 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. |
Forum Index : Windmills : The MPPT Project.
  Page 5 of 7   |
|||||
| Author | Message | ||||
| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I believe you are on the right track. IIRC Kirchoff's Law says the current flowing in is equal to the current flowing out so if we want a decrease in voltage output with a corresponding increase in output current we must segregate the input current from the output current. I can only think of two ways of doing this, a transformer and a motor-generator set. The latter became obsolete about 50 years ago but the transformer is still with us. |
||||
Gill Senior Member  Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Not so John, Like voltage boost circuit, we alternately switch a DC supply between the battery and a capacitor. On the capacitor it charges up, then when switched to battery, the capacitor is discharged in series with the supply. This effectively increases the voltage. No transformer. In a like manner alternately switching a DC supply between an inductor and a battery we can increase current. When on the inductor we build up a magnetic field, then when we switch to battery the inductors back emf is fed in parallel with the supply thereby increasing the current. Again no transformer. No increase in power, just a change in amps and time. It is the duty cycle of the switching that controls the level of current for MPPT. Well that's how I understand the basics. I still can't fathom the buck converter though. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi John Gill Gill is right Mr Kirchoff was only evisaging continuos current flowing into a junction In these cases the current input stores energy in the magnetic field then releases it after current stops the switch mode cct using push pull still does this but uses a secondary winding allowing the transformer turns ratio to make for a easier design. Varying the on/off period will still give effective ratio control so we can control from pixaxe or control chips designed for this. Herb |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Neither can I but I do know it is not magic. |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Ummm, errr, if you say so. I just cant see it myself, I cant see how there can be a current transformation without two circuits, for example in a transformer. |
||||
| herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi John At least push pull will appear conventional hey. can you breifly state how you insert quotes Herb By the way Gill just hoped out of a hot shower used that hot water us Kiwi's strife for. |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
|
||||
nweeks Newbie  Joined: 22/01/2007 Location: AustraliaPosts: 36 |
It's the active component in switchmode power supplies. They either boost voltage, or boost current, without a transformer - just an inductor or capacitor (or combinations of both), high-speed switching FETs(and feedback/control units), and relevant smoothing/filtering. . Been around for years. Your computer has at least 4 of them - +5, +12, -12 +24, CPU Rail, +15 for Ethernet, all use switchmode stages. Nigel Weeks nweeks at karbonit dot com |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
...........the PC power supply has a transformer in it. |
||||
| nweeks Newbie Joined: 22/01/2007 Location: AustraliaPosts: 36 |
Certainly does, and then the seperate voltage rails are chopped and controlled from one or two output taps. Severly off topic now, though! :-) How are people going with their controllers? Any updates? And, can these forums break threads across multiple pages? This page is HUGE!!! :-) N Nigel Weeks nweeks at karbonit dot com |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Sure can, found the option in the configuration. Let me know how this looks. It will make the big threads easier to navigate. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| nweeks Newbie Joined: 22/01/2007 Location: AustraliaPosts: 36 |
Now THAT is good! Roll that feature out everywhere!! :-) N. Nigel Weeks nweeks at karbonit dot com |
||||
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi all, has the humble diode been overlooked, for without it none of the ccts would work. Gordon. become more energy aware |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
All hail Lord Diode, indeed, he has a vital part to play, both as a simple rectifier and in the myriad apparently magic electronic dabs of epoxy that can, so I am told, somehow create electrons. |
||||
| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi KiwiJohn, I don't know about creating electrons. I have just started to prototype a buck-boost design. A combination of 2 micros to handle the number crunching and some glue logic has enabled me to make a MPPT that has extended upper and lower mill voltage bounds. It will load the mill from a generated 6-50V and charge a 12 or 24V system. This cct will work with solar panels as well, as the code interpolates to find and maintain the optimum MPP with a changing voltage and current reference. This has been at the top of my wish list for quite a while. cheers, Gordon. become more energy aware |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Sounds like an excellent project Gordon and I admire the skill that must go into designing and building such a thing. Suppose the mill is producing high volts, lets say 50V, at 5 amps. Thats 250 watt output from the mill. How many amps would you expect to see it charging a 12 volt battery? |
||||
| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
High KiwiJohn, I loathe 12V systems, all that heavy copper wire. 1. diode bridge loss around 6W 2. primary switch loss around 7W 2. inductor loss around 6W battery would be at say 13.5V while charging. Probably around 17A. I think a mill specifically wound for 12V charging would charge a battery with about 16.5A with 250W input. The drawback is, this mill would produce no amps when the gen voltage was < bat volts. The MPPT allows a much wider rpm speed range of the rotor and hence the blades will operate at the sweet spot for most of the operating range. This is like a high efficiency electronic auto transmission. The buck cct efficiency increases with a reduced input to output voltage ratio. The boost cct has a similar property. The cct becomes an effective piece of wire when the gen voltage equals the battery voltage. As I have said and others as well, To get highest efficiency the mill voltage should still be closely matched to the load voltage. I hope this helps. cheers, Gordon. become more energy aware |
||||
| herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi Good on you Gordon its a good option but not a easy design at these power levels Do you envisage a MPPT for solar or wind or a hybrid system ?any MPPT system will work better with only one supply but a hybrid input would have economic sense. When time is available I am working with a push pull cct at present reading up on net and stripping old psu computers. It was originally my idea to modify one of these but better start scratch. much discussion on net about core saturation if unbalenced , good info out there tho John do serach on SMPS buck to get heap theory then try boost you will be an expert in no time. Cheers Herb |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hookaaay! Thanks for your patience guys but I am obviously just a little too thick to see how this all works!  More amps out than in without a transformer still seems like magic but if it all works there is no doubt it is I who is the klutz!
Gordon, I agree entirely regarding low voltage work, it just makes everything so much harder though I thought we had semi-conductor junctions with very insignificant forward voltage drop available nowadays? Its about now that I should confess that, so far, my actual experience of windmills is pretty slim! My only sucessful project has been a permanent magnet (ex tape drive) motor fitted to a 2ft diameter air conditioner fan which friends took on an expedition to Campbell Island. I carefully made regulators and such like but when they returned they said the "black thing" (the regulator pass transistors and heat sink) had got hot so they just connected the motor to their batteries. Nowadays we live on a suburban section in Wellington though my garage does harbour all the bits for future projects just as soon as the opportunity presents!  |
||||
Chris Senior Member Joined: 12/09/2005 Location: AustraliaPosts: 146 |
Gday guy's. I really wish i had a big enough windmill up to do some stuff like this! Im happy to help you guys with some C code if you wanna put this onto a bigger micro with some more features. Maybe a Mega8? |
||||
| Page 5 of 7 |
|||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
