A problem with a mechanical brake that may come up is, instead of burning out stator coils you will then start breaking blades. Using permanent magnet generators is a cheap solution but one with a problem with regulation. Because you can't easily regulate the out-put.

Not knowing what type of generator your using, either a radial or axial style, can you tell us? There is a way of regulating that isn't well known but seems to work pretty well called "field regulation". This is where you add a coil around the stator and put a current through it to counter act the current made in the stator. In effect it counter acts the fields of the rotating permanent magnets. Their using it in some PMDC motors for EVs to create 'field weakening' to get more speed from the motor at light load.

The generator uses a "Delco" style housing such as a traditional alternator.

 

We're far into this thread but I don't feel like I have a grasp of what is needed. Let me reiterate some basic questions:

In high winds, the windmill will spin too quickly if allowed to spin free? Do we know anything about the rpm target? If the goal is to prevent over-rpm, then the braking control system should be based on rpm.

The windmill has built-in electronic braking (shunt load) but this is not robust and has overloaded? Do we know what failed, how and why? Might be easier to fix a flaw than do a re-design. How does the built-in system function? Maybe there is already a rpm detection?

The proposed redesign solution is to add on a mechanical brake (pads and disc?) to be operated by a electrical solenoid or similar? There is electrical power available from the turbine itself and/or from the charged batteries.

The missing information requested by the OP is the control circuitry to monitor the turbine and/or batteries, and somehow control the braking system?

Sorry if all this is obvious to others, but I've grown confused.

 

We're far into this thread but I don't feel like I have a grasp of what is needed. Let me reiterate some basic questions:

In high winds, the windmill will spin too quickly if allowed to spin free? Do we know anything about the rpm target? If the goal is to prevent over-rpm, then the braking control system should be based on rpm.

The windmill has built-in electronic braking (shunt load) but this is not robust and has overloaded? Do we know what failed, how and why? Might be easier to fix a flaw than do a re-design. How does the built-in system function? Maybe there is already a rpm detection?

The proposed redesign solution is to add on a mechanical brake (pads and disc?) to be operated by a electrical solenoid or similar? There is electrical power available from the turbine itself and/or from the charged batteries.

The missing information requested by the OP is the control circuitry to monitor the turbine and/or batteries, and somehow control the braking system?

Sorry if all this is obvious to others, but I've grown confused.

Wayneh, first battery state of charge is the condition that needs to be monitored. The physical speed of the turbine is controlled by the wind force itself effecting yaw. Which limits the output to a manageable current level. The wind generator is "rated" at 1600 watts by the manufacturer, to try and prevent burn up we have configured it to yaw at less than half of its proposed capacity. We have two of them. We also have another 1000 watts of solar generation capacity. The problem arises when the batteries have reached full charge and there is not enough load thru the inverter or other DC loads to consume the excess charge capacity. The diversion controller does a poor job of managing this, even with manufacturer support. We have burned up too many turbines and risk damaging the batteries. I am attempting to devise an alternate means of controling the turbine automatically without allowing excess current, and therefore heat, to distroy the turbine.

The problem with the control system ( shunt load ) is the coils of the stator itself. They do not have the wire size and insulation to sustain high current operation once the batteries have reached a full state of charge and the resistive load applies to much current drain for the batteries. If the shunt load was used without the batteries, ( shunt only to load not in parallel with the batteries ) the stator still can't handle the current it can create and burns up.

As for your understanding of what I would like help with.. You are not mistaken. I would like to use a voltage differential derived from the batteries desired state of charge level and the excess voltage level above desired state of charge to control a physical braking device. However I do not want to stop the turbine just slow it down.

I am sorry for any confusion. I am trying to answer the questions as thoroughly as possible.

 

Thank you to all who have viewed this thread and asked questions and posted suggestions.

With respect, I don't need help with the physical aspects of this. I need help designing a control "circuit" for it.

 

I apologize for making you repeat yourself, but please restate or point to the post describing what sort of electrical or electronic device you need to control in order to effect the braking. I got lost in the details.

 

The problem arises when the batteries have reached full charge and there is not enough load thru the inverter or other DC loads to consume the excess charge capacity. The diversion controller dies a poor job of managing this, even with manufacturer support. We have burned up too many turbines ...

The problem with the control system ( shunt load ) is the coils of the stator itself. They do not have the wire size and insulation to sustain high current operation once the batteries have reached a full state of charge and the resistive load applies to much current drain for the batteries. If the shunt load was used without the batteries, ( shunt only to load not in parallel with the batteries ) the stator still can't handle the current it can create and burns up.

Thanks for explaining this, but I remain confused. Not by your words. I don't understand why, other than poor design, you need to send power to the shunt and thereby overload the turbine leading to its premature death. This loading would make sense if it the load was being used to slow the turbine blades to protect them - electronic braking - but it sounds like you don't need that function because you have yaw control to protect the blades. I don't really see a need for the shunt load at all, or maybe it could be substantially reduced. Am I missing something?

 

I apologize for making you repeat yourself, but please restate or point to the post describing what sort of electrical or electronic device you need to control in order to effect the braking. I got lost in the details.

an electromagnetic coil sourced from an electric trailer brake system. each coil can sustain about 10 amps current I would like to use two to provide even loading on the rotor.

