware that mine is the Lockridge device.

I didn't realize that I was operating the motors in a resonant circuit until Peter Lindemann pointed it out in an Email, It was then that I realized that the motor could be AC as well as Pulsed DC.

[nueview]

MBrown
do you have a 10 amp auto transformer so that you can adjust the voltage to an induction motor yet keep the frequency the same as well as a variable frequqncy generator so you can raise and lower the frequency?
i have some older motors made in the 1930's cast iron housing and wire wound rotor they are made for 60 cycle period and run very well resonant. newer motors made for the global markets are made for 50/60 hz and are nowhere near as good and as i have found need more than 60 hz to be as good as the older motors depending on motor manufacturer it ranges from 55hz to 70 hz.
if you consider power of a wave as a volume of energy then varing the voltage should effect the resonant characteristic and it does.
how would you make a motor generate without altering the drive stability?
this is a trick question and you have touched on the answer already.
Martin

[nueview]

when watching this please think about the field actions in relation to the steel.

Magnetic gear box 4:1 (work with AC motor) - YouTube

Martin

[mbrownn]

MBrown
do you have a 10 amp auto transformer so that you can adjust the voltage to an induction motor yet keep the frequency the same as well as a variable frequqncy generator so you can raise and lower the frequency?
i have some older motors made in the 1930's cast iron housing and wire wound rotor they are made for 60 cycle period and run very well resonant. newer motors made for the global markets are made for 50/60 hz and are nowhere near as good and as i have found need more than 60 hz to be as good as the older motors depending on motor manufacturer it ranges from 55hz to 70 hz.
if you consider power of a wave as a volume of energy then varing the voltage should effect the resonant characteristic and it does.
how would you make a motor generate without altering the drive stability?
this is a trick question and you have touched on the answer already.
Martin

No, I have a variac 0 to 250v and two 12v 10 amp battery chargers as well as lots of batteries. I realy nead a function generator but don't have the funds for that yet.

I have found pre WWII motors to be very good having more turns for the same resistance ie more inductance.

Increasing the voltage of a pulse increases not only the current but also the duration of the coil discharge or oscillation resulting in more current out than in, provided the coil does not reach saturation. Is that what you have seen?

We do not want the motor to generate at all as that is the BEMF. The trick here is to use a high voltage, high speed motor at low speed so it does not generate so much but operating a motor like this, power will not rise to the load. To compensate for this our generator must drop its generation faster than the motor drops power so that an equilibrium can be found. An AC generator will do that as its speed drops off its generating function drops off. The difference between maximum generation and no generation when attached to the grid is only a few percent speed drop, this way equilibrium can be achieved and motor speed controlled.

Is this what you mean in your trick question?

I like how you did the magnetic gearbox.

Mike

[nueview]

mike a magnet is always saturated and if the steel is run close to saturation then the magnetic field does not react like an iron haveing residual field flow for the magnet it is then like a magnet to magnet action like the iron post in the video.

yes this is similar to how i am thinking about it but i want the generator to make as much voltage as possible and impedance match down in steps to keep the current low in the generator.

the trick part is to find a motor or generator that is close to the specs all in the same unit so that one can avoid any of kromrey's interaction effects of the two units fields were in the same unit this may not be possible but it may be what balances the power.

don't feel bad i had to use a gas generator and run it over cycle to do the hz test.
Martin

[mbrownn]

It looks like your objective is the opposite to mine, for me the voltage is not so relevant apart from the higher it is the more losses due to ohms law. It is the current flow multiplied by the number of turns that causes magnetism so I want current. All the current passes through a coil and only voltage is lost so its like water with pressure and flow. We can store that current and use it again, it is only a pressure loss in effect. Voltage is required to cause current to flow over a resistance as ohms law says but during a field collapse the coil becomes a negative resistance and we need to apply no voltage for the current to flow, It creates its own voltage in effect. This flow of current cost us nothing as the current used to create it has already passed through.

[wrtner]

I really nead a function generator but don't have the funds for that yet.

You could put one together out of a 555 chip (and possibly a transistor
switch to switch a current bigger than the 555 wants to deal with).

Try putting 555 and "frequncy generator" into Google.

[mbrownn]

You could put one together out of a 555 chip (and possibly a transistor
switch to switch a current bigger than the 555 wants to deal with).

Try putting 555 and "frequncy generator" into Google.

I am doing that got a bread board and playing around with it but its not very stable. It should be able to give me enough to work out what frequency is best but when it comes to a motor control circuit I don't think it will be up to it.

Thanks for the input anyway.

[nueview]

i want to pass some things along that we did this last weekend i t was not motor related directly but has its place for information.

we tested a few small inverters one from radio shack a 150 watt with a surge to 240 watt against some of the other kind rated the same at 150 watts but some are 90 watt with a peak surge of 150 watt so be carefull about what you buy. that was first thing we found.

both type of inverters are made to work off automotive power port for in vehicle charging of cell phones and computers but we were running some CFL lights just to see how well they would perform both power the lights to there rated outputs for continous power levels and resonablely well.

i still need to check a regular 60 watt incandesant bulb just for comparison but i need a good current meter to get good DC and AC readings.

next we tried the french flip-flop driver with a transformer and the transformer was a bit big for the mosfets gotten from radio shack as they were 2 amp rated for continous running the 60 what incandesant would glow but that was the best it could do. the 40W CFL would light bright at first then it would dim down. but it would run the mosfets were hot but not at there limits but deffinately need to be of a bigger rating for current. the CFL appeared cool as it had a yellow glow to it.

next we replaced the transformer and with a smaller rated one 600 ma and got much better results from the CFL it lights white now but the mosfets still run warm i would think the flip-flop driver needs to be running a bit faster.

all in all it was a good learning experience and is similar to the motor driver i will be using so it is all good information. i just need some good meters and add some proper capacitors to finnish this testing out.
Martin

[mbrownn]

Yes I am aware of the misleading ratings on devices, I noticed this to be the case not only on cheap Chinese goods but also on top branded goods too. The price or brand is no guideline to use when choosing to buy anything, read the small print.

