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#Post#: 5389--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 2, 2015, 10:08 am
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Cheers lynx, that was quick !
#Post#: 5390--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 2, 2015, 10:37 am
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Guys, please bear with me, if my stupidity reigns...
Take this example..
A generator of 6 coils & 8 poles is connected to a turbine who's
spec is say TSR=2 @ 10m/s 240 RPM giving output 'X'.
If another generator with 60 coils & 80 poles is connected to
the same turbine(same size coils, same spec poles, set at larger
diameter, but same spacing between poles & coils etc), wouldn't
it @10m/s simply need to turn @24 rpm (TSR 0.2) to produce the
same output ie number of poles past the coils for the same time
periods?
So what i'm trying to get a handle on, would a generator with 60
coils & 80 poles be nigh impossible to turn connected to a 48v
load/battery bank. If there is no cogging when unloaded, is it
the back EMF that makes it so difficult to turn once loaded and
is this directly proportional?
#Post#: 5391--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: lynx wind Date: February 2, 2015, 10:47 am
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It depends on how the alt is designed. Each turn of copper wire
has a current induced as a magnet passes at 90 degrees. Each
turn of copper adds up - as if you connect many small batteries
in series. Bigger magnets = higher voltage. More turns =
higher voltage. Bigger wire = less resistance. Less resistance
= more power to load.
All things being equal, yes your 60 coil alt will need to turn
much slower to put out the same voltage. More magnets = higher
cost
The biggest challenges as you learn this stuff is keeping costs
down, resistance low, achieving a matched alternator to a
specific wind turbine design. Starting with a tried and true
design and gently tweaking is a good place to start. Look at
the WindGenKits alt. Its designed to do 12 volts at 60 rpm and
for a 12 sq ft turbine. It costs about $1500 when you get it
completed. A 60 watt solar panel is probably a better
investment.
#Post#: 5392--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 2, 2015, 10:55 am
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Thanks lynx, just trying to educate myself( getting harder every
year lol), i already have the solar investments done, 2.59Kwp
gridtied array(we get a great feed in tariff over here), plus i
built my own solar thermal panel, for heating my hot
water(serpentine flat plate type, not evacuated tube), so great
in summer, not so good in winter.
If i start off with a known design, then i pretty much know what
i will end up with. If i was going to go down this route, i
would probably prefer do it through a company like yourself,
which is currently active....windgenkits appeared to be ahem
'down for maintainence' when i looked a while ago.
I would much rather come up with my own tweaks if i can, just
don't want to make simple basic mistakes (some chance lol)
#Post#: 5395--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 2, 2015, 11:12 am
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lol CG,
Guess lynx is beginning to feel like this guy....
I'd better lay off the questions for a while, before i wear out
my welcome...lol
HTML https://www.youtube.com/watch?v=wN9LdSdJbgw
#Post#: 5397--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: lynx wind Date: February 2, 2015, 12:25 pm
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@max
What specifically are you trying to make/experiment with? I
would be happy to get you started with some options and then
some general pointers. All of our wind turbines benefit from
the non-cogging type PMAs. But they can take many different
forms:
1. single phase
2. 3 phase
3. axial
4. dual plate
5. single plate
6. radial
I would recommend starting with the swept area of the turbine
first and then design the alt. Then think of the overall cost
of the alternator and rescale maybe. Also, how much turbine are
your neighbors willing to look at.
#Post#: 5399--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 2, 2015, 12:49 pm
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@lynx,
Load would effectively be the equivalent of a small fridge( ie
to power a fridge size compressor and a small pump...for another
design i'm working on).
I have a poor wind resource, basically when i read Hugh P's
book, it convinced me not to even try...but i'm stubborn(insert
stupid...lol), and came back to it. Mean winds are 5.5-6ms
(maximum winds last year were around 23mph, this year so far
38mph at my location) I do have a 'tunnel' effect at my house,
but it wont be laminar flow(I had to remove a tree which was
getting bent over in the wind towards the house.) Wind rose data
for the area, means that by far, the prevailing winds buffet
directly against the front face of my house, so hoping i can
exploit this. Also hoping to exploit the 'red zone' in the pic
below.
PMA design i'm hoping to build would be a dual rotor single
stator type, looking to wire the stator with three sepentine
coils(3 phase), using 22AWG 4in hand to keep resistance low, but
still give me adequate no of turns. I have several things i wish
to adapt to my circumstances/locale, but i need to get a better
grasp of the basics.
Turbine could possibly be up to 3m x 3m or any combination in
between....doesn't give me much by way of swept area, i know!
Appreciate your patience. ;)
HTML http://www.imageupload.co.uk/images/2015/02/02/airflow_over_roof.jpg
HTML http://www.imageupload.co.uk/5Cq2
#Post#: 5419--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 7, 2015, 2:24 pm
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Guys,
With my zero experience of electric circuits etc, can a 12v/300W
water tank heating element be run directly of a PM Generator,
producing 3 phase 'DC', (not AC rectified), such that it is the
main load, and only when the thermostat switched the heating
element off, would the 'DC' be directed to the Battery. If so,
how would i connect the three phase cables? Would they need to
go through a smoothing circuit/regulator first or some sort of
buck boost circuit? Would the battery connected after the
heating element still be able to regulate the circuit to 12V?
(sort of reverse to usual dump load scenario)
See diagram of what i am thinking, excuse the circuit(i dont
know how to draw them properly, but you should get the idea).
HTML http://www.imageupload.co.uk/images/2015/02/07/img110.jpg
HTML http://www.imageupload.co.uk/5U1R
Second question....
If i produced a PMG which had smaller magnets, but a lot more
numerous poles/coils, could the potential hz (or poles past
coils) be such at higher RPM, that the 'reactance' could protect
the stator from burn out in exceptional high winds? Ie the
stator would get to a point that it could only produce so much
amps and no amount of increased windspeed would enable it to
produce any more amperage, due to the increasing level of
reactance in the coils? Is this possible and if so, how
difficult would it be to define exactly how many coils/poles
would be needed to achieve such a 'state' at say a specific
windspeed and turbine spec?
#Post#: 5421--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: nessprojects Date: February 7, 2015, 4:07 pm
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Not sure where or why you would want 3 phase DC....Using 6
diodes will convert your 3 phases(AC) down to a single DC line
that will never drop to 0v whilst your turbine is spinning.
If your heater is in the region of 2 or 3 ohms then you could
use the heater on its own without a thermostat connected
directly to the DC turbine power.... but the problem is that you
will most likely load the turbine before the tip speed gets up.
What you really need is a controller to keep a battery charged
to the correct voltage then any overspill (dump) is directed to
your heater.
The diagram you have shown is something similar to what lynx did
with a transformer running a led mains light....Maybe he could
fill you in more than me on the effects this has on the turbine.
#Post#: 5423--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 7, 2015, 5:30 pm
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Thanks NP.
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