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yahoo2
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Posted: 14 May 2018 at 7:29pm | IP Logged Quote yahoo2

there is a basic formula/ principal I am having a hard time remembering ATM, I just got distracted by Janice Peterson's white dress.

if you ignore the 3 phase to DC rectified difference in voltage for a moment, and the resistance in the wire and the potential of MPPT. You can adjust for that later.

Ummm, so the load determines the voltage.

24 volt battery will start at around 26-27volts and finish at 29.6 volts

your wind turbine will output a voltage per rpm based on the resistance of the coils.

here is the tricky bit. No , its no good, Janice is doing it again! Here is the answer I gave someone several years ago. unfortunately the website with the formula doesn't exist anymore. I might have a copy I can post if I can find it.

Quote:
The first section is about calculating volts per revolution or revolutions per volt.
open voltage is the generator spinning with no load or battery connected (amps). so as the turbine spins faster the voltage increases at a constant rate.

The next part is about using this information to calculate the power generated when the turbine is connected to a battery.

The turbine will spin easily until the volts per revolution are equal to the batteries resting voltage. As the turbine spins faster the batteries voltage starts to rise and the resistance of the battery bank gets higher and puts an increasing load on the turbine as it spins faster.

What he is saying in the example is that a 12 volt battery bank will be at its highest practical load at 14.6 volts, as the battery voltage rises above this point the battery will be getting close to fully charged or starting to turn the water in the battery cells to gases instead of loading the turbine.

what gets turned into amps is everything between the battery voltage (14.6) and what the open voltage would have been with no load at that turbine RPM.

So in the example at 885 RPM 20.6 (open) volts minus 14.6 (battery) volts equals 6 volts of potential power.

6 volts divided by the stator ohms
6/0.6 = 10 Amps produced

10 amps * 14.6 volts = 146 watts

from this you can play with the numbers.
what if I used a 48 volt battery (58.4 volts) what would be the rpm at 10 amps produced?
or changed my stator wire resistance?

once you can understand this basic concept everything else is just small added steps to make your calculations more accurate.




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BarkyJ
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Posted: 15 May 2018 at 2:22pm | IP Logged Quote BarkyJ

Thanks Yahoo2
Cracking up reading your comments about Janice - I had to google to figure out who she was. :)

That explains alot, thanks for your post.

I guess in normal applications, people are charging batteries or directly into gridtie inverters etc. I do want to get into that, but to start with I just want to dump everything I can, into the element. This will then give me time to figure out the conditions here, and just understand the windmill itself, without the distraction of batteries etc.

So in terms of wiring configurations for the stator, if I aim for low to mid wind only (we wouldnt see high wind often, and when we did I would likely shut this thing down). If I use a 36Pole 2X6C configuration, and aim for max power into a 36V load, I wonder if that is the best idea.

So because I dont have to overcome battery voltages, nor worry about over charging etc, I just have to ensure I am only putting 900W max in when at 36V.

So based on previous tables, potentially at around 60RPM I would see 36V coming in. I then just adjust the load based on the voltage, and try and keep it around the 36V mark. Does that sound viable?

Do you guys use any sort of RPM sensor? I know the stators have a sensor on them, but I haven't yet looked at what sort of output they give. It would be quite neat to record this and even use it in the calculations. Anyone played with the build on sensors at all? I have a vague recollection they are 3 bit and increment in some sort binary pattern, so even using 1 bit just to get a blip on rotation, likely will suffice...
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DaveP68
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Posted: 16 May 2018 at 1:00pm | IP Logged Quote DaveP68

yahoo2 wrote:
I just got distracted by Janice Peterson's white dress.



Yes had to look up Janice too, I got got distracted...

The IGBT I used is a 600 VDC version with lower current limit IRGBC30S

It can still be use to drive a resistive load of about 20 - 30 ohms if used in the high voltage low current mode. To use the 1.5 ohm heating element will require a lower voltage higher current device.

For an RPM sensor just reuse the RPS unit that was mounted on the 36 pole copper stator.



Has 5x pins +15 VDC, 0 VDC, phases 1, 2 & 3 outputs. Only need to use a single phase output to measure RPM.

24 pulses per/sec = 60 RPM.

David

Edited by DaveP68 on 16 May 2018 at 1:03pm
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BarkyJ
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Posted: 16 May 2018 at 5:44pm | IP Logged Quote BarkyJ

Thanks Dave

So 15VDC for those RPM sensors, is that the limit, or thats the nominal voltage? Can it run from 5VDC?

24 pulses per/sec = 60RPM, is that for a stock stator, and does it change when you change the stator wiring, or totally independent of that?
where does 24 pulses per second come from exactly?

