Saturation?

[mbohuntr]

 Hi!, I've been lurking for a while, and I just received my magnets for a trial coil.   Well... I'm getting .6 ohms coil restistance, at 45 turns. I hooked a 44 ohm resistor across the ends and made up a rotor with 4 magnets hooked up to my cordless drill.   My first attempt used the meter to complete the circuit without the resistor, and it gradually loaded the meter to 12v. I realize that this reading is incorrect, my second attempt used the resistor, and measured the voltage across it. I got hits of around 8vrms on the slow speed. I attempted to repeat it but I don't see any volts??? Switched to dc to check the meter and I am getting readings (small as expected), switched back to AC and still nothing???  Checked the connections, coil resistance, different meter... nothing??? Can a coil become saturated somehow?

Thanks   Mike.

[spinningmagnets]

Are the 4 magnets all on one rotor?

If yes, how are they arranged? by that I mean, if this is a 12 magnets-per-rotor design, are the four magnets located at 12:00, 1:00, 2:00, and 3:00 O'Clock?

[Flux]

No coils don't become saturated. You either have a poor connection or a meter dead on the ac range.

Flux

[ghurd]

Strictly as someone who enjoys watching an ammeter too long,

Check the resistor.

That works out to over 3W.  Resistor could be smoked.  Smoked resistors can do funky things.

G-

[TomW]

G;

Smoked resistors can do funky things.

I find them both hard to roll and even harder to light!





Tom

[ghurd]

Buy wire-wound (AKA pre-rolled)...

They light easy, if the voltage is high enough.  =)

G-

[mbohuntr]

I took an old motor rotor and stuck four magnets with alternating polarities. I later made up a 6 or 7 coil of #12 romex as I KNOW that is good, without resister, meter in series, I see no AC, and pick up a few mA's by moving a magnet by hand. My meters only go to 200mA so I did not want to put the drill to work there. I am picking up DC voltage as expected. I can take the meter to a wall outlet and it works fine?  I was going to hook up my oscilloscope, but until I can get the range, I don't want to smoke it. I didn't see any sign of overheating, but I will recheck the resistor later.  thanks.  I am puzzled because I origionally saw the voltage?.

[Flux]

This is crazy.

Where did you stick your magnets, obviously with no closed magnetic circuit. Do you mean 6 or 7 coils or do you mean a coil of 6 or 7 turns?.

Why mess with a resistor to measure volts it is not needed and it is pointless as an indication of ability to produce volts into a load.

What you are getting in ac volts is obviously lower than the meter can measure so it won't bother your scope.

The only dc volts you will see is a transient figure when moving the magnets slowly it will go alternately positive and negative. There is no mean dc value.

I don't believe you ever saw the voltage.

Flux

[mbohuntr]

 LOL, Sorry for the poor communication, the internet is hard to relay critical information on in a coherent way.  i took an old rotor (with the small windings and steel on it) and stuck 4 neo's on at 12,3,6,and 9 oclock with alternating poles NSNS. I am still is school for my associates in electronics, so I only have my classroom expierence to rely on, they say to always test voltage in parallel, across a resistor, and current in series by opening the circuit. I'm good with DC being a transient observation, because I did not register AC on the meter, This was another way to see if something was happening in the coil.

  After my initial series voltage measurment, I realized I may be overloading the meter's current limits, and the meter was climbing steadily to 12v but not bouncing around like I'd expect to see with AC. I then placed a resister in line and measured across it. i initially got 8.6 vac and was bouncing around a little as expected. When I tried to repeat it, nothing registered AC, but DC would still show small mV bounces as I would expect. I then wound a piece of #12 romex 6 or 7 times into a coil and tested it in case my initial coil was shorting or something. Same response, no AC. Could the rotor steel be making the magnetic field collapse? Or did I fry part of my meter's AC circuit for lower AC measurments?  The meter is a cheap digital radio shack with only 200, and 500 Vac settings. It will still register household voltage... Thanks, I'm off to the garage to check the resistor...Mike

[mbohuntr]

Update, This is stupid... i checked meter with 18v transformer, It's fine. resistor- fine, I reconnected circuit using two magnets,opposite poles,  got a couple of volts on drill slow speed. replaced with 4 magnets, meter immediatly started to climb, loaded slowly and steadily to over 45v on slow speed till my arms got tired (3-5 minutes) turned off, switched to 500v setting, NO VOLTS? switched back, NO VOLTS? switched to analog meter, even ran drill at high speed with meter on 10 vac setting, NOTHING?? 45 VAC converts to about 1 amp at 44 ohms, NOT POSSIBLE!! I'm using a 1/8 watt resister, no heat, smoke, nothing? Is the field acting funky???  Thanks for your patience.

