Good idea, lets see how this could work.
To keep this simple, it's just a 12v battery. Rectifiers have zero voltage drop.
The 3 meter wind turbine cut in speed is 6mph to charge the battery.
The available wind power is around 68 watts.
12mph wind the generators output voltage is now 24 volts.
PM generator output voltage is directly proportionally to RPM, twice the wind, twice RPM, twice the voltage. The wind power is a cubic function, the wind power is 545 watts. (this follows the E=NARPB/2 developed in another thread)
The mis-match of the battery and generator will cause a 50% power loss, that shows up as heat in the generator.
A 3m wind turbine will be rated at 1kw around 20mph.The available wind power is 2525w. Generator's output voltage is 40v.
At 24mph wind, the generator output voltage is 48v.
Wind power is 4364 watts.
The battery – gen mis-match has 75% loss as heat in the generator.
With 3kw of heat, why does not the generator's burn out? Actually it can.
30mph, 60v out, with 8525w wind power. Now were smoking!
Most systems will furl the blades before this point...
Looking over 1kw generator output power vs wind speed, the power is sort of a straight line, not a cubic function as you would expect from the available wind power. Why?
Generator output impedance, lets take a look at a few numbers.
The table below is a numbers game, they don't add up correctly, explain below.
Three generator output impedances:
0.576 0.288 0.144
Wind wind bat power bat power bat power
speed power watts loss watts loss watts loss
- 545 250 250 500 500 1000 1000
- 1841 500 1000 1000 2000 2000 4000
- 4364 750 2250 1500 4500 3000 9000
- 8525 1000 4000 2000 8000 4000 16000
The bat watts is the power going into the battery, notice the linear line of the power vs wind speed. The wind power is not linear. This explains why the plots are a straight line. From this plot the gen impedance can be estimated.
If the sum of the bat watts + power loss is >wind power, then the power is first in the battery any left over goes to the loss. The generators total output power is the sum of the bat and loss power.
If the wind power is greater than the sum, the impedance is limiting the total power the generator can produce.
Now back to what this is all about. Extracting heat from the mis-match of the gen output to battery voltage. Some to most of the power in the loss column can be converted to heat as long as it does not exceed the wind power. More can be used as heat, by reducing power into the battery.
The resistor is added in series between the gen and battery.
Solid state device like several MosFETs could be used. Need to monitor gen frequency and control the voltage across the MosFETs.
If the heat is useful then over all system efficiency can be enhanced greatly.
Have fun,
Scott.