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Forum Index : Electronics : Testing Load Controller
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| Evil Roy Slade Newbie  Joined: 14/01/2008 Location: AustraliaPosts: 11 |
Firstly, let me thank all the learned contributors to this forum for sharing their thoughts with we newbies! I have an idea which I haven't seen used on this forum which probably means it doesn't work or I haven't looked hard enough! The objective is to design a wind generator load controller to make better use of the available power. The basic theory is to monitor the gen output voltage and progressively switch on (or off) current limited output stages. If the output voltage rises above the nominal value an additional output stage is switched on to feed more current and load up the gen a bit more. The opposite happens when the output voltage falls below a nominal value. The prototype uses seven FET output stages current limited using a .1ohm sense resistor and opamp controlled gate voltage. An 8th stage is used to trigger a shutdown. This approach avoids the problems of switching large currents when using PWM however does not have as fine a control on the output. Hopefully this won't be a huge problem as the sampling rate would be set high enough to keep up with changes in the mill's angular momentum. I have built a prototype of the controller and now building an outlandish VAWT to drive my 200W PM generator (ex bicycle motor). I don't have a battery or inverter to use as a load which brings me to the point of the post. (yes...that took a while!!) What type of load can the forum suggest I use until I get a proper load. Of course if my idea has already been tried and dismissed as not being viable then please be kind when you shooting me down! Look forward to your comments. ERS |
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| Janne Senior Member  Joined: 20/06/2008 Location: FinlandPosts: 121 |
Hi, I think this type of controller will work well with resistive loads, for example if you want to use the turbine to heat your water tank. I've used the same base idea before, but just with relaus in place of the FET's. But for battery charging, i think you really need an inductor / transformer to drop the voltage to suit the battery bank better. Without the inductive component, it will be the same situation with the battery being at a constant voltage, and the voltage difference of the generator and battery being dissipated as different losses in between them. But, if you could have switch mode battery chargers as load for your different fet stages, then i think it would work well. If at first you don't succeed, try again. My projects |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I think what you have built is more to a multi stage dump system. It would work well with dumping excess power when charging batteries, but as Janne said i cant see it helpful with the actual current control during charging. I dont think you will be generating a huge excess with the bike motor and a VAWT to require a multi stage control. The 200W you expect will be a BIG ask from this combination, i would think. Could you post a circuit diagram so we can see what you have done. Or some photos as well. Pete. Sometimes it just works |
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| Evil Roy Slade Newbie Joined: 14/01/2008 Location: AustraliaPosts: 11 |
The intention was to regulate the output current as a means of loading/unloading the generator and I hadn't really thought about worrying about the battery yet. The 200W/VAWT combination are being used purely as a test bed and I was not really expecting much useful juice out of them. I will draw the schematic so you guys can better read it and post. The basic block functionality is: Two comparators sense if the gen voltage is too high or low. Comparator outputs feed into an 8bit bidirectional shift register (74LS299) which shifts 1s to the right if the voltage is high and 0s to the left if the voltage is low. The register is clocked at about 1 hertz. Each of the 8 output bits switches on/off a current limited output stage. Using this as a dump system is interesting. Again, hadn't thought of that. ERS |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
To use it for raw loading as you wish to you will require a resistor bank of some discription, and as the voltage rises your circuit will switch in another bank of resistive load. As for the resistors you can buy some big load resistors or make your own. I done an artical on using old oven elements etc a while back and you can find it on the forum front page under encapulated resistors. Or you could wrap some steel wire around a ceramic floor tile or fluro light tube etc and make several of these so you have 1 for each loading stage. Beware all load resistors regardless of construction will run very hot and may glow red. Also you might need some diode gating across the fets as big coil resistors can dump high emf when switched off. The general view is the simpler you can keep a dump control system the more reliable it will be. Hence a single circuit and a relay switch to the dump load. I do like the idea of mulit stage dumping but others have had trouble with such systems and they can attract a little negative press from past failures. Pete. Sometimes it just works |
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| Evil Roy Slade Newbie Joined: 14/01/2008 Location: AustraliaPosts: 11 |
Thanks for your comments and insights guys. I will take a little time now to do some testing and report back if I think this is worth pursuing. ERS |
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