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There's a far easier way to use high voltages from the F&P motors - divide the windings into halves, rectify them, and send it down two wires to the batteries.
This means 80-260VDC down the wires - keeps losses to a minimum
At the batteries, connect four PC power supplies in parallel to the generator, and then connect the +5VDC lines in series - gives you 20V @ 20A.
Most PSU's won't start producing power until HV side reaches ~80V, so it'll let your genny get some speed up first.
The only problem is overspeed - as the mill speeds up, more voltage is produced, which means the switchmode has to draw LESS current from the mill, which provides less load, which increases speed still.
What's needed is a load on the HV side that can be introduced when this voltage exceeds your mills safe limit.
And because it's DC, a 5v zener diode, 47k resistor(reasonable wattage to switch the mosfets), a 100k multi-turn pot, a PicAXE 08x, and a few IRF840R Mosfets soft-starting(so you don't tear the blades off your genny) into a water heater would do the job nicely.
Nige.Edited by nweeks 2007-01-24Nigel Weeks
nweeks at karbonit dot com
brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548
Posted: 07:18am 23 Jan 2007
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Hi Nige, tried just about everything, but your idea is the newest I've seen lately---have you tried it ???
Thanks
Bruce
Bushboy
Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119
Posted: 02:57am 26 Jan 2007
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G'day nweeks, DC from mill into PSU - not quite clear as to where to connect the DC - on the storage capacitors after the input rectifiers? Second question, why would the mill provide less power to the PSU as mill output voltage increases - higher V times lower I could still be more power, all dpends on magnitudes of V and I. I must be missing something!Megawatt Man
Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119
Posted: 03:02am 26 Jan 2007
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Hello brucedownunder2, Next time you have a machine on your test rig, any chance of measuring voltage ouputs no load and say 2-300 watts (at same rotational speed)? Knowing resistance of coils, inductive reactance of machine can then be calculated reasonably closely, so many predictions of performance can be made, design principles firmed up and lots of time saved. Probably wrong forum, but while waiting for an answer from Nige, I can catch you here! All the best.Megawatt Man
herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258
Posted: 04:34pm 21 Feb 2007
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Hi nweeks
Your idea has real merit the use of old psu from computers is somthing i have been working on. I never thought of using 4 in series tho I have modified them to change the output voltage My aim is working to a MPPT unit psu from computers are a dime a dozen and they give us a DC transformer of the shelf (nearly)
Cheers
Herb
Sorry, I haven't been back here for ages!
Just hook it up to the kettle plug in the back (where the 240VAC used to go). It doesn't matter if it's rectified again, and it saves opening the cases.
For your second question, the mill doesn't provide less, the PSU draws less.
For example, lets say you have a 12V 100W light bulb as a load. There's a gentle breeze, and your F&P is just ticking over, producing ~80V open circuit.
(imagine the PSU is 100% efficient)
100W / 80V = ~1.25 amps drawn by the PSU to power that load.
Now, let's say the F&P is hammering, and it's pumping 300V.
100W / 300W = ~0.33 amps.
As you can see, with a switchmode PSU, you get inverse loading in high winds, so you HAVE to have a dummy load to switch in.Nigel Weeks
nweeks at karbonit dot com
Kind of. Inherited 20 240W PSU's from a closing business. Hooked up the 5VDC outputs to get 30VDC, 40A (2 parallel chains of 6 PSU's in series) for charging some forklift batteries I also inherited.
They have very flexible input voltages, so they'd be great for wind situations.Nigel Weeks
nweeks at karbonit dot com
Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119
Posted: 07:15am 27 Mar 2007
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OK nweeks, Thanks for that. I reckon (in my language)you are saying that the lamp is connected to the 12 volt output of the SMPS and the switcher maintains the output voltage via the feedback circuit so that the energy drawn from the alternator stays constant, so higher V means lower I. The same thing would happen with a battery connected say to the 12 volt output. But if the battery and had spare capacity, ie was not fully charged, we'd want every last bit of energy to go into it. So to take advantage of the SMPS, should we not disable the feedback? Megawatt Man
If you connect battery with a lower charge, naturally, it'll draw more current from the 12VDC source.
You've hit the nail on the head. As more VCC is available to the HV side of the PSU, it draws less current from the turbine to power it's load - aka, fly to bits without sufficient EM braking to slow it down.
I'd be inclined to leave the feedback loop in each PSU as is - they're very efficient, and fast acting.
What I would do, however, is monitor the HV voltage with a seperate system, and impose a load with that.
If the wind's picking up, then PSU has to work less to power the loads, thusly the voltage across the high side will skyrocket.
Simply rectify the HV side, pass it though a voltage divider(with a tiny current, as resistors will get hot when you try and drop serious voltages over them at any level of current), and switch in a load on the HV side with the result.
i.e., have a vdivider that produces 0-5v when the HV is for 0-300V in, and have a picaxe driving a few IRF840R's in parallel, with a nice PWM output to automatically keep some load on the turbine
IRF840R's are a 400V 8A mosfet.
Slap it across your floor heating elements, or whatever load you deem worthy of extra electrons.Nigel Weeks
nweeks at karbonit dot com
Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119
Posted: 07:59am 01 Apr 2007
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G'day nweeks again and thanks again for the explanation. This is where I am coming from. I am an electric power man, and am happy to use alternators unmodified so they output three phase high voltage. (ie around mains level voltages). The concept of multiple SMPS sounds good to me, 3x5 volts or multiples has interested me as a means of charging batteries of 12 or 24 volts. My general direction is to run a mains synchronised sine wave inverter from the battery, so it would be a rarity that I would need to switch dummy loads. I reckon that with a nominal 15 volt output from the SMPS units I would always be able to get some charge into the battery. Now getting circuitry for such an inverter is a trick, I have been looking for a coupla years with not much success. What would be ideal is the unit that comes with the 1 kW solar pv module with integral inverter, that you put on your roof and have a sparkie connect it to your main switchboard - after you've paid plenty for it and organised the electricity supplier to sell you the two-way meter. But that unit is a fully commercialised one and there's no way the manufacturer wpould be happy for circuit details to get out.Megawatt Man
Grid interactive inverters are an art to themselves. I've been nutting out the major control sections to building one, and it won't be easy.
I biggest thing is watching the waveform from your energy company, waiting to see when you can push your output as well.
It's a bit like pushing a child on a swing. If you stand in the middle of the arc, and apply pushing force when they're bearing down on you, you'll pop a mosfet(get hit in the face).
It'll require high speed AD converters to watch the incoming waveform, adjustments for your own inverter stage timings, and the finite amount of time your transformer takes to change voltage levels, and the fact that grid interactive inverters HAVE to detect when the mains goes down - to stop livening up any powerlines that hapless linesmen might be hanging off...
It's be an intersting group project to be involved in. You could start from Oatley Electronics's small modified sinewave inverter, and wrap phase controls around it...
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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