[TheCasualTraveler]

     What kind of wire are you using? You say #12 Romex. Is that like house wiring wire with  plastic insulation or is it bare copper wire? I'm hoping your using magnet wire which is copper wire coated with a thin film of, what is it, Lacquer, Varnish? Not to be too simple but is your coil made from magnet wire and have you cleaned off all the insulation from the ends of the wires where you hook up the meter?

     Where exactly are you placing the coil in reference to the spinning magnets? What size are the magnets and what is the dimension of the coil (is the inside hole of the coil about the same size as the magnet?

[mbohuntr]

I am using a coil of magnet wire salvaged from a motor. made a 2x4 coil of 46 turns. I checked it against the twin still in an armature to make sure it isn't shorted. Both read .6 ohms. seems ok. It has ends made up for connectors, and their conductive. The romex was just a scrap I had lying around that has insulation on it. I coiled it to see if perhaps my magnet wire was shorted, but both act the same. Leading me to believe the rotor w/windings is somehow screwing up the field. I will try to make a rotor out of something else.(non steel) I held the rotor outside of each coil while running it. I'm expiermenting with salvage wire only to get a feel for turns vs. voltage vs. rpms.  I realize the salvaged magnet wire is no good for the final coils, but should work ok for trials.  

[Flux]

It's near impossible to discover what you are actually doing without pictures or a very clear description.

No idea of the magnet size, type or pole placement and no idea of how they are mounted or of the geometry between the magnets and the coil.

At best you are not going to see many volts from this set up and I still suspect it is so low that you can't measure it on ac.

Checking the coil resistance with a multimeter will not tell you if the coil is shorted but even if a few turns are shorted it will not prevent you getting something.

Digital multimeters have a high input impedance ( 10 meg commonly) and will read stray voltages if left floating and if you have some stray fields around you may be reading something not even related to the coil. Probably the times you get nothing are when you have a decent connection to the coil.

"I reconnected circuit using two magnets,opposite poles,  got a couple of volts on drill slow speed. replaced with 4 magnets, meter immediatly started to climb, loaded slowly and steadily to over 45v on slow speed till my arms got tired (3-5 minutes)"

Even a couple of volts with the drill on low speed seems optimistic for that set up but may be true.

When you changed to 4 pole was the geometry so bad that you cancelled most of the volts?

"meter immediatly started to climb, loaded slowly and steadily to over 45v on slow speed till my arms got tired ("

What on earth does that mean?  I assume the drill got to speed immediately and didn't creep up to speed over 3 minutes. The volts you got should be instant and should be directly related to drill speed.

No way will that have got even remotely near 45v and if it did you would have fried the resistor so whatever you measured at 45v was not real volts across either the coil or the resistor.

There is no saturation going on with the coils so forget that. You will make things worse if you stick the magnets on wood rather than steel.

If you stick to the analogue meter it will have a lower impedance and I think you will be far less inclined to confuse yourself reading something that doesn't exist.

I appreciate that without experience strange things can seem to happen but just go at it systematically and find out what you are really measuring.

Flux

[mbohuntr]

Thanks flux, I know that the AC measurement should be instant, The drill is a cordless and was held at full power on slow speed. gonna guess 300 rpms. A .1v float on the meter is understandable, but the meter immediately started to climb at a steady rate and only slowed when I backed away the rotor. bringing it closer sped up the rate??? I know it should not do this... They could not be actual volts as it would have fried something. It would also not repeat when I stopped ,changed the meter setting, and started again. The analog meter did not do this. Even on the 10v setting, the meter didn't move. You may be right on the magnet geometry, these are 2x.5x.5 n48 neos. The rotor is maybe 1-1/2" dia.  I was expecting maybe 3-4 volts. They did not look to be at all. Pretty much 90 degrees. Gonna try again w/2 magnets and the analog meter.  I'm not expecting large voltage, only a couple of volts that are repeatable. I will try to get some photo's posted.