 

"you need to send power to the shunt and thereby overload the turbine leading to its premature death. This loading would make sense if it the load was being used to slow the turbine blades to protect them - electronic braking - but it sounds like you don't need that function because you have yaw control to protect the blades. I don't really see a need for the shunt load at all, or maybe it could be substantially reduced. Am I missing something?

To control the battery banks state of charge, with insufficient load on the batteries from inverters and such, the current produced by the generator would over charge the bank. In high wind conditions once the batteries have reached sufficient charge the turbine can "run away" and severely overcharge the bank. the shunt load does absorb this to a point but the wind has overwhelmed the controllers load and the turbines tolerance causing failure. I am just trying to come up with an alternative that wont allow the system to become overwhelmed by our sustained wind speeds. sometimes in excess of 80 mph for three or four days. more often over 40 mph. we have to leave the system unsupervised for up to two months at a time. an automatic limiting control that can not be "electrically" overwhelmed would be very helpful.

In theory I would like to eliminate the diversion load completely and have control over the system using speed control alone. Ideally this would be by variable pitch prop, but I can’t afford a system that complex and I do not have the machining skills required to build it myself.

 

an electromagnetic coil sourced from an electric trailer brake system. each coil can sustain about 10 amps current I would like to use two to provide even loading on the rotor.

I think I had one of those left over from towing my Jeep behind my motorhome. It was a BF solenoid which pulled on the brake pedal. Sound familiar?
Do you want to PWM the voltage/current to modulate the force?

 

Do your blades have pitch control?

What's the name of that old 60s song? "You beat me to the punch..da da da".

Yes, this would be the ideal method.

 

What's the name of that old 60s song? "You beat me to the punch..da da da".

Yes, this would be the ideal method.

Yeah, and in retrospect, it was probably a dumb question on my part.

 

Do you want to PWM the voltage/current to modulate the force?

PWM? Pulse width modulator?

 

PWM? Pulse width modulator?

Yep, that's what PWM stands for (among other things).

 

That would probably be good, though current is the primary driver for the coil. pulse modulation would allow "softer" brake start.

 

To control the battery banks state of charge, with insufficient load on the batteries from inverters and such, the current produced by the generator would over charge the bank.

By "would", I guess you mean if it were not for the controller acting to divert current to the shunt. A properly controlled charger won't allow an overcharge no matter the supply does. When the batteries are charged, no more current goes into them. Period.

... our sustained wind speeds. sometimes in excess of 80 mph for three or four days. more often over 40 mph.

Holy crap! Well that explains why the design is inadequate. Not too many places on Earth "enjoy" that much wind. Around here (midwest US), mills are designed to operate at 5-15mph to cover most operating days. They'd never see 50 mph except in storms.

I think a lesser shunt load, one that would not over-current the windings even at 80mph, might be the ticket. It would provide some braking to slow the blades but wouldn't roast the alternator windings. What is your shunt, a big resistor on a heat sink? You might consider some light bulbs if you can use the light. Some folks use immersion water heaters.

 

That would probably be good, though current is the primary driver for the coil. pulse modulation would allow "softer" brake start.

Current times resistance=voltage, as we all know. With DC current drive, any portion of the total supply voltage not appearing across your solenoid will be across the driver, whatever it is. Analog control of several Amps will severely stress your driver (P=V*I). PWM switches the voltage off and on at a rate which is high enough that the inductance of the solenoid integrates, causing a current which low ripple, but the DC value proportional to the duty cycle of the control voltage.

 

...sustained wind speeds. sometimes in excess of 80 mph for three or four days. more often over 40 mph.

Are you near Laramie?

 

A properly controlled charger won't allow an overcharge no matter the supply does. When the batteries are charged, no more current goes into them. Period.

Wind generators are not chargers.. they are the supply for the charger.. The controller is the charger, and under most circumstances I would agree. But, unlike conventional charging systems that are supplied by solar or mains power, wind generators cant be shut off to control the current flow. They "push" current reguardless of the state of charge in the batteries. the controller attempts to handle this by "diverting" the excess to an alternate load. in the situation we run in, the loads ability to absorb the current is overwhelmed, continueing to push current to the batteries, overcharging them.

Holy crap! Well that explains why the design is inadequate. Not too many places on Earth "enjoy" that much wind. Around here (midwest US), mills are designed to operate at 5-15mph to cover most operating days. They'd never see 50 mph except in storms.

We are endowed with a special place to call home. Wyoming can blow you away and it's beautiful too..

I think a lesser shunt load, one that would not over-current the windings even at 80mph, might be the ticket. It would provide some braking to slow the blades but wouldn't roast the alternator windings. What is your shunt, a big resistor on a heat sink? You might consider some light bulbs if you can use the light. Some folks use immersion water heaters.

The shunt load we use is 2 ohm 300 watt ceramic resistors work well until the wind gets going good.

 

Ron H, North about 70 miles..

 

Current times resistance=voltage, as we all know. With DC current drive, any portion of the total supply voltage not appearing across your solenoid will be across the driver, whatever it is. Analog control of several Amps will severely stress your driver (P=V*I). PWM switches the voltage off and on at a rate which is high enough that the inductance of the solenoid integrates, causing a current which low ripple, but the DC value proportional to the duty cycle of the control voltage.

cool.. LOL its been along time since I have had to delve into any kind of design. I think I was in tech school with the airforce at the time. I need more "learnin".

Thats why I have come to Yall for help.. LOL