Motor Generators

[pmgriphone]

Do I need the core in place to take that measurement, or can it be taken without a core? Is it just the "wire" that allows for resonance? Because I see it happening at DIFFERENT RPM's when I switch from ferrite to iron cores, and I assumed it was because the core material accepted the flux at a different "finite" rate. I know an air core coil has a different RPM also. At least that is what I see on the bench.

So far, using 200 watt light bulbs as my resistive loads has not detuned the resonance of the coil at the correct RPM, but I have been thinking that there has to be a way to adjust the RPM of the rotor to stay in continuous resonance as the load changes. Either that or some kind of adjustable capacitor in parallel with the coil. Definitely not my area of expertise, but something to think about for the future if I don't want constant loads of the same value.

You will need to measure them with the core in place as the inductance and most likely the capacitance as well will be different for different cores (and thus also the resonance frequency as you noted). Now, if you happen to have the cores out (or if they come out easily), measure the inductance and capacitance as well without the core for reference so you have a record of that. That will also enable me to calculate the permeability of the core material.

Now if you really want to be complete, also measure the inductance and capacitance when the full coil is in place (with core) in the machine when the rotor magnet is in place (top dead center). This will enable me to calculate a couple more things.

The resistance CAN detune the resonance frequency (see the wiki page), but not necessarily has to (see that wiki page).

And lastly, please also let me know the rotor RPM at which resonance occurs (and also please state the number of magnets on your rotor; I watched all your videos, but don't exactly recall how many magnets you have on this last black beauty.i think it was 22 all faced with same pole outward).

[Turion]

I can do all of that today except give you the RPM at which the effect occurs. That may take a bit and I am under the gun on my house remodel. Contractor coming Monday to rebuild my back deck structural supports and I haven’t removed decking. Once I complete that, I can spend some time figuring out the RPM. This is a new rotor with 22 magnets so the RPM will be different than my old 12 magnet rotor. I SHOULD be able to get to it sometime in the next couple days. Have a doctor appointment this AM, so will work on the other stuff the minute I get back.

[Turion]

OK, got a video made. I took all the measurements you asked of a coil with an iron core that is what I have used for the last few years. It overheats, so I am looking at options. It is the ONLY coil I have with an iron core at the current time. I cannot take the core out of the coil I used, but this afternoon I will bare the wires on a brand new coil that has no core in it yet. It is "supposed" to be identical to the one I just did the video of, minus the core, and should provide the rest of the data you requested. The video is being processed by my YouTube program, to upload to YouTube, but I need to leave for my doctor appointment, so that may screw it up and I may have to start over when I get home. Should be a couple hours at most. Have a few errands to run in town.

Oh, it just finished. Gotta run
https://youtu.be/OKSOBxzcXLA

[alexelectric]

Mr. Dave's Coil Data

146.6 mh without magnet
126.5 mh with magnet
5.9 ohm coil ohm

You can see the difference in the induction of the coil versus the magnet, very good, lack of obtaining the capacitance, the tester does not reach to measure it, or it must be obtained in another way.

I made measurements on my coil and the data was:

7.3 ohm

I observe that I have a difference with respect to the coil of Mr. Dave, that is to say that I have more wire wound in my coil
With my meter reading capacitance it did not give me any measurement like Mr. Dave.

In order to obtain the capacitance of my coil, I did the following, I got a small capacitor which I obtained a reading of 13.77 nf, then I proceeded to connect it in series with the coil and the reading was 13.03 nf, so we have a difference of 0.74 nf, if the test is ok my coil has a capacitance of 0.74 nf.

I hope it can serve as a reference for you Mr. Dave. In my case I do not have an inductance meter for now, I am about to acquire one.

When I have the complete data, I will be able to obtain the pertinent calculations of the resonance, the generator worked at a frequency of 280 Hz.

Thanks to all who join in with their contributions and information to help improve the prototypes.

[pmgriphone]

Wow, you are fast!

I have thought about this a little bit more and I guess it's a bit more complicated that just hooking up the probes. Here is what I found online:

https://www.amazon.com/dp/B071WNNYQT...ing=UTF8&psc=1

There is a video on the Amazon link above, so take a look at that as well. In L/R mode the display should show a "1" when the probes are not connected. In C mode, it should read "0", to be adjusted with the black round knob.

The meter uses it's own frequency to try and determine L and C.

One of the Amazon comments says: "For what it's worth I attached a scope to my BM4070 (no coil) and in Inductance mode I measured the following: in 200uH mode: 1.19 kHz. In all other modes, 325Hz."

So the meter uses a 325Hz frequency to measure L and C.

Assuming that your motor probably runs around 2500rpm (correct me if I am way off) with 22 magnets on the rotor, this will translate into an overall magnet frequency of around 900Hz. So the meters measuring frequency of 325Hz should be well below the resonant coil frequency. So it is probably OK to measure L and C like this with this meter.

