Author Topic: Anybody guess what this is going to be???  (Read 17613 times)

Offline Don1966

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Re: Anybody guess what this is going to be???
« Reply #45 on: June 29, 2013, 02:30:35 AM »

I was able to light a large LED with the full wave DC, but when I took out the rectifier, it wouldn't light with straight AC. 

Chuck
The reason they didn't lite is because with the rectifier you had both halves of the sine wave. The LED is a rectifier and only conducts one way so you only had half of a cycle and half voltage.
I still stand by the fact that the magnets need to be the size of the pole piece to get max flux coverage.

Don

Offline MuellerNick

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Re: Anybody guess what this is going to be???
« Reply #46 on: June 29, 2013, 11:47:34 AM »
Looking at the basic physics of a generator, we see two things we want (or not) to get out of it: Voltage and amperage.


Voltage is a function of flux-change. The higher the speed of flux-change, the higher the voltage. That means more RPM and/or more poles for more voltage.
Amperage is a function of flux-strength. Need more amps? Stronger magnets and/or improve the flow of the flux through the coils. But not the problem here.


If you look at a motor, and keep in mind that it is just the reverse of a generator, things get more obvious. The higher the voltage, the faster it turns. The more poles, the faster it turns.
The higher the load, the more amps.

On edit, an addition:
If we see that the voltage is substantially higher without a load compared to with a loaded generator, we see that it doesn't provide enough current. So we need to improve flux-strength too to get what we want.



Nick
« Last Edit: June 29, 2013, 11:53:17 AM by MuellerNick »

Offline Don1966

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Re: Anybody guess what this is going to be???
« Reply #47 on: June 29, 2013, 01:13:21 PM »

If you look at a motor, and keep in mind that it is just the reverse of a generator, things get more obvious. The higher the voltage, the faster it turns. The more poles, the faster it turns.
The higher the load, the more amps.




Nick
Nick, I Think you are talking about a DC Motor, speed is a function of poles and Frequency of the source for AC motor.
Voltage is a function of coil turns and flux change for Generator. Speed will also cause higher voltage output.

Don
« Last Edit: June 29, 2013, 01:17:28 PM by Don1966 »

Offline MuellerNick

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Re: Anybody guess what this is going to be???
« Reply #48 on: June 29, 2013, 01:36:34 PM »
Quote
Nick, I Think you are talking about a DC Motor, speed is a function of poles and Frequency of the source for AC motor.


Frequency is just an other means of speed of flux-change. Look at the collector as a mechanical VFD.


Nick

Offline b.lindsey

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Re: Anybody guess what this is going to be???
« Reply #49 on: June 29, 2013, 01:53:50 PM »
This stuff is like greek to me...do you guys know of one or two good basic texts for explaining motors/generators/alternators for us non electrical types?

Bill

Online steamer

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Re: Anybody guess what this is going to be???
« Reply #50 on: June 29, 2013, 03:11:39 PM »
Though I haven't seen a schematic yet, If you take a google look at small wind turbine generators for home build...you'll find a lot of information....I have some of these articles somewhere....just can't put my hand on it at the moment..


Dave
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Offline cfellows

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Re: Anybody guess what this is going to be???
« Reply #51 on: June 29, 2013, 04:54:33 PM »
The basics of a generator (or alternator) are much as Nick says.  However, you can also increase the voltage by increasing the number of windings.  And I think Don and Nick are right that I can increase the current (amperage) by increasing the number and/or strength of the magnets and by reducing the spacing between the magnets and the stator poles. 

I agree with Don that having the magnet(s) the same width as each stator pole, or in this case each stator winding, would be optimum and if I use the remaining magnets that I've ordered, my armature will have three magnets side by side that will add up to about the same width as a stator coil.  This will, of course, also add more magnetic strength which will increase the current.

So, the quandry is why 3.4 DC volts would light the bulb and 3.6 AC volts wouldn't.  I realize with the AC voltage, that current would only flow for 1/2 of each cycle and the other half is essentially wasted, but I would have thought that would still be enough to light the bulb.  Perhaps the amount of current being produced is so small, 1/2 a cycle just isn't enough.

