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WineGuy Newbie Joined: 16/04/2008 Location: United StatesPosts: 10
Posted: 05:43pm 16 Apr 2008
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I'm a newbie, so I may be wrong but here's the way I see it.
Assume that you have the two gens connected to the battery in parallel. The voltage at the battery is the voltage at the battery, there is only one number.
The voltage at the gen terminals must be higher than this voltage to produce any power.
The voltage difference (gen volts - battery volts) divided by the wire resistance is the current provided by this one individual generator.
The same holds true for the other generator. It is possible to have one generator producing power while the other one has not reached it's cut-in speed.
I believe that the above is true regardless of what the system voltage is, as long as you are running the generators in parallel.
If you run them in series, you add the voltages, but the current is limited by the generator with the smallest windings.
This sounds right to me. I have a reasonable amount of "theory", but not a lot of experience in the real world.
Hope this helps.
Sure wish I was smart instead of so darn cute!
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 12:53am 17 Apr 2008
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What is this full amperage? The only amperage you mentioned was the first post and this is not related to what you are trying to do now. You have only since provided some voltage measurements. Unless you provide a wiring layout and some useful amperage results from a controlled test, this is not going far.... Gordon. become more energy aware
Mertz Newbie Joined: 03/04/2008 Location: United StatesPosts: 15
Posted: 02:59pm 17 Apr 2008
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By full amperage I meant that it was not reduced by the voltage booster. I have been seeing over 8 amps in windy conditions from the Indiana and from 3 to 4 from the Ametek with the same wind until I hooked up the booster. I have not checked amperage on the Ametek with the booster connected by it should not be effecting the amperage output of the Indiana.
Therefore I go back to my original statement that if I have a 15.5+ volt input from the Ametek and an 8 amp input from the Indiana shouldn't I be making 124 watts?
Does anyone make a kwh meter for DC wind generators that I can use to track power output. I will ask the same question on a separate post so other people can find it who aren't interested in the booster question.Mertz
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 02:48am 18 Apr 2008
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Hi Mertz,
Wineguy has summed up the series/parallel differences.
Until you provide a basic layout of what you have done, then NO. This is like the specs for the generator. Each of the RPM data, give zero power output. Do you think the power output could be the product of the open cct voltage and the short cct current at these RPM's.?
The 15.5V you have given cannot be the battery voltage.
There may be a time in quite a bit stronger winds that you could expect 124W. This would occur at around 7m/s windspeed, for the total output from the two windmills that you have given rotor dimensions for.
Here are some of the relationships.
The wind energy follows a cubic relationship to the wind speed. If the windspeed doubles then the wind energy is 8x. Blades extract approx 1/4 to 1/3 of the energy from the wind in this size windmill. The energy extracted is proportional to the swept area of the rotor.
The economics of a grid connect system may be poor. The price you are paid per kWhr will be significant to the viability.
You should post some battery current v windspeed readings. These will enable more accurate responses.
check out Wattsup meters. These are US made.... Gordon.become more energy aware
Mertz Newbie Joined: 03/04/2008 Location: United StatesPosts: 15
Posted: 10:36pm 18 Apr 2008
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This is were I get a little lost. I don't know how a grid tie inverter will limit the voltage on the generators. A battery is controlled by the voltage of the battery. With batteries connect I reached 14+ volts in yesterdays winds which average 8 mph with gust to 22. So say I have 14 volts at the measured 8 amps equals 112 watts. I have actually seen higher than 14v.
With the Wattsup meter I could give you better current versus windspeed readings. I record my wind speeds at http://www.wunderground.com/weatherstation/WXDailyHistory.as p?ID=KWAREARD2&day=17&year=2008&month=4 If I can record my current in the same manner (based on time of day) I can determine exactly what my current to windspeed is.
I know the economics of grid tie is poor but not as poor as producing power to a battery which I can't use. The inverter is going to cost $300. If it doesn't severly limit the voltage to it, I can produce enough power to cut my electric bill by one months use. You can see by the chart that the Indiana has good potential. I am looking for another one to build a third mill or replace the Ametek30 with an Indiana. I would not even consider doing this if I had to pay the $2000 for an Outback inverter that still requires batteries.