60 RPM = 1 RPS so 1 rotation is 24 pulses... ? But arent there 36 coils, split into 3 phases, so wouldnt you get a 12 pulses on each phase output of the sensor, each rev? How do you get 24?

Sorry I have no idea how these work, just trying to get my head around it.

Thanks :)
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DaveP68
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Posted: 16 May 2018 at 6:46pm | IP Logged Quote DaveP68

I have no problem with your questions, as you're still new at this.

The 24 pulses translates to 24 Hz, which intern refers to the black rotor cap having 48 magnets (24 North poles + 24 South poles). So 1 rotation per/sec produces 24 pluses out of each Hall effect sensor.

The 15 VDC supply will be their upper operating limit and they will still work down as low as 10 VDC.

When using a 42 pole stator with a 56 magnet rotor cap the output of the RPS (it uses a different version) will be 28 pulses (28 Hz) for 1 rotation per/sec.

In the past I used a Fluke multimeter in frequency mode to measure RPM.

Now I use a Fisher and Paykel motor controller board with only the RPS unit connected (motor disconnected) to show RPM. When in diagnostic mode it can give you the true RPM reading. These F&P motor controllers aren't isolated so all connections in & out of the board are considered at mains (230 VAC) potential!!



Here's a display module connected to a motor controller I use to measure RPM.

Edited by DaveP68 on 16 May 2018 at 6:55pm
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Posted: 16 May 2018 at 11:57pm | IP Logged Quote BarkyJ

Awesome thanks Dave

ok 24 pulses it is then. I hope to set up a bench test using an old drum to start with, and a drill, and start putting together some sort of basic controller with LCD readout, and have it vary a load and just see how it reacts.

Thanks again
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Posted: 16 May 2018 at 11:58pm | IP Logged Quote BarkyJ

I think the best FET for me to use is the IRF3006 which is 60V 195A rated, and logic level compatible so simple to control, so at 5V its fully on and capable of switching the full current.

Sad the RPM sensor doesnt work down at at 5V, but thats alright, ill make it work or even put on a different RPM sensor entirely.
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Posted: 17 May 2018 at 4:50pm | IP Logged Quote DaveP68

Hi BarkyJ

Have you checked out my topic on F&P Electronic Dynamic braking ?

The circuit that is published lower down on page 2 can be modified to operate in a dual mode that controls both the voltage and current to achieve MPPT. Also the IGBT can be substituted for a IRF3006 and simpler to control like you say.

David
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BarkyJ
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Posted: 17 May 2018 at 5:08pm | IP Logged Quote BarkyJ

Hi David

I had seen that circuit when I was reading as many posts as I could.
Isnt it something for your dynamic breaking, rather than voltage current control?
You are talking about this Dynamic Breaking concept circuit, right?



You are doing pure hardware control are you, rather than software controlled hardware?
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Posted: 18 May 2018 at 9:33am | IP Logged Quote BarkyJ

Popped back to the trusty Dump shop again today, and this time they gave me a hi-vis jacket and let me out the back. Wowzers, so many machines out there.
Most of them are old though, but I found another Black Rotor, another Copper Stator 36 pole, 2 White 48 Magnet rotors (for a rainy day), and 2 modern drive shafts/nuts etc.

Also arrived today is my AC/DC Element for my load, 1x AC 29ohm 240V ring, and 2x DC 3ohm 36V rings to parallel into 1.5ohm. Measured it and its actually 1.4ohm at room temp.

Before putting the element into our main cylinder, I have a 25L under bench cylinder which I will do testing on first. Glorified dump load really.

Making progress.

Edited by BarkyJ on 18 May 2018 at 9:36am
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Posted: 18 May 2018 at 7:41pm | IP Logged Quote BarkyJ

So I just went to the shed and had a play with my F&P bits. Cleaned all the drive shafts I have and started thinking.
Went outside and got one of the outer drums with the bearings in it, and put a newer shaft in it, copper 36 pole stator on and then started thinking about dual stator...
On one end it looks simple with stator and black rotor and centre built-in bolt to the shaft. The other end.... hmm.
I got my 2nd black rotor and popped out the centre built-in bolt and then put that on the other end of the shaft.
I then got one of the old shafts and threaded that into the end of the 1st shaft and it damn near makes a perfect fit, thread through the black rotor. New shaft is female both ends. Old is mal3 both ends...

I cant be the discoverer of this... surely.
I could lathe off the bulk of the 2nd shaft and use that to bolt to the prop....
No welding required potentially.
Needs more investigation.

Ill go take a picture.


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Posted: 18 May 2018 at 9:28pm | IP Logged Quote BarkyJ



New shaft in machine drum.
Black rotor on shaft like normalbut without plastic bolt in rotor.
Old shaft threaded into new shaft through black rotor hole.
Cut off old shaft after spline nut.

Zzzzz
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