I have to verify this but I believe my dynamo is set up like this: 

1.  There are 8 stator poles with the coils all hooked in series and alternating coils wound in the opposite direction.  Each coil is 200 turns of #27 wire.  The total resistance of the stator is about 22 ohms.

2.  There are 8 sets of magnets comprised of 2 magnets each, both with the same pole facing out.  Alternating sets have the opposite poles facing out.  The magnets seem pretty strong.  They are 1" long x 1/4" wide x 1/8" thick.  Don't know the Gaussian rating but the KJ Magnetics web site rates them at 7.34 pounds.  Adding one more magnet will add another 50% magnetic strength to the armature.

By the way, I'm assuming when I measure the AC at 3.6 volts, that means 3.6 volts positive wave followed by 3.6 volts negative wave.  Don't know if that is peak voltage or RMS.

Chuck

So many projects, so little time...

Offline Don1966

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Re: Anybody guess what this is going to be???
« Reply #52 on: June 29, 2013, 05:55:57 PM »

So, the quandry is why 3.4 DC volts would light the bulb and 3.6 AC volts wouldn't.  I realize with the AC voltage, that current would only flow for 1/2 of each cycle and the other half is essentially wasted, but I would have thought that would still be enough to light the bulb.  Perhaps the amount of current being produced is so small, 1/2 a cycle just isn't enough.


By the way, I'm assuming when I measure the AC at 3.6 volts, that means 3.6 volts positive wave followed by 3.6 volts negative wave.  Don't know if that is peak voltage or RMS.

Chuck


One of the reasons the that would not illuminate  the LED lite, would be its turn on voltage, some require over 1.5 volts to light. Being half wave rectifier give half voltage on AC, so you my not have had enough to forward bias the LED.
The voltage you measured would be RMS if you used a meter to read it with.
By the way you should read less DC voltage that AC. Voltage. The rectifier will droop 1.4 volts across it and the conversion from AC to DC depending on the frequency will give you less.
This link should help you. http://cas.web.cern.ch/cas/Warrington/PDF/Visintini.pdf
Don
« Last Edit: June 29, 2013, 06:44:23 PM by Don1966 »

Offline Admiral_dk

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Re: Anybody guess what this is going to be???
« Reply #53 on: June 29, 2013, 09:14:00 PM »
You need to pay premium prices to get at "True RMS" meter  :old:  all cheap multimeter's can't measure RMS .... or more correctly they can IF the voltage is a PURE sine - if not the measured voltage might be as much as 90% wrong  :old:

Since I often repair old tube amps for guitars (not pure sine out), I bought a "True RMS" meter years ago, and I can tell you it makes quite a difference on the result I get on power output.

Chucks alternator will deliver a pure sine (if the armature, windings and the magnets a perfectly equally spaced), when loaded with a pure resistive load !!!!

But loaded with a rectifier and / or LED's => all bets are off, except to say that the output is anything but a pure sine => all measurements with a non "True RMS" meter might be up to 90% off - so comparing the AC and DC voltages doesn't tell you anything usefull in explaining why one works and the other not.

I can admittedly not remember if you'll measure a higher of lower result in this case - sorry.

Alternative to the "True RMS" meter can be a oscilloscope - it will not be perfect, but it will give you a ballpark voltage across the load, within a few %.

Offline Bezalel

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Re: Anybody guess what this is going to be???
« Reply #54 on: June 30, 2013, 04:39:28 AM »
So, the quandry is why 3.4 DC volts would light the bulb and 3.6 AC volts wouldn't.  I realize with the AC voltage, that current would only flow for 1/2 of each cycle and the other half is essentially wasted, but I would have thought that would still be enough to light the bulb.  Perhaps the amount of current being produced is so small, 1/2 a cycle just isn't enough.

Chuck

Hi Chuck
 
There are a number of factors that could be at play here.
 
1. What is the colour of the led you are trying to illuminate.
 
The higher the wavelength the higher the forward bias voltage you need to get it to conduct and illuminate.
 
2. what is the device you are using to measure the AC voltage.
 As you said you don't know whether it is RMS or not.
 
It will depend on a number of things.
 
