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#Post#: 5425--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 4:56 am
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Thanks CG, but i doesn't really answer my questions. If i make a
generator, whose output is 3phase DC (not AC), and i didn't
really want to charge a battery, i only wanted to heat water,
what is the most direct circuit, which would keep control of the
turbine but not stall it? Could a low power water heater run off
'un smoothed' 3 phase DC with its spikes etc, or does it need
the 'DC' waveform regulated thro a circuit first? If i do it the
way NP suggests, then i am continually topping up a battery,
which has its own losses. Obviously, when amperage generated
becomes to high for the heating element, i need a way to deal
with that. Just hoping you electrical guys can steer me right on
what is possible, rather than what would be the 'normal' way of
doing things.
Hopefully LW might answer the second question posed previously.
Got my Lynxwind Seagull75 zipfile today, so can always rely on
that if all my experimentations fail .....lol.
#Post#: 5427--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: lynx wind Date: February 8, 2015, 9:10 am
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You can power a heating element but you need to rectify the
three phase. A resistive load such as a heating element will
work fine on rectified 3 phase, but not so well on 3 phase.
Second question - you need to balance the turbine with a
alternator. They should be matched. You can overbuild an
alternator for a turbine but you should over build a turbine for
an alternator. In really strong winds the alternator needs to
be capable of outputting the power without catching on fire. At
a certain point in high winds the stator can be dissipating 85%
of the power as heat due to internal resistance. This would be
extremely rare, but that is how you have to design. Another way
to look at it is the alternator needs enough braking power so if
you throw the stop switch the turbine will slow. As for lots of
small magnets and coils vs few magnets and big coils? It
doesn't really matter except that you get higher voltage with
more magnets more frequency all else being equal.
So lets say at 10 mph a wind turbine is 35% efficient and output
is 35 watts. That means the power in wind is 100 watts. So at
20 mph there is 800 watts power in the wind and the turbine is
20% efficient and outputs 160 watts. Now at 40 mph there is
6400 watts of power in the wind and the turbine may be 10%
efficient and output 640 watts. What power will the stator have
to dissipate in an 80 mph wind? How many watts per sq inch of
stator? Think about a 100 watt bulb and how hot it gets, or a
1500 watt toaster. You want enough surface area to dissipate
the heat. Or build a stator with really low resistance but that
requires a lot more magnets.
#Post#: 5429--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 9:29 am
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Thanks guys,
The heating element i was looking at was this one(see link
below), at 7.5/8.5 amps per section, so hoping each separate
part of it could be utilised as the amps increase.
LW, what is the means of rectifying DC, as opposed to the bridge
rectifier on AC? Would the 3 phases be connected in star or
delta fashion in a similar manner as AC or what would be the
difference in circuitry required? I thought perhaps the
buck/boost system might handle the varying DC peaks and output
rectified as necessary?
link...
HTML http://www.ebay.co.uk/itm/low-voltage-12-volt-300w-water-heater-camper-boat-solar-wind-dump-load-x1-/291367916070?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item43d6e19226
Regarding the points made on Turbine/generator matching, i had
thought that as the windspeed/rpm's increased past a critical
level(whatever was designed into it), that the increasing
reactance set up in the higher number of coils, creating its own
magnetic field in opposition to the normal flow, would in effect
slow the turbine down(have a negative effect on magnets), thus
lessening the need to dissipate so much heat?
Thanks
jim.
#Post#: 5434--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: nessprojects Date: February 8, 2015, 6:02 pm
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@max
Not sure if you know but a alternator puts out AC power and to
charge a battery you would need to convert this to DC using
either Diodes or Bridge Rectifiers.....Running a heating element
would work with either but converting 3 phase to a single DC
supply would utilize all the stator coils.
Connecting your stator in star would yield about 1.7 times the
voltage but lower amps at any given rpm.
connecting your stator in delta would yield about 1.7 times the
current but lower volts at any given rpm.
My thoughts on what you are trying to do is to convert from 3
phase AC to DC then you would have to run some kind of pulse
width modulation controller that would be governed by your
turbine speed.
#Post#: 5436--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 6:14 pm
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Thanks NP,
I was aware of these things, but the initial question on
smoothing out 3 phase DC, not taking AC and rectifying
it(Attempting to build a 3phase DC generator). These are all
losses in efficiency, by the time you rectify AC, battery losses
etc etc.
If i could take 3 phases of DC and smooth out the wave forms,
then put this DC directly through the heating element as the
load, with only a Battery connected in such a manner as to come
into play, when either, the thermostat shut off the heating
element or else, the amperage got to high. I'm just not sure on
methodology of bringing together 3 phase DC and the capacitors
required for smoothing.
The second part of my previous question was regarding inductive
reactance and that does involve AC from what i can see. It
relates to the counter-emf being the source of opposition to
current flow. A constant direct current has a zero rate of
change, and sees an inductor as a short circuit. An alternating
current has a time averaged rate of change that is proportional
to frequency, this causes the increase in inductive reactance
with frequency.
#Post#: 5438--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: nessprojects Date: February 8, 2015, 6:25 pm
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Are you building a 3 phase motor to get Direct Current ?
Not sure on what generator you are planning on building that
will output DC from the outset.
Once you have DC then Capacitors will smooth out the voltage but
would not be needed on a heating element.
#Post#: 5439--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 6:31 pm
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Thanks NP. I thought i would need control circuitry for
regulating output to 12V and when(if) amps exceeded power rating
of heating element.
#Post#: 5441--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 7:02 pm
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CG, i have already built a solar thermal flatplate collector,
which does great in summer, but was only putting through 39degC
in this cold weather during the short daylight periods. I was
looking into potentially doing a thermodynamics type panel using
refridgerant and a fridge compressor(reverse fridge cycle, like
a heat pump), so collecting latent heat down to i think around
-16degC, but thought i would look at using the generally higher
winter winds instead, in a more direct approach. I enjoy coming
up with different ways of doing things. With the feed in tariff
we get here, my PV system(see photo below) on upper roof
actually pays for all my annual Electric and Gas heating bills,
so all this tinkering about is really hobby fun.
HTML http://www.imageupload.co.uk/images/2015/02/09/jimssolar001.jpg
HTML http://www.imageupload.co.uk/5UuW
#Post#: 5443--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 7:33 pm
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Not sure if that was similar to something i read, which was a
'printed' stator type thingy?
Think i'm probably a couple of hundred miles from NP. I was
hoping NP might draw me some circuits, but my next door
neighbour is a spark, so will probably bend his ear. ;D
Edit...on doing some reading, its not as above.
#Post#: 5445--------------------------------------------------
Re: Newbies Questions - PMA Generators
By: maximoney1 Date: February 8, 2015, 7:47 pm
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Cool CG.
Gotta exit mate, almost 2am here. Laters. :)
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