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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 02:55am 06 Jun 2009
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I had mentioned an active braking system on another thread.
I have just finished a 3phase PCB, rectifier/active elecronic brake, that could be micro controlled. This unit replaces the main 3phase rectifier and works with the capacitor voltage doubler system as well.
The usual 3phase, 6diode type rectifier is per usual. Between the negative and each phase output is a N-channel Mosfet, Across / in parallel with a diode. This Mosfet effectively is used to short the diode to ground. The 3 parallel systems effectively short the windings together. Mosfets do not make very good diodes, so the normal diodes have to stay. I sense the rectified output voltage and this is used to activate the mosfets to short the windings, when the sensed voltage rises above 5VDC. With a voltage doubler, the AC voltage from the mill may only be 2VAC. Not much power to dissipate, and the shorting provided will keep the mill in stall. The gate of the mosfet can be pulled high or low, independently, if required. A switch, or micro can control this signal level. A single small SPST switch can be used to shut the mill down for servicing. There will still be battery isolation with the top diodes in the 3phase bridge.
The main logic function is powered from the mill and requires < 1mA to operate. I have this arrangement, but 4phase on my original AxFx mill.
Mechanical switches across the windings can still be used as a backup. The active cct could be connected to a battery maintenance control system. My windmill has to work in conjunction with solar, so when the battery is charged, the windmill is turned OFF in an automated way. The solar is easier to manage with a typical regulator.
PWM type diversion loading, used to fully charge a battery, in wind only RE systems forces the windmill to operate all of the time. The windmill [mechanical] would be better turned OFF, and the final charging reigime performed by solar.[non mechanical]
This active electronic brake can allow the windmill to be controlled as a simple part of a complex RE setup. The operation would not be much different to controlling solar panels. As long as the windmill can be stopped with the shorting of the windings, then this system will work effectively.
Gordon.become more energy aware
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 07:22am 07 Jun 2009
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Hmmm,
Makes my forklift relays seem a bit Neanderthal. It certainly seems more elegant.
I assume it gives you progressive control if pulsed. (mine is all or nothing I'm afraid).
I will get a picture tomorrow perhaps of my "rustic" version.
..........oztulesVillage idiot...or... just another hack out of his depth
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 10:36am 07 Jun 2009
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Hi oztules,
The F&P is not an ideal candidate for this braking mechanism. I tested my proto and if the wind is too strong, the F&P mill keeps spinning, the same as when a mechanical shorting switch is applied. The AxFx is a better candidate.
The mechanical relays are fine when there is power to spare. I wince if the current is over 10-20mA. Must have been so many years working on solar cars in the WSC.
Gordon.
become more energy aware
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 02:36pm 07 Jun 2009
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Gordon, isn't windmill braking the very time that there is power to spare available? 10-20mA is nothing compared to what you use up by heating the dummy load.Klaus
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:34pm 07 Jun 2009
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Klaus,
My relays are using the normally closed contacts. So default is short circuit. This uses no power to brake the mill. However, it does use maybe 10 watts to hold them off when generating.
This is the power that Gordon is loath to lose. In good wind it is immaterial....
His braking system discards the use of heating elements. It runs when you need it, it is not running when you dont..... and if you pulse it with a Pic or similar, everywhere in between I guess.
........oztulesVillage idiot...or... just another hack out of his depth
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 01:30am 09 Jun 2009
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Hi oztules,
As you have mentioned, I don't have any dummy loads on my windmills. The controller is a similar function to your normally closed relay system. When the control switch/micro output allows the gate to go high, the mill is shorted. If the unit is connected to a battery, the mill will stay OFF, but if there is no load, the mill will cycle ON-OFF with the speed controlled from approx 5, up to 10rpm.
The 10 watts or more power you mention required by the relay is too much a burden to have on all of the time the windmill is enabled. This is more power than my logging laptop uses. We all wish for the wind energy that passes your place. There is plenty at my place at the moment though. Both my mills have been shedding power today. I have been forced to turn ON the TV to avoid wasting it. This is always a good time to catch up on recorded stuff on the PVR, or a DVD. This is what rainy days are for I suppose.
The Chinese windmill PWM brake, that I have on my F&P mill cuts in at 29.8V or so. When the battery maintenance controller goes into boost, or equalize mode, the PWM controller activates at the peak of a wind gust. There is this moaning sound from the F&P when this happens. This becomes tiresome after half an hour or more.
Once I finish my new AxFx and controller, this will be a 48V setup. Still some more to be done.
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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