[ghurd]

Wire salvaged from a motor?

Not good.  That has to be worse than from a transformer.

I had some crazy stuff happen with salvaged wire.  A mild short may not even show until voltage is present.  

Readings were all over.  Every test was different.  Same at the time, but never repeatable.

Guess what?  Flux straightened me out.

G-

[mbohuntr]

Sounds like I need some new magnet wire. Thanks. Keep you posted.

[ghurd]

Think CRT TV or monitor degaussing coil?

Maybe ~#19, lots of yards, easy remove the black tape and use.

G-

[TheCasualTraveler]

OK, stop the madness. I'm calling a "Do Over"

     So, welcome Mike. You say you just got your magnets, eh? What is your plan for them? What size are they and how many do you have? Do you have an idea of what you want to build with them. If it's an alternator than just giving us the size and number of magnets will narrow the field quite a bit as far as what you can do. What's that? You say you have ""2x.5x.5 n48 neos"" Great! Are those numbers in inches or metric?  Now How Many do you have? You also mentioned getting some magnet wire. Before you spend too much on that just get the $5 assortment from Radio shack. That will work fine for test coils till you know what you need for your project. Good Luck, hope to hear from you soon.

[mbohuntr]

Ok... I'd like to build the round air core alternater shown on windstuff now. Eventually I will work on the rectification, regulation and storage. I have almost completed my degree in electronics, so I understand most of the concepts. I bought 8 2"x1/2"x1/2" n48's I will probably use 4 on the rotor.  I had a old motor that I removed the windings from, there didn't seem to be too much varnish on it so it may be ok for tests. It still has the ends made up on it. I wrapped it around a piece of thin plastic pipe 2"x4" 46 turns. At a guess, I'm saying AWG 20. I took the rotor from the small motor and stuck 4 magnets on it at 90 degrees , alternating poles. I held the drill parallel to the windings so the magnets spin perpendicular to them(across them)Outside of the coil. I put a small resistor across the ends and clipped the meter across it. Running the drill on slow speed, (300 rpms) the volts kept climbing steadily??? after 3-5 minutes, my arm got tired, and the meter read 45vac??? Can't be right, it would smoke the resister. I flipped the meter to 500v, then back to 200v and tried again, no voltage??  putting it on DC, the meter bounces around a tenth amp. when the drill runs... so the coil is doing something...    

[TheCasualTraveler]

     Ok, lets forget your tests and results for now. To get a clearer picture of what your doing is the motor you stripped and put the 4 magnets on the same motor you plan to use for your project? Also, which of Ed's projects are you referring to? If you can, pull up the page of the project that you want to replicate on windstuffnow , copy the URL and post it so we can see. Yes, you were getting something from the coil. You can't spin magnets around copper coils without something happening but it may have been insignificant. A little more clear info and you will get top notch help from the Elders here.

[mbohuntr]

Actually I have no solid plans yet, more like trying to see if the calculations are close enough to anticipate voltage and current output. I thought it would be easier to produce a couple of volts for a tests. I am not planning on using the for anything, I just compared the coil still in it with the one I wound for ohms to check for a short. I'm going to have to set something up to take pictures, digital camera won't work on my laptop. Here is the link, It's the round one.

 http://www.windstuffnow.com/main/radial_air_core_alternator.htm

[TheCasualTraveler]

     Good. That's more clear. If you want to continue to see what you can get out of those magnets, try winding a coil where the inside open space of the coil is the same size as the magnet. (Ed of windstuffnow is really good with those layered/overlapping windings but that kind of stuff is a little more advanced.) Then, with magnets mounted to your rotor place the test coil as close as possible without hitting the magnets (1/16"). Expect to see a fraction of a volt at a couple hundred RPM's. When testing coils, it is customary to check the open circuit volts. You are correct about using a load (resister) for checking voltages in other applications but for this application you want to know the open circuit volts of the coil. If you can find open circuit volts of a given coil of a set size and number of turns and at a set RPM then you will be able to calculate the number of turns required to get you the voltage you want at a given RPM. Then after you know the number of turns, if you know the physical dimensions a coil can fill you can estimate the gauge wire you can use. Finally, from that you will be able (roughly) to estimate the power you can generate.