Mertz
WineGuy Newbie Joined: 16/04/2008 Location: United StatesPosts: 10
Posted: 12:21am 19 Apr 2008
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Hi Mertz,
You wrote
With batteries connect I reached 14+ volts in yesterdays winds which average 8 mph with gust to 22. So say I have 14 volts at the measured 8 amps equals 112 watts.
This is close, but not quite right. Yes you DO have 8 amps, but in order to calculate the power you need to know the voltage DIFFERENCE between the gen and the battery. The generator produces no power until the gen voltage gets ABOVE the battery voltage.
If the gen is running at about 14 volts, and the battery is at at 12 volts (approximate numbers) You get (14 gen volts - 12 battery volts) * 8 amps, or 16 watts, This is much more in line with the 8 mph wind speed you quoted.Sure wish I was smart instead of so darn cute!
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 02:09am 19 Apr 2008
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Hi WineGuy,
The calculation you presented sort of matches the expected wind energy, but I would wait for a layout. You have calculated some sort of power loss in the wiring. The 8 amps has been quoted a lot. I think that this may have been a maximum reading at some time.
Hi Mertz,
until you provide some sort of wiring layout diagram for your system, we really are guessing.
as an example:
your mills, 1.5m rotor x 2, gives 3.53m^2 total.
my mill is 2.1m dia, area 3.46m^2, your total output would be expected to be similar to mine in the same winds.
I currently have 2-3.5m/s winds and my mill is producing 4-20W.
2m/s=4knots=4.4mph, 3.5m/s=7knots=7.7mph
the expected power of my mill is 4.5W@2m/s and 24W@3.5m/s.
The actual readings above do compare well with the predictions. The current at my battery voltage is 0.14A@2m/s and 0.7A@3.5m/s.
This is fairly typical with my mill and I have a maximiser. My mill is only generating 8-13V for this output. I am supplying a 24V nom battery, that is currently at 28.4V and this power is being fed back to the grid. The VxI from the mill is converted to the battery VxI by my maximiser cct. This is a dynamic converter. The only time the maximiser system regulates the output voltage is when the mill is producing more than the load can absorb or all loads are disconnected. This will then electrically shut down the mill.
The link you provided to your windspeed data does not appear to be a valid page on the underground weather site. The data would only be valid if it was gathered in close proximity to the windmill anyway. My weather station sensors are within 5m of my windmill.
This will continue to be a futile exercise until it is clear what you are doing..... Gordon.
become more energy aware
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 12:38am 22 Apr 2008
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Hi Mertz,
I am not trying to discourage you asking for some sort of wiring layout. Can you confirm that the Indiana produces the current even without the Ametek connected? This will confirm that you have a parallel or series arrangement. Each of the machines are brush type and will require a blocking diode from the battery.
Your concerns with voltage changes without a battery are valid. The degree of fluctuation will depend on the type of control used by the inverter. Windmills should have a dump type maximum voltage regulation system.
What type and brand is the grid connect inverter you have mentioned? .. .. Gordon.become more energy aware
Mertz Newbie Joined: 03/04/2008 Location: United StatesPosts: 15
Posted: 07:54pm 22 Apr 2008
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I am sure I have a parallel connection. I have switches installed so I can switch either or both generator off. I still get readings from the Indiana with the Ametek turned off and visa versa. I have blocking diodes at each generator just before the parallel connection after the switch. From there it goes to the batteries. I have multimeters connected before the diodes at both generators and one at the point of parallel connection.
I am looking at the SWEA inverter from Holland. The older solar units had a input range from 0 to 36v which I think would be ideal for my installation. They have an interchangable CPU that can convert them to different voltages. One supplier told me he could get a 12v version but that is not what the factory in Holland told me. They go for $300 for a 250 watt unit and higher for the 500 watt unit which is supposed to be 12v.Mertz
dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574
Posted: 11:08pm 22 Apr 2008
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Mertz
Have you try to look at Australian made inverter Latronicis and Selectronic both have very goog range of pure sine inverter
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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