However, when you use the meter, you need to make sure the probes are disconnected when you turn the meter and want to measure capacitance. Also make sure (DH, display hold) is not showing in the display window.

When you are in capacitance mode, you will need to zero out the initial reading when the probes are not connected with the black round adjustment knob in the right lower corner. You will need to do this whenever you change capacitance scale. Start off with the largest scale (uF). Looks like in the start of the video you never went higher than the 200nF scale. Maybe your coil has larger capacitance than that since it is a parallel wire winding that is connected in series. That might be why you are reading a "1" in capacitance mode (clipped scale). So go up in scale and make sure you zero the capacitance reading whenever you change scale.

At the end of your video, you did go past the last uF scale and the meter wanted to read something there, but you went over it too fast, so give that another shot and make sure to zero the scale first with probes disconnected.

Anyway, this looks very promising if you are getting uF readings on the capacitance! Usually coil capacitance is in the order of pF. Based on my initial calculations, a capacitance on the order of uF is expected if my RPM estimate is correct.

The meter shows your inductance as 146.6mH (with iron core without magnet) and 126.6mH (with iron core and the magnet).

The resistance is 5.9ohms. What is your AWG wire gauge for this wire and how long is the wire approximately? I think you said you have 12 wires parallel wound, then connected in series. So how long is each of those 12 wires?

[pmgriphone]

Mr. Dave's Coil Data

146.6 mh without magnet
126.5 mh with magnet
5.9 ohm coil ohm

You can see the difference in the induction of the coil versus the magnet, very good, lack of obtaining the capacitance, the tester does not reach to measure it, or it must be obtained in another way.

I made measurements on my coil and the data was:

7.3 ohm

I observe that I have a difference with respect to the coil of Mr. Dave, that is to say that I have more wire wound in my coil
With my meter reading capacitance it did not give me any measurement like Mr. Dave.

In order to obtain the capacitance of my coil, I did the following, I got a small capacitor which I obtained a reading of 13.77 nf, then I proceeded to connect it in series with the coil and the reading was 13.03 nf, so we have a difference of 0.74 nf, if the test is ok my coil has a capacitance of 0.74 nf.

I hope it can serve as a reference for you Mr. Dave. In my case I do not have an inductance meter for now, I am about to acquire one.

When I have the complete data, I will be able to obtain the pertinent calculations of the resonance, the generator worked at a frequency of 280 Hz.

Thanks to all who join in with their contributions and information to help improve the prototypes.

Alex, your calculation is off. The capacitances are in series, so your coil capacitance is about 0.24uF.

[alexelectric]

ok thanks, I check it

[Turion]

Thanks for the tips. I was in a hurry this morning and then I worked all day on my remodel project, so I’m beat. But now is a good time to kick back and actually read the book on how to use the LCR meter and watch some you tube videos. I have a two channel scope, with an attachment for reading amps I plan on using that to measure the output of the coil as a generator coil, along with an analogue meter.

My wire size is AWG #23 each strand 253 feet in length with 28” hanging off the coil at each end for connections. So 250 feet actually wound on the coil.

I will print out what you wrote and work my way through it either later tonight or in the AM. Then post the data.

[pmgriphone]

The resistance of 1000ft of AWG #23 wire is 20.36 ohms. Total calculated resistance of 253ft of length is then 5.16ohms. So each of the 12 strands is 253/12=21ft long.

The calculated resistance of 5.16ohms is close to what you measured at 5.9ohms (maybe a bit of additional connection losses in the connector block and the meter leads).

I also note that the maximum current through AWG #23 is 4.7amps (chassis wiring in air or for a single wire), so you probably want to put a conservative fuse in series with your coils. Maybe start off with a 2 or 3amp (car) fuse just to make sure the copper wires don't burn out. You could increase the fuse rating later on to 5amps if things don't heat up too much when you attach a resistive load. Just play it safe so you don't burn out any coils. That would be a lot of work to redo those.

[pmgriphone]

Another couple of things that I need for calculations are the diameter of the opening of the coil (air/iron/ferrite area), the length of the coil and outside diameter of the coil (measured at the outer copper windings, not the bobbin). Not sure if you remember how many turns you have on the coil, but if not, I can estimate based on those dimensions and the wire length.

Also, I think you mentioned that you are use N52 magnets, correct?

[Turion]

Area of core 3/4" x 3 1/4
Diameter of wire 3 3/8 x 3 1/8 (minus core)
Yes, N52 magnets

[Quantum_well]

Is this something like?

IMG_20210403_151734~2.jpg

[alexelectric]

Imag.jpg Here are the spool measurements for the coil

[Turion]

Alex,
where did you get that. I lost my bookmark to where I ordered them from and my friend who is building these machines needs to order more bobbins. I’m OuT! I bought a CASE last time, so that shows you how many coils I have wound for the various versions I have built.

[Quantum_well]

Alex, thank you for that, if you have time could you please say the diameter of a finished coil.