Typically compact fluorescent bulbs have the same issues, they have been designed for a life of 1000 hours at 20C, you probably have noticed that they get hotter than that. Also some have built in power factor correction and others don't and this usually isn't reflected in the price.

Makita power tools have a good name but when you find out their power ratings are peak and not continuous then you find them very expensive when put in comparison with other tools. Look at their size that's your first clue. in addition to this it is now becoming common practice to put aluminum windings in the coils instead of copper, these windings can produce the same peak results but are much lower than copper on continuous power, the result being burn outs. The resistance of these coils goes higher when hot thus producing even more heat accelerating the burn out.

Pulling universal motors out of power tools led me to this discovery. Where this becomes relevant to this thread is what happens to the voltage in a coil when you have it in resonance, the voltage rises and power goes up. A 1kw motor may be rated 220v 60 cycles but once we get it in resonance that voltage will rise considerably and we will be exceeding the rated power with the same input voltage. Because of the higher voltage we get more heat loss under ohms law and burn out.

We will either have to reduce the input voltage or limit the current to prevent this. Current limiting will result is a shorter oscillation.

I have just run a test on a 220v 360W universal motor with my variac. The variac can produce 0 to 280v. I limited the current with PWM and got the same heat in the motor at 280v input at a little over half the current, around 200w. The stator windings are aluminum, not sure about the rotor.

On a motor with copper windings I didn't notice a difference in heat as long as the power was the same.

[nueview]

yeah i new most of what you posted it is just that i don't think i could rate anything i built like that.

one of the guys in our group here called today as he got his TEG (thermal electric generator) in yesterday and got it hooked up today so he will be heating his house with the wood stove and charging his battery bank with the TEG.
it has a 48v output at 20 amps so it should work real well as the stove goes 24/7 here in alaska we really wanted to check these out and see if we could make any improvements. i will let you guys know how it goes. so far it looks like the stove temperature is the only weak link.

i didn't get the parts i wanted but am wondering if anyone here has tried to paralell mosfets to get there total power output higher? is this something you just shouldn't do or just not a good idea?
Martin

[mbrownn]

As some of you are aware I am researching and testing in an attempt to build a Lockridge type device. I will post this particular information here as this is the most relevant thread I have for it.

I have been pulsing a 220v 2kw universal motor of unknown inductance and observing the oscillations. Initially the oscillation was so small as to be negligible but as the voltage increased so did the oscillation. As I don't have a 10x probe for my scope I cant really say what happened once the voltage got above 160v but I believe something did happen. I have the motor in parallel with a capacitor to make an LC circuit and a resonant recovery circuit made to multiply the voltage

The pulse frequency was around 1khz at approximately 30% duty cycle

I was able to get the motor to spin although the power/torque was poor. My variac will only supply 4 amps maximum continuous current although the motor would require around 9 amps at full power.

The interesting thing that happened with the motor drawing around 1.8 amps was heat Theoretically the motor is running at around 440 watts but the heat produced was significantly greater than expected

The circuit is here representing the loaded motor Circuit Simulator Applet

I'm not saying that the real figures are as the simulation because I have no idea as my scope could not handle the voltage and the digital meters were all over the place because of the pulsing.

What the unexpected heat shows is that the excess energy in the motor is possibly real and is being dissipated as heat instead of motor power.

[mbrownn]

The voltage sources and diodes below the inductor are to simulate BEMF in the motor.

[nueview]

something alters the voltage to current ratio in motors that are resonant run.
having that high of voltages you need to find how to get the current up.
this is like the Don Smith replications i have seen it done with small wire and with copper tubing but when it is right the voltage goes down and the current rises many times.
i am not sure how this is done.
Martin

[mbrownn]

something alters the voltage to current ratio in motors that are resonant run.
having that high of voltages you need to find how to get the current up.
this is like the Don Smith replications i have seen it done with small wire and with copper tubing but when it is right the voltage goes down and the current rises many times.
i am not sure how this is done.
Martin

You are spot on, voltage alone has no effect on motor output power, we need the current to increase but all the normal methods of increasing current reduces the gain in power except for lowering resistance.

Just try disconnecting the diode on the recovery circuit and watch the power go up and current fall. This is the opposite to what I want as I want the current to rise. I know the trick will have something to do with the trifilar coil on the Lockridge device but its time for experiments to see if the theory works out in practice.

Seeing the rise in heat output was the first sign that the overunity is real and I am pleased with that but it isn't much use to us in that form. Of course a transformer can turn high voltage low amps into low volts high amps but that robs the resonant circuit of its power and we loose the gain. I need to think about this and sort a better way to switch the circuit than what I have but I am working on it.