Methods of holding down heat in the stator

[HenryVG]

I'm trying to get a better understanding of what will cause heat in the stator, as when I get past the "thinking" stage I want to understand the design parameters of a generator.

If I understand correctly, if the generator is making more current than can go into batteries or a resistive dump, it "backs up" as heat in the stator. So if I have my 48V generator providing 10a of current to my 12V batteries, once they hit 14V or so, they can't accept any more storage, so I have created a big resistor out of my batteries and this heats the stator.

Am I looking at this right?

I am imagining that balancing my storage with my expected output is key to keeping heat down. Do I just do this by keeping the voltage 'drop' from the generator into my batteries small, or by not running a large blade dia, or by having a big battery bank, or am I missing something?

[sdscott]

Hi, read this for a better understanding; http://www.fieldlines.com/story/2006/3/17/185646/194

[finnsawyer]

Current does not "back up".  The total current that flows in a "circuit" depends on the total resistance in the circuit and the voltage applied to the circuit.  The total resistance is the sum of the alternator resistance and the battery resistance.  The applied voltage is the alternator voltage, usually taken as the open circuit voltage.  The power causing heating in the alternator is equal to the current (in a given phase) squared times the phase resistance times three as there are three phases supposedly balanced.  This is further complicated by the fact that the currents in the alternator are pulses meaning that the power dissipated varies with time.  That is, each phase produces a positive pulse of current for one sixth of the time and a negative pulse for one sixth of the time.  So, one usually deals with average power or simply looks at the power delivered to the battery and hopes the alternator can cope.  At the very least you should get a book on circuit theory.

[ghurd]

Heat is made by watts used in the stator.  If the stator has 1 ohm resistance and the flowing amps change...

Amps x Amps x Ohms = Watts.

Then 1A x 1A x 1ohm = 1W of heat in the stator.

And 2A x 2A x 1ohm = 4W.

And 4A x 4A x 1 ohm = 16W.

So 4x the amps mean 16X the heat.  Heat is wasted power.

Also notice the losses due to resistance.  

The above numbers show a waste of 16W at 4A charging current.

If the resistance is doubled to 2 ohms, the 1A charging current wastes 2W, while 4A wastes 32W.

Power used in the 1 ohm example for 4A at 12V is 16W.  48W(battery) + 16W(heat)  = 64W the blades need to make.  75% efficient.

For 2 ohm coils at 4A, 48W + 32W = 80W for only 60% efficient.

It doesn't look like a lot at first, but it is a 25% increase in efficiency.  The blades don't need to work as hard, and the stator makes less heat.

The 16W difference in the stator losses of a small 12V machine can mean an amp more charging current.

G-

[Nando]

A method to manage the heat in a stator is one that minimizes the dissipation in the stator windings.

Minimize the internal resistance of the windings.

Produce the highest possible voltage

Have a load that it is at least 10 or more times the internal resistance of the windings.

Use a controller that has MPPT ( Maximum Power Point Tracking) which allows the wind mill to rotate to the highest best RPM to maximize the harvesting of the power available in the wind, corresponding to the area of the wind mill and generator capacity.

UNHAPPILY, most to the wind mills still use the OLD technology of the late 1800's that due to the lack of the proper ways to produce and control the generated power, the wind mills were designed to produce a voltage a bit higher than the battery bank that was close to the wind mill - the principle of clamping the generated power to the battery bank level -- STILL used thinking that it is the best.

Wind mills with battery clamping, normally, have a maximum efficiency of around 43 to 50 %.

Using present technology with a controller with MPPT and the generator designed for high voltage , the efficiency may reach up to 85+ %.

Another problem is the type of power regulation using FURLING to control the angle of attack of the wind mill itself to the wind.

A better solution is the power regulation using PITCH control of the blades that is always frontal to the wind.

In addition for even better stability and better wind mill protection and life is the PITCH control activated by the torque of the generator and not using fly weights to control the pitch of the blades.

It is worthy to note that the wind mill with Pitch control via Generator Torque, may minimize its power and lower RPM if the Generator load does not exist.

So a 1 KW peak power using old technology if changed to the present technology that wind mill may be able to produce around 1.6 to 1.8 KW.

Indeed, many may say that it is too expensive to do it, but it is more expensive if the wind mill crashes due to the limited protection of the Furling system (sometimes indeed work well, though not very often).

Ideal wind mill:

Wind mill with PITCH CONTROL

Pitch control via generator torque

wind mill with a power controller ( charger or inverter).

Nando

[finnsawyer]

"Minimize the internal resistance of the windings.

Produce the highest possible voltage"

In other words use the strongest magnets with the heaviest wire that you can to get the output you need.  A simple engineering requirement, which the modern magnets have aided in solving.  So, things are not quite the same as the late 1800's.  In fact, if it were not for the modern magnets this site would probably not exist.