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Forum Index : Windmills : F&P unmodified output curves and loading
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| SpmP Newbie  Joined: 10/10/2010 Location: New ZealandPosts: 32 |
Gidday all, Years ago I put my F&P genny in the lathe (just) and did some load testing with with a toaster and a battery bank of 16 12v batteries, measuring the torque with an old scales. The genny was unmodified as it is on the turb. atm, straight into a three phase bridge. I noticed some odd things: I got maximum power delivered into half the open circuit voltage. This makes me wonder about load matching, power factor and all that. So the questions for the venerable experts: 1) I'me redoing the blades, and dont have the old data available. Is there any torque/RPM/Volt/Current data around for unmodified 60 series F&P if Ime not loading into batteries, rather resistive load, or smps. Basically need what I can to choose appropriate TSR. ( I want close to max power in 6.4m/s if pos. fibreglass blades, rad <2.5m would be good) 2) How do you properly load match the F&P. Ive tried the uni library etc. and cant find anything about genny load matching. Is there such a thing? What was I seeing with full power into half open circuit? 3) Is there anything wrong with the idea of loading into an smps or low resistance and using PWM to control loading? Thanks, trying to get things that have been puzzling me for a while off my chest. Jasper. |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hi Jasper I think I can answer some of this, others will hopefully fill in where I leave out! You get maximum power transfer when the source impedance matches the load impedance. An open circuit is an infinitely high impedance so of course no power transfer, a short circuit is a very low impedance so little if any power transfered there either. If you know what voltage gave you maximum power transfer then aim around that for your load voltage, I think. |
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| SpmP Newbie Joined: 10/10/2010 Location: New ZealandPosts: 32 |
Thanks Kiwijohn. Great so its the same(ish) as transformers. How do I measure the source impedance? I assume this is freq. dependant. My DMM never gives a good idea of phase resistance due to the inductance.... What effect does the bridge rect. have on all this? (i.e is there any advantage of active rectification in this case?) I am controlling the turbine with pwm into a resistive load atm. so just match the resistance to the source impedance... So i guess when designing the smps (to replace the resistive load) which part would I be using to match this? Or would an impedance matching transformer before the bridge make more sense? Too many questions when there are still more to answer 8) Cheers. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
> I noticed some odd things: I got maximum power delivered into half the open circuit voltage. Well, that not a "odd thing", that is the way you find the source impedance (resistance in this case if you were loading up with pure resistive loads)! Check out this article: here Due to harmonic content I be surprised if the source impedance looked purely resistive. Maybe, close enough for practical purposes. Maintaining the correct loading over a wide range of input power seems to be a pretty big challenge. Good luck. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
> So i guess when designing the smps (to replace the resistive load) which part would I be using to match this? Adjusting the duty cycle to load the generator to achieve maximum power transfer. I would suggest reading MPPT threads on this site and in general. I know issues like response time and getting correct loading at the low end cut-in have been discussed. Also, mechanical matching seems to be as or more important. |
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| SpmP Newbie Joined: 10/10/2010 Location: New ZealandPosts: 32 |
Thanks Davef. Indeed some of the niggling worries I had about high voltage are coming to haunt me. Part of the motivation was that my 3.3kw inverter has a 196V DC bus (240V charging), but thats a pretty high cutin. After all is said and done, are the line losses going to be less than loss due to poor load matching over the voltage range? and in the case of high voltage batery bank, would I still be better to go low voltage from the turbine and use a boost converter.... this is all backwards from where I have been aiming!!! In regards to mmpt, this is what we are attempting to do. either through adjusting the step down converters op voltage, and hence the load to the battery, or duty cycle... Is there any data like what rpm vs peak power/voltage. Unfortunatley y Dr Tom Chalko's experiment is for fixed rpm, so cant use this. cheers. Jasper |
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