     On a side note, a fun thing to do when playing with coils is to short out the leads of the coil and hold it in your fingers next to the spinning magnets. You will feel the coil vibrate in your fingers. Play with it, move it in and out, turn it sideways and watch how the vibrations grow or diminish. You will feel beyond a doubt in what position the coil is reacting to the magnets most strongly. Oh, and watch your fingers. Don't do anything thats going to cause an injury. Keep the RPM's low for this.

[wooferhound]

I would have to ask how the magnets are polarized.

Are the North/South faces on the Ends, or are they on one of the 2 inch sides?

[mbohuntr]

Soo... The guage isn't dependent on the max current at max(a really bad day!!)rpms? I was looking at avoiding a meltdown during High winds.... Doh... That's why you furl isn't it, you guys get higher voltage through max turns and furl sometime before it smokes!!! AN EPIPHANY!!! Ouch...I think I hurt my brain... this just got a little more complex... If you run high resistance and fewer coils,you can't generate with slow winds, you run minimal resistance and shut er down when rpms raise the voltage/current to high. So... I could really use say...AWG 24,and get more turns in a coil...  (searches for aspirin...)   Woof,the magnets are polarized thru the thickness.  THANK-YOU ALL!!! We'll talk...

[TheCasualTraveler]

No. Slow down.

[TheCasualTraveler]

If I understand what you just said you have it wrong.

     Smaller gauge wire and more turns will make for more resistance, more heat and lower power (albeit higher voltage).

     For a test coil the gauge of the wire is not that critical as all you are determining with the test coil is how much voltage you can get using the magnets you have. For example, if you do a test and get 1 volt using a coil with 100 turns, then using the same magnets at the same speed you should get .5 volts using a coil with 50 turns. 25 turns would be .25 volts, you see it's linear. (These are hypothetical numbers based on imagined results from your particular magnets so don't misunderstand and think that all coils with 25 turns put out .25 volts.) You can then use that information and the proper formulas to calculate your turns depending on the number of coils, phases, how it's wired and rectified and what your target voltage is.

     The gauge of the wire is important and will determine how much power you can extract, the larger the wire, the more amps are possible and ultimately the size of the wire will be limited by the physical space allotted to the coil.

[mbohuntr]

 Sorry, night shift, too much coffee. your measuring open voltage to determine voltage output as it relates to that peticular coil configuration. What determines final current then? and since I will be wiring this in star configuration, If I decide to charge at 12 volts, will I need to add the voltages per coil together to get 12v per phase?    

[Flux]

I was right in the first place, what you would get out is too low for your meter to measure.

With the greatest of respect a degree in electronics doesn't help much with electrical machines. There have to be certain things correct to generate useful voltage, you have managed the concept that the magnet poles need to be alternate but you seem to have missed the concept that each pole of the magnet must link the coil in turn.If you have a coil about 2" diameter and you offer it up to some tiny magnets stuck on a rotor you will have several magnets acting within the hole of the coil.

In your case it may have worked to some extent with 2 magnets as one would be behind the steel rotor even if the geometry was crazy. With 4 magnets it seems almost certain that at any instant you would have 2 magnets of opposite polarity trying to push flux through the coil and the net result would be not a lot greater than zero.

See if you can find an old basic book on electrical machines the modern stuff is too complicated and the stuff on the internet is a mixture of the very useful and a load of crap and beginners seem somehow attracted to the crap ( probably looks more impressive than the genuine stuff).

Somehow your rogue voltages that didn't exist caused more confusion as you had convinced yourself that it did work at some point ( possibly if you had held the magnets in the correct relation to the coil by accident it may even have worked).

If your magnets are only 1/2" square, try again with a coil 2" long but with the hole about 1/2" wide ( wind it round a stick 2" long and 1/2" thick).

This time you will get something, it will not be a lot with those little magnets and no magnetic circuit but the same wire would probably get you 100 turns and with a reasonable drill speed you ought to get into the working range of your meter ( probably best stick to the analogue one).

Don't be too disappointed failure is not a disaster as long as you find out why it failed and know how to avoid it in future.

Flux

[Darren73]

Looks like someone's been smoking the low tar carbon film ones again Tom :-)