If the meter is a galvanometer type the voltage will most likely be moving the coil meter movement by average rectified voltage of the waveform applied or 0.637 of the peak if it is a sin wave, in many voltmeters this is often calibrated to assume the waveform is sinusoidal  and therefore read the RMS voltage of 0.707 (or half the square root of two) of the peak voltage.
 
If the voltmeter is a DMM the possibilities are equally as vague - because the input can be either rectified averaged in the same way as the galvanometer type or in a more accurate meter, the input can be chopped at high frequencies and take instantaneous dc readings of each pulse and mathematically calculate the true RMS voltage whatever the waveform is.
 
I am guessing your meter is likely to be indicating a Pseudo RMS.
 
This leans us towards the likelyhood that the problem is LED colour, which if white could need as much as 3 to 4 volts to turn on because you need the full visible spectrum of wavelengths to get white light. ( often achieved by internally parallelling multiple LEDs of different colours, in the single package)
 
You could test this forward bias limitation issue by using clear lens red LEDs as they require lowest voltage to illuminate. If the red LEDs give you a good illumination then bias voltage threshold is probably the issue.
 
note that illuminating a LED with AC it will only lite up while the voltage is above the forward bias voltage.
 
so if your peak AC voltage is 4 volts and the turn on voltage of the LED is 3.5V, then the LED will only be conducting - maybe 10-15% of the time, with the result being of a very dim illumination and one that is probably not visible.
 
I hope this information will help you find the problem.
 
Of course all the other suggestions to help increase the voltage and current capabilities of the generator will most likely over come the issue any way, but it will be interesting to identify the real reason for the apparently buzzar behaviour of your LEDs. 
 
Bez
« Last Edit: June 30, 2013, 04:53:20 AM by Bezalel »
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Offline cfellows

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Re: Anybody guess what this is going to be???
« Reply #55 on: July 12, 2013, 07:15:38 PM »
Just a quick progress report here.  I wasted a week thinking I had ordered more magnets when in fact I hadn't.  So it took another week to get a second batch of magnets delivered.  Previously, I had 2 magnets per pole but was missing 1 magnet on 1 pole (breakage). 

When the new magnets arrived, I installed the 1 magnet needed to complete the 2-magnets-per-pole armature.  When I test spun it with my cordless drill at around 1500 RPM, I measured right at 4.0 volts AC.  So, I (finally) located my stash of bright green LED's and hooked up 18 of them in parallel, every other one wired in the opposite direction.  Then I hooked up the alternator with no rectifier, just straight AC,  all 18 LED's lit up very brightly.  So I'm pretty happy with it at this point.  However, I'm planning to build another stator using a 1" length of 4" pipe, 1/4" wall.  The poles will be made up with steel cores that I can wind separately, then attach to the stator ring.  Probably won't be the most efficient set up in the world, but should give me more power.  I do want to put some kind of load on the engine and I don't think the current setup with LED's is going to do it.

Chuck
So many projects, so little time...

Offline Roger B

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Re: Anybody guess what this is going to be???
« Reply #56 on: July 12, 2013, 07:22:04 PM »
Definitely moving in the right direction  :ThumbsUp:

I always like to see engines driving something.
Best regards

Roger

Offline b.lindsey

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Re: Anybody guess what this is going to be???
« Reply #57 on: July 13, 2013, 12:26:23 AM »
That's good news Chuck, sounds like things are moving in the right direction :)

Bill

Offline Rustkolector

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Re: Anybody guess what this is going to be???
« Reply #58 on: July 13, 2013, 04:42:12 AM »
Chuck,
You are definitely are the right track. Many poles, many turns, and a steel stator will give you a reasonably high voltage output at low RPM. How are you planning on managing the cogging effect that a steel stator and permanent magnets will create?

Jeff

Offline cfellows

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Re: Anybody guess what this is going to be???
« Reply #59 on: July 13, 2013, 05:55:12 AM »
Chuck,
You are definitely are the right track. Many poles, many turns, and a steel stator will give you a reasonably high voltage output at low RPM. How are you planning on managing the cogging effect that a steel stator and permanent magnets will create?

Jeff

At the moment I don't have a plan other than hoping it won't be too strong...

Chuck
So many projects, so little time...